WO2014133405A2

WO2014133405A2 - Cell-based methods for coupling protein interactions and binding molecule selection and diversification

Info

Publication number: WO2014133405A2
Application number: PCT/PT2014/000016
Authority: WO
Inventors: João Manuel BRAZ GONÇALVES; Frederico Nuno Castanheira Aires Da Silva; Sofia VOLKER CÔRTE-REAL; Soraia Rafaela SANTIAGO DE OLIVEIRA
Original assignee: Technophage, Investigação E Desenvolvimento Em Biotecnologia, Sa
Priority date: 2013-03-01
Filing date: 2014-03-03
Publication date: 2014-09-04
Also published as: US20140249044A1; ES2872048T3; EP3588089A1; JP2016511405A; PT3588089T; EP2962103A2; WO2014133405A3; US9487773B2; EP3588089B1

Abstract

The invention provides cell-based methods for diversifying, expressing and selecting binding molecules, e.g., antibodies, and target molecules to which they bind, all of which are expressed in the same cell. The target molecule can be a member of a ligand binding pair comprising a cell-surface expressed ligand binding receptor molecule and its cognate ligand, which interact within the cell. The methods provide retaining either the antibody or its target in a cell organelle as the site of binding and interaction. By performance of the methods, the binding or non-binding of the antibody to its target molecule within the cell produces a cell phenotype that is detectable at the cell surface via high throughput assays, e.g., flow cytometry. The methods are particularly useful for generating, recovering and providing antibodies that have optimal target molecule binding properties or activities for potential therapeutic use. Methods for generating genetic diversity and increased binding properties for such antibodies are also provided.

Description

TITLE OF THE INVENTION

CELL-BASED METHODS FOR COUPLING PROTEIN INTERACTIONS AND

BINDING MOLECULE SELECTION AND DIVERSIFICATION

SEQUENCE LISTING

[0001] This application contains a Sequence Listing which has been submitted electronically in ASCII format and is hereby incorporated by reference in its entirety. The ASCII copy of the Sequence Listing, created on February 28, 2014, is named 14116-105012PCT_SL.txt and is 23,884 bytes in size.

PRIORITY

[0002] This application claims the benefit of U.S. Provisional Patent Application No. 61/771,562, filed on March 1, 2013, the contents of which are hereby incorporated by reference in their entirety

FIELD OF INVENTION

[0003] The present invention relates generally to methods of selecting a binding molecule, such as an antibody, in a cellular environment, wherein the binding molecule specifically binds to a target molecule, such as a ligand binding protein or its cognate ligand, as well as to methods of generating genetic diversity in one or more binding molecules, such as antibodies or functional portions thereof, having specificity for a particular target molecule, e.g., a protein or antigen, and having the potential for improved binding and/or functional properties or activities.

BACKGROUND OF THE INVENTION

[0004] Since the discovery of hybridoma technology in 1975 and with the subsequent development of recombinant DNA technologies, the genes encoding binding proteins, particularly antibodies, have been engineered to manipulate the binding protein or antibody in some way, e.g., reduction in size, such as a single-chain variable fragment (scFv) or variable fragments from antibody light chain (VL) and heavy chain (VH); rebuilding into multivalent high- avidity reagents; and fusion with a variety of molecules (e.g. enzymes, toxins). In addition, several selection methods and experimental approaches have been developed in order to select monoclonal antibodies (mAbs) with higher affinity and specificity. [0005] Antibody selection techniques using an antibody library can be performed totally in vitro, without the requirement of cell transformation, or in vivo, in which cells may be transformed, .e.g., using vectors encoding an antibody library. In vitro antibody selection includes techniques such as ribosome, RNA and DNA display, while in vivo antibody selection includes techniques such as phage-display, two-hybrid systems, cell-display, e.g., in bacteria, yeast, or mammalian cells and protein fragment complementation assays (PCA). Phage-display is broadly used due to its simplicity, versatility and ability to be adapted to many specific conditions. Yeast, bacterial, and mammalian cell display platforms offer an advantage over phage-display in that fluorescence activated cell sorting (FACS) can be coupled with cell surface antibody display to allow monitoring of both antibody expression on the cell surface and the ability of that antibody to bind to its target. On the other hand, ribosomal display technology allows the screening of larger libraries and facilitates the diversity and efficient antibody maturation in vitro.

[0006] Although a large number of antibodies have been selected by various technologies, most need to be affinity improved or enhanced. Such improvement in antibody affinity and subsequent selection of specific antibody are typically achieved through the use of one or more methods, systems, or technologies, such as multimerization of antibodies; E. coli mutator strains; B-cell lines, e.g., RAMOS, DT-40, or HEK293T cells and activation-induced cytidine deaminase (AID); retrovirus display systems; error-prone PCR; immunoglobulin chain or CDR shuffling; directed mutagenesis.

[0007] Despite the various methodologies developed to improve the affinity and subsequent selection of antibodies, significant problems are prevalent. Examples of problems that have been detected and reported include potency/affinity, expression, correct folding and post- translation modifications of isolated antibodies. Thus improved and new processes are needed for selecting specific and functional antibodies and optimizing them, as well as other types of binding molecules, particularly for therapeutic utility. It is therefore important to develop new strategies related to improved and useful methods for introducing diversification into the genes or nucleic acid sequences encoding binding molecules, such as antibodies, and to provide novel and efficient methods for selecting the expressed molecules, particularly for generating new, improved and useful therapeutic biological products. SUMMARY OF THE INVENTION

[0008] The invention provides an intracellular platform technology and methods for the effective expression and selection of a binding molecule, such as an antibody or immunoglobulin molecule, an antibody mimetic, or other type of recogmtion/binding molecule, which binds to a specific target molecule, such as a target protein, polypeptide, or peptide, within the environment of a cell. The technology and methods of the invention further provide a means for genetic diversification of the binding molecule, or a fragment or portion thereof, such as an antibody, and its selection following binding to a target molecule within the environment of a single cell. It is to be understood that the term "a cell" as used herein may encompass one cell, or a single cell, in a population of cells or a cell line, or it may encompass a pool, population, or plurality of cells, such as a cell line comprising a plurality of individual cells.

[0009] The invention further provides methods for selecting a binding molecule, such as an antibody, by using recombinant technology, cellular machinery and cellular mechanisms for localizing within the cell the target of the binding molecule, for example, a member of a ligand binding pair wherein one member is, for example, a ligand binding protein and the other member is its cognate ligand. In accordance with the methods of the invention, the binding molecule, such as an antibody, specifically binds to its target, which may be either the ligand binding protein, e.g., a receptor protein, or the cognate ligand of the interacting ligand binding pair. In an embodiment, the target is the cognate ligand which is retained in a cell organelle such as the endoplasmic reticulum (ER) or the Golgi. In an embodiment, the target is the receptor protein. In an embodiment, the binding molecule, or a binding portion thereof, is retained in the cell organelle, e.g., the ER or the Golgi. In an embodiment, the binding of the binding molecule, such as an antibody, or a binding portion thereof, to its target disrupts, neutralizes, or blocks the binding or interaction between the ligand binding protein and its cognate ligand, resulting in the appearance on the cell surface of the member of the binding pair not retained or localized in the cell. The disruption or blocking of binding and appearance of binding pair member on the cell surface is indicative of the specific binding activity of the binding molecule, such as an antibody, or a binding portion thereof, to its target and allows for the selection from the cell of the binding molecule as the effector of the disruption, neutralization, or blocking activity, based on the detection of the binding pair member not retained or localized in the cell. [0010] In one of its aspects, the invention provides a selection method employing knockdown expression of cellular receptor proteins, cell-surface membrane-bound proteins, antigens, or ligand proteins by an antibody, or a member of an antibody library, or a functional portion thereof, or by a genetically diversified antibody, or a member of a genetically diversified antibody library, all of which can be co-expressed in the same cell. The expressed cellular receptor proteins, cell surface membrane-bound proteins, or ligand proteins are molecularly engineered to harbor and express retention signal sequences or tags, which allow these proteins to be expressed, for example, as fusion proteins having a retention signal and to be selectively retained in a cell organelle, such as the ER or the Golgi. In an embodiment, one member of an antibody library or one member of a ligand binding molecule library can be co-expressed in the cell with its target molecule, e.g., a cellular receptor protein, a cell-surface membrane-bound protein, or antigen in a cell.

[0011] In another of its aspects, the invention provides selection methods which take advantage of specific, and optionally natural, protein-protein interactions within a cell. The proteins can be target antigens that are recognized by a binding molecule such as an antibody, or a binding fragment or portion thereof. Such target antigen interactions include, without limitation, the interaction between a particular cellular receptor protein, or receptor protein capable of being expressed on the plasma membrane surface, with its cognate ligand or protein ("binding pair member"). In the environment of the cell, a target antigen can be bound by a binding molecule such as an antibody, or by a member of an antibody library or a library of other binding molecules, all of which can be co-expressed in the same cell. In an embodiment, within a cell, the binding molecule, e.g., the antibody or a binding portion thereof, binds to either the cellular receptor protein or receptor protein capable of being expressed ou the plasma membrane surface as target, or to the cognate ligand or protein as target. This binding by the binding molecule or antibody disrupts, blocks, neutralizes, or inhibits the binding interaction that typically occurs between the cellular receptor protein or receptor protein capable of being expressed on the plasma membrane surface and its cognate ligand or protein. In an embodiment, the binding molecule, antibody, or a binding portion thereof, binds the cognate ligand. In an embodiment, the binding molecule, antibody, or a binding portion thereof, binds the cellular receptor protein or receptor protein. [0012] In another of its aspects, the invention provides a selection method involving the intracellular retention of a ligand binding protein, or receptor protein, which is normally expressed at the cell surface, by its cognate ligand following the interaction of the receptor protein with its cognate ligand, and the inhibition of the interaction between the receptor protein with its cognate ligand by a binding molecule, or a binding fragment or portion thereof, resulting in the appearance and detection of the receptor protein on the cell surface. The binding molecule, or a binding fragment or portion thereof, can be a member of a binding molecule library, such as an antibody library, or a member of a genetically diversified binding molecule library, such as a diversified antibody library. Within a cell, the antibody, or member of the library, recognizes and binds to either the ligand binding protein or its cognate ligand, all of which are co-expressed in the same cell. In an aspect of the invention, the ligand binding protein or the cognate ligand is retained in the endoplasmic reticulum (ER) of the cell by virtue of operable linkage or fusion to an ER retention signal sequence.

[0013] In another aspect, the invention provides a method of molecularly introducing genetic variability and diversification into a binding molecule, in particular, an antibody, or a binding fragment or functional portion thereof, or a library thereof. The diversified binding molecule, antibody, or library thereof can be used in the inventive selection methods described herein so as to select and identify a binding molecule, or a member of a library of binding molecules, having potentially improved or optimal binding of and/or activity toward a target molecule, such as a receptor protein expressed on the cell surface, or the ligand of such a receptor protein. The methods can generate populations of binding molecules, e.g., antibodies, having increased diversity and that can be screened or selected for improved or optimized properties or activities, such as target specificity, binding and/or functional properties.

[0014] The methods of selecting binding molecules having specificity for binding target molecules according to the invention are especially conducive for selecting one or more of the genetically diversified antibodies as described herein. In an aspect, genetic variability and diversification of an antibody binding molecule is effected by the introduction of zinc finger protein recognition sites into the complementarity determining regions (CDRs), for example, CDR1 and/or CDR3, of antibody heavy and/or light chain variable regions, i.e., VH and/or VL, respectively, to generate modified or non-naturally occurring CDRs. Gene disruption is induced by the targeting of recognition sequences molecularly engineered within one or more of the CDRs and is effected by the creation of novel zinc finger nucleases (ZFNs) and their associated cleavage activity. In an embodiment and as described herein, one or more of the CDRs is molecularly engineered to contain one or more zinc finger DNA binding protein recognition sequences as targeting site sequences. In an embodiment, two ZFN cleavage sites comprise each CDR in a VH or VL antibody domain. For example, if a VL region comprises a modified CDR, that CDR is molecularly engineered to contain two zinc finger recognition target sites such that a pair of ZFNs generated according to the invention would cleave at or near the two recognition sites within the CDR. In an embodiment, the generation of further genetic variation, which can produce improved and/or increased ligand or antigen recognition and binding capability of binding molecules such as antibodies, or binding portions thereof, is provided by increasing and improving mutagenesis frequency and genetic diversity through the co-expression of Tax and Tdt enzymatic proteins in cells that are engineered to express the CDR modified antibody binding molecules and the appropriate ZF nucleases as described herein. In an embodiment, only the Tax protein, or a protein having similar function, is expressed in the cells in which CDR modified binding molecules and ZF nucleases are also expressed. In an embodiment, only the TdT protein is expressed in the cells in which CDR modified binding molecules and ZF nucleases are also expressed. In other embodiments, chemical inhibitors of ATM kinase, as described herein, can be used to induce further genetic variation and diversity in antibody binding proteins according to the methods of the invention.

[0015] In another of its aspects, the invention provides a method of selecting a binding molecule which blocks or disrupts an interaction between a cell surface expressed receptor protein and its cognate ligand within a cell, wherein the method comprises expressing in the same cell a receptor protein which is expressible on the surface of the cell; expressing in the cell a cognate ligand of the receptor protein, wherein the cognate ligand is molecularly tagged with a sequence for retaining the ligand in an intracellular organelle under conditions allowing for the retention of the ligand in the organelle and the interaction of the receptor protein and the cognate ligand in the organelle such that the receptor protein would also be retained within the cellular organelle when bound to the tagged ligand; introducing into the cell a binding molecule which specifically binds either the receptor protein or the ligand protein retained in the intracellular organelle as its target antigen; and detecting the level of the receptor protein expressed on the cell surface; wherein, if the binding molecule binds to either the receptor protein or the ligand and blocks or disrupts their interaction in the organelle, the receptor protein thereby transits through the organelle and is expressed and detectable on the cell surface. Accordingly, the binding molecule, which has bound its target antigen, blocks or disrupts the receptor protein and ligand interaction and is selectable from the cell following detection of the presence of receptor protein on the cell surface, e.g., by a detectable label binding, flow cytometry and growth expansion of the cells. In embodiments, the retention occurs in the ER or the Golgi.

[0016] In another of its aspects, the invention provides a method of detecting whether a binding molecule, or a binding fragment or portion thereof, e.g., an antibody, or a binding portion thereof, specifically binds to a cell surface expressed target protein within a cell, wherein the method comprises expressing in a cell a target protein which is expressible on the surface of the cell; expressing in the cell the binding molecule, or a binding fragment or portion thereof, which is molecularly fused or coupled to a sequence for retaining the binding molecule in an intracellular organelle, e.g., the ER or Golgi. Accordingly, if the binding molecule, or a binding fragment or portion thereof, specifically binds to the target protein in the cell, the target protein is retained in the intracellular organelle via its being bound by the binding molecule, or the binding fragment or portion thereof, which is retained in the organelle by virtue of its fusion to the retention signal, thereby preventing expression of the target protein on the cell surface. The level or amount of the target protein expressed on the cell surface is detectable, e.g., via suitable detection methods like flow cytometry, such that a virtually non-detectable or low level of the target protein detected on the cell surface relative to a suitable control indicates binding of the binding protein, or a binding fragment or portion thereof, to the target molecule inside the cell.

[0017] In an embodiment of the above-described methods, the selected binding molecule, or a binding portion thereof, can be recovered or isolated from the cell. In another embodiment, the binding molecule is selected from an antibody, or a binding fragment or portion thereof, a member of an antibody library, or a member of a single domain antibody library, e.g., VL and/or VH domains. Such antibodies or libraries may be genetically diversified. In another embodiment, the antibody, or a binding fragment or portion thereof, is selected from a polyclonal antibody, a monoclonal antibody, a chimeric antibody, a humanized antibody, a fully human antibody, a single chain antibody (Fv), or a diabody. In another embodiment, the binding fragment or portion is selected from an Fab fragment, an Fab' fragment, an F(ab')2 fragment, an Fd fragment, an Fv fragment, a single-chain variable fragment (scFv), a domain antibody (dAb), a heavy chain variable domain (VH), a light chain variable domain (V_L), or a complementarity detennining region (CDR). In an embodiment, the binding molecule is an antibody, or a binding fragment or portion thereof, directed against a ligand binding receptor molecule or receptor protein, e.g., human tumor necrosis factor alpha (hTNF-a receptor 1) receptor protein. In an embodiment, the ligand binding receptor molecule or receptor protein is expressible and/or is expressed on the surface of a cell. In an embodiment, the binding molecule is an antibody, or a binding fragment or portion thereof, directed against a cognate ligand (or ligand protein) of the ligand binding receptor protein or receptor protein, e.g., human tumor necrosis factor alpha (hTNF-a). In another embodiment, the binding molecule is a non antibody molecule. In another embodiment, the receptor protein or target molecule is a human receptor protein selected from growth factor receptors, hormone receptors, enzyme receptors, Fc receptors, metabolic enzyme receptors, neurotransmitter receptors, chemokine receptors, cytokine receptors, lymphokine receptors, interleukin receptors, tumor antigen receptors, tumor suppressor antigen receptors (e.g., p53, Rb, k-Rev, DCC receptors), multidrug resistance protein receptors, coagulation factor receptors, Factor VII receptor, Factor VIII receptor, Factor ΓΧ receptor, trophic factor receptors, cell recognition or stimulatory molecule receptors, apolipoprotein receptors, EGFR, ErbB-lR, HER1, HER2, aFGFR, bFGFR, NGFR, VEGFR, FltR, TGFR, TGFR-a-1, TGFR-β, TNFR (a), BDNFR, insulin receptor, insulin-like growth factor receptor (IGFR), PDGFR, HGFR, TR R, BDNFR, CNTFR, GMFR, NT3R, NT5R, HARPR/pleiotrophinR, TIE receptors, Eph receptors, DDR receptors, ROR receptors, LTK receptors, AXL receptors, RET receptors, TOLL-like receptors; hormone receptors selected from steroid hormone receptors, thyroid hormone receptors, melatonin receptors; adrenergic receptors; peptide receptors selected from receptors for amylin, angiotensinogen, angiotensin, atrial natriuretic peptide, brain natriuretic peptide, calcitonin, corticotropin, erythropoietin, endothelin, enkephalin, follicle stimulating hormone, gastrin, ghrelin, glucagon, human chorionic gonadotropin, inhibin, leptin, luteinizing hormone, melanocyte stimulating hormone, oxitocin, pancreatic polypeptide, parathyroid hormone, prolactin, prolactin releasing hormone, rennin, secretin, somatostatin, thrombopoietin, thyroid stimulating hormone, thyrotropin releasing hormone; GP130 or IL6 receptors. In an exemplary embodiment, the receptor protein is human tumor necrosis factor alpha receptor 1 (hTNF-a receptor 1). In another embodiment, the ligand protein or target molecule is a human ligand protein that is a cognate ligand for one of the aforementioned types of receptor molecules. In another exemplary embodiment, the ligand protein or target protein is human tumor necrosis factor alpha (hTNF-a). In another embodiment, the binding molecule binds to one of the receptor protein, or the cognate ligand as the target protein. In another embodiment, the intracellular organelle is the endoplasmic reticulum (ER) or the Golgi. In another embodiment, the cognate ligand is molecularly tagged with a sequence for retaining the ligand in the endoplasmic reticulum (ER). In another embodiment, the ER retention sequence is KDEL (SEQ ID NO. l).

[0018] In another aspect, the invention provides a method of detecting whether an antibody, or a binding fragment or portion thereof, specifically binds to a cell surface expressed target molecule within a cell, wherein the method comprises expressing in a cell a target molecule which is expressible on the surface of the cell; expressing in the cell an antibody, or a binding fragment or portion thereof, fused to an ER or Golgi retention sequence; wherein, if the antibody, or a binding fragment or portion thereof, specifically binds to the target protein in the cell, the target protein is retained in the ER or Golgi via its being bound to the antibody, or a binding fragment or portion thereof, thereby preventing expression of the target protein on the cell surface; and detecting the level of the target protein expressed on the cell surface, such that a non-detectable or low level of the target protein detected on the cell surface, relative to a suitable control, indicates binding of the antibody, or the binding fragment or portion thereof, to the target molecule in the cell. The antibody, or a binding fragment thereof, is selectable from within the cell via methods known to the skilled practitioner.

[0019] In another of its aspects, the invention provides a method of selecting for an antibody, or a binding fragment or portion thereof, that specifically binds to a target protein expressed on the surface of a cell, wherein the method comprises establishing a cell line which expresses the target protein on the cell surface; wherein the cell surface expressed target protein is capable of being detected by a detectably labeled binding molecule; expressing in the cell line an antibody, or a binding fragment or portion thereof, for selection for binding to the target protein, wherein the antibody, or a binding fragment or portion thereof, is fused to a signal sequence for retaining the antibody, or a binding fragment or portion thereof, in an intracellular organelle under conditions allowing for the interaction and binding of the antibody, or a binding fragment or portion thereof, and the target protein within the organelle; and detecting the level of the target protein expressed on the cell surface with the detectably labeled binding molecule; wherein, if the antibody, or a binding fragment or portion thereof, specifically binds to the target protein in the organelle, the target protein is bindably retained therein, thereby decreasing or virtually eliminating the level of expression of the target protein on the cell surface; and indicating the retention of a selectable antibody, or a binding fragment thereof, that specifically binds to the target protein in the cell.

[0020] In an embodiment of the method set forth directly above, the method further comprises recovering from the cells the antibody, or a binding fragment or portion thereof, that specifically binds to the target protein by conventional methods. In another embodiment, the antibody, or a binding fragment or portion thereof, is fused to a signal sequence for retaining the antibody, or a binding fragment or portion thereof, in the endoplasmic reticulum (ER) intracellular organelle. In another embodiment, the antibody, or a binding fragment or portion thereof, is fused to the KDEL signal sequence (SEQ ID NO:l) which retains the antibody, or a binding fragment or portion thereof, in the ER. In another embodiment, the target protein is a plasma membrane-expressible protein expressed on the cell surface, e.g., a hTNF-a protein. In another embodiment, the cell line is infected or transduced with a lentiviral particle encoding the nucleic acid sequence encoding the antibody, or a binding fragment or portion thereof. In another embodiment, the antibody, or a binding fragment or portion thereof, is a member of an antibody library or a member of a library comprising antibody binding fragments or portions, which may be diversified. In another embodiment, the antibody, or a binding fragment or portion thereof, is a VL and/or VH domain of the antibody. In an exemplary embodiment, the antibody, or a binding fragment or portion thereof, is a VL and/or VH domain that binds hTNF-a. In another embodiment, the antibody, or a binding fragment or portion thereof, is a member of a VL and/or VH domain library. In an exemplary embodiment, the level of the target protein expressed on the cell surface is detected by flow cytometry and a detectably labeled anti-hTNF-a antibody.

[0021] In another of its aspects, the invention provides a method of selecting from a plurality of binding molecules a binding molecule which binds a target antigen that is a member of an interacting pair comprising a cell surface-expressed receptor binding protein and its cognate ligand. Accordingly, the method comprises (a) introducing nucleic acid encoding one of a plurality of binding molecules into cells expressing the receptor binding protein and the cognate ligand fused to a retention signal that retains the cognate ligand in an intracellular organelle; (b) expressing in the cells the nucleic acid of (a), wherein an expressed binding molecule binds to the receptor binding protein or the cognate ligand target antigen retained in the organelle and disrupts or blocks the interaction between the receptor binding protein and the cognate ligand; and (c) detecting the level of receptor binding protein expressed on the cell surface; wherein, if the binding molecule binds to either the receptor binding protein or the cognate ligand in the organelle and disrupts or blocks their interaction, the receptor binding protein is expressed and detectable on the cell surface, and wherein the binding molecule that disrupts or blocks the interaction is selectable. In an embodiment, the nucleic acid encoding one of a plurality of binding molecules is introduced into the cells by lentivirus particles harboring the nucleic acid. In an embodiment, the method further comprises recovering or isolating the selected binding molecule from the cell. In an embodiment of the method, the plurality of binding molecules is selected from an antibody library, a genetically diversified antibody library, a single domain antibody library, a genetically diversified single domain antibody library, a VL library, a genetically diversified VL library, a VH library, or a genetically diversified V_H library. In a specific embodiment, the plurality of binding molecules is a V_L library, a genetically diversified VL library, e.g., as exemplified herein by hTNF-cc VL binding domains. In an embodiment, the binding molecule, or a binding portion thereof, is selected from an antibody, or a binding fragment or portion thereof. In an embodiment, the antibody, or a binding fragment or portion thereof, is selected from a polyclonal antibody, a monoclonal antibody, a chimeric antibody, a humanized antibody, a fully human antibody, or a single chain antibody. In an embodiment, the antibody binding fragment or portion is selected from an Fab fragment, an Fab' fragment, an F(ab')2 fragment, an Fd fragment, an Fv fragment, a single-chain antibody fragment (scFv), a domain antibody (dAb), a diabody, a heavy chain variable domain (V_H), a light chain variable domain (VL), or a complementarity determining region (CDR). In an embodiment, the antibody binding fragment or portion thereof is a VL domain or a genetically diversified VL domain. In an embodiment, the antibody binding fragment or portion thereof is a VH domain or a genetically diversified VH domain. In various embodiments, the intracellular organelle is the ER or the Golgi; the cognate ligand is molecularly tagged with a sequence for retaining the ligand in the ER; and the ER retention sequence is KDEL (SEQ ID NO:l).

[0022] In yet another of its aspects, the invention provides a method of selecting from a plurality of binding molecules, a binding molecule, or a binding portion thereof, that binds a cell surface expressed target antigen. Accordingly, the method comprises introducing into cells nucleic acid sequences encoding one of a plurality of binding molecules operably linked to nucleic acid encoding a intracellular organelle retention signal, wherein the same cells express the target antigen which is expressible on the cell surface; expressing in the cells the plurality of binding molecules comprising the retention signal; wherein, if one of the plurality of binding molecules comprises a binding molecule, or a binding portion thereof, that specifically binds to the target protein, the target protein is retained in the cell organelle through its being bound to the binding molecule, or a binding portion thereof, that is retained in the intracellular organelle via its expressed retention signal, thereby preventing both exit of the target protein from the organelle and expression of the target protein on the cell surface; and detecting the level of the target protein expressed on the cell surface. According to the method, if a non-detectable or low level of the target protein is detected on the cell surface relative to a suitable control, this indicates the specific binding of the binding molecule, or the binding portion thereof, to the target molecule in the cell, wherein the binding molecule, or the binding portion thereof, is selected by the method and may be isolated or recovered from the cells via conventional methods. In an embodiment, the nucleic acid encoding one of the plurality of binding molecules is introduced into the cells by lentivirus particles harboring the nucleic acid. In an embodiment, the method further comprises recovering or isolating the selected binding molecule from the cell. In an embodiment, the plurality of binding molecules is selected from an antibody library, a genetically diversified antibody library, a single domain antibody library, a genetically diversified single domain antibody library, a VL domain library, or a genetically diversified VL library, a VH domain library, or a genetically diversified VH library. In an embodiment, the binding molecule, or a binding portion thereof, is selected from an antibody or a binding fragment or portion thereof. In an embodiment, the antibody, or a binding fragment or portion thereof, is selected from a polyclonal antibody, a monoclonal antibody, a chimeric antibody, a humanized antibody, a fully human antibody, or a single chain antibody. In an embodiment, the antibody binding fragment or portion is selected from an Fab fragment, an Fab' fragment, an F(ab')2 fragment, an Fd fragment, an Fv fragment, a single chain antibody fragment (Fv), a domain antibody (dAb), a diabody, a heavy chain variable domain (VH), a light chain variable domain (VL), or a complementarity determining region (CDR). In an embodiment, the plurality of binding molecules is an antibody V_L library or a genetically diversified VL library. In an embodiment, the antibody binding fragment or portion thereof is a VL domain or a genetically diversified VL domain. In an embodiment, the plurality of binding molecules is an antibody VH library or a genetically diversified V_H library. In an embodiment, the antibody binding fragment or portion thereof is a VH domain or a genetically diversified V_H domain. In an embodiment, the intracellular organelle retention signal is an endoplasmic reticulum (ER) or Golgi retention signal. In an embodiment, the ER retention sequence is KDEL (SEQ ID NO:l).

[0023] In another of its aspects, the invention provides a method of selecting from a plurality of binding molecules a binding molecule which binds a target antigen that is a member of an interacting pair comprising a cell surface-expressed receptor binding protein and a cognate ligand, the method comprising: (a) co-expressing in a single cell which expresses the receptor binding protein: (i) nucleic acid sequence encoding one of a plurality of binding molecules, and (ii) nucleic acid sequence encoding a cognate ligand of the receptor binding protein, wherein either the binding molecule or the cognate ligand is operably coupled to a nucleic acid sequence encoding a retention signal for retaining either (i) or (ii) in an intracellular organelle following expression of (i) or (ii) in the cell; under conditions allowing for retention of the expressed binding molecule or the expressed cognate ligand in the intracellular organelle; wherein, if an expressed binding molecule binds to the receptor binding protein or the cognate ligand as target antigen, such binding disrupts, neutralizes, or blocks the natural interaction between the receptor binding protein and the cognate ligand and releases the receptor binding protein from its interaction with the cognate ligand for expression of the receptor binding protein on the cell surface; and (b) detecting the level of receptor binding protein expressed on the cell surface such that a high level of receptor binding protein expression of the cell surface indicates the expression and selection of a specific binding molecule which binds target antigen within the cell. In an embodiment of the method, the plurality of binding molecules is selected from an antibody library, a genetically diversified antibody library, a single domain antibody library, a genetically diversified single domain antibody library, a V_L domain library, a genetically diversified VL domain library, a VH domain library, or a genetically diversified VH domain library. In an embodiment, the binding molecule is an antibody or a binding fragment or portion thereof, such as an Fab fragment, an Fab¹ fragment, an F(ab')2 fragment, an Fd fragment, an Fv fragment, a single-chain variable fragment (scFv), a diabody, a domain antibody (dAb), a heavy chain variable domain (VH), a genetically diversified heavy chain variable domain (VH), a light chain variable domain (VL), a genetically diversified light chain variable domain (VL), or a complementarity determining region (CDR). In embodiments, the binding molecule is a VL domain, a genetically diversified V_L domain, a VH domain, or a genetically diversified V_H domain. In embodiments, the binding molecule is a full length antibody comprising light chain variable domains and light chain constant domains, and heavy chain variable domains and heavy chain constant domains, such as an IgG antibody or a subclass thereof, e.g. an IgGl antibody. In embodiments, the intracellular organelle is the endoplasmic reticulum (ER) or the Golgi and the intracellular organelle retention signal is a KDEL amino acid sequence (SEQ ID NO:l). In embodiments the target antigen can be the types of receptor proteins or cognate Iigands as described herein.

[0024] In yet another aspect, the invention provides a method of preventing or "knocking down" cell surface expression of a ligand-binding receptor protein, wherein the method comprises expressing in a cell the ligand-binding receptor protein; expressing in the cell a ligand protein capable of being bound by the ligand-binding receptor protein, wherein the ligand protein is fused to an exogenous signal sequence for retaining the ligand protein in an intracellular organelle, under conditions permitting the interaction of the ligand-binding receptor protein and the ligand protein in the organelle; measuring the level of the ligand-binding receptor protein expressed on the cell surface; wherein the binding of the ligand-binding receptor protein to the ligand protein retained in the organelle concomitantly retains in the organelle the ligand-binding receptor protein bound to the ligand protein, thereby preventing or "knocking down" the cell surface expression of the ligand-binding receptor protein.

