WO2009103753A1

WO2009103753A1 - Methods for identifying and/or sorting cells by secreted molecule and kits for performing such methods

Info

Publication number: WO2009103753A1
Application number: PCT/EP2009/051957
Authority: WO
Inventors: Guy Hermans
Original assignee: Ablynx Nv
Priority date: 2008-02-20
Filing date: 2009-02-19
Publication date: 2009-08-27

Abstract

A method is provided for the identification and/or sorting of living cells that secrete one or more molecules based on their secreted molecule. The specific molecules are captured onto the cell membrane by use of a lipid-coupled capture reagent that can be anchored to the cell membrane of cells without being cytotoxic. The invention also provides kits for performing the method of the invention.

Description

METHODS FOR IDENTIFYING AND/QR SORTING CELLS BY SECRETED MOLECULE AND KITS FOR PERFORMING SUCH METHODS

FIELD OF THE INVENTION The present invention relates to the identification and/or sorting of living cells that secrete one or more molecules. More particularly, the present invention provides a method for the identification and/or sorting, from a large cell population, of cells that secrete one or more molecules based on their secreted molecule. The invention further provides kits for performing the method of the invention.

BACKGROUND ART

Detection of individual cells that produce a specific molecule from a large cell population is a very slow, labor intensive and costly task as each cell has to be screened individually for the production of the specific molecule. In some cases, the specific molecule with the desired characteristics is only produced by a very limited number of cells in the large cell population and, consequently, a very large number of individual cells has to be screened. High throughput selection of cells that produce a specific molecule has been done using e.g. flow cytometric methods. These methods are, however, only possible if the specific molecule produced by the cell is a cell associated (preferably at the extracellular side of the cell membrane) molecule or if the production of the specific molecule is linked to the production of another detectable entity (e.g. co-expression of a detectable surface marker or intracellular fluorescent protein). Some lymphocytes (memory B-cells), for example, display the immunoglobulin produced on their cell-surface. High throughput selection of lymphocytes that produce (and display) the immunoglobulin of interest can then easily be performed on the original cells, cell sample or tissue itself (e.g. used in the Nanoclone® method, where surface-displayed immunoglobulin is detected to identify and sort cells that produce the immunoglobulin variant of interest, described in WO 06/079372).

In some cases, however, the specific molecule produced is secreted directly into the surrounding medium and diffuses away from its producing cell. In these cases, little to no molecule will remain associated with the exterior cell membrane of the individual cell producing the specific molecule and the producing cell cannot be identified from other cells in the cell population as producing the specific molecule of interest. This may be the case, for example, with activated B lymphocytes or plasma cells (or similar type of cells in lower animals such as shark) which secrete the immunoglobulin produced. This may also be the case with the detection of desirable hybridoma cells which produce and secrete specific monoclonal antibodies at high rates, and to high levels. Detection of desirable hybridoma cells, at present, is tedious and involves significant manual labor as each cell has to be analysed individually. Also transfected cells that secrete a molecule that is expressed unlinked to another selectable marker can, at present, not be identified from a cell population.

Some high throughput methods have already been proposed for the identification and sorting of cells according to their secreted molecule. Manz et al. (Proc. Natl. Acad. Sci. USA. 1995. 92(6):1921-5) describe an artificial affinity matrix, created on the cell surface and specific for the secreted molecule, based on bispecific antibody reagents. The secreted molecules bind to the affinity matrix on the secreting cell and are subsequently labeled with specific fluorescent or magnetic staining reagents for cytometric analysis and cell sorting. Powell and Weaver (Biotechnology (NY) 1990, 8(4):333-7) and WO 89/10566 combine flow cytometry with gel microdroplets (GVEDs) for determining the secretion of biologically important macromolecules from each of many individual cells within a large population.

Both methods, however, require specialized reagents or methods (bireactive immunoreagents, gel encapsulation), mostly also combined with many different discrete steps to apply the matrix to cells and/or detect the captured secreted product. Specifically, for a system using bireactive reagents (Manz et al.. see supra), a priori knowledge of surface antigens and access to suitably reactive antibodies is required to construct a bireactive reagent.

SUMMARY OF THE INVENTION

The present invention provides a method for the identification and/or sorting, from a (large) cell population, of cells that secrete one or more specific molecules. In the method of the present invention said one or more specific molecules are captured onto the cell membrane making use of a lipid-coupled capture reagent (also referred herein as "'lipid- coupled capture reagent of the invention'') that can be anchored to the cell membrane of cells without being cytotoxic. The lipid-coupled capture reagent of the invention comprises or essentially consists of a lipid based membrane-integrating entity coupled to a capture reagent. The lipid-coupled capture reagent of the invention can be anchored into the cell membrane of cells using a simple co-incubation step as will be described further herein. When the lipid- coupled capture reagent is anchored into the cell membrane, the capture reagent will retain the secreted molecule on the membrane of the cell, making it accessible to techno logics for detection of surface markers. The cell-surface retained secreted molecules (also referred to herein as "cell-captured secreted molecules^*') can subsequently be identified in any detection method such as the high throughput methods as described further herein, without requiring encapsulation or knowledge of and/or access to cell surface reactive immunoreagents. This capturing of the secreted molecules before they diffuse away into the medium allows the identification and/or sorting of large numbers of cells on the single-cell level based on their secreted molecules.

Accordingly, the present invention provides a method for the identification and/or sorting, from a (large) cell population, of cells that secrete one or more molecules comprising the steps of: a) providing a cell population, wherein said cell population comprises at least one cell that expresses and secretes or is capable of expressing and secreting one or more molecules: b) incubating the cell population with a lipid-coupled capture reagent of the invention under conditions allowing the anchoring of the lipid-coupled capture reagent into the membrane of the cells in the cell population and subsequently capturing the one or more secreted molecules by the capture reagent: c) detecting the one or more secreted molecules captured on the cell membrane of the at least one cell that expresses and secretes or is capable of expressing and secreting one or more molecules.