[0025] In another of its aspects, the invention provides a method of generating genetic diversity or variability in a binding molecule, or a binding portion thereof, such as an antibody, by modifying immunoglobulin complementarity detenrnning regions (CDRs), wherein the method involves (a) introducing into one or more CDR-encoding nucleic acid sequences one or more zinc finger DNA binding domain recognition sequences, thereby producing one or more non-identical targeting sites within the one or more CDR-encoding nucleic acid sequences for binding one or more zinc finger nucleases (ZFN) and producing a modified CDR-encoding nucleic acid sequence; (b) introducing into a nucleic acid sequence encoding a zinc finger nuclease (ZFN) at least one of the one or more zinc finger DNA binding domain recognition sequence targeting sites of (a), which sequences are operably linked to a nucleic acid sequence encoding a DNA cleavage domain of a type IIS restriction enzyme, wherein DNA cleavage by the ZFN is determined by the targeting site within the modified CDR-encoding nucleic acid sequence of (a); and (c) expressing the nucleic acid sequences of (b) in a cell containing nucleic acid encoding at least an antibody heavy chain variable domain (VH) and/or at least an antibody light chain variable domain (VL) containing the modified CDR-encoding nucleic acid sequence of (a) under conditions in which the expressed ZFN binds and cleaves the modified CDR- encoding nucleic acid sequence within the targeting site sequence. It will be appreciated that the one or more zinc finger DNA binding domain recognition sequences are introduced into the nucleic acid sequences encoding one or more of the CDR regions of a nucleic acid sequence encoding an antibody variable region.

[0026] In accordance with this method, within the cell, the processes of recombination, repair and rejoining of cleaved DNA within the modified CDR-encoding nucleic acid sequences provides for hypermutation in and/or around the targeting site sequences, or "hotspots" where the ZFN binds and cleaves the DNA within the CDR. Expression of the resulting CDRs within at least the VH and/or VL regions expressed in the cell ultimately provides genetically diversified binding molecule or antibody products having the potential to exhibit improved or optimal binding to a target antigen. In an embodiment, in (a), the CDR-encoding nucleic acid sequences are contained within a nucleic acid vector or cassette, e.g., a DNA vector, suitable for carrying out molecular biology techniques and genetic manipulation. The zinc finger DNA binding recognition sequences are introduced into the CDR-encoding nucleic acid sequences which are harbored in the vector or cassette to produce the one or more modified CDRs, for example, CDR1, CDR2, or CDR3 of an antibody light chain and/or CDR1, CDR2, or CDR3 of an antibody heavy chain. In an embodim nt, the nucleic acid vector or cassette comprising the one or more modified CDRs is thereafter introduced into nucleic acid sequence encoding a V_L and/or a VH domain such that the resulting locations of the expressed CDRs are in the orientation in which they are normally expressed in the heavy or light chain variable region. In an embodiment, in (a) of the method, the CDR-encoding nucleic acid sequences are contained within nucleic acid sequences encoding an antibody heavy chain variable domain (VH) and/or nucleic acid sequences encoding an antibody light chain variable domain (VL) at the time that the zinc finger DNA binding domain recognition sequences are introduced into the CDR-encoding nucleic acid sequence. In an embodiment, in (c), the modified CDR-encoding nucleic acid sequence is contained within a full length antibody comprising nucleic acid sequences encoding a heavy chain variable domain (V_H) and a heavy chain constant region (C_H), and comprising nucleic acid sequences encoding a light chain variable domain (V_L) and a light chain constant region (CL), wherein the resulting nucleic acid sequences encode full length antibodies comprising V_H and V_L domains comprising modified CDRs. In an embodiment, the method further comprises amplifying and, optimally, cloning the nucleic acid sequences encoding the V_H and/or V_L domain proteins from the cell.

[0027] In another aspect, the invention provides a method of generating a genetically diverse antibody, or a binding fragment or portion thereof, comprising modified complementarity determining regions (CDRs), wherein the method comprises producing one or more modified CDRs by introducing into nucleotide sequences encoding the one or more individual CDRs of antibody V_H and/or V_L domains, one or more zinc finger DNA binding domain nucleic acid recognition sequences (or targeting sites) for binding zinc finger nucleases (ZFNs) that have been engineered to contain the one or more zinc finger binding domain targeting sites as introduced into the CDR-encoding nucleic acid sequences covalently linked to the DNA cleaving domain of a type IIS endonuclease, such as Fokl; wherein the ZFNs cleave within the CDRs as determined by the specificity of the CDR-containing zinc finger DNA binding domain nucleic acid recognition sequences of (a). Nucleic acid sequences encoding V_H and/or V_L domains containing the one or more modified CDRs, or encoding full-length immunoglobulin molecules encoding V_H and/or VL domains containing the one or more modified CDRs, are expressed in cells under the appropriate conditions and time for the ZFNs to cleave within the specific targeting sequence sites in the CDRs and for the cellular recombination and repair proteins to genej ate V_H and/or V_L domains comprising genetically diversified binding regions by virtue of the cleavage within the CDR sequence and the rejoining of sequences within the CDRs with consequent mutations in the original sequence resulting from the intra-CDR hotspots or sites within the CDRs that are bound and cleaved by the ZFNs. In this way, a genetically diverse set of CDR sequences comprising the binding regions of expressed V_H and/or V_L domains, or antibodies comprising such domains, are obtained. Such diversity provides an antibody or a population of antibody molecules which can have improved or optimized binding properties for the target antigen. Additional embodiments embrace the expression of other enzymes or agents, such as chemical agents, that contribute to increasing the genetic diversity of binding regions, particularly those containing one or more modified CDRs as described. Such enzymes or agents include Tax, TdT, or chemical inhibitors of ATM kinase as described herein. In some embodiments, both Tax and TdT are co-expressed; in some embodiments, only Tax or an enzyme having similar function is expressed; in some embodiments, only TdT or an enzyme having similar function is expressed; in some embodiments, Tax, TdT and chemical inhibitors of ATM kinase are co-expressed.

[0028] In the described methods, the nucleic acid sequences encoding the one or more CDRs may originate or be obtained from an antibody or antibodies that bind a known antigen, or they may originate or be obtained from a library encoding antibody molecules having a variety of binding specificities, or unknown target binding specificities. The CDRs may originate or be derived from immunoglobulins of different animal species, including, for example, mammals such as humans, mice, rats, rabbits, guinea pigs, dogs, sheep, cows, horses, pigs and the like. In an embodiment, the CDRs are human CDRs. In an embodiment, the CDRs are non-human CDRs, such as rabbit CDRs, or mouse CDRs, or rat CDRs.

[0029] In embodiments of the methods, the nucleic acid sequences of the modified CDRs and the ZFNs, and, optionally, other enzymes, such as Tax and/or TdT, that contribute to or effect recombination and genetic modification and variation, are introduced into a host cell under conditions in which the ZFNs target and cleave the modified CDRs within the introduced zinc finger binding recognition sites and under conditions for producing genetically diverse, i.e., mutation-containing, antibody products, or binding portions thereof. The mutations resulting from the practice of the genetic diversification methods of the invention may be in the form of, for example, insertions, deletions or substitutions of nucleotides (base pairs) within the CDR hypervariable regions of V,- i and/or VL domains. Such mutations may, following expression of the antibody products, positively affect the binding of the resulting, expressed binding regions to target antigen, i.e., by providing better binding specificity and/or affinity for the target antigen. In an embodiment of the methods, the CDR-encoding nucleic acid sequences are genetically modified outside of the VH and/or V_L domains, e.g., within a nucleic acid vector and/or cassette, and are subsequently introduced into the VH and/or VL domain-encoding nucleic acid sequences. In an embodiment, the CDR-encoding nucleic acid sequences are genetically modified in the CDR locus within the V_H and/or V_L domains in which they reside. In an embodiment of the methods, the modified CDR-encoding nucleic acid sequences are introduced into the nucleic acid sequences encoding the VH and/or VL domains of an antibody protein. In an embodiment, the nucleic acid sequences encoding the VH and/or VL domains comprising the genetically modified CDRs are, in turn, molecularly cloned to be operably expressed with nucleic acid sequences encoding antibody heavy (H) and light (L) chains, wherein the resulting nucleic acid sequence encodes an antibody protein comprising modified CDR regions comprising different ZFN recognition sites within the VH and V_L domains.

[0030] In an embodiment, the nucleic acid sequences encoding the modified CDRs; or the nucleic acid sequences encoding VH and/or VL domains into which the modified CDRs have been introduced; or the nucleic acid sequences encoding a full-length antibody comprising VH and/or VL domains comprising modified CDRs, are expressed in a suitable host cell using one or more suitable expression vectors, e.g., lentivirus vectors. The resulting V_H and/or VL domains comprising modified CDRs, or one or more antibodies comprising VH and/or VL domains comprising modified CDRs, can be screened or selected for binding to a target antigen within the same cell according to the described methods herein. In an embodiment, the selection method comprises the methods of the invention described herein in which the VH and/or VL domain or antibody binds to target antigen, i.e., one member of a binding pair comprising a receptor binding protein or its cognate ligand, within the same cell. As described in detail herein, the cognate ligand is typically fused or coupled to a retention signal that retains the ligand in an organelle such as the ER. If the VH and/or VL domain or antibody comprising such V_H and/or VL domains binds either the receptor binding protein or its ligand within the environment of the ER, the binding interaction between receptor protein and cognate ligand is disrupted, neutralized, or blocked. The ligand is retained in the organelle by virtue of its retention signal; however, the receptor protein, freed from its interaction with its ligand, can transit through the ER and be expressed on the cell surface. Such cell surface expression of the "released" receptor is detectable (and quantifiable) by the binding of specific antibodies and detection thereof, e.g., by flow cytometry. The detection of signal, relative to controls, indicates that the cell contains a VH and/or VL domain or antibody which binds to the target molecule within the cell, and that such a binding event has effectively disrupted, neutralized, or blocked the receptor-ligand interaction.

[0031] In other embodiments, the methods further comprise isolating or recovering the nucleic acid sequence encoding the binding molecule, or a binding portion thereof, e.g., an antibody or a binding portion thereof, produced in the cells, amplifying the encoding nucleic acid sequences, e.g., by PCR, and cloning the nucleic acid sequences encoding binding molecule, or a binding portion thereof, e.g., an antibody, or a binding portion thereof, or a genetically diverse form thereof from the cell.

[0032] In the methods of intracellularly generating a genetically diverse binding protein, such as an antibody, or a binding fragment or portion thereof, comprising one or more modified CDRs and ZF nucleases as described herein, further genetic diversity and variability leading to improved or increased binding capability, activity, or function by the binding molecule is achieved, in addition to ZFN activity, by expressing Tax protein, or a protein having similar function to Tax, together with terminal transferase (TdT) in the cell, or by expressing only a Tax protein. In accordance with the methods of the invention, an intracellularly genetically modified and diversified binding protein (antibody or a binding portion thereof) can be detected on the cell surface through its binding to a labeled, detectable antigen using conventional detection methods. Cell surface expression of an antibody, or a binding portion thereof, containing modified CDR regions and genetically diversified in a cell through the methods of the invention as described herein is accomplished, for example, by creating a fusion molecule comprising at least the binding region of the antibody and a suitable transmembrane (TM) domain and a leader sequence as known and used in the molecular arts and as described and exemplified herein (e.g., Example 6)·

[0033] In another of its aspects, the present invention provides a method of screening or selecting for a small molecule which blocks, inhibits, or disrupts an interaction between a cell surface expressed binding protein and its cognate ligand within a cell, in which the method comprises i) expressing in the same cell a binding protein which is expressible on the surface of the cell and a cognate ligand of the binding protein, wherein the cognate ligand is molecularly tagged or fused with a sequence for retaining the ligand in an intracellular organelle under conditions allowing for the retention of the ligand in the organelle and the interaction of the binding protein and the cognate ligand in the organelle, such that the binding protein is retained within the cellular organelle when bound to the tagged ligand; ii) introducing into the cell a small molecule to determine if it binds, associates, or interacts with either the binding protein or the ligand protein retained in the intracellular organelle; and iii) detecting the level of the binding protein expressed on the cell surface; wherein, if the small molecule binds intracellularly to either the binding protein or the ligand and blocks, inhibits, or disrupts the interaction of the binding protein and its ligand in the organelle, the binding protein is no longer retained in the organelle through its interaction with ligand and thereby transits through the organelle and is expressed and detectable on the cell surface. The binding protein can be a receptor protein as described herein. The ligand can be a protein as described herein. The small molecule can be, without limitation, a small molecule chemical compound, a low molecular weight organic compound, a drug, or a chemical agent. The molecular weight of the low molecular weight organic compound is typically less than or equal to 500 Daltons or is less than 900 Daltons. According to the method, the ligand is fused or tagged with a retention sequence for retention in an intracellular organelle such as the ER or the Golgi. For retention in the ER, the retention sequence (tag sequence) comprises KDEL (SEQ E) NO:l). Pursuant to the method, the small molecule, which has bound, associated or interacted with one or both of the binding protein and/or its ligand, thereby inhibits, blocks, interrupts, or disrupts the binding protein and ligand interaction, allowing the cell surface expressible binding protein, which can no longer interact with its ligand, to transit from the intracellular organelle and become expressed on the cell surface where it can be detected, e.g., by a detectable label binding or flow cytometry, and/or growth expansion of the cells. The method is suitable for use with pools or populations of candidate small molecules and/or for screening or selecting sets of candidate small molecules, e.g., chemical libraries and other collections of small molecules. In addition, the method can be used to screen or select sets of derivatives or analogs of a particular small molecule compound.

BRIEF DESCRIPTION OF THE DRAWINGS

[0034] FIGS. 1A-1D show a schematic depiction of an aspect of the invention as described herein in which a KDEL- (SEQ ID NO:l) tagged ligand protein is retained in the endoplasmic reticulum of the cell. Briefly, as shown, FIGS. 1A-1D present a demonstration of the technology and method of the invention as tested using recombinant antibodies directed either to the ligand binding receptor protein hTNF-a receptor I, or to its cognate ligand protein hTNF-a and showing that both types of antibodies can block or disrupt the interaction between the ligand receptor protein hTNF-a receptor I and its cognate ligand hTNF-a. As depicted, a Jurkat cell line expressing a representative receptor protein, i.e., hTNF-a receptor I, at the surface of the cell was molecularly engineered to express and retain certain of the expressed proteins in accordance with the invention. The presence of the receptor at the cell surface can be detected by a detectably labeled, e.g., fluorescence, antibody directed to hTNF-a receptor I. Abbreviations: ER, endoplasmic reticulum; hTNF-a, human tumor necrosis factor alpha; KDEL (SEQ ID NO:l), retention signal for ER; VL, light chain variable region from anti- hTNF-a receptor I antibody.

[0035] FIGS. 2 A and 2B show a schematic representation of an antibody (VL domain) tagged with the KDEL sequence (SEQ ID NO:l) to retain the antibody in the ER. . As shown in FIG. 2A, the cell surface-expressed hTNF-a protein is detected at the surface of the cell by a detectable antibody that specifically recognizes and binds the cell surface-expressed hTNF-a protein. In FIG. 2B, because the cells are transduced with VL antibody-KDEL molecules ("KDEL" disclosed as SEQ ID NO:l), the V_L antibody that specifically binds to hTNF-a protein retains this target protein in the ER, and the hTNF-a protein is no longer detected at the surface of the cell by the detectable antibody. Abbreviations: ER, endoplasmic reticulum; hTNF-a, human tumor necrosis factor alpha; KDEL (SEQ ID NO:l), retention signal for ER; VL, light chain variable region from an hTNF-a antibody; "TNF-a-tmd-TEV", a TNF-a target protein comprising a transmembane domain (tmd) and fused to the TEV protease (catalytic domain of the Nuclear Inclusion a (NIa) protein encoded by the tobacco etch virus (TEV)) as a cytoplasmic domain.

[0036] FIG. 3 shows the localization of zinc finger target sequences as introduced into the CDR regions, e.g., CDR1 and CDR3, of the human heavy chain variable domain (VH) and the human light chain variable domain (VL). The zinc-finger target sequences were introduced into the CDR region with three different sequence frames to suppress frame shift and a consequent lack of antibody production. The resulting human variable domains were reintroduced into human immunoglobulin type Gl (IgGl), resulting in a complete antibody protein with molecularly engineered CDR1 and CDR3 regions containing different zinc-finger recognition sites. In each CDR, two different zinc-finger recognition sites were positioned and were able to be recognized by two different zinc-finger-nucleases. CDR1 and CDR3 were targeted by this strategy to induce specific cleavage within these sites, leading to genetic diversification of the resulting antibodies. Depending on the variability desired, CDR2 can remain unchanged, or can also be subjected to zinc-finger targeting, similar to that achieved for the CDR1 and CDR3 regions. In an intact IgG immunoglobulin protein, a total of four distinct zinc-finger "hotspots", i.e., nucleic acid recognition sequences of zinc finger DNA binding proteins introduced into the CDRs for targeting by specific zinc finger nucleases (ZFNs) as described herein, in the human heavy chain variable domain (hVn) and four distinct zinc-finger hotspots in the human light chain variable domain (tiV_L) were introduced for generating diversity and variability in antibody binding regions in accordance with the present invention.

[0037] FIG. 4 shows the localization of zinc finger target sequence sites in the human V_H and V_L regions so as to encompass all three reading frames. Each zinc-finger hotspot was positioned in frames +1, +2 and +3 to compensate for the random insertion and deletion of nucleotides. The combinatorial factor of different zinc-finger hotspots positioned in all frames is 81 different constructs in each variable chain. Thus, a total of 6561 different variants of zinc- finger hotspots in IgG VH and V_L regions can be generated. Constructs harboring the described variable regions containing zinc finger sites within the CDRs can be introduced into IgGl, IgG2 or IgG4 immunoglobulin backbones by molecular techniques to generate different antibody classes having diverse and variable binding specificities.

[0038] FIG. 5 shows a schematic depiction of the plasmids constructed to express all Zinc Finger Nucleases 1-4 in tandem in the backbone of the lentiviral vector FugW. In one plasmid zinc-fmger-nuclease was cloned by overlap PCR with a 2A sequence separating each gene. ZFN1 VH and ZFN2VH target CDRl in the heavy chain variable region; ZFN3 VH and ZFN4VH target CDR3 in the heavy chain variable region; ZFNIVL and ZFN2VL target CDRl in the light chain variable region; and ZFN3VL and ZFN4VL target CDR3 in the light chain variable region. The lentiviral vector for zinc-finger-nucleases targeting V_H contains a puromycin resistance gene; and the lentiviral vector for zinc-finger-nucleases targeting V_L contains a neomycin resistance gene. Abbreviations: ZFN1, ZFN2, ZFN3, ZFN4, Zinc Finger Nucleases 1-4; IRES, Internal Ribosome Elongation Sequence. As understood by the skilled practitioner, the internal ribosome entry site (IRES) is a noncoding RNA fragment with the ability to initiate high levels of cap-independent protein synthesis in mammalian cells. IRES sequences are used to express two proteins from a single promoter in an expression construct or a transgenic construct. A single RNA is produced, but due to the presence of the IRES, a second translational start is possible on the same RNA. As utilized in the described vectors, IRES sequences permit expression of the ZFN together with a selection marker for construction of cell lines.

[0039] FIGS. 6A-6E show schematic representations of various plasmids used to construct cell lines for demonstrating and carrying out the methods of the present invention. (A) PV_L18- IRES-DsRed, (B) pV_L18KDEL-IRES-DsRed (" DEL" disclosed as SEQ ID NO:l), (C) pTNFKDEL-IRES-DsRed ("KDEL" disclosed as SEQ ID NO:l), (D) pTNF-TEV, and (E) pT AX-IRE S-DsRed. BamHl restriction enzyme; c-Myc: c-Myc tag; DsRed: red fluorescence protein; Eco l: restriction enzyme; HA: hemagglutinin tag; Tax: Transactivator of HTLV-I; His₆ (SEQ ID NO:48): histidine tag; Hpal: restriction enzyme; hTNF-a, human tumor necrosis factor alpha; PDGFR tmd: transmembrane region of the platelet derived growth factor receptor (PDGFR); hUbc: human ubiquitin C promoter; IgG -chain leader: murine Ig-K-chain leader sequence; IRES: internal ribosome entry site; KDEL (SEQ ID NO:l): retention signal for endoplasmic reticulum; Nhel: restriction enzyme; Sfil: restriction enzyme; and TEV: tobacco etch virus protease.

[0040] FIGS. 7A and 7B show verification results of the selection methods of the invention as determined by flow cytometry screening analysis of anti-hTNF-a antibody libraries diversified using the zinc finger nuclease methodology described herein. (7 A): Antibody library without diversification; (7B): Antibody library with diversification. Cell populations were produced which expressed antibody in the absence of zinc-finger hotspots and induced diversification (7A). Other cell populations were produced which expressed antibody engineered to contain zinc finger hotspots and induced genetic diversification and which also expressed zinc finger proteins and Tax. (7B). After several cycles of sorting by flow cytometry those cells selected by the methods of the invention for having reduced expression of antigen (hTNF-a) at the cell surface, antibodies and clonal populations thereof, which bind a target molecule and reduce expression of hTNF -a at cell surface were isolated.

[0041] FIG. 8 shows the results of an ELISA assay ("Ab-KDEL" (SEQ ID NO: 1)) in which antibody fragments derived from the selection methods of the invention were cloned into the pT7 expression vector (Sigma- Aldrich. St. Louis, MO), expressed and assayed by ELISA for binding to hTNF-a. A selected antibody/clone was grown in auto-induction medium. After 16 hours, the cells were lysed and the supernatant was used for the expression and binding assay in ELISA (using 200 ng of hTNF-a). BL21: bacteria used for transformation by the vectors harboring antibody-encoding DNA (used as negative control); hF63: single-domain antibody VL selected via phage-display against HIV-l gp41 antigen (used as irrelevant control); VL18, single-domain antibody VL against hTNF-a; VHH: camel-single-domain antibody against hTNF-a (Ablynx); #1-14 VL18 maturation: clones chosen after VL18 antibody maturation in transformed cells; #1- 14 hF63 maturation: clones chosen after hF63 antibody maturation in transformed cells. The results as shown indicate maturation of a light chain antibody fragment (VL) that binds to hTNF- <X(VL18) as produced via the diversification methods according to the invention. The irrelevant antibody (F63) that does not bind hTNF-a was used as a control in assays performed in parallel As depicted in the graph, several monoclonal V_L antibodies derived from VL18 showed higher binding to hTNF-a indicating maturation of the antibody. Similarly, antibodies derived from F63 also showed higher binding, indicating that these antibodies have evolved to recognize a different antigen.

[0042] FIGS. 9 A and 9B show the results of experiments in which diversified antibody is expressed on the surface of cells and assayed for binding to detectably labeled, purified antigen, as described in Example 6 herein. The expressed antibody was produced in 293T cells in which co-expressed tax protein (Tax) and terminal transferase (TdT) proteins were either present or absent. FIG. 9A (VHH anti-IgG (ZFN)) shows single VHH antibody clones into which ZF recognition sites were introduced, which were expressed on the surface of 293T cells and identified as having specificity for binding to IgG antigen. The 293T cells of FIG. 9A were transfected with nucleic acid constructs encoding the VHH antibody and ZF nucleases, without expression of Tax and terminal transferase (TdT) proteins. FIG. 9B (VHH anti-IgG (ZFN + Tax/TdT)) shows single VHH antibody clones into which ZF recognition sites were introduced, which were expressed on the surface of 293 T cells and identified as having specificity for binding to IgG antigen. The 293T cells of FIG. 9B were transfected with nucleic acid constructs encoding the VHH antibody and ZF nucleases, and also with co-expression of Tax and TdT proteins.

[0043] FIGS. 10 A and 10B show the nucleic acid sequence of the Tax gene of HTLV-1 (Genbank: AB038239.1), (FIG. 10A, SEQ ID NO:46); and the nucleic acid sequence (mRNA) of Homo sapiens terminal deoxynucleotidyltransferase (TdT), (GenBank: AB046378.1), (FIG. 10B, SEQ ID NO:47).

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0044] Described herein are a platform technology and methods for selecting a binding molecule, e.g., an antibody, or a binding portion thereof, that specifically recognizes and binds a target molecule, preferably a protein, polypeptide, or peptide, within a cell. The methods involve the co-expression in a cell of (i) the binding molecule, (ii) its target, which, in an aspect of the invention can be a cognate ligand member of a cell-surface expressible receptor protein-cognate ligand binding pair, and (iii) the cell-surface expressible receptor protein with which the cognate ligand interacts. The cognate ligand can be fused to an intracellular organelle retention signal, (e.g., an endoplasmic reticulum (ER) retention signal), such that when the cognate ligand binds and interacts with the receptor protein in the cell, both are retained and localized in the cell organelle by virtue of the ligand's possessing the retention signal. The presence of the binding molecule within the same cell as its target, the cognate ligand, allows the binding molecule to bind its target within the cell, thereby disrupting, neutralizing, or blocking the typical binding interaction between the cognate ligand target and its receptor protein. This disruption of the interaction between the ligand binding pair by the binding molecule allows the receptor protein to exit the organelle, travel to the cell surface and be expressed on the cell surface, while the cognate ligand is retained in the cellular organelle. The receptor protein, displayed on the cell surface is detectable by a specific detectable agent and detection methods, and indicates the presence of the binding molecule within the cell. The binding activity of the binding molecule to its target (the cognate ligand member of the ligand binding pair) results in the release of the receptor protein from its binding interaction with cognate ligand and its expression and detection on the cell surface. The binding molecule can be isolated from the cell in which it has been selected by the methods of the invention. Variations on the technology and methods of the invention are further described herein.

[0045] The technology and methods of the invention are useful and advantageous for (i) reducing undesirable variables due to recombinant and amplification techniques; (ii) combining affinity and expression maturation o binding molecules, such as antibodies; (iii) promoting binding molecule or antibody selection for target proteins at a native location in the cell; and (iv) integrating the foregoing features using high-throughput screening or selection methods. Accordingly the invention encompasses a new platform technology and methods that couple the aspects of effective selection, expression and maturation of binding molecules, such as antibodies, with their binding to target proteins or antigens in a cellular environment, in which both the binding and the target molecules are located and expressed.

[0046] In an embodiment, the binding molecule is an antibody, or a binding fragment or portion thereof, which specifically binds a target molecule or antigen, as described herein. In an embodiment, the binding molecule is a V_L and/or a VH domain portion of an antibody. In an embodiment, the VL and/or VH domain, or the antibody, or a binding fragment or portion thereof, is genetically diversified as described herein. In an embodiment, a library of binding molecules is used for selecting or screening for those member molecules that specifically bind a target molecule or antigen in accordance with the methods of the invention. In an embodiment, an antibody library, either constructed or otherwise obtained, is used for selecting or screening for those antibodies that specifically bind a target molecule or antigen. In an embodiment, the antibodies, or binding portions thereof, are genetically diversified by the methods as described herein and are selected or screened for binding to a target antigen utilizing the cellular selection methods described herein.

[0047] In an embodiment, the target molecule is a ligand binding molecule, e.g., a ligand binding receptor protein, i.e., "receptor protein", that is expressed on the cell surface. In an embodiment, the receptor protein is a membrane-spanning receptor protein comprising an extracellular domain that can be recognized and bound by a specific antibody. In an embodiment, the target molecule is a protein or antigen, e.g., a cognate ligand, that binds and interacts with a ligand binding molecule, e.g., a ligand binding receptor protein. The cognate ligand is preferably a protein, polypeptide, or peptide. In an embodiment, the cognate ligand or ligand binding protein can be expressed, or can be molecularly engineered to be expressed, in the cell's plasma membrane.

[0048] Expression of the ligand binding molecule, or receptor protein, or the cognate ligand in the cell membrane relates to the ability of the ligand binding molecule or the cognate ligand to be recognized and specifically bound by a detectable molecule, such as an antibody, in a suitable detection assay. Accordingly, a bindable portion of the ligand binding molecule or the cognate ligand is exposed to the extracellular environment such that it (and its relevant epitopes) can be specifically recognized and bound by the detectable molecule or antibody. In an embodiment, the detectable molecule or antibody, e.g., a "first" antibody, can be directly labeled with a detectable label, which can be detected, measured, or quantified by conventional methods. In an embodiment, the detectable molecule or antibody is not directly labeled, but instead is specifically bound by a secondary binding molecule or antibody, which is detectably labeled and can be detected, measured, or quantified. The detectable secondary binding molecule or antibody serves as an indirect label for the first antibody, which may provide a higher or more optimal signal, such as in flow cytometry detection methods.

[0049] As used herein a "binding molecule" refers to a molecule, or a binding fragment or portion thereof, that binds to a target molecule or antigen. A binding molecule is preferably a protein, polypeptide, or peptide that can recognize and bind to a target molecule or antigen. The target molecule or antigen is preferably a protein, a glycoprotein, a polypeptide or a peptide. The binding molecule can be an antibody or immunoglobulin, or a binding or functional fragment or portion thereof. A functional fragment or portion of an antibody or immunoglobulin encompasses a binding fragment or portion thereof, such as a VL and/or a V_H domain, that specifically binds to a target molecule. The binding molecule may also be a non-antibody molecule or a functional fragment or portion thereof.

[0050] The target molecule or antigen that is bound by a binding molecule or antibody may be a ligand binding protein (or ligand binding receptor protein), polypeptide, or peptide, such as a receptor protein, e.g., a cell-surface expressed receptor protein, that typically binds to a cognate ligand or ligand protein. A "cognate ligand" or "ligand protein" refers to the ligand / protein / peptide, etc. with which the Ugand binding protein typically interacts and/or binds. The cognate ligand may be modified, derivatized, or fused to other sequences or domains; however, it can still interact with its ligand binding protein or receptor protein. Alternatively, the target molecule or antigen that is bound by a binding molecule or antibody may be a cognate ligand that interacts with and/or binds to its ligand binding protein to form an interacting ligand binding protein/cognate ligand pair, also termed a "binding pair" herein. A nonlimiting example of a ligand binding receptor protein is human TNF-a receptor 1 (hTNF-a receptor 1), while a nonlimiting example of its cognate ligand is human TNF-a (hTNF-a). Illustratively, human TNF-a receptor 1 interacts with and binds human TNF-a (hTNF-a) and together they form a binding pair, with each protein being a member of the binding pair. It will be understood that throughout this application, human TNF-a receptor 1 (hTNF-a receptor 1) represents a nonlimiting example of a ligand binding receptor protein that interacts with and binds human TNF-a (hTNF-a), which represents a nonlimiting example of a cognate ligand. Accordingly, verification of the selection and diversification methods of the invention using such a ligand binding protein-cognate ligand pair, for example, as set forth in the Examples herein, are not intended to limit the various embodiments of the invention in any way. [0051] The term "antibody" includes an intact immunoglobulin having four polypeptide chains, two heavy (H) chains and two light (L) chains linked by disulfide bonds. The term "antibody" is synonymous with the term "immunoglobulin" and encompasses polyclonal antibodies, monoclonal antibodies (mAbs), chimeric antibodies, humanized antibodies, fully human antibodies, single chain antibodies and molecules having functionality to bind a specified target, protein, or antigen. The term "antibody" also encompasses antibody fragments or portions thereof, illustratively including, but not limited to, fragments such as an Fab fragment, an Fab' fragment, an F(ab')2 fragment, an Fd fragment, an Fv fragment, a single-chain variable fragment (scFv), a diabody and a domain antibody (dAb). Also encompassed by "antibody" are the variable (V) regions of the H and L chains of the antibody, i.e., V_H and VL, respectively, that contain complementarity detennining regions (CDRs) or regions of hypervariability that typically interact with epitopes on antigen or target molecules that are specifically targeted, recognized and bound by antibodies. Preferably, antibodies and fragments and portions thereof are functional fragments and portions in that they target and specifically bind a target antigen or target protein, such as a ligand binding protein or a cognate ligand protein in accordance with aspects of the invention. The antibodies may be from any species or derivable therefrom, e.g., human, non-human primate, sheep, goat, mouse, rat, rabbit, dog, cow, pig, and the like. In an embodiment, the antibodies are human antibodies. In an embodiment, the antibodies are humanized antibodies. In addition, the antibodies, or binding fragments or portions thereof, may be of any class, e.g., IgM, IgA, IgD, IgG, or IgE, or of any subclass thereof, e.g., IgGl, IgG2, IgG2a, IgG2b, IgG3, or IgG4. In an embodiment, the antibody, or a binding fragment thereof, is an IgGl antibody. The antibody light chains, or fragments or portions thereof, may be of the kappa or lambda type. It will be understood that as used herein, the term antibody is meant to encompass a binding and/or functional fragment and portion thereof.