As described above, the lipid-coupled capture reagent of the invention comprises or essentially consists of a lipid based membrane-integrating entity coupled to a capture reagent. Preferred lipid based membrane-integrating entities have basically the following structure:

lipid - [PEG]_n - reactive group wherein:

- the lipid is defined as any fat-soluble (hydrophobic) molecule that is capable of inserting into a cell membrane structure. The term is more-specifically used to refer to fatty-acids and their derivatives (including tri-, di-. and monoglycerides and phospholipids) as well as other fat-soluble sterol-containing metabolites such as cholesterol. Preferably, the lipid is composed of fatty acid chains between 14 and 24 carbon atoms, such as 16 or 18-carbon fatty acids. The fatty acid may be saturated or unsaturated. In a preferred aspect of the invention, the fatty acid is selected from laurate, myristate, palmitate. stearate, arachidate. behenate. Hgnocerate, palmitoleate, oleate. linoleate, Iinolenate and arachidonate. In another preferred aspect of the invention, the fatty acid is selected from palmitate (C 16. saturated) and oleate (Cl 8, one double bond). In a preferred aspect, the lipid is a phospholipid such as a phosphoglyceride selected from (but not in any way limited to) phosphatidyl choline, phosphatidyl serine, phosphatidyl ethanolamine, phosphatidyl choline, phosphatidyl inositol and phosphatidyl glycerol or a sphingomyelin. In another preferred aspect of the invention, the lipid is a phosphatidyl ethanolamine and the fatty acid is oleate, such as e.g. in dioleylphosphatidylethanolamine; - the polyethylene glycol (PEG) chain can be of variable length, wherein n represents the average number of the ethylene oxide unit repeats present in the membrane integrating entity. The PEG chain usually has an average number of ethylene oxide unit repeats between 20 and 250. more preferably between 40 and 200. such as e.g. 40. 90, 1 10 or 180; - the reactive group should be capable of binding the capture reagent. The reactive group can be any reactive group know to the skilled person and will depend on the capture reagent used to capture the secreted molecule. In a preferred aspect of the invention, the capture reagent is a protein and the reactive group is capable of binding the amino groups, sulfhydryl or carbohydrate moieties of the protein. Without being limiting, preferred reactive groups can be selected from N-hydroxysuccinimide

(NHS), isothiocyanate (ITC), maleimide-. iodoacetamide- or hydrazide derivatives, or other protein conjugation chemistries known to those skilled in the art. Alternatively, the reactive group could be replaced by a chemically reactive group for indirect crosslinking to a capture reagent, i.e. via a hetero- or homobifunctional linker molecule. Such reactive groups could be. but are not iimited to, free amino-, carboxy-, epoxy- or sulphonate groups. Homo- or heterobi functional linkers typically combine two or more reactive groups such as N-hydroxysuccinimide (NHS), isothiocyanate (ITC), maleimide-. iodoacetamide- or hydrazide derivatives, either linked directly or via a non-reactive spacer. In a preferred aspect of the invention, the membrane-integrating entity is similar to the

"BAM" series of reagents described by Kato et al. (Biotechniques 2003, 35(5): 1014-8. 1020- 1 ; Biotechnol. Prog. 2004, 20(3):897-904) which can easily be coupled to other molecules (e.g. capture reagents) and are non-cytotoxic. Preferred membrane integrating entities are e.g.. without being limiting. BAM40. BAM90. BAM 180 (such as e.g. sold by NOF Corporation, Tokyo, Japan with the product names SUNBRIGHT OE-020CS, SUNBRIGHT OE-040CS and SUNBR1GHT OE-060C) and DOPE-BAM80.

The membrane-integrating entity is coupled to a capture reagent (also referred herein as "capture reagent of the invention") to form the lipid-coupled capture reagent of the invention. The capture reagent of the present invention is selected such that it contains specific sites to which the secreted molecule, upon secretion by the cell, will bind. Without being limiting, the capture reagent can be an immunoglobulin or antibody (monoclonal, polyclonal) or derivative (such as e.g. scFv. Fab. dAb or Nanobody) or artificial entity (aptamer, affibody, etc.). as will be known to the skilled person, reactive to the secreted molecule or to a tag attached to it (Fc, 6His, c-myc. etc.). The capture reagent may also be an antigen for which the secreted product is a binder (e.g. if the secreted molecule is an immunoglobulin or derivative).

The capture reagent may be specific or generic. A specific capture reagent may be one which binds only few of the possible secreted molecule variants. Such a capture reagent might e.g. be specific for a certain immunoglobulin isotype (e.g. specific only for IgGl). or specific for a heavy chain immunoglobulin while not capturing conventional four-chain immunoglobulins. A specific capture reagent might be an antigen for which reactive secreted molecule variants (such as e.g. immunoglobulins, antibodies or fragments thereof specific for the antigen) are being searched for. A generic capture reagent may be one which binds many possible secreted molecule variants, e.g. an isotype non-specific polyclonal antiserum, protein A. protein G and the like, as will be clear to the skilled person.

Coupling of the membrane-integrating entity to the capture reagent of the invention will depend on the reactive group in the membrane-integrating entity and the capture reagent used to capture the secreted molecule. Coupling can be done by any method which allows the coupling of two entities. If needed, suitable spacers or linkers can be used as will be clear to the skilled person. Coupling should not in any way affect or at least not seriously hamper the capturing of the secreted molecule by the capture reagent (as further described herein).

The present invention also relates to a kit for performing the method of the invention. More particularly, the present invention relates to a kit. more particularly a cell identification and/or sorting kit (also referred to herein as "cell identification and/or sorting kit of the invention"), for use in the identification and/or sorting of cells that secrete one or more molecules, based on their secreted molecule. The cell identification and/or sorting kit of the invention at least comprises a lipid-coupled capture reagent of the invention. The cell identification and/or sorting kit of the invention may further comprise, without being limiting, a detector molecule, a label and/or a buffer as will be clear to the skilled person. In a preferred aspect, the cell identification and/or sorting kit of the invention comprises a lipid- coupled capture reagent of the invention, a label and a detector molecule. The methods and kits of the present invention will have a wide range of applications in biotechnology and biomedical research where detection of cells that secrete one or more specific molecules is needed. The methods and kits of the present invention can be used for the identification and/or sorting of any kind of cell that produces and secretes one or more specific molecules, such as. without being limiting, prokaryotic cells, eukaryotic cells, native cells as well as transformed cells and/or transfected cells.

In one aspect, the methods and kits of the present invention are used for the identification, analysis, sorting and/or purification of a transfected cell population. Transfected cells may produce the foreign molecule and secrete it into the surrounding medium, where it diffuses away from the transfected cells. In these cases, it will be very difficult to identify and/or sort the transfected cells according to their secreted molecule.

Incubation of the transfected cells with the ϊipid-coupled capture reagent of the invention will allow the capturing of the secreted molecule onto the cell membrane of the transfected cell that produces and secretes the foreign molecule. Identification and/or sorting of the transfected cell based on its secreted molecule can subsequently easily be done by detection of the cell-captured secreted molecule on the surface of the transfected cell e.g. by technologies for detection of surface markers known to the skilled person and further described herein. Quantitative detection of the cell-captured secreted molecule on the surface of the transfected cell will allow, for example, for the selection of high transgene expressing cells (high producers) from the non-transfected cells and/or from the low transgene expressing cells.

In another aspect, the methods and kits of the present invention are used for the identification and/or sorting of microorganisms that secrete one or more molecules. The microorganism used with the methods and kits of the present invention can be any microorganism that secretes one or more molecules in the surrounding medium, such as, without being limiting, a bacteria, a yeast, a fungi, etc. The one or more molecules secreted by the microorganism may be one or more native molecules, produced by the microorganism, and/or may be one or more recombinant proteins produced after introduction (transformation, transfection, mutation, genetic modification, etc.) of foreign DNA into the microorganism. As the one or more molecules secreted by the microorganism into the surrounding medium will diffuse away from the microorganism, it is very difficult to identify and/or sort the microorganisms based on their secreted molecule. Incubation of the microorganisms with the lipid-coupled capture reagent will allow the capturing of the one or more secreted molecules onto the cell membrane of the microorganism that produces and secretes the molecule. Identification and/or sorting of the microorganisms based on their secreted molecule can subsequently easily be done by detection of the cell-captured secreted molecule on the surface of the microorganism e.g. by technologies for detection of surface markers known to the skilled person and further described herein. Quantitative detection of the cell-captured secreted molecule on the surface of the microorganism will allow, for example, for the selection of high expressing and secreting microorganisms (high producers) from the non- producing microorganisms and/or the low expressing and/or secreting microorganisms.

In another aspect, the methods and kits of the present invention are used for the identification, quantitation and/or sorting of functionally discrete subsets of an otherwise undefined cell population subset, where the function is defined (at least partially) by the pattern of secreted soluble proteins (e.g. ThI or Th2 cytokine secretion pattern within the CD4- subset of T-cells). Incubation of the cell population with the lipid-coupled capture reagent of the invention will allow the capturing of the secreted soluble proteins onto the cell membrane of the functionally discrete subset of cells. Identification, quantitation and/or sorting can subsequently easily be done by detection of the cell-captured secreted molecule on the surface of the functionally discrete subset of cells e.g. by technologies for detection of surface markers known to the skilled person and further described herein.

In another aspect, the methods and kits of the present invention are used for the identification and/or sorting of rare cells, or genetic variants of interest. The method of the invention can. for example, be used for the identification and/or sorting of hybridoma cells that secrete a certain specific monoclonal antibody at high rates, and to high levels. Incubation of the hybridoma cells with the lipid-coupled capture reagent of the invention will allow the capturing of the monoclonal antibody onto the cell membrane of the hybridoma cell that secretes the monoclonal antibody. Identification and/or sorting of the hybridoma cell based on its secreted monoclonal antibody can subsequently easily be done by detection of the cell-captured monoclonal antibody on the surface of the hybridoma cell e.g. by technologies for detection of surface markers known to the skilled person and further described herein. Quantitative detection of the cell-captured monoclonal antibody on the surface of the hybridoma cell will allow, for example, for the selection of hybridoma cells that secrete a specific monoclonal antibody at high level from the hybridoma cells that do not produce and secrete the specific monoclonal antibody and/or that produce and/or secrete the specific monoclonal at lower level. In another aspect, the methods and kits of the present invention are used for identifying, sorting, selecting, generating and/or cloning immunoglobulin sequences from individual B- cells that do not display their immunoglobulins on the cell surface, but secrete the immunoglobulin produced into the surrounding medium (e.g. from activated B lymphocytes and/or plasma cells). In particular, the method of the invention can be used for identifying, sorting, selecting, generating and/or cloning immunoglobulin sequences, wherein said immunoglobulin sequences are heavy chain antibodies or conventional four-chain antibodies or antigen binding fragments thereof. More particularly the method of the invention can be used for identifying, sorting, selecting, generating and/or cloning variable domain sequences of heavy chain antibodies (also referred to herein as V_HH) or of four-chain antibodies (also referred to herein as VH).

For a genera] description of heavy chain antibodies and the variable domains thereof, reference is inter alia made to the prior art cited herein, to the review article by Muyldermans in Reviews in Molecular Biotechnology 74(2001 ). 277-302: as well as to the following patent applications, which are mentioned as general background art: WO 94/04678. WO 95/04079 and WO 96/34103 of the Vrije Universiteit Brussel; WO 94/25591. WO 99/37681, WO

00/40968. WO 00/43507. WO 00/65057, WO 01/40310. WO 01/44301. EP 1134231 and WO 02/48193 of Unilever. WO 97/49805, WO 01/21817, WO 03/035694. WO 03/054016 and WO 03/055527 of the Vlaams lnstituut voor Biotechnologie (VIB): WO 03/050531 of Algonomics N.V. and Ablynx N.V.: WO 01/90190 by the National Research Council of Canada; WO 03/025020 (= EP 1 433 793) by the Institute of Antibodies: as well as WO 04/041867. WO 04/041862, WO 04/041865. WO 04/041863. WO 04/062553 , WO 05/044858. WO 06/40153, WO 06/079372. WO 06/122786. WO 06/122787 and WO 06/122825, by Ablynx N.V. and the further published patent applications by Ablynx N.V. Reference is also made to the further prior art mentioned in these applications, and in particular to the list of references mentioned on pages 41-43 of the International application WO 06/040153, which list and references are incorporated herein by reference.

In addition to Camelids, heavy chain antibodies also occur naturally in, for example, certain species of sharks (see for example the International application WO 03/014161, Bernstein et al. 1996. Proc. Natl. Acad. Sci. USA 93: 3289; Roux et al. 1998. Proc. Natl. Acad. Sci. USA 95: 1 1804). Although variable domains derived from such heavy chain antibodies may be used in the invention, the use of Camelid-derived heavy chain antibodies and/or of the variable domain sequences thereof is much preferred, inter alia because the latter are derived from a species of mammal and/or because the latter will generally be easier to "humanize'^" (as described below).