[0052] In some embodiments, the methods encompass the use of an antibody library, e.g., a cloned library of immunoglobulins, or a library of functional fragments or portions of antibodies, such as a single domain antibody (SDA) library, e.g., library of V_L regions. Antibody libraries, including diversified antibody libraries, are particularly useful for selecting antibodies with high or optimal affinity or specificity for binding a given target protein in accordance with the methods of the invention as further described herein. Antibodies or portions thereof that are derived or produced from antibody libraries that have been genetically diversified by the methods described herein are also useful for selecting for their binding capabilities to a given target antigen / target protein within a cell in accordance with the methods of the invention.

[0053] Antibodies and antigen binding antibody fragments and methods for their generation, e.g., employing conventional molecular techniques, are known in the art and are described in further detail, for instance, in Antibody Engineering, Kontermann, R. and Dubel, S. (Eds.), Springer, 2001; Harlow, E. and Lane, D., Antibodies: A Laboratory Manual, Cold Spring Harbor Laboratory Press, 1988; Ausubel, F. et al., (Eds.), Short Protocols in Molecular Biology, Wiley, 2002; J. D. Pound (Ed.) Immunochemical Protocols, Methods in Molecular Biology, Humana Press; 2nd ed., 1998; B. K. C. Lo (Ed.), Antibody Engineering: Methods and Protocols, Methods in Molecular Biology, Humana Press, 2003; and Kohler, G. and Milstein, C, Nature, 256:495-497 (1975) [1].

[0054] In other embodiments, the binding molecules encompassed by the invention include proteins, polypeptides, peptides, modified and derivatized forms thereof; antibody mimetics, e.g., designed ankyrin repeat proteins (DARPins), affilins, affitins, avimers, anticalins, monobodies, affibody molecules; or a molecule or substance that interacts with the cell membrane and binds a protein or can be bound, e.g., haptomers, aptamers, etc.

[0055] In an embodiment, the binding molecule, e.g., an antibody, which has been introduced into a cell by recombinant techniques, expressed and produced in the cell and demonstrated to bind to a target molecule as described herein, can be recovered or isolated from cells using conventional methods in the art. For example, genomic DNA can be isolated and specific fragments amplified using primer oligonucleotides from a cell that has been selected for expression of an antibody which binds a particular target molecule as described in the methods of the invention. A plasmid vector constructed to harbor the amplified DNA fragments can be used to transform bacteria and colonies expressing cloned segments containing antibody- encoding DNA are assayed by binding analysis for expression of antibodies having specific binding properties. See, e.g., Example 4 herein. Antibodies can be expressed directly from the isolated cell clones, without the need for re-cloning. In addition, the cell clones can be isolated and antibody-encoding genes, e.g., IgG antibody-encoding genes, can be amplified, e.g., by polymerase chain reaction (PCR), and re-cloned, for example, in a mammalian expression plasmid for expression and subsequent purification. Optionally, the binding molecule, e.g., an antibody, can be further modified, developed, or purified for therapeutic use using methods known to the skilled practitioner. In an embodiment, the binding molecule, e.g., an antibody, which binds to a ligand binding receptor protein or a ligand protein is identified, recovered, or isolated from cells, and optionally purified, for further use.

[0056] According to the invention, antibodies generated and/or selected by the described methods may be employed as therapeutic biological agents. For example, antibodies selected using the described methods may demonstrate improved, more desirable, and/or optimal structural and functional properties compared with known or used antibodies. Through the genetic diversification and selection methods of the invention, binding molecules are provided which may show improved, desirable and/or optimal binding to a cell receptor protein or its cognate ligand, either of which may be associated with a disease, pathology or condition in a subject, such as a human patient, needing treatment. Such binding molecules, e.g., antibodies, when employed as therapeutic agents, may, for example, block, inhibit, or disrupt the binding of a ligand to its cell surface-expressed receptor and prevent activation of intracellular signaling events leading to cell transformation, uncontrolled cell proliferation, or cancer. If the binding molecule is an antibody, the antibody may be directed against a cell surface ligand binding receptor protein and may exhibit enhanced binding and/or functional properties. An antibody as binding molecule may alternatively be directed against a ligand binding protein and may exhibit enhanced binding and/or functional properties.

[0057] In an exemplary embodiment in which the selected antibody is directed against human tumor necrosis factor-a (hTNF- a) receptor, such an antibody may be used, for example, in blocking or antagonizing the binding of hTNF- a to its receptor so as to treat a disease or condition associated with hTNF- a expression, e.g., aberrant expression or over-expression, in a subject, preferably a human subject, although treatment of other non-human species is encompassed for the binding molecule products of the methods described herein. Similarly, an antibody directed against the hTNF- a ligand of the hTNF- a receptor may also serve to block the binding of the ligand to its receptor, thereby antagonizing the receptor-ligand interaction and treating a hTNF- a-associated disease or condition. For example, human TNF (such as TNF-a) binding molecules or antagonists, e.g., antibodies and fusion proteins, are useful in the treatment of several immune-mediated, e.g., autoimmune, inflammatory diseases, such as rheumatoid arthritis (RA), juvenile rheumatoid and psoriatic arthritis, plaque psoriasis, ankylosing spondylitis, or inflammatory bowel disease (IBD). Also encompassed by the invention are binding molecules, such as antibodies, that are selected, or diversified and selected, by the cellular methods described herein, wherein the binding molecules, or antibodies, bind other types of receptors expressed on the cell surface, or their cognate ligands. By binding to either the ligand binding receptor protein or the cognate ligand, such antibodies may block, disrupt, inhibit, or eliminate the receptor-ligand interaction.

[0058] An antibody, binding molecule, or binding protein included in the embodiments of the present methods may include, or be detectable using, a detectable label. Detectable labels may also be used in various aspects and embodiments of the described methods, e.g., for detection and confirmation of the presence of intracellularly expressed proteins, including binding molecules or antibodies, by flow cytometry methods in which a detectably labeled antibody (or reporter molecule) is used to bind cell surface expressed proteins. Illustrative examples of detectable labels include, without limitation, fluorescent labels, e.g., fluorescein isothiocyanate (FITC), rhodamine, green fluorescent protein (GFP), DsRed; radioactive labels, e.g., ¹³C, ¹³ 'i, ¹²⁵I, ³H; chemiluminescent labels, e.g., luminol; enzyme labels, e.g., alkaline phosphatase, horseradish peroxidase, glucose oxidase, beta-galactosidase; FRET labels, e.g., europium, in which the detectable label is a FRET donor which interacts via FRET with a FRET acceptor incorporated into a given substrate; biotin label and strepavidin label for the subsequent binding of biotin and strepavidin, wherein either biotin or strepavidin is present on one or the other member of binding pair of molecules. When an enzyme is used as the labeling substance, detection is performed using a suitable substrate depending on the enzyme used. For example, if peroxidase is used as an enzyme label, the substrate o-phenylenediamine (OPD), tetramethyl benzidine (TMB), or the like, is used. If alkaline phosphat se is used as an enzyme label, the substrate p-nitrophenyl phosphate (PNPP), or the like is used.

[0059] In an embodiment, a fluorescent label is used and is detectable and quantifiable by flow cytometry methods. In another embodiment, an antibody against a cell-surface expressed target molecule or protein is detectably labeled with a fluorescence label and the binding or non- binding of the antibody to the cell-surface expressed target molecule or protein is determined, thereby allowing, in turn, detection and quantification of the level of the target molecule or protein on the cell surface. In another embodiment, a labeled secondary antibody is used, which specifically binds to the antibody that binds to the cell-surface expressed target molecule. [0060] Examples of ligand binding proteins or receptor proteins as referred to herein include, without limitation, growth factor receptors, hormone receptors, enzyme receptors, Fc receptors, metabolic enzyme receptors, neurotransmitter receptors, chemokine receptors, cytokine receptors, lymphokine receptors, interleukin receptors, tumor antigen receptors, tumor suppressor antigen receptors (e.g., p53, Rb, k-Rev, DCC receptors), multidrug resistance protein receptors, coagulation factor receptors (e.g., Factor VII, Factor VIII, Factor IX receptors), trophic factor receptors, cell recognition or stimulatory molecule receptors, apolipoprotein receptors, and the like. Particular binding proteins or receptors include, without limitation, receptors in receptor families such as EGFR, ErbB-lR, HER1, HER2, aFGFR, bFGFR, NGFR, VEGFR, FltR, TGFR, TGFR-a-1, TGFR-β, TNFR (a), BDNFR, insulin receptor, insulin-like growth factor receptor (IGFR), PDGFR, HGFR, TRKR, BDNFR, CNTFR, GMFR, NT3R, NT5R, HARPRpleiotrophinR, TIE receptors, Eph receptors, DDR receptors, ROR receptors, LTK receptors, AXL receptors, RET receptors, TOLL-like receptors; hormone receptors, such as steroid hormone receptors, thyroid hormone receptors, melatonin receptors, adrenergic receptors; peptide receptors, e.g., receptors for amylin, angiotensinogen, angiotensin, atrial natriuretic peptide, brain natriuretic peptide, calcitonin, corticotropin, erythropoietin, endothelin, enkephalin, follicle stimulating hormone, gastrin, ghrelin, glucagon, human chorionic gonadotropin, inhibin, leptin, luteinizing hormone, melanocyte stimulating hormone, oxitocin, pancreatic polypeptide, parathyroid hormone, prolactin, prolactin releasing hormone, rennin, secretin, somatostatin, thrombopoietin, thyroid stimulating hormone, thyrotropin releasing hormone; or GP130 or IL6 receptors. Also included are cell surface molecules that bind and/or interact with virus proteins and peptides. The foregoing is not meant to be an exhaustive list; other receptors that may find use in the invention will be understood to be useful by one having skill in the art. The ligand binding molecules, or receptor proteins, are preferably expressed on the cell surface and may be membrane receptors or transmembrane receptors. The ligand binding proteins may be modified, post-translationally modified or non-post-translationally modified, glycosylated or non-glycosylated. In an embodiment, a binding molecule or antibody as described herein specifically recognizes and binds to the ligand binding protein, or receptor protein. Encompassed herein are the nucleic acid sequences (DNA and RNA) and genes which encode the binding molecules, receptor proteins, or fragments or portions thereof. [0061] Examples of cognate ligands (ligand proteins or antigens), which are recognized and bound, preferably specifically recognized and bound, by ligand binding proteins or receptor proteins, include, without limitation, the cognate ligand partner(s) of each of the above-listed, exemplary receptors. For example, ligands, such as growth factors, hormones, enzymes, metabolic enzymes, lipid transfer proteins, neurotransmitters, chemokines, cytokines, lymphokines, tumor-associated antigens, tumor suppressor antigens (e.g., p53, Rb, k-Rev, DCC), multidrug resistance proteins, coagulation factors (e.g., Factor VII, Factor VIII, Factor DC), cell recognition molecules, cell stimulatory molecules, and the like. More specifically, nonlimiting examples of ligand proteins (or peptides) include EGF, aFGF, bFGF, VEGF, Fit, TGF-β, TNF (TNF-a, TNF-β), NGF, insulin, insulin-like growth factor (IGF), PDGF, HGF, TRK, BDNF, CNTF, GMF, NT3, NT5, HARP/pleiotrophin. Such cognate ligands may be soluble or membrane-bound. The ligand proteins may be modified, post-translationally modified or non- post-translationally modified, glycosylated or non-glycosylated. In an embodiment, a binding molecule or antibody as described herein specifically recognizes and binds to a cognate ligand (protein). In an exemplary embodiment, the ligand protein is human tumor necrosis factor- a (hTNF-a). Also included are virus proteins and peptides which bind and/or interact with cell surface molecules. Encompassed herein are the nucleic acid sequences (DNA and RNA) and genes which encode the cognate ligands, ligand proteins or antigens, or fragments or portions thereof.

[0062] It will be understood that isolated nucleic acids (genes) encoding binding molecules such as antibodies, ligand binding proteins, receptors, ligand proteins, or any target protein according to the invention, can be inserted into appropriate vectors, which are used to transfect, transduce, or infect suitable host cells, particularly for subsequent expression in the cells, using methods known to the skilled practitioner in the art. The nucleic acids can be deoxyribonucleic acid (DNA) or ribonucleic acid (RNA) and can comprise naturally occurring sequences and sequences of synthetic or artificial origin. Suitable nucleic acids can include genomic DNA, cDNA, mRNA, tRNA, rRNA, hybrid sequences, synthetic or artificial sequences, or semisynthetic or semi-artificial sequences. The nucleic acids sequences can be eukaryotic or mammalian and of human origin or of non-human origin, e.g., animal or plant. In some cases, the nucleic acid sequences can be bacterial, viral, yeast, etc. [0063] Such nucleic acids encoding a target protein, or binding molecule, or antibody, can be obtained by conventionally known techniques and methods practiced by those having skill in the art. Illustratively, nucleic acid sequences encoding proteins of interest can be obtained by screening nucleic acid/sequence libraries or gene banks, by chemical synthesis, or by a combination of methods including chemical or enzymatic modification of sequences obtained by screening nucleic acid/sequence libraries, cloned nucleic acids (DNA), or gene banks. Nucleic acid sequences encoding vast numbers of proteins of interest, including ligand binding molecules (cell-membrane associated), ligands and immunoglobulins, along with the encoded protein sequences, are available to the practitioner through public databases, such as the National Center for Biotechnology Information (NCBI), accessible via the worldwide website (ncbi.nlm.nih.gov), and through nucleotide and protein databases such as GenBank, RefSeq, or UniProtKB/Swiss- Prot. In addition, full length immunoglobulin libraries, e.g., human IgG, and immunoglobulin domain libraries are commercially available to one skilled in the art.

[0064] Suitable vectors include expression vectors that are expressible in mammalian or eukaryotic cells as host cells. Such vectors allow for the proper expression, cellular processing and production of members of a protein binding pair (e.g., a ligand binding molecule and its cognate ligand). In general, an expression vector encompasses any DNA cloning vector recombinant construct comprising a nucleic acid sequence to be expressed operably linked to a suitable control sequence capable of allowing the expression and control the transcription of the inserted nucleic acid in a suitable host. Such vectors, or plasmids, may be readily modified to construct expression vectors that produce the desired sequence in a variety of host organisms, including, e.g., E. coli, Sf9 (for baculovirus), yeast and mammalian cell hosts.

[0065] Vectors also relate to recombinant DNA cloning vectors, which are autonomously replicating constructs, which may include, without limitation, plasmids, phages, and viruses, comprising a DNA molecule to which one or more additional nucleic acids have been added.

[0066] Nonlimiting examples of vectors include viral vectors (e.g., lentivirus, modified form of HIV- 1, adenovirus, adeno-associated virus vectors for infecting or transducing cells), phage particles, plasmid vectors, eukaryotic expression vectors, prokaryotic vectors, wherein the nucleic acid, including heterologous sequence(s) encoding a protein of interest, may or may not integrate into the host cell's genome. Within the vectors, the nucleic acid sequence or gene to be expressed and produced in a cell is operably linked to a control sequence in a manner allowing for expression, e.g., transcription and translation, of the nucleic acid sequence or gene in a host cell. Control sequences are known to those in the art and are selected to express the nucleic acid encoding the protein of interest, e.g., a ligand binding protein or receptor, a ligand protein, or a binding molecule, e.g., an antibody according to the invention, and to control the transcription. Such control sequences include, but are not limited to, a polyadenylation signal, a promoter (a natural or synthetic promoter), e.g., gene promoters such as CMV, RSV, MLP, E1A, etc., or an enhancer to effect transcription, an optional operator sequence to control transcription, a locus control region or silencer to allow tissue-specific transcription, a sequence encoding suitable ribosome binding sites on the mRNA, sequence(s) for stabilizing mRNA, sequences that control termination of transcription and translation.

[0067] Other sequences can be included with, or operably linked to, the nucleic acid or gene to be expressed in a vector, as will be appreciated by one skilled in the art, such as detectable or selectable biomarker sequences, tag sequences, selectable marker sequences, e.g., antibiotic resistance sequences, etc, or cellular signal sequences (e.g., either natural to the gene product or artificial, positioned upstream of the gene of interest and which directs the gene product synthesized into the secretion pathways of the host cell). Further, the expressed proteins may be additionally modified by including activation sequences, regulation sequences, organelle retention signal sequences, etc.

[0068] The technology and methods described herein are applicable to mammalian or eukaryotic cell expression systems and mammalian or eukaryotic host cells or cell lines for expression, activity and function of the components of the methods. It will be apparent to the skilled practitioner to use a cell line that has the capability of expressing a selected or desired ligand binding protein or receptor, or ligand, or target protein at the cell surface. As described herein, a given ligand protein may be engineered to be expressed within the cell membrane and/or on the cell surface. Eukaryotic expression systems are not limited for use in a particular host cell. A variety of eukaryotic host cells are available, for example, from depositories such as the American Type Culture Collection (ATCC), Manassas, VA., and may be used with a variety of vectors. The selection of a host cell is related to the character of the expression vector used and will be known to one skilled in the art. Nonlimiting examples of eukaryotic or mammalian cells and cell lines suitable for use in the methods of the invention include T-cell lines, e.g., Jurkat cells and JLTRG-R5 cells described herein; HEK293 cells, COS cells, CHO cells, 293T cells, B-lymphocyte lines, T-lymphocyte lines, etc. Cultured cell populations or cell lines can be developed or established from tissue or organ explants or immortalized cells. In an embodiment, the cell line is a human or human-derived cell line. In an embodiment, the cell line is a non- human primate cell line or a non-human primate-derived cell line. In an embodiment, the cell line is from or derived from a non-human species or a non-human primate species.

[0069] The expression and production of protein sequences composed of amino acids by recombinant techniques is well known and can be carried out by the skilled practitioner using conventional and standard methods. (See, e.g., Sambrook, J., Fritsch, E.F. and Maniatis, T., 1989, Molecular Cloning: A Laboratory Manual and later editions, e.g., 1991, 2001 and 2012 (J. Sambrook)). In general, the recombinant preparation of a protein, or a fusion protein which harbors additional sequence, such as a retention signal or tag, is carried out by either selecting the desired native nucleic acid sequence, e.g., DNA sequence, or by modifying a native DNA sequence, by fransforming the DNA sequence into a suitable host and expression of the native or modified DNA sequence to form the desired protein sequence. A vector for expressing a protein can be introduced into a host cell using any suitable method, e.g., transformation, electroporation, transfectioh using calcium chloride, rubidium chloride, calcium phosphate, DEAE dextran, or other substances, microprojectile bombardment, lipofection, infection, or transduction. Methods for introducing DNA into a host cell by one of the foregoing processes are found, for example, in Sambrook, J., 1989, supra.

[0070] The recovery or isolation of the desired protein can be performed using methods and procedures that are standard in the art, including separating the host cells from the medium by centrifugation or filtration, if necessary after disruption of the cells, precipitating the proteinaceous components from the supernatant using a salt, e.g., ammonium sulfate, followed by purification using a number of chromatographic techniques, e.g., ion exchange chromatography, affinity chromatography or similar, known procedures.

Methods for Intracellular Selection and Screening of Binding Molecules

[0071] Provided herein are methods for selecting and screening for binding molecules, or genetically diversified binding molecules, within a cell. The binding molecules, which bind or interact with a target molecule within a cell, may have optimal binding properties and/or activity toward the target molecule. Encompassed by the methods is the intracellular localization and retention of binding molecules, as well as target molecules, which allows for the subsequent selection of a binding molecule that specifically binds to a target molecule within an intracellular organelle or compartment in the cell. Preferred but nonlimiting examples of suitable binding molecules are antibodies, or a binding fragment or portion thereof, antibody domains, e.g., VL and VH, and libraries thereof.

[0072] In an embodiment of the invention, an antibody or a member of a genetically diversified antibody population, or a binding fragment or portion thereof, having a specific binding activity for a target molecule is effectively expressed, matured and selected in a cellular environment that also harbors its target molecule, thereby providing a convenient technique for antibody detection, selection and recovery based on the co-expression of the antibody as binding molecule and its target antigen within one cell. Thus, an advantage of the present selection methods is that only a single cell is needed to express an antigen binding molecule, e.g., an antibody, or a member of a diversified library or population of antigen binding molecules or antibodies, as well as its target antigen, and to select for the binding molecule or antibody that specifically and/or optimally binds to its target. In addition, such single cell methods of generating and selecting an antibody from a diversified antibody population advantageously do not involve ribosomal or nucleic acid display, or phage or cell display systems and do not require the use of particular B-cell lines harboring enzymes such as AID; nor do they involve conventional affinity maturation, receptor editing, or somatic hypermutation techniques. The cell-based methods of the invention can be used to select those antibodies or diversified antibodies that show optimal properties of binding and/or interaction with a given target molecule or antigen all expressed within the same cell, wherein that same cell can be assayed to determine the binding properties of an expressed antibody, and selected for recovering a desired antibody.

[0073] Several compartments within the secretory pathway are capable of retaining a protein. For each compartment, a particular amino acid sequence can be fused or coupled to a protein (or "signal sequence") to retain the protein in the specific cellular location. Illustratively, for retention of a protein in the ER, the KDEL (SEQ ID NO:l) amino acid sequence may be employed; for retention of a protein in the trans-Golp. network, the YQRL (SEQ ID NO:2) amino acid sequence may be used; for retention of a protein in peroxisomes, the SKL amino acid sequence may be used; for retention of a protein in the plasma membrane of a cell, an H-Ras or K-Ras CAAX (SEQ ID NO:3) amino acid sequence may be used; for retention of a protein in mitochondria, MSVLTPLLLRGLTGSARRLPVPRAK (SEQ ID NO:4) amino acid sequence may be used; and for retention of a protein in the nucleus, the PPKKKRKV (SEQ ID NO:5) amino acid sequence may be used. The ER with its tubular architecture combined with the precise channeling of the proteins through the secretory pathway and with the presence of ER- resident chaperones makes this organelle an optimal intracellular location for the retention of proteins. It will be appreciated that post-translationally modified, e.g., glycosylated, or glycan- containing proteins will typically be retained in the Golgi if such proteins comprise a Golgi retention sequence such as YQRL (SEQ ID NO:2), while non-glycosylated proteins will typically be retained in the ER, if such proteins comprise an ER retention signal such as the KDEL amino acid sequence (SEQ ID NO:l).

[0074] In an embodiment, a method is provided to capture or retain within a cell a target protein that is recognized and bound by a binding molecule, e.g., an antibody, for selection, in accordance with the selection methods of the invention. In a related embodiment, a method is provided to specifically select one or more antibodies that neutralize, interrupt, block, disrupt, or eliminate an interaction between a ligand binding receptor and its cognate ligand, wherein either the ligand binding receptor or the ligand is the target protein which is specifically recognized and bound by the antibody, and wherein the target protein is retained with the cell, thereby localizing the target protein intracellularly and allowing binding access by the antibody within the cell.

[0075] In an embodiment, the binding molecule, e.g., an antibody or a binding portion thereof, specifically targets and binds to the receptor protein, which is expressible on the cell surface. In an embodiment, the binding molecule, e.g., an antibody or a binding portion thereof, specifically targets and binds to the cognate ligand protein. In an embodiment, the cognate ligand protein is molecularly engineered to be expressible on the cell surface. In various embodiments as described herein, either the binding molecule, e.g., an antibody, or the target protein, comprises an ER retention signal, which is the carboxy-terminal sequence KDEL (SEQ ID NO:l), that prevents proteins from following the normal secretory pathway by inducing the retrograde transport from c/s-Golgi, thereby effectively retaining the protein in the organelle. The binding molecule, e.g., an antibody, or the target protein may also be retained in other intracellular organelles or compartments by engineering them to express, or molecularly fusing them to, other signal sequences, for example, the YQRL (SEQ ID NO:2) sequence for retention in the Golgi, the SKL sequence for retention in peroxisomes, or the CAAX (SEQ ID NO:3) sequence for retention in the plasma membrane.

Selection methods based on a receptor-negative cell phenotype

[0076] One embodiment of the invention relates to a selection method of the invention in which a receptor-negative phenotype of a cell is generated. In such an embodiment, a cell line is molecularly engineered to express both a cell-surface-expressed receptor protein and its cognate ligand protein, which is fused to the KDEL (SEQ ID NO:l) retention signal sequence to retain the cognate ligand protein in the ER. The cognate ligand protein is expressed and retained in the ER by virtue of the KDEL sequence (SEQ ID NO:l). Within the ER, the cognate ligand protein interacts with its expressed receptor protein. Because the cognate ligand protein was retained in the ER, the receptor protein, through its interaction with the ER-retained cognate ligand, is also consequently retained within the ER in the cells. Accordingly, the receptor protein is not transported from the ER and expressed or displayed at the cell surface as it typically would have been absent a retention signal. Retained in the cell organelle, the receptor protein is not detectable by a detectably labeled molecule specific for the receptor protein, thereby creating a receptor-negative phenotype for the cell. The receptor-negative phenotype of the cells containing the ligand binding receptor protein bound to its cognate ligand and retained in the ER can be assessed by flow cytometry utilizing a detectable antibody directed against the cell- surface ligand binding receptor protein. This aspect can be visualized and exemplified advantageously through the interaction of the ligand binding receptor, hTNF-a receptor I, and its cognate ligand, hTNF-a, as schematically depicted in FIGS. 1A and IB.

[0077] As exemplified herein, a Jurkat cell line expresses a representative receptor protein, i.e., hTNF-a receptor I, that is displayed on the surface of the cell. As described in Example 1 herein, JLTRG R5 cells express the hTNF-a receptor I and can be readily transduced to express and retain certain proteins intracellularly in accordance with the invention. For example, the JLTRG R5 cell line can be transduced to express the ligand protein hTNF-a, fused to a KDEL sequence (SEQ ID NO:l), (hTNF-a-KDEL (SEQ ID NO:l)). The hTNF-a-KDEL fusion protein ("KDEL" disclosed as SEQ ID NO: 1) binds to its hTNF-a receptor I protein binding partner intracellularly, and both proteins are retained in ER. The presence and expression of the ligand protein can be further efficiently detected, for example, by the expression of a detectable label, e.g., DsRed, inside the cell. The receptor protein, due to its retention in ER via binding to its cognate ligand, which is also retained in the ER, is not detected at the surface of the cell using flow cytometry and a labeled anti- hTNF-a receptor I antibody. (FIGS. 1A and IB), thereby creating a receptor-negative selection cell phenotype.

Selection methods based on a receptor-positive cell phenotype

[0078] Another embodiment of the invention relates to a selection method in which a receptor-positive phenotype of a cell is generated. This embodiment relates to the selection of a binding molecule that specifically binds a target antigen / protein. To select a binding molecule according to this embodiment, nucleic acid encoding a binding molecule is introduced into a cell line, such as the above-described cell line which expresses a cell surface expressed receptor protein. In an embodiment, the cells are transduced with lentiviral particles comprising a binding molecule, i.e., a specific antibody, or a binding portion thereof, e.g., a V_L domain, that recognizes and binds to a target antigen. In an embodiment, the particles introduce into the cells one of a plurality of binding molecules, such as genetically diversified binding molecules or antibodies, one or more of which may have been genetically modified to possess optimal binding properties and to bind with high specificity or affinity to a target antigen/ protein and be selected for. The target antigen of the binding molecule or antibody can be either the cell surface expressed receptor protein or the ligand of this receptor protein fused to the ER retention sequence for retention in the ER. Upon binding to either the receptor protein or the ligand protein target in the ER of the cell, the expressed antibody blocks and disrupts the interaction between the receptor protein and its cognate ligand.

[0079] The blocking of the binding of the receptor protein to its cognate ligand due to the presence and binding of the binding molecule or antibody in the ER results in the transit and release of the receptor protein from the ER and allows for its expression at the surface of the cell. The resulting receptor-positive cell phenotype can be assessed by flow cytometry utilizing a detectable antibody directed against the cell-surface ligand binding receptor protein expressed on the surface of the cell. The cell may further be engineered to contain a detectable label, such as DsRed, that is useful for selecting and sorting cells via flow cytometry. This aspect is schematically depicted in FIGS. 1C and ID. A receptor-positive cell phenotype is determined by measuring a quantifiable level of receptor protein on the cell surface by virtue of its being bound by a detectably labeled antibody. The binding molecule, e.g., antibody, can be recovered or isolated from the cell and, optionally, further purified for use by employing standard techniques and methods. For example, the cells that have been sorted as being positive for binding by anti-receptor antibody and/or cell staining, based on fluorescence detection and mean fluorescence intensity, can be seeded and growth expanded. Such cells will harbor the binding molecule or antibody that bound to target antigen. DNA can be extracted from the expanded cell population, and the binding molecule or antibody can be isolated and further characterized using conventional methods practiced by those in the art.

[0080] As specifically demonstrated in FIGS. 1C and ID using a representative, exemplified target antigen, the JLTRG R5 cell line is transduced with lentiviral particles encoding the V_L domain (or region) of antibodies that target and bind hTNF-a receptor I. The binding of one or more of the transduced VL antibody domains blocks or disrupts the interaction between the ligand binding receptor and its cognate ligand, thereby releasing the receptor from the ER and permitting its expression on the surface of the cell. In FIG. 1C, the VL antibody, i.e., VL binding domain, is shown to bind to the hTNF-a ligand protein portion of the hTNF-a-KDEL ligand fusion protein ("KDEL" disclosed as SEQ ID NO:l), thereby blocking the interaction of hTNF-a with the hTNF-a receptor I in the ER and allowing the hTNF-a receptor I protein to be transported to and expressed on the cell surface. In FIG. ID, the V_L antibody is shown to bind to the hTNF-a receptor I protein, thereby blocking the interaction of hTNF-a with hTNF-a receptor I in the ER and allowing the hTNF-a receptor I protein to be transported to and expressed on the cell surface. Such cell-surface displayed receptor is detectable using a detectable binding agent, such as a receptor-specific antibody. It will be appreciated that in a case in which the antibody, or a binding molecule, binds specifically to a receptor protein as its target and permits the receptor protein to transit through the ER and be expressed in the plasma membrane of the cell due to the disruption or neutralization of the binding of the receptor protein to its cognate ligand that is retained in the cell organelle, the binding of the antibody, or binding molecule, to the receptor protein optimally does not concomitantly impede or block the expression of the receptor protein in the cell membrane.

[0081] To determine if a binding molecule such as an antibody, e.g., a VL antigen binding domain, has blocked, inhibited, neutralized, or disrupted the receptor-cognate ligand interaction by specifically binding to the receptor or to the ligand in the cell organelle, cells are exposed to a detectably labeled antibody directed to the expressed receptor protein, e.g., hTNF-a receptor I, and can be sorted in a flow cytometer (cell sorter). Typically, fluorescence detection is used. In addition, the cells may also be constructed to contain a detectable label to facilitate sorting, such as DsRed, GFP and the like. Illustratively, the measurement of the level of labeled antibody bound to ligand binding receptor protein on the cell surface indicates that a specific binding molecule, e.g., antibody or VL domain, within the cell has bound either the ligand binding receptor, or its cognate ligand, and has prevented, disrupted, neutralized, or blocked the interaction of the ligand binding receptor to its cognate ligand in the organelle, such as the ER. The blocking of the receptor-ligand interaction permits the receptor to exit the ER and be expressed on the cell surface where it can be detected by a detectably labeled specific binding molecule. Analysis of the cells is conducive to high throughput assays, including FACS and flow cytometry analyses and variations thereof.

[0082] In one illustrated embodiment, specific antibody, or a binding fragment or portion thereof, a cell-surface expressible ligand binding receptor protein and its cognate ligand fused to an ER retention signal are co-expressed in the same cell. At the time that the three types of proteins are present in the ER, the antibody, which, in this embodiment, is directed to the cognate ligand, specifically targets and binds to the cognate ligand retained in the ER. Consequently, the interaction between the receptor protein and its cognate ligand within the ER is blocked, neutralized, or disrupted by the antibody bound to cognate ligand as target, thereby effectively releasing the cognate ligand from its interaction with the receptor protein in the ER and liberating the receptor protein, allowing its transit from the ER to the plasma membrane of the cell where it is expressed on the cell surface. A detectably labeled antibody directed against the cell-surface expressed receptor protein is able to bind the receptor protein on the cell surface and serves to quantify the level of expressed receptor protein. The detection of expressed receptor on the cell surface is indicative of the presence of a binding molecule, e.g., an antibody, or a binding fragment or portion thereof, expressed in the cell. Conventional methods can be employed to recover and isolate the binding molecule, or antibody, and amplify its expression. Thus, the binding molecule having specific binding properties is selected through the method of the invention. [0083] In another illustrated embodiment, specific antibody, or a binding fragment or portion thereof, a cell-surface expressible ligand binding receptor protein and its cognate ligand fused to an ER retention signal are co-expressed in the same cell. At the time that the three types of proteins are present in the ER, the antibody binds not to the cognate ligand retained in the ER, but instead is directed to and specifically targets the ligand binding receptor protein. In this case, the interaction between the receptor protein and its cognate ligand is still blocked, neutralized, or disrupted by antibody binding. In this embodiment, the receptor protein is similarly effectively released from its interaction with its cognate ligand retained in the ER. Accordingly, the receptor protein can transit from the ER and be expressed on the cell surface where it can be detected as described. For each of these embodiments, a detectably labeled antibody directed against the extracellularly-expressed portion of the cell-surface receptor protein can bind and be used to quantify the level of cell-surface expressed receptor protein. In accordance with the selection method, the gene encoding a binding molecule or antibody that has bound to either the receptor protein or the cognate ligand within the cell can then be isolated or recovered from the cell as desired. See, e.g., Example 4 herein. For example, the genes can be isolated by polymerase chain reaction or isolated from cellular DNA by cleavage using suitable restriction enzymes recognizing cleavage sites surrounding the gene of interest. In addition, not only can DNA encoding the binding molecule or antibody of interest be recovered from a pool of cells expressing the encoding DNA, but single clones expressing the DNA can be detected by FACS analysis, and the encoding DNA can be extracted from a single clone.

[0084] In another embodiment, a method is provided to select antibodies that bind to a specific target within a cell. Such antibodies preferably show optimal binding to a specific target, and preferably have high affinity or binding specificity. As a representative example of the method, a cell line expressing a desired target molecule (protein) capable of being expressed at the surface of the cell is constructed. To this end, the cell line is engineered to express and produce the target protein, which, in turn, is molecularly engineered, as necessary, to be expressed in the plasma membrane of the cell. For example, the target protein can contain, or be constructed to contain, a transmembrane domain and a cytoplasmic domain, as well as its extracellular domain, for appropriate expression (and detection) in the plasma membrane. Nucleic acid sequences encoding antibodies are introduced into the cell line, e.g., via transduction by lentivirus particles. Accordingly, the cells are transduced with lentiviral particles containing nucleic acid sequences encoding antibodies (e.g., VL and/or VH binding domains) fused to the KDEL signal sequence (SEQ ID NO:l) for retention in the ER. At a time when antibody and target protein are expressed and present in the ER, the antibody is able to bind specifically to its target molecule (protein). In accordance with the method, the target protein is retained in the ER by virtue of its being bound by the ER-retained antibody. As a consequence, the antibody-bound target molecule (protein) is unable to transit from the ER, and the expression level of the target molecule (protein) at the surface of the cell is decreased or nil. Accordingly, virtually no detection of cell-surface-expressible target protein results.

[0085] A decrease in expression of a target molecule (protein) on the cell surface is able to be determined relative to a positive control, e.g., cells expressing the target molecule on the surface, or relative to cells that express the target molecule (protein), but that are not transduced with lentiviral vectors encoding the target molecule (protein)-specific antibodies harboring an ER retention signal. In the absence of such expressed antibody in the control cells, the cell- surface expressible target molecule (protein) is not retained in the ER, is transported to and expressed in the plasma membrane, and can be detected by detectably labeled agents on the surface of the cell. Alternatively, a control may be included in which lentiviral vectors carrying nucleic acid sequences encoding an irrelevant or non-specific protein, e.g., antibody, or a binding portion thereof, can be used in parallel to transduce cells for comparative purposes. In a manner similar to that of the other embodiments described herein, the surface receptor positive or negative phenotype can be detected, for example, via flow cytometry, by employing a detectable antibody specific to the target molecule (protein), and thereafter, cells expressing the desired antibody can be selected and antibody recovered.

[0086] FIGS. 2A and 2B demonstrate and exemplify an embodiment of the selection methods of the invention. As depicted and exemplified, a cell line is constructed to express hTNF-a, a representative cell surface-expressed target protein, having an extracellular domain fused to a transmembrane domain and a TEV sequence, a representative cytoplasmic domain for appropriate anchoring of the protein in the cell membrane. In the figure, the expressed hTNF-a is detectable at the surface of the cell using a labeled antibody directed against hTNF-a. (FIG. 2A). The cell is transduced with lentiviral particles expressing the L chain variable regions (VL) of anti-hTNF-a antibodies fused to the KDEL sequence (SEQ ID NO:l), (V_L (antibody)-KDEL ("KDEL" disclosed as SEQ ID NO: 1)) resulting in antibody retention in the ER, as described in the Examples herein. If a VL antibody specifically binds and/or binds with high affinity to the target protein in the ER, the complex comprising antibody bound to the hTNF-a target protein is retained in the ER, and the hTNF-a target protein is no longer detected or detectable at the surface of the cell. (FIG. 2B) The resulting cellular phenotype, i.e., the presence or absence of the target protein at the cell surface, is detected by flow cytometry employing a detectably labeled antibody directed against the target protein. As shown in FIG. 2A, the cell surface- expressed hTNF-a protein is detected at the surface of the cell by an antibody that specifically recognizes and binds the cell surface-expressed protein. In FIG. 2B, because the cells are transduced with antibody-KDEL molecules ("KDEL" disclosed as SEQ ID NO:l), the antibody that binds to hTNF-a protein retains this target protein in the ER, and the hTNF-a protein is no longer detected at the surface of the cell.

[0087] The platform technology and methods of the invention are particularly amenable to a high throughput screening or detection format. For example, flow cytometry is suitable for detecting and screening engineered cells that express or do not express a given protein, e.g., a target protein such as a ligand binding receptor protein or a ligand, on the cell surface; which express an antibody or antibodies or interest; or which contain retained proteins in a cell organelle. Other screening or detection methods suitable for use include immunoassay methods, such as enzyme linked immunosorbant assays (ELISA), radioimmunoassay (RIA), fluoroimmunoassay (FIA), chemiluminescent immunoassay (CIA), fluorescence resonance energy transfer (FRET), homogeneous time resolved fluorescence (HTRF), luminescent assay ("glow"-type signals), evanescent wave analysis, etc., which may be performed by conventional methods as known by those having skill in the art.

Intracellular Methods for Genetic Diversification of Antibody Binding Molecules

[0088] Zinc fingers, e.g., Cys₂His₂ zinc fingers, comprise the most common transcription factor family in organisms ranging from yeast to humans. Zinc finger proteins designed or purposefully re-engineered to contain certain DNA-binding specificities provide technology suitable for targeting functional domains to a gene of interest in various cell types. Zinc finger nucleases (ZFNs) provide a powerful tool for performing targeted genomic manipulation within a variety of cell types. [0089] Zinc finger nucleases (ZFNs) are synthetic proteins containing an engineered DNA- binding zinc finger domain linked to a non-specific endonuclease domain. In particular, ZFNs may contain an engineered DNA-binding zinc finger domain fused to the DNA cleaving domain of the Fokl restriction endonuclease. ZFNs can introduce double-stranded breaks (DSBs) that stimulate both homologous and non-homologous recombination processes that can be harnessed to perform genomic manipulation and result in genetic diversity and variation. These cellular processes can be harnessed to generate precisely-targeted in vitro or in vivo genomic edits with targeted gene deletions, i.e., knockouts, integrations, or other modifications. Targeting a double- strand break to a specific site in the genome with ZFNs has been used to disrupt permanently the genomic sequence surrounding the ZFN target site in a variety of eukaryotic organisms via imperfect DNA repair by nonhomologous end joining (NHEJ), (Ho M, Pastan I (2009), Methods Mol Biol., 525: 337-352, xiv). Gene targeting is a method that can repair or inactivate any desired gene of interest. Gene targeting strategies use the introduction of a DSB into a genomic locus to enhance the efficiency of recombination, e.g., with an exogenously introduced homologous DNA "repair template". DSBs can stimulate recombination efficiency several thousand-fold, approaching gene targeting frequencies as high as 50%.

[0090] In accordance with the invention, the use of ZFNs and the molecular processes related thereto are used as a genetic approach to generate one or more, e.g., a population of, diversified antibodies, i.e., antibodies, or binding fragments or portions thereof, having diversity in their specific interactions and binding capabilities with target proteins and antigens. The diversity or variability resulting from directed cleavage and repair within the DNA encoding the CDRs of an antibody molecule can generate one or more diversified antibodies with specific and optimal binding properties, wherein the diversified antibodies bave the potential to possess higher specificity, affinity, avidity, and the like, in interacting and binding with their target molecules/proteins and target antigens. In general, a diversified antibody or an optimum binding antibody from a population of diversified antibodies, or portions thereof, as described herein may be screened or selected for using methods known in the art, e.g., ribosomal or nucleic acid display, phage or cell display systems, or using particular B-cell lines harboring enzymes such as AID. Alternatively, a diversified antibody or an optimum binding antibody from a population of diversified antibodies, or portions thereof, can be conveniently and advantageously screened or selected for using the single cell selection methods described herein. [0091] Accordingly, in another of its aspects, the invention provides methods of inducing variability in specific locations of binding domains of binding molecules, e.g., antibodies, using nucleic acid recognition sequences of zinc finger DNA binding proteins and zinc finger nucleases designed to bind to the recognition sequences. In an embodiment, zinc-finger recognition sites, i.e., nucleic acid sequences, are introduced into the established immunoglobulin CDR architecture of the variable domain of immunoglobulin heavy chains, for example, a human variable heavy chain domain (IIVH), and/or the variable domain of immunoglobulin light chains, for example, a human variable light chain domain (IIVL). Depending upon the extent of variability desired, zinc-finger recognition sequences can be introduced into one, two, or all three CDRs, i.e., CDR1, CDR2, CDR3, in either or both of the VH and VL domains of the heavy and light antibody chains, e.g., V_H and/or V_L domains.

[0092] The introduction of zinc-finger recognition sites into the CDR locus allows for targeted gene disruption induced by zinc-finger nucleases. The DNA-binding domains of individual ZFNs typically contain between three and six individual zinc finger repeats and can each recognize between about 9 to about 18 base pairs. If the zinc finger domains are perfectly specific for their intended target site, then even a pair of 3 -finger ZFNs that recognize a total of 18 base pairs may target a single locus in a mammalian genome. The determination of suitable ZFN recognition sites, including finding zinc finger protein target sites and designing proteins, e.g., ZFNs, that target them, can be facilitated by available information in the art, for example, through publications and publicly available and interactive internet websites, such as are provided for use by the skilled practitioner, e.g., from the Laboratory of Carlos F. Barbas III, Ph.D., The Scripps Research Institute (TSRI), La Jolla, CA. (worldwideweb.zincfingertools.org) and the Laboratory of Daniel Voytas, a member of The Zinc Finger Consortium, which provides publicly-available information on zinc finger design (worldwideweb.zincfingers.org).

[0093] As indicated in the "zincfingertools" website, significant progress has been made to date in the development of modular protein domains that recognize specific triplets of DNA sequence. These domains can be fused together to create proteins that can bind to a chosen DNA sequence. The Cys₂-His₂ zinc finger motif, identified first in the DNA and RNA binding transcription factor TFIIIA, is perhaps the ideal structural scaffold on which a sequence-specific protein might be constructed. A single zinc finger binding domain consists of approximately 30 amino acids with a simple ββα fold stabilized by hydrophobic interactions and the chelation of a single zinc ion. Presentation of the a-helix of this domain into the major groove of DNA allows for sequence specific base contacts. Each zinc finger domain typically recognizes three base pairs of DNA, though variation in helical presentation can allow for recognition of a more extended site. In contrast to most transcription factors that rely on dimerization of protein domains for extending protein-DNA contacts to longer DNA sequences or addresses, simple covalent tandem repeats of the zinc finger domain allow for the recognition of longer asymmetric sequences of DNA by this motif. Since each zinc finger domain typically binds three base pairs of sequence, a complete recognition alphabet requires the characterization of 64 domains. The TSRI has taken a systematic approach toward generating a modular recognition alphabet using selection by phage display and refinement by site directed mutagenesis to prepare the zinc finger domains representing the 5'-GNN-3', 5'-ANN-3' and 5 -CNN-3' subsets of this 64-member recognition code. Further, publications by the Barbas Laboratory have provided several 5'-TNN- 3' domains and information on this recognition alphabet.

[0094] As will be understood by the skilled practitioner, the main parameters to optimize when designing a ZFP are typically the specificity and affinity for DNA binding. Illustratively, a 6- finger protein intended to recognize an 18 bp target site and constructed using the canonical TGEKP linker (SEQ ID NO:49) provides an exemplary solution for endogenous gene regulation. Proteins that bind their target with an affinity of 10 nM or better are productive regulators; ZFPs with an affinity of 1 nM or better have optimal activity. The affinity for a ZFP can be determined by performing an Electrophoretic Mobility Shift Assay (EMSA). Publicly accessible, interactive information regarding zinc finger binding proteins facilitates the determination of particular recognition sites. In accordance with the present invention, recognition sites of the form (XXX)3N6(XXX)3, where "XXX" are triplets for which zinc fingers exist and "N" is any nucleotide. The ZFN1 through ZFN4 zinc finger nucleases described herein were created by this methodology.

[0095] In an embodiment of such methods, zinc-finger recognition sequences are introduced into one of the three CDRs in either or both of the VH and VL domains. In an embodiment, zinc- finger recognition sequences are introduced into two of the three CDRs, in any combination, in either or both of the VH and VL domains. In an embodiment, zinc-finger recognition sequences are introduced into all three of the CDRs, in any combination, in either or both of the V_H and VL domains. In an embodiment, zinc-finger recognition sequences are introduced into at least one CDR in either or both of the VH and VL regions of the heavy and light antibody chains, respectively. In an embodiment, zinc-finger recognition sequences are introduced into each of CDRl and CDR2 of the VH and VL regions of the heavy and light antibody chains, respectively. In an embodiment, zinc-finger recognition sequences are introduced into each of CDR2 and CDR3 of the VH and VL regions of the heavy and light antibody chains, respectively. In an embodiment, zinc-finger recognition sequences are introduced into each of CDRl and CDR3 of the VH and VL regions of the heavy and light antibody chains, respectively. In an embodiment, zinc-finger recognition sequences are introduced into each of the CDRs, namely, CDRl, CDR2, or CDR3, of the VH and VL regions of the heavy and light antibody chains, respectively. In an embodiment, at least one recognition sequence is introduced into a given CDR. In an embodiment, two or more recognition sequences are introduced into a given CDR. In an embodiment, two recognition sequences are introduced into a given CDR. In an embodiment, two recognition sequences are introduced into two given CDRs, such as, for example, CDRl and CDR3.

[0096] In a specific embodiment, the CDRl and CDR3 sequences within the light-chain and heavy-chain variable domains contain different zinc-finger DNA binding protein recognition sequences. More specifically, each of CDRl and CDR3 contains two different zinc-finger DNA binding protein recognition sequences. For the different target sites in each CDR, two zinc- finger protein (ZFP) DNA-binding domains, i.e., nucleic acid recognition sequences, each containing four zinc-finger motifs (recognizing a total of 24 base pairs), are assembled in vitro in accordance with published methods, e.g., Moore, M., Choo, Y. & Klug, A., Proc. Natl. Acad. Sci. USA 98, 1432-1436 (2001); Jamieson, A.C., Miller, J.C. and Pabo, CO., Nat. Rev. Drug Discov., 2, 361-368 (2003). In total, four recognition sequences are introduced in the VH domain and four recognition sequences are introduced in the VL domain. The zinc-finger DNA binding protein recognition sequences are coupled to the DNA cleavage domain of the type IIS restriction enzyme, Fold, to produce novel ZFNs in which the location of DNA cleavage is determined by the DNA-binding specificity of the engineered ZFP domains (e.g., Urnov, F.D. et al., Nature 435, 646-651 (2005); Moore, M., Choo, Y. and Klug, A., Proc. Natl. Acad. Sci. USA 98, 1432-1436 (2001); Smith, J. et al., Nucleic Acids Res. 28,3361-3369 (2000)).

[0097] In a representative example, VH and VL region CDRl and CDR3 comprising introduced zinc finger targeting sequences are shown in FIG. 3. The rectangular area between the CDR1 and CDR3 regions represents CDR2, which does not contain zinc finger target sequences in this instance. In a 5' to 3' direction, the following is a representative sequence of the CDR region (e.g., both CDR1 and CDR3) with two zinc finger targeting sequences represented by contiguous "Ns", namely: 5' tactca NN N NNN NctgatNNN^ 3' (SEQ ID NO:6). The total number of amino acids in each of the CDR regions of VH and VL differ depending on the specific CDR, the specific antibody or type of antibody, and whether the CDR resides within the L or the H chain of an antibody. In general terms, a CDR comprises from about 6 to about 10 or 15 amino acids; however, CDRs of antibody molecules are well established and can be identified based on sequence information, including framework sequence information, as described, for example, by Wu, T. and Kabat, E.A., 1970, J. Exp. Med., 132:211-250; and Hood, L. et al., 1975, Ann. Rev. Genetics, 9:305-353.

[0098] It will be appreciated that the nucleic acid recognition sequences of zinc finger DNA binding proteins can be introduced into the CDRs outside of the VH and/or VL domains in which they typically reside. For example, the nucleic acid sequences encoding the CDRs, which may be isolated from a V_H and/or a V_L domain, can be molecularly engineered to contain the nucleic acid recognition sequences of zinc finger DNA binding proteins in the context of, e.g., a suitable plasmid or vector construct, or a nucleic acid expression cassette, as known in the art. A nucleic acid construct or a cassette can comprise one, two, or all of the CDRs, namely, CDR1, CDR2, and/or CDR3. The CDRs can be situated linearly or in tandem within the construct or cassette. The one or more CDRs, which have been modified to contain nucleic acid recognition sequences of zinc finger DNA binding proteins, can thereafter be introduced into VH and/or V_L domains, i.e., the nucleic acid sequences encoding such domains, using conventional molecular techniques known to those in the art. Alternatively, the nucleic acid recognition sequences of zinc finger DNA binding proteins can be introduced into the CDRs as they naturally reside within the VH and/or VL domains. Accordingly, the VH and/or VL domain nucleic acid sequences comprising the CDR-encoding nucleic acid sequences are engineered using conventional molecular biology techniques to contain the nucleic acid recognition sequences of zinc finger DNA binding proteins within one or more of the CDR-encoding nucleic acid sequences, thus producing one or more modified CDRs. As will be understood by the skilled practitioner, the VH and/or VL domains comprising the one or more modified CDRs can be molecularly engineered as desired, such that they are operably expressed with suitable immunoglobulin H and L chain constant regions to produce a full-length antibody comprising modified CDRs.

[0099] In an embodiment, the zinc-finger target sequences are introduced into the CDR region with three different sequence frames to suppress frame shift and a consequent lack of antibody production. The resulting engineered human variable domains are reintroduced into human immunoglobulin G (IgG), for example, IgGl, producing a full-length antibody protein with variable regions containing artificial CDRl and CDR3 engineered to include different zinc- finger recognition sequences or targeting sites. (FIGS. 3 and 4). In an embodiment, in each CDR, two different zinc-finger recognition sites are positioned such that the two different zinc finger recognition sites are recognized by two different zinc-finger-nucleases. In this representative case, CDRl and CDR3 are thus targeted by this strategy to induce specific ₍ cleavage at these intra-CDR sequence sites. Depending on the extent of variability desired, CDR2 can remain in its native sequence, or it can be subjected to zinc-finger targeting, in a manner similar to that described for CDRl and CDR3. In total, for a full-length IgG, a total of four different zinc-finger hotspots in the variable heavy-chain and four different zinc-finger hotspots in the variable light-chain can be introduced. (See, e.g., FIG. 3).

[0100] The efficacy and validity of this approach was empirically assessed by introducing variability into immunoglobulin genes within the CDRl and CDR3 regions as described and by expressing zinc finger nuclease (ZFN) proteins targeting the VH and VL sequences in Jurkat T cells. Analysis of the DNA isolated from each cell type employing the Surveyor nuclease assay (such as is available from Transgenomic Inc, USA/Transgenomic, Ltd., Europe), as used to detect ZNF-induced mutations, showed efficient mutation of the IgGl gene. The Surveyor nuclease assay is a simple and flexible mutation detection technology for the discovery and mapping of both known and unknown mutations. This technology is based on a mismatch- specific DNA endonuclease from celery, Surveyor nuclease, which is a member of the CEL nuclease family of plant DNA endonucleases. Surveyor nuclease cleaves with high specificity at the 3' side of any mismatch site in both DNA strands, including all base substitutions and insertion/deletions up to at least 12 nucleotides. Surveyor nuclease technology involves four steps: (i) PCR to amplify target DNA from both mutant and wild-type reference DNA; (ii) hybridization to form heteroduplexes between mutant and wild-type reference DNA; (iii) treatment of annealed DNA with Surveyor nuclease to cleave heteroduplexes; and (iv) analysis of digested DNA products using the detection/separation platform of choice. The technology is highly sensitive. Sequence analysis of cloned immunoglobulin genes amplified from Jurkat T cells was employed to confirm the presence of ZFN-induced insertions and deletions in the corresponding gene.

[0101] In some embodiments, in addition to the ZFN-mediated genetic mutation and diversity described herein, the mutagenesis efficiency within the CDRs can be further increased. This can provide further genetic diversity for binding molecules such as antibodies, or binding portions thereof. Increasing and improving mutagenesis frequency and genetic diversity can be achieved by co-expression in cells that express one or more binding molecules, e.g., antibodies, or binding portions thereof, comprising modified CDRs and one or more members of a ligand receptor-cognate ligand pair bindable by the binding molecule(s), other regulatory proteins involved in DNA and recombination events, including but not limited to, the viral-derived Tax regulator protein, (FIG. 10A, (SEQ ID NO:46)), (Lemoine, F. et al., 2000, AIDS Research and Human Retroviruses, 16(16):1623-1627; Chandhasin, C. et al., 2008, J. Virology, 82(14):6954- 6961; Ishikawa, C, et al., 2011, Carcinogenesis, 32(1): 110-119; and Baydoun, H. et al., 2012, PLOS One, 7(8):e42226); viral-derived p30 (Baydoun, H. et al., 2011, Blood, 117(22): 5897- 5906); terminal transferase (Terminal deoxynucleotidyl Transferase, TdT), (Bollum, J, 1974, Terminal deoxynucleotidyl transferase, The Enzymes, the third edition (Boyer, P.D., ed.3, Academic Press, New York, vol.10), pp. 145-171), (FIG. 10B, SEQ ID NO:47)); or by chemical treatment. In accordance with such embodiments, the ATM-dependent, double stranded break (DSB) response (DSBR) in cells recognizes DNA DSBs and generates chromatin-associated complexes around DSBs that promote DSB repair via C-NHEJ. For this process, the activation of several phosphatidylinositol-3-kinase-like serine/threonine kinases, including DNA-PKcs and ATM, is required. The ATM-dependent DSB response leads to the assembly of macromolecular foci over large (e.g., two megabases or more) chromatin regions flanking the DSB. These foci are thought to serve as scaffolds to stabilize DSB ends and facilitate the recruitment of additional repair and checkpoint signaling factors. For example, DNA-PKcs-deficient cells require ATM for the repair of RS ends, indicating that DNA-PKcs and ATM have overlapping roles in the context of immunoglobulin V(D)J recombination. Therefore, to increase C-NHEJ, the use of ATM kinase inhibitors, e.g., (2-Morpholin-4-yl-6-thianthren-l-yl-pyran-4-one), or DNA-PK inhibitors, e.g., (2-(Morpholin-4-yl)-benzo[h]chromen-4-one, LY293646) can increase the variability of CDR diversification in accordance with the methods of the invention.

[0102] In particular embodiments of the methods of the invention, the generation of further genetic variation, which can produce improved and/or increased ligand or antigen recognition and binding capability of binding molecules such as antibodies, or binding portions thereof, is provided by increasing and improving mutagenesis frequency and genetic diversity through the co-expression of Tax (FIG. 10A, SEQ ID NO:46) and/or TdT (FIG. 10B, SEQ ID NO:47) enzymatic proteins in cells that are engineered to express the CDR modified binding molecules, e.g., antibodies or binding portions thereof, and the appropriate ZF nucleases, whose activity also produces genetic variability, as described herein. In an embodiment, only the Tax protein, or a protein having similar function, is expressed in the cells in which CDR modified binding molecules and ZF nucleases are also expressed. In other embodiments, chemical inhibitors of ATM kinase, as noted above, can be used to induce further genetic variation and diversity in binding proteins such as antibodies according to the methods of the invention.

[0103] As described herein, sequences of zinc finger nucleases are used together with the zinc finger protein targeting sequences inserted into the VH and/or VL CDRs in accordance with the described methods of generating diversity, particularly, diversity in target antigen binding activity, in one or more antibody molecules. The ZFNs used in the methods herein are designed to contain at least one, e.g., two, zinc finger protein DNA binding recognition sequence ("targeting region"), which directs the expressed ZFNs to bind to the recognition sequences or targeting regions introduced into the CDRs. Illustratively, but without limiting the invention, FIG. 5 presents representative constructs designed to express zinc finger nucleases in the cells into which one or more antibodies (or one or more diversified antibodies) and target proteins are also co-expressed in accordance with the methods of the invention.

[0104] The invention encompasses a method of generating antibody genetic diversity or variability by modifying immunoglobulin complementarity determining regions (CDRs). Accordingly, the method comprises (a) introducing into one or more CDR-encoding nucleic acid sequences one or more zinc finger DNA binding domain recognition sequences to generate one or more non-identical targeting sites within the CDR-encoding nucleic acid sequences for binding one or more zinc finger nucleases (ZFN), thereby producing modified CDR-encoding nucleic acid sequences; (b) introducing into a nucleic acid sequence encoding a zinc finger nuclease (ZFN) the zinc finger DNA binding domain targeting site sequences of (a) operably linked to a nucleic acid sequence encoding a DNA cleavage domain of a type IIS restriction enzyme, wherein DNA cleavage by the ZFN is determined by the targeting site sequences within the modified CDR-encoding nucleic acid sequence of (a); and (c) expressing the nucleic acid sequences of (b) in a cell containing nucleic acid encoding at least an antibody heavy chain variable domain (VH) and/or at least an antibody light chain variable domain (VL) comprising the modified CDR-encoding nucleic acid sequence of (a) under conditions in which the expressed ZFN binds and cleaves the modified CDR-encoding nucleic acid sequence within the targeting site sequence.

[0105] In an embodiment of the above method for generating genetically diverse binding molecules, the zinc finger DNA binding domain recognition sequences that are introduced into one or more of CDRl, CDR2 and CDR3 comprise different recognition sequences. In various embodiments, the one or more zinc finger DNA binding domain recognition sequences are introduced into one or more of CDRl, CDR2 and CDR3; the one or more zinc finger DNA binding domain recognition sequences are introduced into each of CDRl, CDR2 and CDR3; the one or more zinc finger DNA binding domain recognition sequences are introduced into each of CDRl and CDR3. In various embodiments, one zinc finger DNA binding domain recognition sequence is introduced into one or more of CDRl, CDR2 and CDR3; at least two zinc finger DNA binding domain recognition sequences are introduced into one or more of CDRl, CDR2 and CDR3; or two zinc finger DNA binding domain recognition sequences are introduced into one or more of CDRl, CDR2 and CDR3. In various other embodiments, one zinc finger DNA binding domain recognition sequence is introduced into each of CDRl, CDR2 and CDR3; at least two zinc finger DNA binding domain recognition sequences are introduced into each of CDRl, CDR2 and CDR3; or two zinc finger DNA binding domain recognition sequences are introduced into each of CDRl, CDR2 and CDR3. In an embodiment, the introduced zinc finger DNA binding domain recognition sequences are different. In an embodiment, two different zinc finger DNA binding domain recognition sequences are introduced into each of CDRl and CDR3.

[0106] In yet other embodiments of the above-described method, two different zinc finger DNA binding domain recognition sequences are introduced into one or more of CDRl, CDR2 and CDR3 or into each of the three CDRs. In an embodiment, the two different zinc finger DNA binding domain recognition sequences introduced into each of the CDRs comprise SEQ ID NO:6. In an embodiment, the two different zinc finger DNA binding domain recognition sequences introduced into each of CDRl and CDR3 comprise SEQ ID NO:6. In another embodiment, the two different zinc finger DNA binding domain recognition sequences introduced into each of CDRl and CDR3 of the VH and the VL antibody domains comprise a total of 24 base pairs. In another embodiment, in (b) of the above method, the type II restriction enzyme is Fok I. In an embodiment, in (b) of the method, the nucleic acid sequences encoding the zinc finger nucleases (ZFNs) are introduced into a construct which comprises a first ZFN sequence for cleavage within CDRl of a VH domain , a second ZFN sequence for cleavage within CDRl of a VH domain, and a first ZFN sequence for cleavage within CDR3 of a VH domain and a second ZFN sequence for cleavage within CDR3 of a V_H domain. In an embodiment, the method encompasses (i) the first ZFN sequence for cleavage within CDRl comprises a targeting sequence as set forth in SEQ ID NO: 7 and a ZFP recognition sequence as set forth in SEQ ID NO:8, and the second ZFN sequence for cleavage within CDRl comprises a targeting sequence as set forth in SEQ ID NO: 9 and a ZFP recognition sequence as set forth in SEQ ID NO: 10; and (ii) the first ZFN sequence for cleavage within CDR3 comprises a targeting sequence as set forth in SEQ ID NO: 11 and a ZFP recognition sequence as set forth in SEQ ID NO: 12, and the second ZFN sequence for cleavage within CDR3 comprises a targeting sequence as set forth in SEQ ID NO: 13 and a ZFP recognition sequence as set forth in SEQ ID NO: 14. In an embodiment, in (b) of the method, the nucleic acid sequences encoding the zinc finger nucleases (ZFNs) are introduced into a construct which comprises a first ZFN sequence for cleavage within CDRl of a VL domain , a second ZFN sequence for cleavage within CDRl of a VL domain; and a first ZFN sequence for cleavage within CDR3 of a VL domain and a second ZFN sequence for cleavage within CDR3 of a VL domain. In an embodiment, the method encompasses (i) the first ZFN sequence for cleavage within CDRl comprises a targeting sequence as set forth in SEQ ID NO: 15 and a ZFP recognition sequence as set forth in SEQ ID NO: 16, and the second ZFN sequence for cleavage within CDRl comprises a targeting sequence as set forth in SEQ ID NO: 17 and a ZFP recognition sequence as set forth in SEQ ID NO: 18; and (ii) the first ZFN sequence for cleavage within CDR3 comprises a targeting sequence as set forth in SEQ ID NO: 19 and a ZFP recognition sequence as set forth in SEQ ID NO:20, and the second ZFN sequence for cleavage within CDR3 comprises a targeting sequence as set forth in SEQ ID NO:21 and a ZFP recognition sequence as set forth in SEQ ID NO:22. In embodiments, the construct comprises a lentivirus vector. In various embodiments, the full length antibody is selected from an IgG, IgM, IgA, IgD, or IgE antibody; the full length antibody is an IgG antibody; the IgG antibody is an IgGl, IgG2a, IgG2b, IgG3, or IgG4 antibody; or the antibody is an IgGl antibody. In an embodiment, in (c) of the method, the cell is a T-cell line or a Jurkat T- cell line. In an embodiment, the method further comprises (d) expressing in the cell a receptor protein which is expressible on the cell surface and which is a potential target biddable by the VH and/or V_L domain comprising modified CDRs of (c); (e) expressing in the cell a cognate ligand of the receptor protein, the cognate ligand being molecularly tagged with a sequence for retaining the ligand in an intracellular organelle under conditions allowing for the retention of the ligand in the organelle and the interaction of the receptor protein and the cognate ligand in the organelle, wherein the cognate ligand is a potential target bindable by the VH and/or VL domain of (c); and (f) detecting the level of the receptor protein expressed on the cell surface; wherein, if the VH and/or V_L domain binds to either the receptor protein or the cognate ligand and blocks or disrupts their binding interaction in the organelle, the receptor protein transits through the organelle and is expressed and detectable on the cell surface, and wherein the VH and/or VL domain which blocks or disrupts the receptor protein and ligand interaction is recoverable from the cell. In various embodiments of the method, the intracellular organelle retention sequence is an ER or Golgi retention sequence; and the ER retention sequence is the KDEL amino acid sequence (SEQ ID NO: 1).