For a general description of variable domain sequences of conventional four-chain antibodies, also referred to as domain antibodies or single domain antibodies or "dAb^"s^"\ reference is made to Ward et al. (Nature 1989 Oct 12: 341 (6242): 544-6). EP 0 368 684 and HoUiger and Hudson (Nature Biot. 2005, 23: 1126-1136).

In particular, the amino acid sequence of V_HH, V₁₁. (single) domain antibodies or "dAb's" can be considered - without however being limited thereto - to be comprised of four framework regions or -'FRV and three complementary determining regions of "CDRY^* as described further for Nanobodies.The variable domain sequences obtained using the method of the invention, humanized and camelized variants as well as artificial mutants thereof can be used as Nanobodies ® [Note: NanobodyM.-, Nanobodies^, and NanocloneΦ-' are subject to trademark protection] or they can be used as starting point for generating Nanobodies®. Nanobodies®. as well as different Nanobody® constructs and formats are extensively described in. for example WO 06/040153, WO 06/122825, WO 06/122786. WO 07/042289, WO 07/104529 and PCT/EP2007/058587. For a description of V_HH. V_H and Nanobodies® reference is further made to WO 06/079372.

In this aspect, the methods and kits of the invention are preferably used on a sample or population of cells that is enriched in cells expressing, or capable of expressing, an immunoglobulin (such as a heavy chain antibody or a conventional four-chain antibody) against a desired antigen, i.e. by immunizing an animal, such as a mammal, with the desired antigen, using a suitable regimen. The methods and kits of the invention can be used with such an enriched sample or population as a starting material to identify and/or sort individual cells expressing an immunoglobulin (such as a heavy chain antibody or conventional four- chain antibody) against the desired antigen, from which in subsequent steps immunoglobulin sequences against said antigen can be obtained. As mentioned below, said immunoglobulin sequences can be full-chain antibodies, single chains thereof or antigen-binding fragments thereof, or nucleotide sequences/nucleic acids encoding the same. According to one preferred, but non-limiting embodiment, the methods and kits of the invention are used to provide V_HH domains. V_H domains, or nucleotide sequence/nucleic acids encoding the same.

In a preferred aspect, the methods and kits of the invention are used on a sample or population of cells that is enriched in cells expressing, or capable of expressing, a heavy chain antibody against a desired antigen, i.e. by immunizing a Camelid with the desired antigen, using a suitable regimen. The methods and kits of the invention can be used with such an enriched sample or population as a starting material to provide individual cells expressing a heavy chain antibody against the desired antigen, from which in subsequent steps heavy chain antibody sequences against said antigen can be obtained. As mentioned below, said heavy chain antibody sequences can be full-chain antibodies, single chains thereof or antigen-binding fragments thereof, or nucleotide sequences/nucleic acids encoding the same. According to one preferred, but non-limiting embodiment, the methods and kits of the invention are used to provide V_HH domains, or nucleotide sequence/nucleic acids encoding the same. It should be noted that usually, it is not possible to provide a comparably enriched population of cells from a human source (i.e. as a starting material for generating human Vj₁ and V_t sequences), simply because it is not feasible for health reasons to immunize a human being with the desired antigen. Thus, when human V_H or Vi sequences are to be generated, usually a naϊve non-enriched population of cells is used as a starting material. Because this starting material has not been enriched, it contains a much lower percentage of immunoglobulins that recognize the desired antigen (i.e. compared to an enriched population). This in turn means that even a much larger number of cells (i.e. in the region of 10⁸-l O¹² sequences) needs to be screened in order to identify a suitable immunoglobulin. Thus, in this aspect, the methods and kits of the invention are used for generating or cloning nucleic acid or nucleotide sequences that encode an immunoglobulin or an antigen- binding fragment thereof, wherein said immunoglobulin or antigen-binding fragment is directed against a specific antigen, said method comprising the steps of: a) providing a cell population from an animal, such as a mammal immunized with said antigen, or a population of cells from a non-immune animal, wherein said cell population comprises at least one cell that expresses and secretes or is capable of expressing and secreting an immunoglobulin directed against said antigen; b) incubating the cell population with a lipid-coupled capture reagent of the invention under conditions allowing the anchoring of the lipid-coupled capture reagent into the membrane of the cells in the cell population and subsequently capturing the immunoglobulin by the capture reagent: c) detecting the immunoglobulin captured on the cell membrane of the at least one cell that expresses and secretes or is capable of expressing and secreting an immunoglobulin; d) isolating from said cell population said at least one cell that expresses and secretes or is capable of expressing and secreting an immunoglobulin directed against said antigen; e) obtaining from said at least one cell a nucleic acid or nucleotide sequence that encodes an immunoglobulin directed against the specific antigen or that encodes an antigen-binding fragment thereof directed against said specific antigen. Methods of obtaining cells from an animal, such as mammals, and especially B-cells, are known in the art. and further extensively described in WO 06/079372. For example, peripheral blood mononuclear cells (PBMC) can be prepared from the purified blood and optionally the tissues of the animal after the final immunisation. Methods for obtaining PBMC are known in the art. According to one aspect. PBMC can be obtained by centrifuging blood of the animal on a Ficoll Paque™ PLUS density gradient (Amersham Biosciences. Buckinghamshire, United Kingdom). B-lymphocytes can be recovered from PBMC. Such recoverj' may include the steps of lysing erythrocytes, depleting monocytes from the PBMC and using the resultant supernatant which contains B-lymphocytes, labeling B-cells using monoclonal antibodies or polyclonal antisera and sorting B-cells using flow cytometry and/or immunomagnetically and/or density altering particles, labeling all cells but B-cells using monoclonal antibodies or polyclonal antisera and sorting the non-labelled cells using flow cytometry and/or immunomagnetically and/or density altering particles. Incubation of the cells with the lipid-coupled capture reagent of the invention can be done by any method that allows for the anchoring of the lipid-coupled capture reagent into the membrane of the ceils. Suitable incubation conditions for anchoring the lipid-coupled capture reagent of the invention into the membrane of the cells will be known to the skilled person and are further described herein. Detection of the cell-captured immunoglobulin and subsequent identification and isolation of the desired cells from the cell population can be done by any technique which allows for the detection of surface markers, known to the skilled person and further described herein. Suitable techniques will usually involve the use of an antigen, an immobilized antigen and/or a suitable marker to identify cells secreting the immunoglobulin directed against said antigen, as is further described herein. Different B-cell staining and separating protocols are extensively described in WO 06/079372 (see e.g. on pages 24 to 32, 96 to 97).

The method of the invention allows for the identification and/or sorting of activated ceils that express and secrete immunoglobulins. Activated B-cells (''plasma cells'^") produce and secrete large amounts of soluble immunoglobulin, but display only minor quantities of this immunoglobulin on their cells membrane. The method of the invention now provides for the anchoring of the secreted immunoglobulins to the cell membrane by the lipid-coupled capture reagent of the invention. By anchoring of the secreted immunoglobulins to the cell membrane of the activated plasma ceUs/B-cells. the activated plasma celis/B-cells that express and secrete immunoglobulins can be identified and/or separated from the other cells in the sample (i.e. cells that do not express immunoglobulins, cells that do not express immunoglobulins with the desired specificity), collected as and/or separated into single cells, and then used in the further steps described below. One advantage of the method of the present invention is that such activated cells generally contain much higher levels of mRNA for the desired immunoglobulin - and also may produce higher levels of immunoglobulins - compared to non-activated or '"memory^" B-cells. Such activated plasma cells/B-celis ma> be separated from the other cells in the sample using any technique known per se. including but not limited to cell sorting techniques as described further herein. In a preferred aspect, the method of the invention is used for generating or cloning nucleic acid or nucleotide sequences that encode a heavy chain antibody or an antigen- binding fragment thereof, wherein said heavy chain antibody or antigen-binding fragment thereof is directed against a specific antigen, said method comprising the steps of: a) providing a cell population from a Camelid immunized with said antigen, or cell population from a non-immune Camelid, wherein said cell population comprises at least one cell that expresses and secretes or is capable of expressing and secreting a heavy chain antibody directed against said antigen: b) incubating the cell population with a lipid-coupled capture reagent of the invention under conditions allowing the anchoring of the lipid-coupled capture reagent of the invention into the membrane of the cells in the cell population and subsequently capturing the heavy chain antibody by the capture reagent; c) detecting the heavy chain antibody captured on the cell membrane of the at least one cell that expresses and secretes or is capable of expressing and secreting a heavy chain antibody: d) isolating from said cell population said at least one cell that expresses and secretes or is capable of expressing and secreting a heavy chain antibody directed against said antigen; e) obtaining from said at least one cell a nucleic acid or nucleotide sequence that encodes a heavy chain antibody directed against the specific antigen or that encodes an antigen-binding fragment thereof directed against said specific antigen. In this respect, it should be noted that a population of antibody-expressing cells obtained from a Camelid will usually comprise cells that express heavy chain antibodies {e.g.. in the region of 1-60 %, usually between 10 and 30% of all antibody expressing cells), as well as cells that express conventional four-chain antibodies. For camels, about 50% of all antibody expressing cells express heavy chain antibodies. For llamas, about 30% of all antibody expressing cells express heavy chain antibodies.

Thus, preferably, this aforementioned separation of the cells that express the heavy chain antibody against the desired antigen is most preferably performed in such a way that onϊy cells are obtained that express heavy chain antibodies against the desired antigen, and not cells that express conventional four-chain antibodies against the desired antigen. For this purpose, before, during or after the selection with the desired antigen, the cells may be subjected to a step in which cells that express heavy chain antibodies are separated from cells that express conventional four-chain antibodies. Suitable techniques will be clear to the skilled person, and may for example involve the use, as detector molecules (as will be further defined herein), of antibodies specifically directed against heavy chain antibodies, which may be either suitably labeled or attached to a suitable carrier or surface.

Thus, in the above aspect of the invention, step d) may comprise any suitable combination of the following steps: d-1) separating cells that express antibodies from cells that do not express antibodies: d-2) separating cells that express antibodies against the desired antigen from cells that express antibodies directed against other antigens; d-3) separating cells that express heavy chain antibodies from cells that express conventional four-chain antibodies; in which said steps may be performed in any order and in which each two or all three of said steps may also be performed as a single step. Further details and embodiments of this Nanoclone© method can be found in WO 06/079372 which is incorporated, by reference, herein.

In another aspect, the methods and kits of the present invention can be used for the identification and/or sorting of (activated) B-cells from a transgenic non-human animal that express and secrete human or human-like conventional four-chain antibodies against a desired antigen (i.e. raised through suitable administration), optionally after enrichment for the desired antigen-expressing and secreting cells. One non-limiting example of such a transgenic animal is the XenoMouse™ of Abgenix (CA. USA), a transgenic mouse that expresses human antibodies upon immunization with an antigen. Thus, a sample of antibody- expressing cells obtained from a XenoMouse™ can be used as a starting material for use in the methods and kits of the invention. Activated B-cells may secrete the antibodies into the surrounding medium, where they diffuse away from the B-cells. It will be very difficult to identify and/or sort the activated B-cells according to their secreted antibody. Incubation of the cell population with the iipid-coupled capture reagent of the invention will allow the capturing of the antibodies onto the cell membrane of the activated B-cell that produces and secretes the antibody. Identification and/or sorting of the activated B-cell based on its secreted antibody can subsequently easily be done by detection of the cell-captured secreted antibody on the surface of the activated B-cell e.g. by technologies for detection of surface markers known to the skilled person and further described herein.

When the cells that express and secrete the antibody against the desired antigen have been either collected as single cells, or collected and then separated into single cells, a nucleic acid encoding said immunoglobulin or an antigen-binding part thereof can be obtained from said individual cell. This can again be performed in a manner known per se, as will be clear to the skilled person. Suitable techniques will usually involve an amplification step using suitable primers (e.g. using PCR or another suitable amplification techniques, and using as a template cDNA generated from mRNA obtained from the individual cell(s)). followed by isolation of the amplified products. Reference is made to the prior art referred to above as well as to WO 06/079372 (e.g. pages 99 to 104).

For example, for the amplification of variable domain sequences (i.e. V_HH or V_H sequences), some of the primers known per se for the amplification of heavy chain variable domain sequences can be used, for which reference is made to the prior art cited above. Some particularly preferred primers for the amplification of V_HH sequences are the primers referred to in the international application WO 03/54016, as well as some of primers described in the other patent applications by Ablynx N. V. mentioned above. Suitable conditions and reagents for performing said amplification, as well as suitable techniques for isolating the amplified sequences, will also be clear to the skilled person. Reference is again made to the prior art and the handbooks referred to above.