[0107] In an embodiment, in (a) of the above method, the CDR-encoding nucleic acid sequences are contained within a nucleic acid construct or a cassette. In an embodiment, the CDR-encoding nucleic acid sequences are contained within nucleic acid sequences encoding an antibody heavy chain variable domain (VH) and/or nucleic acid sequences encoding an antibody light chain variable domain (VL). In an embodiment, in (c) of the above method, the modified CDR-encoding nucleic acid sequence is contained within a full length antibody comprising nucleic acid sequences encoding a heavy chain variable domain (VH) and a heavy chain constant region (CH), and comprising nucleic acid sequences encoding a light chain variable domain (V L) and a light chain constant region (CL), wherein the resulting nucleic acid sequences encode full length antibodies comprising VH and VL domains comprising modified CDRs. In an embodiment, the above method further comprises amplifying the nucleic acid sequences encoding the V_H and/or VL domain proteins and cloning the VH and/or V_L domain proteins from the cell.

[0108] In another embodiment, in (b) of the above method, the type II restriction enzyme Fok I. In an embodiment, in (b) of the above method, the nucleic acid sequences encoding the zinc finger nucleases (ZFNs) are introduced into a construct which comprises a first ZFN sequence for cleavage within CDRl of a VH domain , a second ZFN sequence for cleavage within CDRl of a VH domain, and a first ZFN sequence for cleavage within CDR3 of a VH domain and a second ZFN sequence for cleavage within CDR3 of a VH domain. In an embodiment, the above method encompasses (i) the first ZFN sequence for cleavage within CDRl comprises a targeting sequence as set forth in SEQ ID NO:7 and a ZFP recognition sequence as set forth in SEQ ID NO:8, and the second ZFN sequence for cleavage within CDRl comprises a targeting sequence as set forth in SEQ ID NO:9 and a ZFP recognition sequence as set forth in SEQ ID NO: 10; and (ii) the first ZFN sequence for cleavage within CDR3 comprises a targeting sequence as set forth in SEQ ID NO:l 1 and a ZFP recognition sequence as set forth in SEQ ID NO: 12, and the second ZFN sequence for cleavage within CDR3 comprises a targeting sequence as set forth in SEQ ID NO: 13 and a ZFP recognition sequence as set forth in SEQ ID NO: 14. In an embodiment, in (b) of the above method, the nucleic acid sequences encoding the zinc finger nucleases (ZFNs) are introduced into a construct which comprises a first ZFN sequence for cleavage within CDRl of a V_L domain , a second ZFN sequence for cleavage within CDRl of a VL domain; and a first ZFN sequence for cleavage within CDR3 of a VL domain and a second ZFN sequence for cleavage within CDR3 of a VL domain.

[0109] In an embodiment, the above method encompasses (i) the first ZFN sequence for cleavage within CDRl comprises a targeting sequence as set forth in SEQ ID NO: 15 and a ZFP recognition sequence as set forth in SEQ ID NO: 16, and the second ZFN sequence for cleavage within CDRl comprises a targeting sequence as set forth in SEQ ID NO: 17 and a ZFP recognition sequence as set forth in SEQ ID NO: 18; and (ii) the first ZFN sequence for cleavage within CDR3 comprises a targeting sequence as set forth in SEQ ID NO: 19 and a ZFP recognition sequence as set forth in SEQ ID NO:20, and the second ZFN sequence for cleavage within CDR3 comprises a targeting sequence as set forth in SEQ ID NO:21 and a ZFP recognition sequence as set forth in SEQ ID NO:22. In embodiments, the construct comprises a lentivirus vector. In various embodiments of the above method, the full length antibody is selected from an IgG, IgM, IgA, IgD, or IgE antibody; the full length antibody is an IgG antibody; the IgG antibody is an IgGl, IgG2a, IgG2b, IgG3, or IgG4 antibody; or the antibody is an IgGl antibody. In an embodiment, in (c) of the above method, the cell is a T-cell line or a Jurkat T-cell line.

[0110] In an embodiment, the above method further comprises (d) expressing in the cell a receptor protein which is expressible on the cell surface and which is a potential target bindable by the VH and/or V_L domain comprising modified CDRs of (c); (e) expressing in the cell a cognate ligand of the receptor protein, the cognate ligand being molecularly tagged with a sequence for retaining the ligand in an intracellular organelle under conditions allowing for the retention of the ligand in the organelle and the interaction of the receptor protein and the cognate ligand in the organelle, wherein the cognate ligand is a potential target bindable by VH and/or VL domain of (c); and (f) detecting the level of the receptor protein expressed on the cell surface; wherein, if the VH and/or VL domain binds to either the receptor protein or the cognate ligand and blocks or disrupts their binding interaction in the organelle, the receptor protein exits the organelle and is expressed and detectable on the cell surface, and wherein the V_H and/or VL domain which blocks or disrupts the receptor protein and ligand interaction is recoverable from the cell. In various embodiments of the method, the intracellular organelle retention sequence is an endoplasmic reticulum (ER) or Golgi retention sequence; and the ER retention sequence is DEL (SEQ ID NO: 1).

[0111] In another embodiment, the invention provides a method of generating a genetically diverse antibody, or a binding fragment or portion thereof, comprising modified complementarity determining regions (CDRs), wherein the method comprises: (a) preparing modified CDRs by introducing into one or more individual CDR-encoding nucleic acid sequences within the CDR locus of antibody VH and VL domains one or more zinc finger DNA binding domain recognition sequences, which are recognized by zinc finger nuclease proteins (ZFN), thereby producing one or more non-identical target sites in the VH and VL CDR-encoding nucleic acid sequences for specific binding of ZFNs; (b) preparing isolated nucleic acid sequences encoding zinc finger nucleases (ZFNs) having specificity for and targeting the CDR- containing zinc finger DNA binding domain recognition sequences of (a) and linked to a cleavage domain derived from a Typell restriction endonuclease, wherein cleavage by the ZFNs is determined by the DNA binding protein recognition sequences within the modified CDRs of (a); (c) introducing the modified CDR-encoding nucleic acid sequence regions of (a) into nucleic acid sequences encoding the VH and/or VL domains, thereby producing VH and/or VL domains comprising one or more modified CDRs; (d) optionally, introducing the VH and/or VL of (c) into isolated nucleic acid sequences encoding an antibody protein comprising heavy (H) and light (L) chains, wherein the resulting nucleic acid sequences encode a full-length antibody protein comprising modified CDR regions comprising different ZFP recognition sites within its VH and V_L domains; and (e) expressing the nucleic acid sequences of (b) and (c) in a suitable host cell wherein the expressed ZFNs target the modified CDRs within the VH and VL sequences of the antibody protein under conditions for producing mutations and genetic diversity in the CDR regions of the expressed VH and/or VL domains, or expressed antibody, thereby generating genetically diverse antibodies, or binding portions thereof, that may possess improved or optimal target antigen binding properties.

[0112] In an embodiment of the above method, the method further comprises isolating the nucleic acid sequence encoding the antibody produced. In another embodiment, the method further comprises amplifying and subsequently cloning the nucleic acid sequences encoding the genetically diverse antibody protein from the host cell in which they are expressed. In an embodiment, one or more zinc finger DNA binding domain recognition sequences are introduced into one or more of CDRl, CDR2 and CDR3, which are isolated from the VH and/or the VL antibody domains, for example, within a vector or cassette, and which are subsequently reintroduced into the VH and/or VL domains or into the VH and VL domains of full-length antibodies by conventional molecular biology techniques. In another embodiment, in (a) of the method, the one or more zinc finger DNA binding domain recognition sequences is introduced into each of CDRl, CDR2 and CDR3 of the VH and -the V_L antibody domains. In another embodiment, in (a) of the method, the one or more zinc finger DNA binding domain recognition sequences is introduced into each of CDRl and CDR3 of the VH and the VL antibody domains. In another embodiment, in (a) of the method, two different zinc finger DNA binding domain recognition sequences are introduced into each of CDRl and CDR3 of the VH and the V_L antibody domains. In an embodiment of the method, the two different zinc finger DNA binding domain recognition sequences introduced into each of CDRl and CDR3 of the VH and the VL antibody domains comprise SEQ ID NO:6. In an embodiment of the method, the two different zinc finger DNA binding domain recognition sequences introduced into each of CDRl and CDR3 of the VH and the VL antibody domains comprise a total of 24 base pairs. In another embodiment, in (b) of the method, the ZFNs comprise zinc finger DNA binding domain recognition sequences coupled to a cleavage domain of the type II restriction enzyme Fok I.

[0113] As shown by the present invention, the co-expression of immunoglobulin genes, or binding portions thereof, engineered to contain zinc-finger binding domain hotspots, i.e., the introduced targeting sequences for zinc finger protein binding and activity and recognition by ZFNs, together with ZFN-encoding genes engineered to bind the DNA targeting sequences, and a target protein or antigen in a T-cell line results in a novel cellular system that conveniently couples binding molecule/antibody diversity and selection simultaneously. In accordance with the methods of the invention, an antibody, or a binding portion thereof, from a library, a diversified library, or a population of diversified antibodies, having binding specificity for a target antigen can be selected, identified and characterized by constructing cells or cell lines to contain and express the appropriate target antigen, e.g., a receptor protein or its cognate ligand, and retention signals to allow binding of a specific, expressed antibody, or a binding portion thereof, and retention of the appropriate interacting molecules within the environment of the cell.

[0114] The diversity in antibodies that can be generated by the CDR modification methods of the invention is on the order of 10⁶ to 10¹⁸, or 10⁶ to 10¹⁴, or 10⁶ to 10¹² different antibody binding sites. As will be appreciated by the skilled practitioner, the variability in antibodies and their binding specificities attained in accordance with the methods of the invention, for example, in the combination of ZFN-targeted CDRl and CDR3, will depend upon the efficiency of nuclease activity in each CDR, or in both CDRs together.

[0115] An aspect of the above described methods for generating genetic diversity or variability in the binding regions of binding molecules, such as antibodies or binding portions thereof, which contain modified CDRs comprising zinc finger (ZF) hotspots that are acted upon by ZF nucleases in host cells co-expressing these proteins, is further exemplified below and more specifically in Example 6 herein. For illustrative purposes herein, the bmding molecule is an antibody or binding portion thereof. In this aspect, the method embraces the expression of one or both of the above described Tax and/or TdT proteins in the cells to provide increased and improved genetic diversification for the CDR modified antibody. Such an antibody can be identified and selected according to the CDR diversification method described herein involving ZF nucleases, after the antibody is expressed on the surface of cells into which the appropriate expression constructs have been transfected, transduced, or otherwise introduced. In accordance with this aspect of the methods, a detectable antigen recognized and bindable by the diversified antibody is utilized to identify and select cell surface expressed antibody that binds to the antigen. Advantageously, such antigen can be in a purified or isolated form, for example, substantially or completely removed from other proteins or contarriinating components. Nonlimiting examples of antigens that bind to the expressed, CDR modified antibody and can be utilized for identification, detection and selection of the antibody include proteins, e.g., glycoproteins and receptor proteins, polypeptides, peptides, enzymes, immunoglobulins and fragments thereof, and the like, as well as non-proteins, e.g., nucleic acids, lipids, glycolipids, and the like. Antigens, especially, protein and peptide antigens, can be suitably labeled for detection by a number of means known in the art as described supra. Briefly, suitable detectable labels include, without limitation, fluorescent labels, e.g., fluorescein isothiocyanate (FITC), rhodamine, green fluorescent protein (GFP), DsRed; radioactive labels, e.g., C, I, I, H; chemiluminescent labels, e.g., luminol; enzyme labels, e.g., alkaline phosphatase, horseradish peroxidase, glucose oxidase, beta-galactosidase; FRET labels, e.g., europium; biotin label and strepavidin label for the subsequent binding of biotin and strepavidin. When an enzyme is used as the labeling substance, detection is performed using a suitable substrate depending on the enzyme used.

[0116] According to the above method, and as exemplified in Example 6, a plasmid expression construct harboring nucleic acid sequences (genes) encoding an antibody engineered to contain zinc finger hotspots in one or more of its CDR regions, e.g., CDR1 and CDR3, as described and exemplified herein, is introduced into a host cell (e.g., a 293T cell) for expression therein. The host cell is also engineered to contain constructs that express the corresponding ZF nucleases (ZFNs) as described supra and in other embodiments of the invention. To allow surface expression in the cell membrane, the expressed antibody is preferably molecularly fused to a transmembrane (TM) domain, i.e., a TM domain from a protein that localizes to and is situated in the cell membrane and contains such TM domains. Nonlimiting examples of TM- containing proteins include growth factors and their receptors, e.g., the PDGF TM domain as described herein. Many proteins containing TM domains whose sequences are suitable for use in the method are known and used by those having skill in the art. In addition, the antibody contains or is molecularly designed to contain a leader sequence, for example and without limitation, the leader sequence of the IL-2 protein, suitable for protein expression in a cell, particularly in the cell membrane. Many proteins containing leader sequences suitable for use in the method are known and used by those having in the art.

[0117] In addition, and as described hereinabove, mutagenesis efficiency within the modified CDRs of the expressed antibody is further increased by co-expressing in the cell other regulatory proteins involved in DNA and recombination events, including, but not limited to, the viral- derived Tax regulator protein, viral-derived p30, terminal transferase (TdT), or a combination thereof. Preferably, a combination of the Tax and tenninal transferase proteins, e.g., Tax/TdT, expressed in the cells provides for further genetic diversification of the antibody's CDR binding regions, as well as the generation of an antibody having increased genetic variability in its modified CDRs, which can lead to improved binding properties for antigen. While the Tax protein is preferred, other proteins having a similar function are suitable for use. The nucleic acids encoding Tax and terminal transferase can be introduced into the host cell either together on one plasmid construct, or separately on discrete plasmid constructs. Accordingly, the Tax/terminal transferase (TdT) proteins can be co-expressed in the cell from one plasmid, or they can be expressed as separate proteins from individual plasmids. In some cases, only the Tax protein is expressed in the host cells, without the presence of TdT. In some cases, only the TdT enzyme is expressed in the host cells, without the presence of the Tax protein.

[0118] Identification and selection of a CDR-modified, diversified antibody that binds antigen can be achieved by assaying for binding of labeled antigen to the antibody, which is conveniently expressed on the cell surface. If no binding is detected compared with appropriate controls, such as binding of the labeled antigen to a cell designed or known to express on its surface an antibody specific for the antigen, the diversified antibody is determined not to have specificity for the antigen. Specific and detectable binding of labeled antigen by the diversified antibody demonstrates that the antibody has specificity (or increased specificity) for binding to antigen. The level of specific binding is measured by methods conventionally used in the art, e.g., flow cytometry, ELISA. An increased level of binding of the diversified antibody relative to antigen binding by a positive control may be indicative of an improved or augmented binding capacity of the diversified antibody for the antigen. The antibody-encoding genes can be isolated, cloned and sequenced from cells in which CDR-modified antibody, ZF nucleases, Tax and/or TdT are expressed or co-expressed and which provide the environment for generating a more genetically diverse, modified, and antigen-specific antibody having the capacity to bind antigen with high specificity and/or avidity.

[0119] In another of its aspects, the invention provides a method of screening, identifying, or selecting a small molecule, such as a small molecule chemical compound, low molecular weight organic compound (e.g., typically less than 900 Daltons in molecular weight), drug, or chemical agent which blocks or disrupts an interaction between a cell surface expressed receptor protein and its cognate ligand within a cell, or the interaction between a binding protein and its Jigand within a cell. In addition, the small molecule can affect the function of the binding protein and/or its ligand. In various embodiments, the small molecule is an agonist, an antagonist, or a modulator of the binding protein, e.g., a receptor protein, and/or the ligand. Preferably, the small molecule rapidly diffuses across the cell membrane to reach intracellular sites. In an embodiment, the method comprises expressing, in the same cell, a receptor protein which is expressible on the surface of the cell; expressing in the cell a cognate ligand of the receptor protein, wherein the cognate ligand is molecularly tagged with a sequence for retaining the ligand in an intracellular organelle under conditions allowing for the retention of the ligand in the organelle and the interaction of the receptor protein and the cognate ligand in the organelle such that the receptor protein would also be retained within the cellular organelle when bound to the tagged ligand; and exposing the cell to, and/or introducing into the cell, a small molecule chemical compound, low molecular weight organic compound (e.g., typically less than 900 Daltons in molecular weight; or less than or equal to 500 Daltons in molecular weight), a drug, or a chemical agent. In an aspect, the small molecule is an agonist, an antagonist, or a modulator of the binding protein and/or the ligand. As in other embodiments of the invention, the ligand is fused to an organelle retention sequence, such as KDEL (SEQ ID NO: 1) for retention in the ER. In alternative embodiment, the binding protein is fused to an organelle retention sequence for retention in the organelle, e.g., the ER, preferably if the ligand is naturally, or engineered to be, expressed in the cell membrane, i.e., at the cell surface. In an aspect, the level of the receptor protein (or ligand) expressed on the cell surface is detected and determined after exposure to the small molecule. In an aspect, the function of the binding protein, e.g., a receptor protein or ligand, is assessed or measured using methods known in the art following introduction of the small molecule into the cell. [0120] In accordance with an aspect of this method, if the small molecule binds to, interacts or associates with a portion of either (or both) of the receptor protein and/or the ligand, and blocks, inhibits, or disrupts their interaction in the organelle, the receptor protein does not interact with its ligand, is not retained intracellularly, and thereby transits through the organelle and is expressed and detectable on the cell surface. Accordingly, small molecule, which has blocked, inhibited, or disrupted the receptor protein and ligand interaction is identified and selected based on the detection of the presence of receptor protein on the cell surface, e.g., by a detectable label binding, flow cytometry and growth expansion of the cells. In embodiments, the retention occurs in the ER or the Golgi and the ER retention tag is KDEL (SEQ ID NO: 1).

[0121] In an embodiment, an exogenous ligand that targets the receptor protein is added to the cell as a control for assessing the ability of the small molecule to compete for binding to ligand, as well as for assessing specificity of the small molecule. Following the addition of ligand, e.g., after about an hour, receptor function is assessed and measured. Thus, when the binding molecule is a receptor molecule and the small molecule can affect receptor function in a measurable fashion, the function of the receptor can be measured following addition of the small molecule compound.

[0122] Thus, the present invention also provides methods of selecting non-protein agents such as small molecule compounds, chemical compounds or molecules, drugs, and the like, that interfere with the receptor/ligand interaction in the cell. The methods of the invention can provide the means to screen for and identify small molecule drug development candidates that affect protein-protein interactions and receptor protein function. In addition, the identified small molecules may also be used as research tools to probe biological function and as leads in the development of new therapeutic agents, particularly those that can inhibit a specific function of a multifunctional protein or that can disrupt protein-protein interactions.

[0123] In the present invention, small molecules, drugs, chemical agents, and other compounds are introduced into the cellular environment or directly into cells expressing retained protein that is capable of interacting (binding) with another protein, such as a ligand or binding pair member that is, or is caused to be, expressed on the cell surface. Appropriate assays are performed to determine whether the small molecules, drugs, chemical agents, and other compounds that are introduced and internalized into cells expressing the retained interacting proteins have the ability to disrupt, inhibit, block, interfere with, or otherwise prevent the binding of the ligand and its recognition protein, such as a receptor protein and its ligand, and/or to affect the function of the receptor protein. Illustratively, following the practice of the methods, if the introduced small molecule, drug, chemical agent, or other compound binds or otherwise interacts or associates intracellularly with one or both of the interacting proteins, one of which is retained in the ER, for example, and disrupts, inhibits, blocks, or otherwise prevents the interaction of these proteins, then the protein that is not retained in the ER through its interaction with the retained protein can be detected, such as on the cell surface or in the cell by employing the detection methods described at length herein.

[0124] In another embodiment of this aspect of the invention, a small molecule can be detectably labeled or tagged using methods and reagents conventionally used in the art, such that binding site(s) on the interacting protein(s) and occupied by the small molecule can be determined, identified and studied. In an embodiment, one or both of the interacting proteins can be modified, e.g., by altering, blocking, modifying, or derivatizing sites on the protein, to determine if binding or interference by the small molecule is affected. Alternatively, the small molecule itself can be derivatized or modified to determine whether the modified small molecule affects a protein-protein interaction through the methods of the present invention. Other similar advantages of the methods will be appreciated by the skilled practitioner in the art.

[0125] The following examples are not meant to limit the invention, but are presented to demonstrate and illustrate the invention in its various embodiments and aspects.

EXAMPLES

EXAMPLE 1

Materials and Methods

Plasmids and bacterial cells

[0126] The rabbit V_L Single Domain Antibody (SDA) library of 309 antibodies against hTNF- and the rabbit V_L SDA 18 (V_L18) cloned into the pT7 vector (e.g., as described in PCT/PT2012/000035, F. Aires Da Silva et al., "Anti-tumor necrosis factor-alpha agents and uses thereof filed September 19, 2012, TechnoPhage, Lisbon, Portugal, and U.S. Provisional Application No. 61/538,548, filed September 23, 2011, the contents of which are hereby incorporated by reference in their entirety). The anti-hTNF-a VL dimer library was constructed using the restriction/ligation strategy as previously described (Oliveira SS, Aires da Silva F, Lourenco S, Freitas-Vieira A, Santos ACC, et al. (2012), Biotechnology and Applied Biochemistry 59: 193-204). The rabbit V_L SDA F63 cloned in the pComb3X vector was selected by phage display against gp41 and deimrnunized (e.g., as described in PCT/PT2012/000035, F. Aires Da Silva et al., "Anti-tumor necrosis factor-alpha agents and uses thereof filed September 19, 2012, TechnoPhage, Lisbon, Portugal, and U.S. Provisional Application No. 61/538,548, filed September 23, 2011, the contents of which are hereby incorporated by reference in their entirety; and Santos, A. S., Oliveira, S. S., and Goncalves, J., unpublished results). The plasmids pHEF-VSVG (AIDS Research and Reference Reagent Program, Division of AIDS, NIAED, NIH, from Dr. Lung-Ji Chang), pGagPol (Amendola M, Venneri MA, Biffi A, Vigna E, Naldini L (2005), Nat Biotechnol 23: 108-116), pRev (Amendola M, et al. (2005), Nat Biotechnol 23: 108-116), and pFugW (Lois C, Hong EJ, Pease S, Brown EJ, Baltimore D (2002), Science (New York, NY)) 295: 868-872 were used to produce lentiviral particles.

Cell lines and culture conditions

[0127] HE 293T cells (American Type Culture Collection (ATCC), Manassas, VA, USA) were cultured in DMEM supplemented with 10 % FBS (DMEM-10), 2 mM L-glutamine, and 1% penicillin / streptomycin (Thermo Scientific). Jurkat cells (ATCC) and cell lines, e.g., JLTRG-R5 (Ochsenbauer-Jambor C. et al., 2006, BioTechniques, 40(1):91-100), were grown in Roswell Park Memorial Institute medium (RPMI)-1640, supplemented with 10 % FBS (RPMI- 10), 2 mM L-glutamine, and 1 % penicillin / streptomycin. All cell cultures were maintained at 37°C in 5 % C0₂. Cell culture media and reagents, unless otherwise indicated, were purchased from Lonza (Basel, Switzerland).

Plasmid / Vector constructs

Antibody vectors [0128] In general, all of the expression plasmids were constructed by polymerase chain reaction (PCR) using a polymerase with proofreading activity (Phusion High-Fidelity DNA polymerase, Finnzymes, Thermo Fisher Scientific, Vantaa, Finland).

[0129] To express the antibodies with and without a retention signal for endoplasmic reticulum (ER), e.g., KDEL (SEQ ID NO:l), two base vectors were constructed: pV_L18-IRES- DsRed and pV_L18KDEL-IRES-DsRed ("KDEL" disclosed as SEQ ID NO:l), (FIGS. 6A and 6B, respectively). For pV_L18-IRES-DsRed, two fragments were amplified by PCR. The first fragment was generated by amplification of the SDA VL18 from the pT7 vector using the oligonucleotide primers "Leader- Ab-Fl" and "Ab-HA-IRES-Rl" as presented in Table 1. The forward primer "Leader- Ab-Fl" added a murine Ig-K-chain leader sequence, i.e., (NH₂) - METDTLLLWVLLLWVPGSTGD (SEQ ID NO:23) - (COOH), which directs the protein to the secretory pathway (Coloma, MJ et al., 1992, J. Immunol. Meths., 152:89-104), while the reverse primer "Ab-HA-IRES-Rl " added a polyhistidine (His₆ (SEQ ID NO:48)) and a hemagglutinin (HA) tag for detection of the expressed protein via Western blot. The second fragment, IRES- DsRed, was amplified from the pIRES2-DsRed 2 vector (Clontech, Takara Bio Company, CA, USA) using the oligonucleotide primers "HA-IRES-Red-F2" and "IRES-Red-R2" as presented in Table 1. After purification, a PCR overlap of these two fragments was performed using conventional techniques and the oligonucleotide primers "Leader- Ab-Fl" and "IRES-Red-R2" as presented in Table 1. The resulting fragment was gel-purified, digested with restriction endonucleases BamHl and EcoRI and cloned into the FugW vector under the control of the human ubiquitin C promoter.

[0130] To construct the base vector pV_L18KDEL-IRES-DsRed ("KDEL" disclosed as SEQ ID NO:l), the SDA VL18 was amplified with the oligonucleotide primers "Leader- Ab-Fl" and "Ab-HA-KDEL-Rl " ("KDEL" disclosed as SEQ ID NO: 1) as presented in Table 1. The forward primer was the same as described above, and the reverse primer introduced the ER retention signal, 5' aaggatgagctc 3', (SEQ ID NO:24), (NH2)-KDEL-(COOH) (SEQ ID NO: l), in addition to adding the His₆ (SEQ ID NO:48) and HA tags as described. After gel-purification, the PCR fragment was digested with the restriction endonucleases BamHl and Nhel and was cloned into the previously constructed vector pVilS-IRES-DsRed, which was also digested by these enzymes. To facilitate the antibody cloning, the SDA VL18 gene was flanked by two restriction sites for the Sfil endonuclease in both vectors (FIGS. 6A and 6B). The base vectors constructed for use in the examples illustrating the invention are schematically represented in FIGS. 6A-6E.

Table 1 - Oligonucleotides

Name Sense 5'-3' Sequence

aaaggatccatggagacagacacactcctgctatgggtactgctgctctgggttccag

Leader-Ab-Fl Forward gttccactggtgacacggcccaggcggccgagct (βαηϊΆΥ) (SEQ ID

NO:25)

ttaggggggggggagggagaggggcgctagcctaagaagcgtagtccggaacgtc

Ab-HA-IRES-Rl Reverse

gtacgg (SEQ ID NO:26)

gactacgcttcttaggctagcgcccctctccctcccccccccctaacgttactggccga

HA-IRES-Red-F2 Forward

a (SEQ ID NO:27)

IRES-Red-R2 Reverse tttgaattcctactggaacaggtggtggcg (EcoRl) (SEQ ID NO:28)

Ab-HA-KDEL-Rl

("KDEL" ttaggggggggggagggagaggggcgctagcctaeagctcatccttctcgctagaa

pComb-lF Forward gttggccgattcattaatgcag (SEQ ID NO:30)

pComb-lR Reverse aatgaaaccatcgatagcagcac (SEQ ID NO:31)

pComb-3F Forward agcgcaacgcaattaatgtgag (SEQ ID NO:32)

pComb-3R Reverse ggtcatagcccccttattagcg (SEQ ID NO:33)

gtgaccattaaatgcagcggcggcggcagcSHRSHRSHRSHRSHRSH

CDRl-Lib Forward RSHRSHRSHRSHRSHRSHRaecgecggcegcasctgetatcascag aaaccg (SEQ ID NO:34)

CDR1-R Reverse gctgccgccgccgctgcatttaatggtcacggtgcc (SEQ ID NO:35)

acctattattgcagcggcggcggcagcSHRSHRSHRSHRSHRSHRSH

CDR3-Lib Forward RSHRSHRSHRSHRSHRagcggcggcegcagcggcggcggcaccgaa ctggaa (SEQ ID NO:36)

CDR3-R Reverse gctgccgccgccgctgcaataataggtcgccgcatccgc (SEQ ID NO:37) gacgatatcatggagacagacacactc (EcoRV

Leader-TNF-F Forward

(SEQ ID NO:38)

TNF-TEV-R Reverse tttgaattcctactggctgtagactagctc (EcoRI) (SEQ ID NO:39)

TNF-KDEL-F

("KDEL" gacacggcccaggcggcccctgtagcccatgttgtagcaaac (Sfil)

Forward

disclosed as (SEQ ID NO:40)

SEQ ID NO:l)

TNF-KDEL-R atggtgctggccggcctggcccagggcaatgatccc (S^I) (SEO ID

Reverse

("KDEL" NO:41) Name Sense 5'-3' Sequence

disclosed as

SEQ ID NO:l)

Tax-F Forward ctaggatccatggacagcctcttgatgaac (BamHD (SEO ID NO:42) tttgctagctcaaagtcccaaagtacg (Nhel)

Tax-R Reverse

(SEQ ID NO:43)

Seq-Leader-F Forward atggagacagacacactcctgctatgg (SEQ ID NO:44)

Seq-HA-R Reverse gtagtccggaacgtcgtacgggta (SEQ ID NO:45)

The underlined nucleotides indicate the recognition sites of restriction endonucleases used. The double underlines indicate a CDR region with wobble bases, as provided by the UIB code from ThermoScientific, or from the single letter codes for nucleotides as provided by NCBI through its website at www . ncbi . nlm . nih . gov/staff/tao/tools/tool lettercode . html.

Vectors for cell line construction

[0131] For the generation of a cell line expressing hTNF-a protein in fusion with the retention signal DEL (SEQ ID NO:l), the vector pTNFKDEL-IRES-DsRed ("KDEL" disclosed as SEQ ID NO:l) was constructed. (FIG. 6C). The gene encoding hTNF-a (GenBank Accession No. P01375) was amplified by PCR using the oligonucleotide primers "TNF-KDEL- F" ("KDEL" disclosed as SEQ ID NO:l) and "TNF-KDEL-R" ("KDEL" disclosed as SEQ ID NO:l), (Table 1). After gel-purification, the nucleic acid fragment was digested with restriction endonuclease Sfil and cloned into the previously constructed plasmid pV_L18KDEL-IRES-DsRed ("KDEL" disclosed as SEQ ID NO: 1), replacing the SDA V_L18 nucleic acid sequence.

[0132] To construct the cell line expressing hTNF-a, the vector pTNF-TEV (FIG. 6D) was engineered. The hTNF-a gene was amplified by PCR with oligonucleotides "Leader-TNF-F" and "TNF-TEV-R" (Table 1). The amplified nucleic acid fragment was digested with restriction endonucleases £coRV and EcoRl and cloned into the FugW vector, which was digested with BamKl and EcoRI. The synthesized gene was designed to have a murine Ig-K-chain leader sequence and a c-Myc tag upstream of the hTNF-a gene for western blot detection.

[0133] For the development of the cell line expressing a Tax polypeptide, the vector pTax- IRES-DsRed (FIG. 6E) was constructed. Accordingly, the Tax gene (Genbank Accession No. P03409) was amplified using the oligonucleotide primers "Tax-F" and "Tax-R" (Table 1). After purification, the amplified nucleic acid fragment was digested with BamHl and Nhel endonucleases and cloned into the previously constructed vector pV_Ll 8-IRES-DsRed plasmid. This cloning removed the murine IgG leader sequence and the His₆ (SEQ ID NO:48) and HA tags.

[0134] Unless otherwise indicated herein, all enzymes used in the Examples were from Fermentas (Thermo Fisher Scientific, Waltham, MA, USA). Each of the constructed vectors was transformed into the E.coli strain JM109 (Life Technologies, Regensburg, Germany) by electroporation (200 Ω, 25 μΈΌ, 1.8 kV, Bio-Rad Pulse Controller; Bio-Rad, CA, USA) to allow vector propagation and DNA extraction and isolation of desired nucleic acids.

Expression of plasmid constructs in HEK 293T cells

[0135] To evaluate the expression of the plasmid constructs, HEK293T cells were transfected with 5 g of plasmid DNA for each plasmid by the conventional calcium phosphate transfection method. After 48 hours, the cells were washed with phosphate buffer solution (PBS) and lysed with HBS buffer [50 mM HEPES; 150 mMNaCl; 2 mM EDTA; 10 % (v/v) glycerol; 0.5 % (w/v) deoxycholic acid; 1% (v/v) triton X-100] supplemented with a cocktail of protease inhibitors (Roche Diagnostics GmbH). This mixture was incubated on ice for 30 minutes and then was centrifuged at 12.000 x g for 30 minutes at 4°C. The recovered soluble fraction was used for Western blot analysis. The protein concentration was quantified using the Bradford colorimetric assay (BioRad, CA, USA).

SDS-PAGE and immunoblot analysis

[0136] For SDS-PAGE and immunoblot analysis, equal amounts of protein were boiled in Laemmli buffer (Laemmli, 1970) and loaded onto 10% SDS-PAGE gels. Proteins were separated by electrophoresis (Mini-Protean TM tetra electrophoresis system; Bio-Rad) and blotted onto nitrocellulose membrane Hybond-C Extra (Amersham Bioscience UK, Buckinghamshire, UK). The nitrocellulose membranes were soaked in blocking solution (5% (w/v) nonfat milk in Tris-buffered saline plus 0.1 % of Tween20 (TBS-T) buffer) for 1 hour at room temperature. Following blocking, the nitrocellulose membranes blotted with antibody protein expressed from the antibody constructs and with hTNF-a protein expressed from the TNF-a construct were incubated with HRP-conjugated anti-HA monoclonal antibody (clone 3F10; Roche Diagnostics GmbH) or with HRP conjugated anti-c-myc monoclonal antibody (clone 9E10; Roche Diagnostics GmdH), respectively, diluted 1:5.000 in 3% (w/v) nonfat dry milk in TBS-T at room temperature for 1 hour.

Lentiviral particle production and cell line construction

JLTRG-R5 TNFKDEL ("KDEL" disclosed as SEQ ID NO:l) cell line

[0137] For the generation of cell lines stably expressing TNF-KDEL-IRE S-DsRed ("KDEL" disclosed as SEQ ID ΝΟ:1), HEK293T cells (6 x 10⁶ cells) were co-transfected by the conventional calcium phosphate method with pTNFKDEL-IRES-DsRed ("KDEL" disclosed as SEQ ID NO: l), pVSVG, pRev, and pGagPol in the proportions of 1.5:0.2:1:2 to produce lentiviral particles encoding TNFKDEL- IRES-DsRed ("KDEL" disclosed as SEQ ID NO:l). The pVSVG, pRev, and pGagPol plasmids, i.e., lentiviral packaging plasmids as known in the art, are used to provide the necessary proteins for lentivirus production within transduced cells. More specifically, VSV is used as an envelope vector and allows virus endocytosis. Rev, an HrV-1 protein, is a nuclear transactivator that is essential for the expression of viral structural proteins from unspliced (gag pol) and incompletely spliced (env) HIV-1 mRNAs in late phases of infection. GagPol are HIV-1 genes; Gag encodes the HIV-1 Gag polyprotein, which is processed during virus maturation to matrix protein (MA, pi 7), capsid protein (CA, p24), spacer peptide 1 (SP1, p2), nucleocapsid protein (NC, p7), spacer peptide 2 (SP2, pi) and p6. Pol encodes the viral enzymes reverse transcriptase, integrase and HIV protease. The lentivirus particles carry the plasmid construct. After transduction of cells, the DNA is integrated into the genome of the host cell and is expressed along with other host cell genes.

[0138] After 48 hours, lentiviral particles were collected and used to transduce JLTRG-R5 cells. JLTRG-R5 cells express the hTNF-a receptor and also contain an HIV LTR promoter that controls the expression of green fluorescent protein (GFP), which is only activated when the cells are infected by an HIV virus, or when cells are transduced or transfected by plasmids encoding HIV activating proteins, such as the Tat protein, the HIV-1 transcription activator. The cells were resuspended in a lentivirus preparation with polybrene (8 μg/mL) and subjected to spinoculation at 930 x g for 90 minutes at 32 °C. The lentivirus was used in an amount sufficient to produce an approximately 60%-80% transduction efficiency as observed by flow cytometry. The spinoculation was performed in a 24-well plate, with about 2.5 x 10⁵ cells in 250 of RPMI+FBS plus 750 of lentivirus particles in each well of the plate. After 6 hours, the cells were washed and the medium was replaced with RPMI containing 10% FBS. At 72 hours post- transduction, the cells were collected, washed twice with PBS supplemented with 0.5% (w/v) of Bovine Serum Albumin (BSA) fraction V, sorted for DsRed positive cells in a BD FACS ARIA III cell sorter (Beckton Dickinson Bioscience, CA, USA) and seeded in 24- well plates, typically at a density of 5 x 10⁶ cells per 500 uL. Untransduced cells were used as negative control. In this way, when DsRed-positive cells are sorted, the selected cells express both hTNF-a - KDEL (SEQ ID NO:l) and its receptor. After 6 days, the sorted cells were stained for the expression of hTNF-a receptor I with 125 ng of an allophycocyanin (APC)-conjugated mouse monoclonal antibody directed against anti-hTNF-a RI to validate that these cells were able to retain this receptor in the ER due to the expression of TNFKDEL protein ligand ("KDEL" disclosed as SEQ ID NO:l) as described. The FACS ARIA ΠΙ apparatus was used to acquire at least 10,000- gated events from each sample and the data were analyzed using FlowJo software (Tree Star, OR, USA).

JL TRG-RS-TNF-TEV-expressing cell line

[0139] To produce TNF-TEV-encoding lentiviral particles for the construction of the JLTRG-R5-TNF-TEV cell line expressing hTNF-a ligand protein, HEK293T cells were co- transfected by the conventional calcium phosphate method with pTNF-TEV, pVSVG, pRev, and pGagPol in the proportions of 1.5:0.2:1:2. After 48 hours, lentiviral particles were harvested and were used to transduce JLTRG-R5 cells. The cells were resuspended in a lentiviral preparation with polybrene (8 μg mL) and subjected to spinoculation at 930 x g for 90 minutes at 32°C. After 6 hours, cells were washed and medium was replaced. At 72 hours post-transduction, the cells were collected, washed twice with PBS-BSA 0.5 %, and stained for hTNF-a surface expression with 2.5 jig of etanercept (Enbrel®) for 30 minutes at 4°C. The cells were washed two times with PBS-BSA, and etanercept (Enbrel®) binding to hTNF-a was detected by staining the cells with a secondary antibody [alexafluor® 647-conjugated AffiniPure anti-human IgG (alexafluor®)] (1:500) for 30 minutes at 4°C. After staining, the cells were resuspended in PBS- BSA and sorted for etanercept-alexafluor® 647-positive cells in a BD FACS ARIA III (BD Bioscience, CA, USA). Labeled untransfected cells and cells labeled only with secondary antibody were used as negative controls. All data were analyzed using FlowJo software. J TRG-R5-TNF-TEV and Tax-expressing cell line

[0140] To generate a JLTRG-R5 cell line expressing the hTNF-a and Tax polypeptides, a conventional calcium phosphate transfection method was used. Tax-IRES-DsRed-encoding lentiviral particles were produced by co-transfection of HEK293T cells with pTax-IRES-DsRed, pVSVG, pRev, and pGagPol as described above (in the proportions of 1.5:0.2:1:2). After 48 hours, lentiviral particles were collected and used to transduce the JLTRG-R5-TNF-TEV cells expressing hTNF-a protein. Cells were resuspended in a lentiviral preparation with polybrene(8 μg/mL) and subjected to spinoculation at 930 xg for 90 minutes at 32°C. After 6 hours, the cells were washed and the medium was replaced. At 72 hours post-transduction, the cells were collected, washed twice with PBS-BSA 0.5%, and stained for hTNF-a surface expression with 2.5 g of etanercept (Enbrel®) for 30 minutes at 4°C. The cells were washed two times with PBS-BSA, and stained for 30 minutes at 4°C with secondary antibody, alexafluor® 647 (1:500). After staining, the cells were resuspended in PBS-BSA and sorted for DsRed and etanercept- alexafluor® 647-positive cells in a BD FACS ARIA III. Labeled, untransfected cells and cells labeled only with secondary antibody were used as negative controls. The data from BD FACS ARIA III were analyzed using Flo Jo software.

EXAMPLE 2

Cell based assay to select and evolve antibodies that retain target molecules/ligands in the ER

[0141] HEK293T cells were used for the expression and production of antibody-encoding lentiviral particles, in particular, antibodies coupled to the ER retention signal KDEL (SEQ ID NO:l) (antibody-KDEL (SEQ ED NO:l)). To this end, HEK293T cells were co-transfected with pV_L18-IRES-DsRed and with pVSVG, pREV, and pGagPol in the proportions of 1.5:0.2:1:2, respectively. After 48 hours, lentiviral particles were harvested and used to transduce cell lines JLTRG-R5-TNF-TEV or JLTRG-R5-TNF-TEV-Tax. Cells were resuspended in a lentiviral preparation with polybrene (8 μg/mL) and subjected to spinoculation at 930 x g for 90 minutes at 32°C. As a control for the percentage of transduced cells, equal amounts of JLTRG-R5 cells were transduced, also by spinoculation, with an equal amount of lentiviral particles used to transduce the aforementioned cell lines. After 6 hours, the cells were washed and new medium (RPMI supplemented to contain 10% FBS) was added. At 72 hours post-transduction, the cells were collected, washed twice with PBS-BSA 0.5%, stained for hTNF-a with 2.5 μg of etanercept, and 1:500 of secondary antibody alexafluor® 647. Cells that stained positive for DsRed expression and negative for hTNF-a surface expression were sorted in a BD FACS ARIA III, seeded, and were allowed to grow in culture for one to two weeks. The selected cells expressed antibodies that efficiently recognized hTNF-a and retained this target protein in the ER. To support the previously determined phenotype, the cells were recovered, washed, and prepared for another round of cell sorting in the BD FACS ARIA III. Sorted cells were seeded, and five days later genomic DNA from all the sorted cells was extracted with QuickExtract™ DNA Extraction Solution (Epicenter®, an Illumina® company, WI, USA). Antibody encoding genes were recovered from the cells.

EXAMPLE 3

Cell based assay to select antibodies that neutralize/disrupt a ligand pair binding interaction

[0142] HEK293T cells were used to produce the antibody-encoding lentiviral particles. Therefore, the cells were co-transfected withpV_L18-IRES-DsRed, and pVSVG, pREV, pGagPol. After 48 hours, lentiviral particles were collected and used to transduce the cell line JLTRG-R5- TNFKDEL ("KDEL" disclosed as SEQ ID NO:l). The lentiviral particles were typically used in an amount that yielded approximately 60%-80% transduction efficiency; in general, 2.5 x 10⁵ cells in 250 μΐ, of RPMI+FBS plus 750 of lentiviral particles in each well of a 24-well plate. The JLTRG-R5 cells were resuspended in the lentiviral preparation with polybrene(8 μg/mL) and subjected to spinoculation at 930 x g for 90 minutes at 32°C. As a control for the percentage of transduced cells, equal amounts of JLTRG-R5 cells were transduced, also by spinoculation, with an amount of lentiviral particles equal to that used to transduce the JLTRG-R5-TNFKDEL ("KDEL" disclosed as SEQ ID NO:l) cells. After 6 hours, the transduced cells were washed and new medium was added. 72 hour post-transduction, the cells were harvested, washed twice with PBS-BSA 0.5%, stained for hTNF-a Receptor I with 125 ng of APC-conjugated mouse monoclonal antibody anti-hTNF-α RI, and sorted for DsRed and APC positive cells in BD FACS ARIA III. In this way, sorted cells that were positive were demonstrated to express antibodies capable of neutralizing or disrupting the interaction between the hTNF-a and its receptor, thereby allowing the receptor to be expressed on the cell surface and detected by the anti-hTNF- α RI antibody. The sorted cells were seeded and allowed to grow for one to two weeks. To corroborate the detected phenotype, the cells were washed again and prepared for another round of cell sorting in BD FACS ARIA III. The sorted cells that were positive for DsRed and hTNF-a RI expression were seeded. Normally, the cells were cultured in 24- well plates at a density of 5 x 10⁶ cells per 500 μ∑. After five days, genomic DNA was extracted with QuickExtract™ DNA Extraction Solution (Epicenter®, an Alumina® company, WI, USA) so that the antibodies responsible for this phenotype in flow cytometry could be characterized. (See, e.g., FIGS. 7A and 7B).

EXAMPLE 4

Cloning, expression and binding analysis of Single Domain Antibodies (SDA) by ELISA

[0143] The extracted genomic DNA from the different cells was amplified by PCR using the oligonucleotide primers "Seq-Leader-F" and "Seq-HA-R" (Table 1). The amplified fragments (antibodies) were digested with restriction endonuclease Sj?L cloned into the pT7 vector (kindly provided by TechnoPhage), and transformed by electroporation (200 Ω, 25 μ¥Ό, 1.8 kV, Bio- Rad Pulse Controller) into E. coli strain BL21 (DE)3. Several dilutions of transformed bacteria were plated in Luria broth (LB) agar plates supplemented with 100 μg mL of ampicillin. To screen for the sorted antibodies, bacterial colonies from each cloning were isolated, diluted in 200 μL of autoinduction medium (e.g., Overnight Express Autoinduction System, Novagen, San Diego, CA for an automated system such as a robot) in a 96-well plate, and allowed to grow for 16 hours at 37°C and 150 rpm. Each sorted cell population, e.g., the DsRed + alexafluor® 647- negative for the antibody-KDEL (SEQ ID NO:l) assay, or DsRed + APC-positive for the hTNF- a-KDEL (SEQ ID NO:l) assay, was used to extract genomic DNA. From these DNA samples, the antibody genes were amplified and were cloned into the pT7 vector as described herein. Thereafter, BL21(DE)3 bacteria were transformed with the vector. The isolated colonies resulting from the bacterial transformation were picked. For each different antibody and antibody library used, a cloning was performed. Subsequently, bacteria pellets from cell cultures centrifuged for 15 minutes at 900 x g were lysed with the addition of phosphate buffer solution (PBS) and BugBuster Master Mix (Novagen, Merck KGaA, Darmstadt, Germany) (in a proportion of 1:2) supplemented with a cocktail of protease inhibitors (Roche Diagnostics GmbH, Mannheim, Germany). This mixture was incubated for 4 hours at 4 °C in a stirring plate and the soluble periplasmic extract was collected after centrifugation at 900 x g for 15 minutes. The recovered soluble fraction was used for ELISA. [0144] In the expression assay, a 96-well ELISA plate was coated with 55 of bacteria clone soluble fraction for 1 hour at 37 °C. Plate wells were washed with PBS and blocked for 1 hour at 37°C with 3% (w/v) BSA. After washing with PBS, HRP-conjugated anti-HA monoclonal antibody (clone 3F10, Roche Diagnostics GmbH) diluted 1:1000 in 1% (w/v) BSA was added to each well, and the plate was incubated at 37°C for 1 hour. Following the incubation time, the wells of the plate were washed with PBS, and the ELISA detection was performed by the addition of HRP substrate ABTS Chromophore (Calbiochem; Merck KGaA) combined with 0.2 % (v/v) of hydrogen peroxide (Calbiochem; Merck KGaA). The absorbance was measured at 405 run (using 492 ran as reference) on Tecan Infinite M200 (Tecan, Mannedorf, Switzerland) after 30 minutes at 37°C.

[0145] To assess the binding of antibodies to hTNF-a, a 96-well ELISA plate was coated with 200 ng of hTNF-a (Prospec, NJ USA) and incubated overnight at 4°C. After washing with PBS, the wells of the plate were blocked for 1 hour at 37°C with 3% (w/v) BSA. 55 of soluble fraction of each bacterial clone was subsequently added to the wells, and the plate was incubated for another hour at 37°C. Following this incubation time, the plate wells were washed with PBS, and HRP-conjugated anti-HA monoclonal antibody diluted 1:1000 in 1% (w/v) BSA was added to each well. The plate was incubated for 1 hour at 37°C, and the plate wells were then washed with PBS. The ELISA detection was performed by the addition of HRP substrate ABTS Chromophore combined with 0.2% (v/v) of hydrogen peroxide. The absorbance was measured at 405 nm (using 492 nm as reference) on a Tecan mfinite M200 (Tecan Systems Ltd., US and Germany) after 30 minutes at 37°C.

EXAMPLE 5

Production of plasmids containing zinc finger nucleases (ZFN) which specifically target CDRs containing zinc finger DNA binding protein recognition sequences

[0146] In plasmid vectors comprising the backbone of the FugW lentiviral vector, zinc- finger-nucleases were cloned by overlap PCR with a 2A (Angstrom) sequence separating each gene. The zinc finger nuclease, termed ZFNIVH in FIG. 5, was designed to target CDR1 in the variable region of the heavy chain (VH). ZFNIVH comprises a targeting region comprising the nucleic acid sequence gtcgaaaagcca (SEQ ID NO:7) and a zinc finger amino acid sequence

LEPGEKPYKCPECGKSFSTSHSLTEHQRTHTGEKPYKCPECGKSFSRKDNLKNHQRTHT

GEKPYKCPECGKSFSQSSNLVRHQRTHTGEKPYKCPECGKSFSDPGALVRHQRTHTGKK TS SEQ ID NO:8). The zinc finger nuclease, termed ZFN2VH, targets CDRl in the variable region of the heavy chain. ZFN2VH comprises a targeting region comprising the nucleic acid sequence caaaaatcgagct (SEQ ID NO: 9) and the zinc finger amino acid recognition sequence LEPGEKPYKCPECGKSFSTSGELVRHQRTHTGEKPYKCPECGKSFSQSGHLTEHQRTHT GE PY CPECG SFSTTGNLTVHQRTHTGEKPY CPECG SFSQSGNLTEHQRTHTGBCK TS (SEQ ID NO: 10). The zinc finger nuclease, termed ZFN3VH, targets CDR3 in the variable region of the heavy chain. ZFN3VH comprises a targeting region comprising the nucleic acid sequence actcagcgaacg (SEQ ID NO: 11) and the zinc finger amino acid recognition sequence LEPGEKPYKCPECGKSFSRTDTLRDHQRTHTGEKPYKCPECGKSFSQSGHLTEHQRTHT GEKPYKCPECGKSFSRADNLTEHQRTHTGEKPYKCPECG SFSTHLDLIRHQRTHTGKK TS (SEQ ID NO: 12). The zinc finger nuclease, termed ZFN4VH, targets CDR3 in the variable region of the heavy chain. ZFN4VH comprises a targeting region comprising the nucleic acid sequence caatgtcggtaca (SEQ ID NO: 13) and the zinc finger amino acid recognition sequence LEPGEKPYKCPECG SFSSPADLTRHQRTHTGEKPYKCPECG SFSTSGHLVRHQRTHT GE PYKCPECGKSFSDPGALVRHQRTHTGEKPYKCPECGKSFSTSGNLTEHQRTHTGKK TS (SEQ ID NO: 14). The zinc finger nuclease, termed ZFN1VL, targets CDRl in the variable region of the light chain. ZFN1VL comprises a targeting region comprising the nucleic acid sequence gctcaacgtctg (SEQ ID NO: 15) and the zinc finger amino acid recognition sequence LEPGEKPYKCPECGKSFSRNDALTEHQRTHTGEKPYKCPECG SFSSRRTCRAHQRTHT GEKPYKCPECGKSFSQSGNLTEHQRTHTGEKPYKCPECGKSFSTSGELVRHQRTHTGKK TS (SEQ ID NO: 16). The zinc finger nuclease, termed ZFN2VL, targets CDRl in the variable region of the light chain. ZFN2VL comprises a targeting region comprising the nucleic acid sequence aagagaggccca (SEQ ID NO: 17) and the zinc finger amino acid recognition sequence LEPGEKPYKCPECGKSFSTSHSLTEHQRTHTGEKPYKCPECGKSFSDPGHLVRHQRTHTG EKPYKCPECGKSFSQLAHLRAHQRTHTGEKPYKCPECGKSFSRKDNLKNHQRTHTGK TS (SEQ ID NO: 18). The zinc finger nuclease, termed ZFN3VL, targets CDR3 in the variable region of the light chain. ZFN3VL comprises a targeting region comprising the nucleic acid sequence gttgccgagcga (SEQ ID NO: 19) and the zinc finger amino acid recognition sequence LEPGEKPYKCPECGKSFSQSGHLTEHQRTHTGEKPYKCPECGKSFSRSDNLVRHQRTHT GEKPYKCPECGKSFSDCRDLARHQRTHTGEKPYKCPECGKSFSTSGSLVRHQRTHTGKK TS (SEQ ID NO:20). The zinc finger nuclease, termed ZFN4VL, targets CDR3 in the variable region of the light chain. ZFN4VL comprises a targeting region comprising the nucleic acid sequence cgcatggttaag (SEQ ID NO:21) and the zinc finger amino acid recognition sequence LEPGEKPYKCPECGKSFSRKDNLK HQRTHTGE PYKCPECGKSFSTSGSLVRHQRTHT GEKPYKCPECGKSFSRRDELNVHQRTHTGEKPYKCPECGKSFSHTGHLLEHQRTHTGKK TS (SEQ ID NO:22). In the constructs of this Example, the lentiviral vector for zinc finger- nuclease targeting VH contained a puromycin resistance gene, and the lentiviral vector for zinc finger nuclease targeting VL contained a neomycin resistance gene, as well as an IRES sequence.

EXAMPLE 6

Selection of antibodies diversified with zinc finger hotspots, Tax and TdT according to the invention and having specificity for target antigen

[0147] The nucleic acid sequence encoding the antibody VHH, as described supra, and containing zinc-finger hotspots in CDR1 and CDR3, also as described, was cloned in fusion with the nucleic acid sequences encoding the transmembrane domain of PDGF and the leader sequence of the IL-2 protein. This chimeric gene (called "VHH-ZFN") was cloned into the eukaryotic plasmid vector, pcDNA3.1 (Invitrogen) and expressed in host cells in the presence of the corresponding zinc-finger nucleases and/or with Tax- and terminal transferase-encoding nucleic acid sequences, i.e., Tax/TdT genes, as described herein, i.e., Tax: FIG. 10A, (SEQ ID NO:46); and TdT: FIG. 10B, (SEQ ID NO:47). The nucleic acid and amino acid sequences of Tax (Human T-cell lymphotropic virus type 1 proviral Tax) can be found under GenBank Accession No. AB038239.1; the nucleic acid (mRNA) sequence of human TdT can be found under GenBank Accession No. AB046378.1.

[0148] Expression of the chimeric fusion plasmid was performed in 293T cells. The expression of antibody on the surface of transfected 293T cells was assessed using an anti-HA antibody to detect the HA epitope present in the antibody. FITC-conjugated IgG was used as detectable, purified antigen, to which the expressed antibody bound. When the VHH-ZFN antibody alone was expressed and assayed for binding to FITC-conjugated IgG, no binding of the labeled antigen (FITC-conjugated IgG) was detected at the cell surface, thus indicating that the cell surface-expressed antibody did not have specificity for the antigen. However, when VHH-ZFN was co-expressed with ZF-nucleases, specific binding of FITC-conjugated IgG antigen to the cell surface was observed, thus indicating that the antibody was evolving and diversified. Sequencing of VHH-ZFN antibody encoding genes targeted by the ZF-nucleases showed a similar pattern of variability as described herein, indicating that specific antibody clones were likely expressing antibodies having altered CDRs that bound to the FITC-conjugated IgG antigen.

[0149] When VHH-ZFN antibody was co-expressed with both ZF-nuclease and Tax/TdT- encoding nucleic acids (genes), specific binding of FITC-conjugated IgG to the cell surface was observed, with a stronger signal indicating that the antibody was evolving and high-affinity VHH antibodies were expressed at the cell surface. Sequencing of VHH-ZFN antibody encoding genes targeted by the ZF-nucleases showed a similar pattern of variability as described herein. Specific nucleotide signatures of hypermutation were not found. (See, FIG. 9 A).

[0150] Populations of cells having surface expression of VHH-ZFN antibodies specific for binding labeled IgG antigen (i.e., anti-IgG positive cells) were sorted, and the DNA of the VHH antibodies was isolated and cloned into the bacterial expression vector pT7. Isolated VHH antibodies were assayed by ELISA for binding IgG. The results showed strong binding of the antibodies to antigen, thus indicating the generation and selection of antibodies having antigen binding specificity using this methodology. (See, FIG. 9B).

EXAMPLE 7

Screening small molecules that inhibit receptor ligand interaction

[0151] Cells expressing receptor and ligand-KDEL (SEQ ED NO: 1) were cultured in RPMI. Small molecule compounds were added to the cells at 10 μΜ and 100 μΜ or at the indicated concentrations (dose-response). After a 6 hour baseline measurement, receptor protein expression at the cell surface was measured. Further measurements by FACS analysis with anti- receptor antibody were performed at 12 hours and 24 hours. A ligand that targets and interacts with the receptor protein was added as a control for compound specificity during the single-point compound screening. Approximately 1 hour after ligand addition, receptor function was measured in the presence of specific compounds. Percent function for the test small molecule compound (e.g., agonist) was calculated from the maximum readout minus the minimum readings. Statistical analysis was done to identify statistically significant inhibitory compounds that released cell receptor from the endoplasmic reticulum to the cell surface. For significant inhibitors, the assay was repeated in a dose-response format. [0152] All patents, patent applications and publications referred to or cited herein are hereby incorporated by reference in their entireties for all purposes.

[0153] It is understood that the embodiments and examples described herein are for illustrative purposes and that various modifications or changes in light thereof will be suggested to persons skilled in the pertinent art and are to be included within the spirit and purview of this application and scope of the appended claims.

Claims

Claims:

1. A method of selecting a binding molecule which blocks or disrupts an interaction between a cell surface expressed receptor protein and its cognate ligand within a cell, comprising:

expressing in the cell a receptor protein which is expressible on the surface of the cell; expressing in the cell a cognate ligand of the receptor protein, said cognate ligand being molecularly tagged with a sequence for retaining the ligand in an intracellular organelle under conditions allowing for the retention of the ligand in the organelle and the interaction of the receptor protein and the cognate ligand in the organelle;

introducing into the cell a binding molecule, or a binding fragment or portion thereof, which specifically binds either the receptor protein or the ligand protein retained in the intracellular organelle; and

detecting the level of the receptor protein expressed on the cell surface;

wherein, if the binding molecule, or a binding fragment or portion thereof, blocks or disrupts binding of the receptor and the cognate ligand in the organelle, the receptor protein is expressed and detectable on the cell surface, and wherein the binding molecule, or a binding fragment or portion thereof, which blocks or disrupts the receptor protein and ligand interaction is selectable.

2. The method according to claim I, further comprising recovering or isolating the selected binding molecule, or a binding fragment or portion thereof, from the cell.

3. The method according to claim 1 or claim 2, wherein the binding molecule, or a binding fragment or portion thereof, is selected from an antibody, or a binding fragment or portion thereof, a genetically diversified antibody, or a binding fragment or portion thereof, a member of an antibody library, or a binding fragment or portion thereof, a member of a genetically diversified antibody library, or a binding fragment or portion thereof, a single domain antibody, a member of a single domain antibody library, a member of a genetically diversified single domain antibody library, a V_H domain, a genetically diversified V_H domain, a V_L domain, or a genetically diversified V_L domain, or a complementarity determining region (CDR).

4. The method according to claim 3, wherein the antibody, or a binding fragment or portion thereof, is selected from a polyclonal antibody, a monoclonal antibody, a chimeric antibody, a humanized antibody, or a fully human antibody.

5. The method according to claim 3 or claim 4, wherein the antibody is a full length antibody comprising light chain variable domains and light chain constant domains, and heavy chain variable domains and heavy chain constant domains.

6. The method according to any one of claims 3, 4, or 5, wherein the antibody is an IgM, IgG, IgA, IgE, or IgD antibody or a subclass thereof.

7. The method according to claim 6, wherein the antibody is an IgG antibody or a subclass thereof.

8. The method according to claim 7, wherein the antibody is an IgGl, IgG2a, IgG2b, IgG3, or an IgG4 antibody.

9. The method according to claim 8, wherein the antibody is an IgGl antibody.

10. The method according to any one of claims 3 to 9, wherein the antibody, or a binding fragment or portion thereof, is selected from an Fab fragment, an Fab' fragment, an F(ab')2 fragment, an Fd fragment, an Fv fragment, a single-chain variable fragment (scFv), a diabody, or a domain antibody (dAb).

11. The method according to 3, wherein the antibody binding fragment or portion thereof is a V_L domain or a genetically diversified VL domain.

12. The method according to 3, wherein the antibody binding fragment or portion thereof is a V_H domain or a genetically diversified VH domain.

13. The method according to any one of claims 1 to 12, wherein the binding molecule is an antibody, or a binding fragment or portion thereof, is directed against human tumor necrosis factor alpha (hTNF-a receptor 1) receptor protein.

14. The method according to any one of claims 1 to 12, wherein the binding molecule is an antibody, or a binding fragment or portion thereof, is directed against the human tumor necrosis factor alpha (hTNF-a) ligand protein.