After the amplification step, the nucleic acid thus obtained may be sequenced and/or used to express the immunoglobulins or any antigen binding fragment thereof, for which also reference is made to other patent applications b\ applicant mentioned above. According to one non-limiting embodiment, prior to the amplification, the individual cells may be cultivated, for example under conditions such that the individual cells can divide/multiply/propagate, and/or under conditions such that the cells are stimulated to express or produce and secrete the desired immunoglobulin. Suitable methods and techniques will be clear to the skilled person and are extensively described in WO 06/079372 {e.g. on pages 35 to 36. 97). For example, the cells may be cultivated in a suitable medium in the wells of a multi-well plate. Suitable techniques for stimulating the production or expression and secretion of immunoglobulins will also be clear to the skilled person, and may for example include stimulation with suitable Camelid cells (e.g., helper cells). EL4-B5 cells (see for example Weber et al., Journal of Immunological Methods 278: 249-259. 2003), CD40 ligand or a similar factor, or membrane bound CD40 Hgand (see for example US 6.297.052 and the further references discussed therein).

DETAILED DESCRIPTION

In the present description, examples and claims: a) Unless indicated or defined otherwise, all terms used have their usual meaning in the art, which will be clear to the skilled person. Reference is for example made to the standard handbooks, such as Sambrook et aL "Molecular Cloning: A Laboratory Manual" ( 2nd.Ed.). VoIs. 1 -3. Cold Spring Harbor Laboratory Press (1989): F.

Ausubel et al. eds.. "Current protocols in molecular biology". Green Publishing and Wiley mterscience. New York (1987): Lewin. "Genes IF^". John Wiley & Sons, New York. N.Y., (1985): Old et ai.. "Principles of Gene Manipulation: An Introduction to Genetic Engineering", 2nd edition. University of California Press. Berkeley. CA (1981 ). Roitt et al., "Immunology^" (6th. Ed.), Mosby/Elsevier, Edinburgh (2001): Roitt et ai., Roitt^" s Essential Immunology, 10^th Ed. Blackwell Publishing. UK (2001); and Janeway et al., "'immunobiology'^* (6th Ed.), Garland Science Publishing/Churchill Livingstone, New York (2005), as well as to the general background art cited herein; b) Unless indicated otherwise, the term '"immunoglobulin sequence" - whether used herein to refer to a heavy chain antibody or to a conventional 4-chain antibody - is used as a general term to include both the full-size antibody, the individual chains thereof, as well as all parts, domains or fragments thereof (including but not limited to antigen -binding domains or fragments such as V_HH domains or V_Π/VL domains, respectively). In addition, the term "sequence" as used herein (for example in terms like "'immunoglobulin sequence^", "antibody sequence^", "variable domain sequence^". "Vm₁ sequence^"' or ''protein sequence"), should generally be understood to include both the relevant amino acid sequence as well as nucleic acids or nucleotide sequences encoding the same, unless the context requires a more limited interpretation. Also, the term

"nucleotide sequence" as used herein also encompasses a nucleic acid molecule with said nucleotide sequence, so that the terms "nucleotide sequence" and "nucleic acid^" should be considered equivalent and are used interchangeably herein: c) Unless indicated otherwise, all methods, steps, techniques and manipulations that are not specifically described in detail can be performed and have been performed in a manner known per se, as will be clear to the skilled person. Reference is for example again made to the standard handbooks and the general background art mentioned herein and to the further references cited therein: as well as to for example the following reviews Presta. Adv. Drug Deliv. Rev . 2006. 58 (5-6): 640-56: Levin and Weiss. MoI. Biosyst 2006. 2(1 ): 49-57: Irving et al., J. Immunol. Methods. 2001. 248(1-2). 31-45:

Schmitz et a!.. Placenta, 2000. 21 Suppl. A. S 106- 12, Gonzales et al.. Tumour Biol., 2005, 26(1). 31-43. which describe techniques for protein engineering, such as affinity maturation and other techniques for improving the specificity and other desired properties of proteins such as immunoglobulins. d) The term '-antigenic determinant" refers to the epitope on the antigen recognized by the antigen-binding molecule (such as a Nanobody or a polypeptide of the invention) and more in particular by the antigen-binding site of said molecule. The terms "antigenic determinant and ''epitope'^'' may also be used interchangeably herein, e) An amino acid sequence (such as a Nanobody, an antibody, a polypeptide of the invention, or generally an antigen binding protein or polypeptide or a fragment thereof) that can (specifically) bind to. that has affinity for and/or that has specificity for a specific antigenic determinant, epitope, antigen or protein (or for at least one part, fragment or epitope thereof) is said to be "against^" or "directed against" said antigenic determinant, epitope, antigen or protein.

The present invention provides methods and kits for the identification and/or sorting, from a (large) cell population, of living cells that secrete one or more specific molecules. The present invention allows the detection of subpopulations of cells based on their secreted molecule.

"Identification¹", as used in the present invention means that the cells are differentiated from other cells based on their secreted molecule. Identification includes, without being limiting, the detection, recognition, finding, selection, analysis, counting, examining, etc. of cells that secrete one or more molecules.

"Sorting'^" as used in the present invention means that certain cells are retrieved from the cell population, based on their secreted molecule. Sorting includes, without being limiting, the isolation, selection, separation, purification, etc. of cells from the cell population that secrete one or more molecules. The methods and kits of the invention make use of a ϋpid-coupled capture reagent that can be anchored to the cell membrane of cells. The lipid-coupled capture reagent of the invention comprises or essentially consists of a lipid based membrane-integrating entity coupled to a capture reagent. Accordingly, the present invention provides a method for the identification and/or sorting, from a (large) cell population, of cells that secrete one or more specific molecules comprising the steps of: a) providing a cell population, wherein said cell population comprises at least one cell that expresses and secretes or is capable of expressing and secreting one or more molecules; b) incubating the cell population with a lipid-coupled capture reagent of the invention under conditions allowing the anchoring of the lipid -coupled capture reagent into the membrane of the cells in the cell population and subsequently capturing the one or more secreted molecules by the capture reagent: c) detecting the one or more secreted molecules captured on the cell membrane of the at least one cell that expresses and secretes or is capable of expressing and secreting one or more molecules. d) identifying and/or sorting the at least one cell that expresses and secretes or is capable of expressing and secreting one or more specific molecules based on the one or more secreted molecules that are detected in step c). The (large) cell population from which cells are identified and/or sorted in the methods and kits of the present invention, can be any cell population in which all or part of the cells are thought to produce a secreted molecule, or in which all or part of the ceils are thought to produce both a secreted and a surface-displayed and/or intracellular molecule, but in which all or part of the cells display only a minor fraction of the molecule on the cell surface and/or intracellular}' . Without being limiting, the cell population can be prokaryotic cells, eukaryotic cells, mortal cells, immortalized cells, native cells as well as transformed cells and/or transfected cells.