15. The method according to any one of claims 1 to 12, wherein the binding molecule is a non antibody molecule.

16. The method according to claim 15, wherein the non antibody binding molecule is selected from antibody mimetics, designed ankyrin repeat proteins (DARPins), affilins, affitins, avimers, anticalins, monobodies, affibody molecules, haptomers, or aptamers.

17. The method according to any one of claims 1 to 15 , wherein the receptor protein is a human receptor protein selected from growth factor receptors, hormone receptors, enzyme receptors, Fc receptors, metabolic enzyme receptors, neurotransmitter receptors, chemokine receptors, cytokine receptors, lymphokine receptors, interleukin receptors, tumor antigen receptors, tumor suppressor antigen receptors (e.g., p53, Rb, k-Rev, DCC receptors), multidrug resistance protein receptors, coagulation factor receptors, Factor VII receptor, Factor VIII receptor, Factor IX receptor, trophic factor receptors, cell recognition or stimulatory molecule receptors, apolipoprotein receptors, EGFR, ErbB-lR, HER1, HER2, aFGFR, bFGFR, NGFR, VEGFR, FltR, TGFR, TGFR-a-1, TGFR-β, TNFR-a, BDNFR, insulin receptor, insulin-like growth factor receptor (IGFR), PDGFR, HGFR, TRKR, BDNFR, CNTFR, GMFR, NT3R, NT5R, HARPR/pleiotrophinR, TIE receptors, Eph receptors, DDR receptors, ROR receptors, LTK receptors, AXL receptors, RET receptors, TOLL-like receptors; hormone receptors selected from steroid hormone receptors, thyroid hormone receptors, melatonin receptors; adrenergic receptors; peptide receptors selected from receptors for amylin, angiotensinogen, angiotensin, atrial natriuretic peptide, brain natriuretic peptide, calcitonin, corticotropin, erythropoietin, endothelin, enkephalin, follicle stimulating hormone, gastrin, ghrelin, glucagon, human chorionic gonadotropin, inhibin, leptin, luteinizing hormone, melanocyte stimulating hormone, oxitocin, pancreatic polypeptide, parathyroid hormone, prolactin, prolactin releasing hormone, rennin, secretin, somatostatin, thrombopoietin, thyroid stimulating hormone, thyrotropin releasing hormone; GP130 or IL6 receptors.

18. The method according to claim 17, wherein the receptor protein is human tumor necrosis factor alpha receptor 1 (hTNF-a receptor 1).

19. The method according to any one of claims 1 to 18, wherein the ligand protein is a human ligand protein selected from growth factors, hormones, enzymes, metabolic enzymes, neurotransmitters, chemokines, cytokines, lymphokines, interleukin, tumor antigens, tumor suppressor antigens, multidrug resistance proteins, coagulation factors, Factor VII, Factor VIII, Factor DC, trophic factors, cell recognition or stimulatory molecules, apolipoproteins, EGF, ErbB-1, HER1, HER2, aFGF, bFGF, NGF, VEGF, Fit, TGF, TGF-a-1, TGF-β, TNF-a, BDNF, insulin, insulin-like growth factor (IGFR), PDGF, HGF, TRK, BDNF, CNTF, GMF, NT3, NT5, HARP/pleiotrophin, TIE proteins, Eph proteins, DDR proteins, ROR proteins, LTK proteins, AXL proteins, RET proteins, TOLL-like proteins; hormones selected from steroid hormones, thyroid hormones, melatonin; adrenergic protein; peptides selected from amylin, angiotensinogen, angiotensin, atrial natriuretic peptide, brain natriuretic peptide, calcitonin, corticotropin, erythropoietin, endothelin, enkephalin, follicle stimulating hormone, gastrin, ghrelin, glucagon, human chorionic gonadotropin, inhibin, leptin, luteinizing hormone, melanocyte stimulating hormone, oxitocin, pancreatic polypeptide, parathyroid hormone, prolactin, prolactin releasing hormone, rennin, secretin, somatostatin, thrombopoietin, thyroid stimulating hormone, thyrotropin releasing hormone; GP130 or IL6.

20. The method according to claim 19, wherein the ligand protein is human tumor necrosis factor alpha (hTNF-a).

21. The method according to any one of claims 1 to 20, wherein the binding molecule binds to the receptor protein.

22. The method according to any one of claims 1 to 20, wherein the binding molecule binds to the cognate ligand.

23. The method according to any one of claims 1 to 22, wherein the intracellular organelle is the endoplasmic reticulum (ER) or the Golgi.

24. The method according to any one of claims 1 to 23, wherein the cognate ligand is molecularly tagged with a sequence for retaining the ligand in the endoplasmic reticulum (ER).

25. The method according to claim 24, wherein the ER retention sequence is KDEL (SEQ ID NO.-l).

26. A method of detecting whether a binding molecule, or a binding fragment or portion thereof, specifically binds to a cell surface expressed target protein within a cell, comprising: expressing in a cell a target protein which is expressible on the surface of the cell; expressing in the cell the binding molecule, or a binding fragment or portion thereof, fused to a sequence for retaining the binding molecule in an intracellular organelle;

wherein, if the binding molecule, or a binding fragment or portion thereof, specifically binds to the target protein in the cell, the target protein is retained in the intracellular organelle bound to the binding molecule, or the binding fragment or portion thereof, thereby preventing expression of the target protein on the cell surface; and

detecting the level of the target protein expressed on the cell surface, such that a non- detectable or low level of the target protein detected on the cell surface relative to a suitable control indicates binding of the binding protein, or a binding fragment or portion thereof, to the target molecule in the cell.

27. The method according to claim 26, further comprising recovering or isolating the binding molecule, or a binding fragment or portion thereof, from the cell.

28. The method according to claim 26 or claim 27, wherein the binding molecule, or a binding fragment or portion thereof, is selected from an antibody, or a binding fragment or portion thereof, a genetically diversified antibody, or a binding fragment or portion thereof, a member of an antibody library, or a binding fragment or portion thereof, a member of a genetically diversified antibody library, or a binding fragment or portion thereof, a single domain antibody, a member of a single domain antibody library, a member of a genetically diversified single domain antibody library, a V_H domain, a genetically diversified \¾ domain, a V_L domain, or a genetically diversified V_L domain, or a complementarity determining region (CDR).

29. The method according to claim 28, wherein the antibody, or a binding fragment or portion thereof, is selected from a polyclonal antibody, a monoclonal antibody, a chimeric antibody, a humanized antibody, or a fully human antibody.

30. The method according to claim 28 or claim 29, wherein the antibody is a full length antibody comprising light chain variable domains and light chain constant domains, and heavy chain variable domains and heavy chain constant domains.

31. The method according to any one of claims 28 to 30, wherein the antibody is an IgM, IgG, IgA, IgE, or IgD antibody or a subclass thereof.

32. The method according to any one of claims 28 to 30, wherein the antibody is an IgG antibody or a subclass thereof.

33. The method according to any one of claims 28 to 32, wherein the antibody is an IgGl, IgG2a, IgG2b, IgG3, or an IgG4 antibody.

34. The method according to claim 33, wherein the antibody is an IgGl antibody.

35. The method according to any one of claims 28 to 34, wherein the antibody, or a binding fragment or portion thereof, is selected from an Fab fragment, an Fab' fragment, an F(ab')2 fragment, an Fd fragment, an Fv fragment, a single-chain variable fragment (scFv), a diabody, or a domain antibody (dAb).

36. The method according to any one of claims 28 to 35, wherein the antibody binding fragment or portion thereof is a VL domain or a genetically diversified VL domain.

37. The method according to any one of claims 28 to 35, wherein the antibody binding fragment or portion thereof is a VH domain or a genetically diversified VH domain.

38. The method according to any one of claims 26 to 37, wherein the binding molecule is an antibody, or a binding fragment or portion thereof is directed against human tumor necrosis factor alpha (hTNF-a receptor 1) receptor protein.

39. The method according to any one of claims 26 to 37, wherein the binding molecule is an antibody, or a binding fragment or portion thereof, is directed against the human tumor necrosis factor alpha (hTNF-a) ligand protein.

40. The method according to claim 26 or claim 27, wherein the binding molecule is a non antibody molecule.

41. The method according to claim 40, wherein the non antibody binding molecule is selected from antibody mimetics, designed ankyrin repeat proteins (DARPins), affilins, affitins, avimers, anticalins, monobodies, affibody molecules, haptomers, or aptamers.

42. The method according to any one of claims 26 to 41, wherein the target protein is a human receptor protein selected from growth factor receptors, hormone receptors, enzyme receptors, Fc receptors, metabolic enzyme receptors, neurotransmitter receptors, chemokine receptors, cytokine receptors, lymphokine receptors, interleukin receptors, tumor antigen receptors, tumor suppressor antigen receptors (e.g., p53, Rb, k-Rev, DCC receptors), multidrug resistance protein receptors, coagulation factor receptors, Factor VII receptor, Factor VIII receptor, Factor IX receptor, trophic factor receptors, cell recognition or stimulatory molecule receptors, apolipoprotein receptors, EGFR, ErbB-lR, HER1, HER2, aFGFR, bFGFR, NGFR, VEGFR, FltR, TGFR, TGFR- -1, TGFR-β, TNFR-a, BDNFR, insulin receptor, insulin-like growth factor receptor (IGFR), PDGFR, HGFR, TRKR, BDNFR, CNTFR, GMFR, NT3R, NT5R, HARPR/pleiotrophinR, TIE receptors, Eph receptors, DDR receptors, ROR receptors, LTK receptors, AXL receptors, RET receptors, TOLL-like receptors; hormone receptors selected from steroid hormone receptors, thyroid hormone receptors, melatonin receptors; adrenergic receptors; peptide receptors selected from receptors for amylin, angiotensinogen, angiotensin, atrial natriuretic peptide, brain natriuretic peptide, calcitonin, corticotropin, erythropoietin, endothelin, enkephalin, follicle stimulating hormone, gastrin, ghrelin, glucagon, human chorionic gonadotropin, inhibin, leptin, luteinizing hormone, melanocyte stimulating hormone, oxitocin, pancreatic polypeptide, parathyroid hormone, prolactin, prolactin releasing hormone, rennin, secretin, somatostatin, thrombopoietin, thyroid stimulating hormone, thyrotropin releasing hormone; GP 130 or IL6 receptors.

43. The method according to claim 42, wherein the target protein is human tumor necrosis factor alpha receptor 1 (hTNF-a receptor 1).

44. The method according to any one of claims 26 to 41, wherein the target protein is a human ligand protein, capable of being expressed on the cell surface, selected from growth factors, hormones, enzymes, metabolic enzymes, neurotransmitters, chemokines, cytokines, lymphokines, interleukin, tumor antigens, tumor suppressor antigens, multidrug resistance proteins, coagulation factors, Factor VII, Factor VIII, Factor K, trophic factors, cell recognition or stimulatory molecules, apolipoproteins, EGF, ErbB-1, HER1, HER2, aFGF, bFGF, NGF, VEGF, Fit, TGF, TGF-a-1, TGF-β, TNF-a, BDNF, insulin, insulin-like growth factor (IGFR), PDGF, HGF, TRK, BDNF, CNTF, GMF, NT3, NT5, HARP/pleiotrophin, TIE proteins, Eph proteins, DDR proteins, ROR proteins, LTK proteins, AXL proteins, RET proteins, TOLL-like proteins; hormones selected from steroid hormones, thyroid hormones, melatonin; adrenergic protein; peptides selected from amylin, angiotensinogen, angiotensin, atrial natriuretic peptide, brain natriuretic peptide, calcitonin, corticotropin, erythropoietin, endothelin, enkephalin, follicle stimulating hormone, gastrin, ghrelin, glucagon, human chorionic gonadotropin, inhibin, leptin, luteinizing hormone, melanocyte stimulating hormone, oxitocin, pancreatic polypeptide, parathyroid hormone, prolactin, prolactin releasing hormone, rennin, secretin, somatostatin, thrombopoietin, thyroid stimulating hormone, thyrotropin releasing hormone; GP130 or IL6.

45. The method according to claim 44, wherein the target protein is human tumor necrosis factor alpha (hTNF-a).

46. The method according to any one of claims 26 to 45, wherein the intracellular organelle is the endoplasmic reticulum (ER) or the Golgi.

47. The method according to any one of claims 26 to 46, wherein the binding molecule, or a binding fragment or portion thereof, is molecularly tagged with a sequence for retaining the ligand in the endoplasmic reticulum (ER).

48. The method according to claim 47, wherein the ER retention sequence is KDEL (SEQ ID NO:l).

49. A method of detecting whether an antibody, or a binding fragment or portion thereof, specifically binds to a cell surface-expressed target molecule within a cell, comprising:

expressing in a cell a target molecule which is expressible on the surface of the cell; expressing in the cell an antibody, or a binding fragment or portion thereof, fused to an endoplasmic reticulum (ER) or Golgi retention sequence;

wherein, if the antibody, or a binding fragment or portion thereof, specifically binds to the target protein in the cell, the target protein is retained in the ER or Golgi bound to the antibody, or a binding fragment or portion thereof, thereby preventing expression of the target protein on the cell surface; and

detecting the level of the target protein expressed on the cell surface, such that a non- detectable or low level of the target protein detected on the cell surface relative to a suitable control indicates binding of the antibody, or the binding fragment or portion thereof, to the target molecule in the cell, wherein the antibody is selectable in the cell.

50. The method according to claim 49, further comprising recovering or isolating the antibody, or a binding fragment or portion thereof, from the cell.

51. The method according to claim 49 or claim 50, wherein the antibody, or a binding fragment or portion thereof, is selected from a genetically diversified antibody, or a binding fragment or portion thereof, a member of an antibody library, or a binding fragment or portion thereof, a member of a genetically diversified antibody library, or a binding fragment or portion thereof, a single domain antibody, a member of a single domain antibody library, a member of a genetically diversified single domain antibody library, a VH domain, a genetically diversified VH domain, a VL domain, or a genetically diversified VL domain, or a complementarity detennining region (CDR).

52. The method according to any one of claims 49 to 51, wherein the antibody, or a binding fragment or portion thereof, is selected from a polyclonal antibody, a monoclonal antibody, a chimeric antibody, a humanized antibody, or a fully human antibody.

53. The method according to any one of claims 49 to 52, wherein the antibody is a full length antibody comprising light chain variable domains and light chain constant domains, and heavy chain variable domains and heavy chain constant domains.

54. The method according to any one of claims 49 to 53, wherein the antibody is an IgM, IgG, IgA, IgE, or IgD antibody or a subclass thereof.

55. The method according to any one of claims 49 to 54, wherein the antibody is an IgG antibody or a subclass thereof.

56. The method according to any one of claims 49 to 55, wherein the antibody is an IgGl, IgG2a, IgG2b, IgG3, or an IgG4 antibody.

57. The method according to claim 56, wherein the antibody is an IgGl antibody.

58. The method according to any one of claims 49 to 57, wherein the antibody, or a binding fragment or portion thereof, is selected from an Fab fragment, an Fab' fragment, an F(ab')2 fragment, an Fd fragment, an Fv fragment, a single-chain variable fragment (scFv), a diabody, or a domain antibody (dAb).

59. The method according to any one of claims 49 to 51, wherein the antibody binding fragment or portion thereof is a VL domain or a genetically diversified VL domain.

60. The method according to any one of claims 49 to 51, wherein the antibody binding fragment or portion thereof is a VH domain or a genetically diversified VH domain.

61. The method according to any one of claims 49 to 60, wherein the antibody, or a binding fragment or portion thereof, is directed against a target protein selected from a human receptor protein selected from growth factor receptors, hormone receptors, enzyme receptors, Fc receptors, neurotransmitter receptors, chemokine receptors, cytokine receptors, lymphokine receptors, interleukin receptors, tumor antigen receptors, cell recognition or stimulatory receptors, receptors in receptor families selected from apolipoprotein receptors, EGFR, ErbB-lR, HER1, HER2, aFGFR, bFGFR, NGFR, VEGFR, FltR, TGFR, TGFR-a-1, TGFR-β, TNFR-a, BDNFR, insulin receptor, insulin-like growth factor receptor (IGFR), PDGFR, HGFR, TRKR, BDNFR, CNTFR, GMFR, NT3R, NT5R, HARPR/pleiotrophinR, TIE receptors, Eph receptors, DDR receptors, ROR receptors, LTK receptors, AXL receptors, RET receptors, or TOLL-like receptors; steroid hormone receptors, thyroid hormone receptors, melatonin receptors, adrenergic receptors; receptors for peptides selected from amylin, angiotensinogen, angiotensin, atrial natriuretic peptide, brain natriuretic peptide, calcitonin, corticotropin, erythropoietin, endothelin, enkephalin, follicle stimulating hormone, gastrin, ghrelin, glucagon, human chorionic gonadotropin, inhibin, leptin, luteinizing hormone, melanocyte stimulating hormone, oxitocin, pancreatic polypeptide, parathyroid hormone, prolactin, prolactin releasing hormone, rennin, secretin, somatostatin, thrombopoietin, thyroid stimulating hormone, or thyrotropin releasing hormone; or GP130 or IL6 receptors.

62. The method according to any one of claims 49 to 60, wherein the antibody, or a binding fragment or portion thereof, is directed against a human target protein selected from selected from growth factors, hormones, enzymes, metabolic enzymes, neurotransmitters, chemokines, cytokines, lymphokines, interleukin, tumor antigens, tumor suppressor antigens, multidrug resistance proteins, coagulation factors, Factor VII, Factor VIII, Factor IX, trophic factors, cell recognition or stimulatory molecules, apolipoproteins, EGF, ErbB-1, HER1, HER2, aFGF, bFGF, NGF, VEGF, Fit, TGF, TGF-a-1, TGF-β, TNF-a, BDNF, insulin, insulin-like growth factor (IGFR), PDGF, HGF, TRK, BDNF, CNTF, GMF, NT3, NT5, HARP/pleiotrophin, TIE proteins, Eph proteins, DDR proteins, ROR proteins, LTK proteins, AXL proteins, RET proteins, TOLL-like proteins; hormones selected from steroid hormones, thyroid hormones, melatonin; adrenergic protein; peptides selected from amylin, angiotensinogen, angiotensin, atrial natriuretic peptide, brain natriuretic peptide, calcitonin, corticotropin, erythropoietin, endothelin, enkephalin, follicle stimulating hormone, gastrin, ghrelin, glucagon, human chorionic gonadotropin, inhibin, leptin, luteinizing hormone, melanocyte stimulating hormone, oxitocin, pancreatic polypeptide, parathyroid hormone, prolactin, prolactin releasing hormone, rennin, secretin, somatostatin, thrombopoietin, thyroid stimulating hormone, thyrotropin releasing hormone; GP130 or IL6.

63. The method according to claim 49, wherein the antibody, or a binding fragment or portion thereof, is directed against human tumor necrosis factor alpha (hTNF-a receptor 1) receptor protein as the target protein.

64. The method according to claim 49, wherein the antibody, or a binding fragment or portion thereof, is directed against the human tumor necrosis factor alpha (hTNF-a) protein as the target protein.

65. The method according to any one of claims 49 to 64, wherein the antibody protein, or a binding fragment or portion thereof, is fused to an endoplasmic reticulum (ER) retention sequence.

66. The method according to claim 65, wherein the ER retention sequence is DEL (SEQ ID NO:l).

67. A method of selecting for an antibody, or a binding fragment or portion thereof, that specifically binds to a target protein expressed on the surface of a cell, comprising:

establishing a cell line which expresses the target protein on the cell surface; wherein the cell surface expressed target protein is capable of being detected by a detectably labeled binding molecule;

expressing in the cell line an antibody or a binding fragment or portion thereof, for selection for binding to the target protein, wherein the antibody, or a binding fragment or portion thereof, is fused to a signal sequence for retaining the antibody or a binding fragment or portion thereof in an intracellular organelle under conditions allowing for the interaction and binding of the antibody, or a binding fragment or portion thereof, and the target protein within the organelle; and

detecting the level of the target protein expressed on the cell surface with the detectably labeled binding molecule; wherein, if the antibody, or a binding fragment or portion thereof, specifically binds to the target protein in the organelle, the target protein is bindably retained therein, thereby decreasing or eliminating the level of expression of the target protein on the cell surface; and indicating the retention of a selectable antibody, or a binding fragment thereof, in the cell.

68. The method according to claim 67, further comprising: recovering from the cells the antibody, or a binding fragment or portion thereof, that specifically binds to the target protein.

69. The method according to claim 67 or claim 68, wherein the antibody or a binding fragment or portion thereof is fused to a signal sequence for retaining the antibody, or a binding fragment or portion thereof, in the endoplasmic reticulum (ER) intracellular organelle.

70. The method according to any one of claims 67 to 69, wherein the antibody, or a binding fragment or portion thereof, is fused to the KDEL signal sequence (SEQ ID NO:l) which retains the antibody, or a binding fragment or portion thereof, in the ER.

71. The method according to any one of claims 67 to 70, wherein the target protein is a receptor protein or a membrane-expressible ligand protein.

72. The method according to any one of claims 67 to 71, wherein the cell line is transduced with a lentiviral particle encoding the nucleic acid sequence of the antibody, or a binding fragment or portion thereof.

73. The method according to any one of claims 67 to 72, wherein the antibody or a binding fragment or portion thereof is selected from a member of an antibody library, a member of a genetically diversified antibody library, a member of an antibody single domain library, or a member of a genetically diversified antibody single domain library.

74. The method according to any one of claims 67 to 73, wherein the antibody or a binding fragment or portion thereof is an antibody VL domain, a genetically diversified antibody VL domain, an antibody VH domain, or a genetically diversified antibody VH domain.

75. The method according to any one of claims 67 to 74, wherein the antibody, or a binding fragment or portion thereof, is selected from a polyclonal antibody, a monoclonal antibody, a chimeric antibody, a humanized antibody, or a fully human antibody.

76. The method according to any one of claims 67 to 75, wherein the antibody is a full length antibody comprising light chain variable domains and light chain constant domains, and heavy chain variable domains and heavy chain constant domains.

77. The method according to any one of claims 67 to 76, wherein the antibody is an IgM, IgG, IgA, IgE, or IgD antibody or a subclass thereof.

78. The method according to any one of claims 67 to 77, wherein the antibody is an IgG antibody or a subclass thereof.

79. The method according to any one of claims 67 to 78, wherein the antibody is an IgGl, IgG2a, IgG2b, IgG3, or an IgG4 antibody.

80. The method according to claim 79, wherein the antibody is an IgGl antibody.

81. The method according to any one of claims 67 to 80, wherein the antibody, or a binding fragment or portion thereof, is selected from an Fab fragment, an Fab' fragment, an F(ab')2 fragment, an Fd fragment, an Fv fragment, a single-chain variable fragment (scFv), a diabody, or a domain antibody (dAb) .

82. The method according to any one of claims 67 to 81, wherein the level of the target protein expressed on the cell surface is detected by flow cytometry and a detectably labeled antibody.

83. A method of selecting from a plurality of binding molecules a binding molecule which binds a target antigen that is a member of an interacting pair comprising a cell surface-expressed receptor binding protein and a cognate ligand, the method comprising:

(a) introducing nucleic acid encoding one of a plurality of binding molecules into cells expressing the receptor binding protein and the cognate ligand, which is fused to a retention signal that retains the cognate ligand in an intracellular organelle;

(b) expressing in the cells the nucleic acid of (a), wherein an expressed binding molecule binds to the receptor binding protein or the cognate ligand target antigen retained in the organelle and disrupts or blocks the interaction between the receptor binding protein and the cognate ligand; and (c) detecting the level of receptor binding protein expressed on the cell surface; wherein, if the binding molecule binds to either the receptor binding protein or the cognate ligand in the organelle and disrupts or blocks their interaction, the receptor binding protein is expressed and detectable on the cell surface, and wherein the binding molecule that disrupts or blocks the interaction is selectable.

84. The method according to claim 83, wherein the nucleic acid encoding the plurality of binding molecules is introduced into the cells by lentivirus particles harboring the nucleic acid.

85. The method according to claim 83 or claim 84, further comprising recovering or isolating the selected binding molecule from the cell.

86. The method according to any one of claims 83 to 85, wherein the plurality of binding molecules is selected from an antibody library, a genetically diversified antibody library, a single domain antibody library, a genetically diversified single domain antibody library, a VL domain library, a genetically diversified VL domain library, a V_H domain library, or a genetically diversified VH domain library.

87. The method according to any one of claims 83 to 86, wherein the binding molecule is an antibody or a binding fragment or portion thereof.

88. The method according to claim 87, wherein the antibody, or a binding fragment or portion thereof, is selected from a polyclonal antibody, a monoclonal antibody, a chimeric antibody, a humanized antibody, or a fully human antibody.

89. The method according to claim 87 or claim 88, wherein the antibody binding fragment or portion is selected from an Fab fragment, an Fab' fragment, an F(ab')2 fragment, an Fd fragment, an Fv fragment, a single-chain variable fragment (scFv), a diabody, a domain antibody (dAb), a heavy chain variable domain (VH), a genetically diversified heavy chain variable domain (VH), a light chain variable domain (VL), a genetically diversified light chain variable domain (VL), or a complementarity determining region (CDR).

90. The method according to any one of claims 83 to 89, wherein the plurality of binding molecules is an antibody VL library or a genetically diversified V_L library.

91. The method according to any one of claims 87 to 90, wherein the antibody binding fragment or portion thereof is a VL domain or a genetically diversified VL domain.

92. The method according to any one of claims 83 to 89, wherein the plurality of binding molecules is an antibody V_H library or a genetically diversified VH library.

93. The method according to any one of claims 87 to 90, wherein the antibody binding fragment or portion thereof is a V_H domain or a genetically diversified V_H domain.

94. The method according to claim 87 or claim 88, wherein the antibody is a full length antibody comprising light chain variable domains and light chain constant domains, and heavy chain variable domains and heavy chain constant domains.

95. The method according to any one of claims 87 to 94, wherein the antibody is an IgM, IgG, IgA, IgE, or IgD antibody or a subclass thereof.

96. The method according to any one of claims 87 to 94, wherein the antibody is an IgG antibody or a subclass thereof.

97. The method according to any one of claims 87 to 94, wherein the antibody is an IgGl, IgG2a, IgG2b, IgG3, or an IgG4 antibody.

98. The method according to claim 97, wherein the antibody is an IgGl antibody.

99. The method according to any one of claims 83 to 98, wherein the intracellular organelle is the endoplasmic reticulum (ER) or the Golgi.

100. The method according to any one of claims 83 to 99, wherein the cognate ligand is molecularly tagged with a sequence for retaining the ligand in the endoplasmic reticulum (ER).

101. The method according to claim 100, wherein the ER retention sequence is KDEL (SEQ ID NO:l).

102. The method according to any one of claims 83 to 101, wherein the expressed binding molecule binds a receptor binding protein target antigen selected from growth factor receptors, hormone receptors, enzyme receptors, Fc receptors, neurotransmitter receptors, chemokine receptors, cytokine receptors, lymphokine receptors, interleukin receptors, tumor antigen receptors, cell recognition or stimulatory receptors, receptors in receptor families selected from apolipoprotein receptors, EGFR, ErbB-lR, HER1, HER2, aFGFR, bFGFR, NGFR, VEGFR, FltR, TGFR, TGFR-a-1, TGFR-β, TNFR-a, BDNFR, insulin receptor, insulin-like growth factor receptor (IGFR), PDGFR, HGFR, TRKR, BDNFR, CNTFR, GMFR, NT3R, NT5R, HARPR/pleiotrophinR, TIE receptors, Eph receptors, DDR receptors, ROR receptors, LTK receptors, AXL receptors, RET receptors, or TOLL-like receptors; steroid hormone receptors, thyroid hormone receptors, melatonin receptors, adrenergic receptors; receptors for peptides selected from amylin, angiotensinogen, angiotensin, atrial natriuretic peptide, brain natriuretic peptide, calcitonin, corticotropin, erythropoietin, endothelin, enkephalin, follicle stimulating hormone, gastrin, ghrelin, glucagon, human chorionic gonadotropin, inhibin, leptin, luteinizing hormone, melanocyte stimulating hormone, oxitocin, pancreatic polypeptide, parathyroid hormone, prolactin, prolactin releasing hormone, re nin, secretin, somatostatin, thrombopoietin, thyroid stimulating hormone, or thyrotropin releasing hormone; or GP130 or IL6 receptors.

103. The method according to any one of claims 83 to 101, wherein the expressed binding molecule binds a cognate ligand target antigen selected from growth factors, hormones, enzymes, metabolic enzymes, neurotransmitters, chemokines, cytokines, lymphokines, interleukin, tumor antigens, tumor suppressor antigens, multidrug resistance proteins, coagulation factors, Factor VII, Factor VIII, Factor DC, trophic factors, cell recognition or stimulatory molecules, apolipoproteins, EGF, ErbB-1, HER1, HER2, aFGF, bFGF, NGF, VEGF, Fit, TGF, TGF-a-1, TGF-β, TNF-a, BDNF, insulin, insulin-like growth factor (IGFR), PDGF, HGF, TRK, BDNF, CNTF, GMF, NT3, NT5, HARP/pleiotrophin, TIE proteins, Eph proteins, DDR proteins, ROR proteins, LTK proteins, AXL proteins, RET proteins, TOLL-like proteins; hormones selected from steroid hormones, thyroid hormones, melatonin; adrenergic protein; peptides selected from amylin, angiotensinogen, angiotensin, atrial natriuretic peptide, brain natriuretic peptide, calcitonin, corticotropin, erythropoietin, endothelin, enkephalin, follicle stimulating hormone, gastrin, ghrelin, glucagon, human chorionic gonadotropin, inhibin, leptin, luteinizing hormone, melanocyte stimulating ho>mone, oxitocin, pancreatic polypeptide, parathyroid hormone, prolactin, prolactin releasing hormone, rennin, secretin, somatostatin, thrombopoietin, thyroid stimulating hormone, thyrotropin releasing hormone; GP130 or IL6.

104. A method of selecting from a plurality of binding molecules, a binding molecule, or a binding portion thereof, that binds a cell surface expressed target antigen, comprising:

introducing into cells a nucleic acid sequence encoding one of a plurality of binding molecules operably linked to nucleic acid encoding a intracellular organelle retention signal, wherein the cells express the target antigen which is expressible on the cell surface; expressing in the cells one of the plurality of binding molecules comprising the retention signal; wherein, if the plurality of binding molecules comprises a binding molecule, or a binding portion thereof, that specifically binds to the target protein, the target protein is retained in the cell organelle through its being bound to the binding molecule, or a binding portion thereof, retained in the intracellular organelle, thereby preventing both exit of the target protein from the organelle and expression of the target protein on the cell surface; and

detecting the level of the target protein expressed on the cell surface, such that a non- detectable or low level of the target protein detected on the cell surface relative to a suitable control indicates specific binding of the binding molecule, or the binding portion thereof, to the target molecule in the cell, wherein the binding molecule, or the binding portion thereof, is selectable from the cells.

105. The method according to claim 104, wherein the nucleic acid encoding one of a plurality of binding molecules is introduced into the cells by lentivirus particles harboring the nucleic acid.

106. The method according to claim 104 or claim 105, further comprising recovering or isolating the selected binding molecule from the cell.

107. The method according to any one of claims 104 to 106, wherein the plurality of binding molecules is selected from an antibody library, a genetically diversified antibody library, a single domain antibody library, a genetically diversified single domain antibody library, a V_L domain library, a genetically diversified V_L domain library, a VH domain library, or a genetically diversified VH domain library.

108. The method according to any one of claims 104 to 107, wherein the binding molecule or a binding portion thereof is an antibody or a binding fragment or portion thereof.

109. The method according to claim 108, wherein the antibody, or a binding fragment or portion thereof, is selected from a polyclonal antibody, a monoclonal antibody, a chimeric antibody, a humanized antibody, or a fully human antibody.

110. The method according to 109, wherein the antibody binding fragment or portion is selected from an Fab fragment, an Fab' fragment, an F(ab')2 fragment, an Fd fragment, an Fv fragment, a single-chain variable fragment (scFv), a diabody, a domain antibody (dAb), a heavy chain variable domain (VH), a genetically diversified heavy chain variable domain (V_H), a light chain variable domain (VL), a genetically diversified light chain variable domain (VL), or a complementarity determining region (CDR).

111. The method according to any one of claims 104 to 107, wherein the plurality of binding molecules is an antibody VL library or a genetically diversified VL library.

112. The method according to any one of claims 104 to 107, wherein the plurality of binding molecules is an antibody VH library or a genetically diversified VH library.

113. The method according to any one of claims 104 to 107, wherein the binding molecule, or a binding portion thereof, is a VL domain or a genetically diversified VL domain.

114. The method according to any one of claims 104 to 107, wherein the binding molecule, or a binding portion thereof, is a VH domain or a genetically diversified VH domain.

115. The method according to claim 108 or claim 109, wherein the antibody is a full length antibody comprising light chain variable domains and light chain constant domains, and heavy chain variable domains and heavy chain constant domains.

116. The method according to any one of claims 107 to 115, wherein the antibody is an IgM, IgG, IgA, IgE, or IgD antibody or a subclass thereof.

117. The method according to any one of claims 107 to 116, wherein the antibody is an IgG antibody or a subclass thereof.

118. The method according to any one of claims 107 to 117, wherein the antibody is an IgGl, IgG2a, IgG2b, IgG3, or an IgG4 antibody.

119. The method according to claim 118, wherein the antibody is an IgGl antibody.

120. The method according to any one of claims 104 to 119, wherein the intracellular organelle is the endoplasmic reticulum (ER) or the Golgi.

121. The method according to any one of claims 104 to 120, wherein the intracellular organelle retention signal is a KDEL amino acid sequence (SEQ ID NO.l).

122. The method according to any one of claims 104 to 122, wherein the target antigen is selected from growth factor receptors, hormone receptors, enzyme receptors, Fc receptors, neurotransmitter receptors, chemokine receptors, cytokine receptors, lymphokine receptors, interleukin receptors, tumor antigen receptors, cell recognition or stimulatory receptors, receptors in receptor families selected from apolipoprotein receptors, EGFR, ErbB-lR, HER1, HER2, aFGFR, bFGFR, NGFR, VEGFR, FltR, TGFR, TGFR-a-1, TGFR-β, TNFR-a, BDNFR, insulin receptor, insulin-like growth factor receptor (IGFR), PDGFR, HGFR, TRKR, BDNFR, CNTFR, GMFR, NT3R, NT5R, HARPR/pleiotrophinR, TIE receptors, Eph receptors, DDR receptors, ROR receptors, LTK receptors, AXL receptors, RET receptors, or TOLL-like receptors; steroid hormone receptors, thyroid hormone receptors, melatonin receptors, adrenergic receptors; receptors for peptides selected from amylin, angiotensinogen, angiotensin, atrial natriuretic peptide, brain natriuretic peptide, calcitonin, corticotropin, erythropoietin, endothelin, enkephalin, follicle stimulating hormone, gastrin, ghrelin, glucagon, human chorionic gonadotropin, inhibin, leptin, luteinizing hormone, melanocyte stimulating hormone, oxitocin, pancreatic polypeptide, parathyroid hormone, prolactin, prolactin releasing hormone, rennin, secretin, somatostatin, thrombopoietin, thyroid stimulating hormone, or thyrotropin releasing hormone; or GP130 or IL6 receptors.

123. The method according to any one of claims 104 to 122, wherein the target antigen is selected from growth factors, hormones, enzymes, metabolic enzymes, neurotransmitters, chemokines, cytokines, lymphokines, interleukin, tumor antigens, tumor suppressor antigens, multidrug resistance proteins, coagulation factors, Factor VII, Factor VIII, Factor IX, trophic factors, cell recognition or stimulatory molecules, apolipoproteins, EGF, ErbB-1, HER1, HER2, aFGF, bFGF, NGF, VEGF, Fit, TGF, TGF-a-1, TGF-β, TNF- , BDNF, insulin, insulin-like growth factor (IGFR), PDGF, HGF, TRK, BDNF, CNTF, GMF, NT3, NT5, HARP/pleiotrophin, TIE proteins, Eph proteins, DDR proteins, ROR proteins, LTK proteins, AXL proteins, RET proteins, TOLL-like proteins; hormones selected from steroid hormones, thyroid hormones, melatonin; adrenergic protein; peptides selected from amylin, angiotensinogen, angiotensin, atrial natriuretic peptide, brain natriuretic peptide, calcitonin, corticotropin, erythropoietin, endothelin, enkephalin, follicle stimulating hormone, gastrin, ghrelin, glucagon, human chorionic gonadotropin, inhibin, leptin, luteinizing hormone, melanocyte stimulating hormone, oxitocin, pancreatic polypeptide, parathyroid hormone, prolactin, prolactin releasing hormone, rennin, secretin, somatostatin, thrombopoietin, thyroid stimulating hormone, thyrotropin releasing hormone; GP130 or IL6.

124. A method of producing antibody genetic diversity or variability by modifying immunoglobulin complementarity determining regions (CDRs), the method comprising:

(a) introducing into one or more CDR-encoding nucleic acid sequences one or more zinc finger DNA binding domain recognition sequences to generate one or more non-identical targeting site sequences within the one or more CDR-encoding nucleic acid sequences for binding one or more zinc fmger nucleases (ZFN), thereby producing CDRs comprising modified nucleic acid sequences; and

(b) expressing in a cell, a nucleic acid encoding at least an antibody heavy chain variable domain (VH) and/or at least an antibody light chain variable domain (VL) comprising the modified CDR-encoding nucleic acid sequence of (a) under conditions in which the expressed ZFN binds and cleaves the modified CDR-encoding nucleic acid sequence within the targeting site sequence, said cell expressing a nucleic acid sequence encoding a zinc finger nuclease (ZFN) into which is introduced the zinc finger DNA binding domain targeting site sequences of (a) operably linked to a nucleic acid sequence encoding a DNA cleavage domain of a type IIS restriction enzyme, wherein DNA cleavage by the ZFN is determined by the targeting site sequences within the modified CDR-encoding nucleic acid sequence of (a).

125. The method according to claim 124, wherein in (a), the nucleic acid sequences encoding the CDRs are isolated from a VH and/or a VL domain and are harbored in a suitable DNA construct.

126. The method according to claim 125, wherein the DNA construct is selected from a DNA plasmid, vector or nucleic acid expression cassette.

127. The method according to claim 126, wherein the DNA construct comprises nucleic acid encoding CDR1, CDR2, CDR3, or a combination thereof.

128. The method according to any one of claims 124 to 127, wherein the nucleic acid sequences encoding the one or more modified CDRs are introduced into nucleic acid sequences encoding a VH and/or a VL domain to produce VH and/or VL domains comprising one or more modified CDRs.

129. The method according to any one of claims 124 to 128, wherein in (a) the CDR-encoding nucleic acid sequences are contained within nucleic acid sequences encoding an antibody heavy chain variable domain (VH) and/or nucleic acid sequences encoding an antibody light chain variable domain (VL).

130. The method according to any one of claims 124 to 129, wherein, in (b), the modified CDR-encoding nucleic acid sequence is contained within a full length antibody comprising nucleic acid sequences encoding a heavy chain variable domain (VH) and a heavy chain constant region (CH), and comprising nucleic acid sequences encoding a light chain variable domain (VL) and a light chain constant region (CL), wherein the resulting nucleic acid sequences encode full length antibodies comprising VH and VL domains comprising modified CDRs.

131. The method according to any one of claims 124 to 130, further comprising amplifying the nucleic acid sequences encoding the VH and/or VL domain proteins and cloning the VH and/or V_L domain proteins from the cell.

132. The method according to any one of claims 124 to 131, wherein, in (a), the one or more zinc finger DNA binding domain recognition sequences are introduced into one or more of CDRl, CDR2 and CDR3, or each of CDRl, CDR2 and CDR3.

133. The method according to any one of claims 124 to 132, wherein, in (a), the one or more zinc finger DNA binding domain recognition sequences are introduced into each of CDRl and CDR3.

134. The method according to any one of claims 124 to 133, wherein, in (a), two different zinc finger DNA binding domain recognition sequences are introduced into each of CDRl and CDR3.

135. The method according to claim 134, wherein the two different zinc finger DNA binding domain recognition sequences introduced into each of CDRl and CDR3 comprise SEQ ID NO:6.

136. The method according to claim 134 or claim 135, wherein, the two different zinc finger DNA binding domain recognition sequences introduced into each of CDRl and CDR3 of the V_H and the VL antibody domains comprise a total of 24 base pairs.

137. The method according to any one of claims 124 to 136, wherein, in (b), the type II restriction enzyme Fok I.

138. The method according to any one of claims 124 to 137, wherein, in (b), the nucleic acid sequences encoding the zinc finger nucleases (ZFNs) are introduced into a construct which comprises a first ZFN sequence for cleavage within CDRl of a VH domain, a second ZFN sequence for cleavage within CDR1 of a VH domain, and a first ZFN sequence for cleavage within CDR3 of a VH domain and a second ZFN sequence for cleavage within CDR3 of a VH domain.

139. The method according to claim 138, wherein (i) the first ZFN sequence for cleavage within CDR1 comprises a targeting sequence as set forth in SEQ ID NO:7 and a ZFP recognition sequence as set forth in SEQ ID NO:8, and the second ZFN sequence for cleavage within CDR1 comprises a targeting sequence as set forth in SEQ ID NO:9 and a ZFP recognition sequence as set forth in SEQ ID NO: 10; and (ii) the first ZFN sequence for cleavage within CDR3 comprises a targeting sequence as set forth in SEQ ID NO: 11 and a ZFP recognition sequence as set forth in SEQ ID NO: 12, and the second ZFN sequence for cleavage within CDR3 comprises a targeting sequence as set forth in SEQ ID NO: 13 and a ZFP recognition sequence as set forth in SEQ ID NO: 14.

140. The method according to claim 138, wherein the construct comprises a lentivirus vector.

141. The method according to any one of claims 124 to 137, wherein, in (b), the nucleic acid sequences encoding the zinc finger nucleases (ZFNs) are introduced into a construct which comprises a first ZFN sequence for cleavage within CDR1 of a VL domain , a second ZFN sequence for cleavage within CDR1 of a VL domain; and a first ZFN sequence for cleavage within CDR3 of a VL domain and a second ZFN sequence for cleavage within CDR3 of a VL domain.

142. The method according to claim 141, wherein (i) the first ZFN sequence for cleavage within CDR1 comprises a targeting sequence as set forth in SEQ ID NO: 15 and a ZFP recognition sequence as set forth in SEQ ID NO: 16, and the second ZFN sequence for cleavage within CDR1 comprises a targeting sequence as set forth in SEQ ID NO: 17 and a ZFP recognition sequence as set forth in SEQ ID NO: 18; and (ii) the first ZFN sequence for cleavage within CDR3 comprises a targeting sequence as set forth in SEQ ID NO: 19 and a ZFP recognition sequence as set forth in SEQ ID NO:20, and the second ZFN sequence for cleavage within CDR3 comprises a targeting sequence as set forth in SEQ ID NO:21 and a ZFP recognition sequence as set forth in SEQ ID NO:22.

143. The method according to claim 141, wherein the construct comprises a lentivirus vector

144. The method of according to claim 130, wherein the full length antibody is selected from an IgG, IgM, IgA, IgD, or IgE antibody.

145. The method according to claim 144, wherein the full length antibody is an IgG antibody or a subclass thereof.

146. The method according to claim 144 or claim 145, wherein the IgG antibody is an IgGl, IgG2a, IgG2b, IgG3, or IgG4 antibody.

147. The method according to claim 146, wherein the antibody is an IgGl antibody.

148. The method according to any one of claims 124 to 147, wherein in (b), the cell is a T-cell line.

149. The method according to any one of claims 124 to 147, wherein, in (b) the cell is a Jurkat T-cell line.

150. The method according to any one of claims 124 to 149, further comprising:

(c) expressing in the cell a receptor protein which is expressible on the cell surface and which is a potential target bindable by the VH and/or VL domain comprising modified CDRs of (b);

(d) expressing in the cell a cognate ligand of the receptor protein, the cognate ligand being molecularly tagged with a sequence for retaining the ligand in an intracellular organelle under conditions allowing for the retention of the ligand in the organelle and the interaction of the receptor protein and the cognate ligand in the organelle, wherein the cognate ligand is a potential target bindable by V_H and/or VL domain of (b); and

(e) detecting the level of the receptor protein expressed on the cell surface;

wherein, if the VH and or VL domain binds to either the receptor protein or the cognate ligand and blocks or disrupts their binding interaction in the organelle, the receptor protein exits the organelle and is expressed and detectable on the cell surface, and wherein the VH and/or VL domain which blocks or disrupts the receptor protein and ligand interaction is recoverable from the cell.

151. The method according to claim 150, wherein the intracellular organelle retention sequence is an endoplasmic reticulum (ER) or Golgi retention sequence.

152. The method according to claim 150 or claim 151, wherein the intracellular organelle retention sequence is an endoplasmic reticulum (ER) retention sequence.

153. The method according to any one of claims 150 to 152, wherein the ER retention sequence is DEL (SEQ ID NO:l).

154. The method according to any one of claims 150 to 153, wherein the cell surface expressible receptor protein is selected from growth factor receptors, hormone receptors, enzyme receptors, Fc receptors, neurotransmitter receptors, chemokine receptors, cytokine receptors, lymphokine receptors, interleukin receptors, tumor antigen receptors, cell recognition or stimulatory receptors, receptors in receptor families selected from apolipoprotein receptors, EGFR, ErbB-lR, HER1, HER2, aFGFR, bFGFR, NGFR, VEGFR, FltR, TGFR, TGFR-a-1, TGFR-β, TNFR-a, BD FR, insulin receptor, insulin-like growth factor receptor (IGFR), PDGFR, HGFR, TR R, BDNFR, CNTFR, GMFR, NT3R, NT5R, HARPR/pleiotrophinR, ΤΓΕ receptors, Eph receptors, DDR receptors, ROR receptors, LTK receptors, AXL receptors, RET receptors, or TOLL-like receptors; steroid hormone receptors, thyroid hormone receptors, melatonin receptors, adrenergic receptors; receptors for peptides selected from amylin, angiotensinogen, angiotensin, atrial natriuretic peptide, brain natriuretic peptide, calcitonin, corticotropin, erythropoietin, endothelin, enkephalin, follicle stimulating hormone, gastrin, ghrelin, glucagon, human chorionic gonadotropin, inhibin, leptin, luteinizing hormone, melanocyte stimulating hormone, oxitocin, pancreatic polypeptide, parathyroid hormone, prolactin, prolactin releasing hormone, rennin, secretin, somatostatin, thrombopoietin, thyroid stimulating hormone, or thyrotropin releasing hormone; or GP130 or IL6 receptors.

155. The method according to any one of claims 150 to 154, wherein the cognate Iigand of the receptor protein is selected from growth factors, hormones, enzymes, metabolic enzymes, neurotransmitters, chemokines, cytokines, lymphokines, interleukin, tumor antigens, tumor suppressor antigens, multidrug resistance proteins, coagulation factors, Factor VII, Factor VIII, Factor IX, trophic factors, cell recognition or stimulatory molecules, apolipoproteins, EGF, ErbB-1, HER1, HER2, aFGF, bFGF, NGF, VEGF, Fit, TGF, TGF-ct-1, TGF-β, TNF-a, BDNF, insulin, insulin-like growth factor (IGFR), PDGF, HGF, TRK, BDNF, CNTF, GMF, NT3, NT5, HARP/pleiotrophin, TIE proteins, Eph proteins, DDR proteins, ROR proteins, LTK proteins, AXL proteins, RET proteins, TOLL-like proteins; hormones selected from steroid hormones, thyroid hormones, melatonin; adrenergic protein; peptides selected from amylin, angiotensinogen, angiotensin, atrial natriuretic peptide, brain natriuretic peptide, calcitonin, corticotropin, erythropoietin, endothelin, enkephalin, follicle stimulating hormone, gastrin, ghrelin, glucagon, human chorionic gonadotropin, inhibin, leptin, luteinizing hormone, melanocyte stimulating hormone, oxitocin, pancreatic polypeptide, parathyroid hormone, prolactin, prolactin releasing hormone, rennin, secretin, somatostatin, thrombopoietin, thyroid stimulating hormone, thyrotropin releasing hormone; GP130 or IL6.

156. The method according to any one of claims 124 to 155, further comprising expressing one or both of a Tax enzymatic protein and a Terminal deoxynucleotidyl Transferase (TdT) enzymatic protein in the cell.

157. A method of preventing or knocking down cell surface expression of a ligand-binding receptor protein, comprising:

expressing in a cell the ligand-binding receptor protein;

expressing in the cell a ligand protein capable of being bound by the ligand-binding receptor protein, wherein the ligand protein is fused to exogenous signal sequence for retaining the ligand protein in an intracellular organelle, under conditions permitting the interaction of the ligand-binding receptor protein and the ligand protein in the organelle;

measuring the level of the ligand-binding receptor protein expressed on the cell surface; wherein the binding of the ligand-binding receptor protein to the ligand protein retained in the organelle concomitantly retains the ligand-binding receptor protein bound to the ligand protein in the organelle, thereby preventing or knocking down the cell surface expression of the ligand- binding receptor protein.

158. A method of selecting from a plurality of binding molecules a binding molecule which binds a target antigen that is a member of an interacting pair comprising a cell surface-expressed receptor binding protein and a cognate ligand, the method comprising:

(a) co-expressing in a single cell which expresses the receptor binding protein

(i) nucleic acid sequence encoding one of a plurality of binding molecules, and (ii) nucleic acid sequence encoding a cognate ligand of the receptor binding protein,

wherein either the binding molecules or the cognate ligand is operably coupled to a nucleic acid sequence encoding a retention signal for retaining either (i) or (ii) in an intracellular organelle following expression of (i) or (ii) in the cell; under conditions allowing for retention of the expressed binding molecule or the expressed cognate ligand in the intracellular organelle; wherein, if an expressed binding molecule binds to the receptor binding protein or the cognate ligand as target antigen, such binding disrupts, neutralizes, or blocks the natural interaction between the receptor binding protein and the cognate ligand and releases the receptor binding protein from its interaction with the cognate ligand for expression of the receptor binding protein on the cell surface; and

(b) detecting the level of receptor binding protein expressed on the cell surface such that a high level of receptor binding protein expression of the cell surface indicates the expression and selection of a binding molecule which binds a target antigen within the cell.

159. The method according to claim 158, wherein the plurality of binding molecules is selected from an antibody library, a genetically diversified antibody library, a single domain antibody library, a genetically diversified single domain antibody library, a VL domain library, a genetically diversified VL domain library, a VH domain library, or a genetically diversified VH domain library.

160. The method according to claim 158 or claim 159, wherein the binding molecule is an antibody or a binding fragment or portion thereof.

161. The method according to 160, wherein the antibody or a binding fragment or portion thereof is selected from an Fab fragment, an Fab' fragment, an F(ab')2 fragment, an Fd fragment, an Fv fragment, a single-chain variable fragment (scFv), a diabody, a domain antibody (dAb), a heavy chain variable domain (VH), a genetically diversified heavy chain variable domain (VH), a light chain variable domain (V_L), a genetically diversified light chain variable domain (V_L), or a complementarity determining region (CDR).

162. The method according to claim 158 or claim 159, wherein the binding molecule is a VL domain or a genetically diversified VL domain.

163. The method according to claim 158 or claim 159, wherein the binding molecule is a V_H domain or a genetically diversified VH domain.

164. The method according to claim 160, wherein the antibody is a full length antibody comprising light chain variable domains and light chain constant domains, and heavy chain variable domains and heavy chain constant domains.

165. The method according to claim 164, wherein the antibody is an IgG antibody or a subclass thereof.

166. The method according to claim 165, wherein the antibody is an IgGl antibody.

167. The method according to any one of claims 158 to 166, wherein the intracellular organelle is the endoplasmic reticulum (ER) or the Golgi.

168. The method according to any one of claims 158 to 167, wherein the intracellular organelle retention signal is a KDEL amino acid sequence (SEQ ID NO: 1).

169. The method according to any one of claims 158 to 168, wherein the target antigen is selected from growth factor receptors, hormone receptors, enzyme receptors, Fc receptors, neurotransmitter receptors, chemokine receptors, cytokine receptors, lymphokine receptors, interleukin receptors, tumor antigen receptors, cell recognition or stimulatory receptors, receptors in receptor families selected from apolipoprotein receptors, EGFR, ErbB-lR, HER1, HER2, aFGFR, bFGFR, NGFR, VEGFR, FltR, TGFR, TGFR-a-1, TGFR-β, TNFR-a, BDNFR, insulin receptor, insulin-like growth factor receptor (IGFR), PDGFR, HGFR, TRKR, BDNFR, CNTFR, GMFR, NT3R, NT5R, HARPR/pleiotrophinR, TIE receptors, Eph receptors, DDR receptors, ROR receptors, LTK receptors, AXL receptors, RET receptors, or TOLL-like receptors; steroid hormone receptors, thyroid hormone receptors, melatonin receptors, adrenergic receptors; receptors for peptides selected from amylin, angiotensinogen, angiotensin, atrial natriuretic peptide, brain natriuretic peptide, calcitonin, corticotropin, erythropoietin, endothelin, enkephalin, follicle stimulating hormone, gastrin, ghrelin, glucagon, human chorionic gonadotropin, inhibin, leptin, luteinizing hormone, melanocyte stimulating hormone, oxitocin, pancreatic polypeptide, parathyroid hormone, prolactin, prolactin releasing hormone, rennin, secretin, somatostatin, thrombopoietin, thyroid stimulating hormone, or thyrotropin releasing hormone; or GP 130 or IL6 receptors.

170. The method according to any one of claims 158 to 168, wherein the target antigen is selected from growth factors, hormones, enzymes, metabolic enzymes, neurotransmitters, chemokines, cytokines, lymphokines, interleukin, tumor antigens, tumor suppressor antigens, multidrug resistance proteins, coagulation factors, Factor VII, Factor VIII, Factor EX, trophic factors, cell recognition or stimulatory molecules, apolipoproteins, EGF, ErbB-1, HER1, HER2, aFGF, bFGF, NGF, VEGF, Fit, TGF, TGF-cc-1, TGF-β, TNF-a, BDNF, insulin, insulin-like growth factor (IGFR), PDGF, HGF, TRK, BDNF, CNTF, GMF, NT3, NT5, HARP/pleiotrophin, TIE proteins, Eph proteins, DDR proteins, ROR proteins, LTK proteins, AXL proteins, RET proteins, TOLL-Iike proteins; hormones selected from steroid hormones, thyroid hormones, melatonin; adrenergic protein; peptides selected from amylin, angiotensinogen, angiotensin, atrial natriuretic peptide, brain natriuretic peptide, calcitonin, corticotropin, erythropoietin, endothelin, enkephalin, follicle stimulating hormone, gastrin, ghrelin, glucagon, human chorionic gonadotropin, inhibin, leptin, luteinizing hormone, melanocyte stimulating hormone, oxitocin, pancreatic polypeptide, parathyroid hormone, prolactin, prolactin releasing hormone, rennin, secretin, somatostatin, thrombopoietin, thyroid stimulating hormone, thyrotropin releasing hormone; GP130 or IL6.

171. A method of producing a genetically diverse or variable antibody comprising modified or non-naturally occurring immunoglobulin complementarity determining regions (CDRs), the method comprising:

(a) introducing into one or more CDR-encoding nucleic acid sequences one or more zinc finger DNA binding domain recognition sequences to generate one or more non-identical targeting site sequences within the one or more CDR-encoding nucleic acid sequences for binding one or more zinc finger nucleases (ZFN), thereby producing CDRs comprising modified nucleic acid sequences; and

(b) expressing in a cell, a nucleic acid encoding at least an antibody heavy chain variable domain (VH) and/or at least an antibody light chain variable domain (VL) comprising the modified CDR-encoding nucleic acid sequence of (a) under conditions in which the expressed ZFN binds and cleaves the modified CDR-encoding nucleic acid sequence within the targeting site sequence, said cell expressing a nucleic acid sequence encoding a zinc finger nuclease (ZFN) into which is introduced the zinc finger DNA binding domain targeting site sequences of (a) operably linked to a nucleic acid sequence encoding a DNA cleavage domain of a type IIS restriction enzyme, wherein DNA cleavage by the ZFN is determined by the targeting site sequences within the modified CDR-encoding nucleic acid sequence of (a), wherein the cell further contains nucleic acid encoding one or both of a Tax protein and a Terminal deoxynucleotidyl Transferase (TdT) protein.

172. The method according to claim 171, wherein in (a), the nucleic acid sequences encoding the CDRs are isolated from a VH and/or a VL domain and are harbored in a suitable DNA construct.

173. The method according to claim 172, wherein the DNA construct is selected from a DNA plasmid, vector or nucleic acid expression cassette.

174. The method according to claim 123, wherein the DNA construct comprises nucleic acid encoding CDR1, CDR2, CDR3, or a combination thereof.

175. The method according to any one of claims 171 to 174, wherein the nucleic acid sequences encoding the one or more modified CDRs are introduced into nucleic acid sequences encoding a VH and/or a VL domain to produce VH and/or VL domains comprising one or more modified CDRs.

176. The method according to any one of claims 171 to 175, wherein in (a) the CDR-encoding nucleic acid sequences are contained within nucleic acid sequences encoding an antibody heavy chain variable domain (VH) and/or nucleic acid sequences encoding an antibody light chain variable domain (VL).

177. The method according to any one of claims 171 to 176, wherein, in (b), the modified CDR-encoding nucleic acid sequence is contained within a full length antibody comprising nucleic acid sequences encoding a heavy chain variable domain (VH) and a heavy chain constant region (¾), and comprising nucleic acid sequences encoding a light chain variable domain (VL) and a light chain constant region (CL), wherein the resulting nucleic acid sequences encode full length antibodies comprising VH and VL domains comprising modified CDRs.

178. The method according to any one of claims 171 to 177, wherein in (b), the nucleic acid sequences encoding Tax and TdT are harbored in a suitable DNA construct and co-expressed therefrom.

179. The method according to any one of claims 171 to 177, wherein in (b), the nucleic acid sequences encoding Tax and TdT are harbored in separate suitable DNA constructs and expressed therefrom.

180. A method of screening or selecting a small molecule which blocks, inhibits, or disrupts an interaction between a cell surface expressed binding protein and its cognate ligand within a cell, the method comprising:

expressing in the same cell a binding protein which is expressible on the surface of the cell and a cognate ligand of the binding protein, wherein the cognate ligand is molecularly tagged or fused with a sequence for retaining the ligand in an intracellular organelle under conditions allowing for the retention of the ligand in the organelle and the interaction of the binding protein and the cognate ligand in the organelle such that the binding protein is retained within the cellular organelle when bound to the tagged ligand;

introducing into the cell a small molecule to determine if the small molecule binds, associates, or interacts with either the binding protein or the ligand protein retained in the intracellular organelle; and

detecting the level of the binding protein expressed on the cell surface; wherein, if the small molecule binds to either the binding protein or the ligand and blocks, inhibits, or disrupts the interaction of the binding protein and its ligand in the organelle, the binding protein thereby transits through the organelle and is expressed and detectable on the cell surface and the small molecule is selected as a molecule which blocks, inhibits, or disrupts the binding protein and cognate ligand interaction.

181. The method according to claim 180, wherein the small molecule is selected from a small molecule chemical compound, a low molecular weight organic compound, a drug, or a chemical agent.

182. The method according to claim 180 or claim 181, wherein the small molecule is an agonist, an antagonist, or a modulator of the binding protein and/or the ligand.

183. The method according to any one of claims 180 to 182, wherein the molecular weight of the low molecular weight organic compound is less than or equal to 500 Daltons or is less than 900 Daltons.

184. The method according to any one of claims 180 to 183, wherein the ligand is fused or tagged with a retention sequence for retention in the ER or the Golgi.

185. The method according to any one of claims 180 to 184, wherein the retention sequence comprises KDEL (SEQ ID NO. l) for retention in the ER.

186. The method according to any one of claims 180 to 185, wherein the binding protein is a cell surface expressible receptor protein.

187. The method according to any one of claims 180 to 186, wherein the binding protein is a cell surface expressible receptor protein selected from growth factor receptors, hormone receptors, enzyme receptors, Fc receptors, neurotransmitter receptors, chemokine receptors, cytokine receptors, lymphokine receptors, interleukin receptors, tumor antigen receptors, cell recognition or stimulatory receptors, receptors in receptor families selected from apolipoprotein receptors, EGFR, ErbB-lR, HER1, HER2, aFGFR, bFGFR, NGFR, VEGFR, FltR, TGFR, TGFR-a-1, TGFR-β, TNFR-a, BDNFR, insulin receptor, insulin-like growth factor receptor (IGFR), PDGFR, HGFR, TRKR, BDNFR, CNTFR, GMFR, NT3R, NT5R, HARPR/pleiotrophinR, TIE receptors, Eph receptors, DDR receptors, ROR receptors, LTK receptors, AXL receptors, RET receptors, or TOLL-like receptors; steroid hormone receptors, thyroid hormone receptors, melatonin receptors, adrenergic receptors; receptors for peptides selected from amylin, angiotensinogen, angiotensin, atrial natriuretic peptide, brain natriuretic peptide, calcitonin, corticotropin, erythropoietin, endothelin, enkephalin, follicle stimulating hormone, gastrin, ghrelin, glucagon, human chorionic gonadotropin, inhibin, leptin, luteinizing hormone, melanocyte stimulating hormone, oxitocin, pancreatic polypeptide, parathyroid hormone, prolactin, prolactin releasing hormone, rennin, secretin, somatostatin, thrombopoietin, thyroid stimulating hormone, or thyrotropin releasing hormone; or GP130 or IL6 receptors.

188. The method according to any one of claims 180 to 187, wherein the ligand of the receptor protein is selected from growth factors, hormones, enzymes, metabolic enzymes, neurotransmitters, chemokines, cytokines, lymphokines, interleukin, tumor antigens, tumor suppressor antigens, multidrug resistance proteins, coagulation factors, Factor VII, Factor VIII, Factor DC, trophic factors, cell recognition or stimulatory molecules, apolipoproteins, EGF, ErbB-1, HER1, HER2, aFGF, bFGF, NGF, VEGF, Fit, TGF, TGF-a-1, TGF-β, TNF-a, BDNF, insulin, insulin-like growth factor (IGFR), PDGF, HGF, TRK, BDNF, CNTF, GMF, NT3, NT5, HARP/pleiotrophin, TIE proteins, Eph proteins, DDR proteins, ROR proteins, LTK proteins, AXL proteins, RET proteins, TOLL-like proteins; hormones selected from steroid hormones, thyroid hormones, melatonin; adrenergic protein; peptides selected from amylin, angiotensinogen, angiotensin, atrial natriuretic peptide, brain natriuretic peptide, calcitonin, corticotropin, erythropoietin, endothelin, enkephalin, follicle stimulating hormone, gastrin, ghrelin, glucagon, human chorionic gonadotropin, inhibin, leptin, luteinizing hormone, melanocyte stimulating hormone, oxitocin, pancreatic polypeptide, parathyroid hormone, prolactin, prolactin releasing hormone, rennin, secretin, somatostatin, thrombopoietin, thyroid stimulating hormone, thyrotropin releasing hormone; GP130 or IL6.

189. The method according to any one of claims 180 to 188, wherein the binding molecule is a receptor molecule and the small molecule affects receptor function.

190. The method according to any one of claims 180 to 189 wherein the binding molecule is a receptor protein and the function of the receptor is measured following addition of the small molecule compound.