The large cell population can be, for example and without being limiting, a transfected cell population that contains untransfected cells as well as transfected cells (with high/medium/low transgene expressing cells) that produce and secrete one or more specific recombinant proteins.

In another aspect of the invention, the cell population may contain or essentially consist of microorganisms that secrete one or more molecules in the surrounding medium, such as. without being limiting, a bacteria, a yeast, a fungi, etc. The one or more molecules secreted by the microorganism may be a native molecule, produced by the microorganism, or may be one or more recombinant proteins produced after introduction (transformation, transfection, mutation, genetic modification, etc.) of foreign DNA into the microorganism.

Alternatively, the large cell population can be native cells such as e.g. a lymphocyte preparation (of e.g. blood, spleen, lymph, node, thymus, bone marrow) containing individual B-cells, plasma cells and/or functional similar cells that produce and secrete immunoglobulins or immunoglobulin- like proteins or peptides, or e.g. activated leucocytes producing cytokines, chemokines. growth factors, etc. The cell population can be a sample or population of cells that is enriched in cells expressing, or capable of expressing an immunoglobulin, against a desired antigen, e.g. by immunizing an animal with the desired antigen. In a preferred aspect of the invention, the cell population can be a sample or population of cells that is enriched in cells expressing, or capable of expressing, a heavy chain antibody against a desired antigen, e.g. by immunizing a camelid with the desired antigen. Immunization leads to both an increased relative abundance of antigen-reactive B- cells, as well as to higher affinity immunoglobulin producing B-cells.

Thus, according to one preferred embodiment of the present invention, the cell- population is obtained from hyperimmunized animals, such as mammals, where the antigen- specific B-cell population has expanded to great numbers (1/100 or more, orders of magnitude greater than 1/10.000).

It should be noted however thai, usually, it is not possible to provide a comparably enriched population of cells from a human source (i.e. as a starting material for generating human V_H and V₁ sequences), simpl> because it is not feasible for health reasons to immunize a human being with the desired antigen. Therefore, when human cells, expressing human immunoglobulins, are to be identified and/or sorted, usually a narve non-enriched population of cells is used as a starting material.

In another non-limiting aspect of the invention, the large cell population can be a hybridoma cell population which produces and secretes specific monoclonal antibodies. ''Secretion" as used in the present invention is the process of segregating, excreting. excluding, separating, giving off. and/or releasing a substance or molecule from a cell.

The secreted molecule can be any molecule that is secreted from a cell. Without being limiting, the secreted molecule can be a native protein, produced by a native, eukaryotic cell (such as e.g. an immunoglobulin produced by a plasma cell; a cytokine produced by a specific T-cell, etc.). a native prokaryotic cell (such as e.g. a toxin produced by a bacteria), as well as an immortalized cell (such as e.g. a monoclonal antibody produced by a hybridoma cell). The secreted molecule can also be a recombinant protein, produced by a transfected cell or a genetically modified microorganism. Preferably the secreted molecule is a protein or a peptide, or a fragment of such a protein or peptide. Without being limiting, the secreted protein might, for example, be used in human or veterinary therapeutics, as a diagnostic, as an affinity reagent in research or production, or in purification workflows.

In a preferred aspect of the invention, the secreted molecule is a monoclonal antibody that is secreted by a hybridoma cell.

In another preferred aspect of the invention, the secreted molecule is an immunoglobulin that is secreted from a plasma cell or activated B-lymphocyte. Without being limiting, the immunoglobulin can be a heavy chain antibody as described, for example, in WO 94/04678, or it can be a conventional four-chain antibody.

In order to prevent the secreted molecule from diffusing away into the medium, a lipid- coupled capture reagent of the invention is anchored into the membrane of the cells in the cell population. The lipid-coupled capture reagent of the invention comprises or essentially consists of a lipid based membrane-integrating entity coupled to a capture reagent as is described in detail herein. The lipid-coupled capture reagent can be anchored into the cell membrane by a simple co-incubation step. Incubation conditions for anchoring the lipid- coupled capture reagent of the invention into the cell membrane will be known to the skilled person and are further described herein (see Example section). As an example, but without being limiting, cells (after washing with phosphate-buffered saline (PBS)) can be treated with the lipid-coupled capture reagent (10 μM) dissolved in serum-free Dulbecco^"s modified Eagle medium (DMEM) or RPMU 640 medium for a certain period of time (e.g. between 5 and 10 minutes) at temperatures between 20⁰C and 37 ⁰C.

Upon anchoring of the lipid-coupled capture reagent into the cell membrane, the capture reagent on the secreting cell will bind the secreted molecule and thus prevent it from diffusing away from the secreting cell into the medium. Incubation conditions for capturing the one or more secreted molecules by the capture reagent will depend on the one or more secreted molecules and the capture reagent, are known to the skilled person and/or are further described herein (see Example section). They may be the same conditions as used for the anchoring of the lipid-coupled capture reagent into the cell membrane or they may be different. Cross-feeding of the secreted molecule to other cells can further be prevented by decreasing the permeability of the incubation medium for the secreted product. The permeability of the incubation medium can, for example, be decreased by addition of any- compound known to decrease permeability of a liquid such as e.g.. without being limiting. gelatin, agarose, starch, polyethlyleneoxide, polyvinylalcohol. methylcellulose and the like as is known to the skilled person. The anchored lipid-coupled capture reagent can also be used for quantitative analysis of the secreted molecules. This will depend largely on the sensitivity of the anchored lipid- coupled capture reagent and on its maximum capacity. The sensitivity of the anchored lipid- coupled capture reagent depends on the affinity of the capture reagent. In a preferred aspect of the invention, the sensitivity of the anchored lipid-coupled capture reagent is between 0.1 ng/ml and 30 μg/ml, preferably between 1 ng/ml and 1 μg/ml, more preferably between 0.01 μg/ml and 0.1 μg/ml such as e.g. between 0.01 μg/ml and 0.05 μg/ml. The maximum capacity of the anchored lipid-coupled capture reagent depends on how many lipid-coupled capture reagent can be attached to the cell surface. In a preferred aspect of the invention, the maximum capacity of the anchored lipid-coupled capture reagent is 10⁵ molecules or more/cell, preferably 10⁶ molecules or more/cell, more preferably 10⁷ molecules or more/cell. The capacity of the anchored lipid-coupled capture reagent can be determined e.g. by adding a saturating amount of secreted molecule externally. In one aspect of the invention, the anchored lipid-coupled capture reagent is sufficient sensitive and has sufficient capacity to collect the secreted molecules in the linear dynamic range over a certain time period. The sensitivity and dynamic range of a given anchored lipid- coupled capture reagent can be measured by titrating various amounts of isolated "secreted molecule'^" into the culture medium, staining the cells and quantitating the staining by e.g. flow cytometry.

Secreted molecules captured on the cell surface (also referred herein as cell-captured secreted molecules) are subsequently detected, in order to enable the identification of cells that secrete the specific molecule and furthermore, if needed, the detection of the secretion rate of the specific molecule b> the individual cells (e.g. in a flow cytometric sorter) and/or if further needed, physical sorting and/or isolation of the individual cells as described further herein. Detection of the cell-captured secreted molecules can be done b> any method known in the art and/or as further described herein, including optical, weighing, sedimentation, field flow sedimentation fractionation, acoustic, magnetic, electrical and thermal means, based on the properties of the secreted molecule. In some cases, for example, naturally occurring optical properties of the secreted molecule provide a naturally occurring optical signal such as light scattering, light absorbance or colorimetric. fluorescence, time-delayed fluorescence, phosphorescence and chemiluminescence.

In most cases, however, a compatible, second reagent (also referred to herein as "'detector molecule^"') is used which is capable of binding to the secreted molecule, to reveal the cell-captured secreted molecules. This preferred aspect is also referred to as staining of the cell-captured secreted molecule. The detector molecule can be any molecule which recognizes (binds) the secreted molecule. Without being limiting, the detector molecule may be an immunoglobulin, antibody or derivative thereof (such as Fab. scFv, dAb, Nanobody®), aptamer. affibody®. etc. detecting a different epitope on the secreted molecule than the capture reagent, or binding the same epitope if the secreted molecule is a multimer of similar or identical subunits.

The detector molecule may also be an antigen if the secreted molecule is an immunoglobulin, antibody, derivative thereof (such as Fab, scFv, dAb, Nanobody®). aptamer. affibody®. etc. If the secreted molecule is an immunoglobulin or the like (first immunoglobulin), the detector molecule may also be a second immunoglobulin, antibody, derivative thereof (such as Fab. scFv, dAb, Nanobody®), aptamer, affibody®, etc. that recognizes said secreted first immunoglobulin. The detector molecule may also he a (natural) ligand or receptor if the secreted protein is a receptor or Hgand respectively binding the corresponding detector molecule. Other detector molecules include, without being limiting, nucleic acids, lectins, enzyme inhibitors, protein A and the like as will be known to those skilled in the art. The detector molecule may be specific or generic. A specific detector molecule may be one which binds only few of the possible secreted molecule variants. Such a detector molecule might e.g. be specific for a certain immunoglobulin isotype (e.g. specific onl) for IgGl). or specific for a heavy chain immunoglobulin while not capturing conventional four- chain immunoglobulins. A specific detector molecule might be an antigen for which reactive secreted molecule variants (such as e.g. immunoglobulins, antibodies or fragments thereof specific for the antigen) are being searched for. A generic detector molecule may be one which binds many possible secreted molecule variants, e.g. an isotype non-specific polyclonal antiserum, protein A, protein G and the like, as will be clear to the skilled person. The detector molecules can be directly labeled for maximal convenience, but they may also be detected using a labeled reagent itself, if left unlabeled. The particular label used in the method is not a critical aspect of the invention, so long as it does not significantly interfere with the specific binding of the detector molecule to the cell captured secreted molecule. The label can be any material having a detectable physical or chemical property. Such detectable labels have been well developed e.g. in the field of immunoassays and, in general, almost any label useful in such methods can be applied to the method of the present invention. Thus, a label is any composition detectable b> spectroscopic, photochemical, biochemical, immunochemical, electrical, optical, radiological and/or chemica! means.

The label may be coupled directly or indirectly to the detector molecule according to methods well known in the art. As indicated above, a wide variety of labels may be used. with the choice of label depending on the sensitivity required, the ease of conjugation with the compound, stability requirements, the available instrumentation and disposal provisions. Non-radioactive labels are often attached by indirect means.

Suitable labels and techniques for attaching, using and detecting them will be clear to the skilled person, and for example include, but are not limited to. fluorescent labels (such as fluorescein, isothiocyanate, rhodamine, Texas red. phycoerythrin, phycocyanin. allophycocyanin. o-phthaldehyde. fiuorescamine. Cy3, Cy5, Cy5.5, Alexi 647 and derivatives, and fluorescent metals such as ¹⁵²Eu or others metals from the lanthanide series), phosphorescent labels, chemiluminescent labels or bioluminescent labels (such as luminal, isoluminoL theromatic acridiiiium ester, imidazole, acridinium salts, oxalate ester, dioxetane or GFP and its analogs), radio-isotopes (such as ³H. ¹²⁵1, ³²P. ³⁵S. ¹⁴C, ⁵¹Cr. ³⁶Cl. ⁵⁷Co, ⁵⁸Co, ^Fe, and ^7r!Se). metals, metal chelates or metallic cations (for example metallic cations such as ^99mTc, ¹²³I. ^{11 1}In. ¹³¹I. ⁹⁷Ru. ⁶⁷Cu. ⁶⁷Ga, and ⁶⁸Ga or other metals or metallic cations that are particularly suited for use in in vivo, in vitro or in situ diagnosis and imaging, such as (¹⁵⁷Gd, "Mn. ¹⁶²Dy. ⁵²Cr, and ³⁶Fe). as well as chromophores and enzymes (such as malate dehydrogenase, staphylococcal nuclease. delta-V-steroid isomerase. yeast alcohol dehydrogenase, alpha-glycerophosphate dehydrogenase, triose phosphate isomerase. biotinavidin peroxidase, horseradish peroxidase, alkaline phosphatase, asparaginase, glucose oxidase, beta-gaiactosidase, ribonuclease. urease, catalase. glucose-VI-phosphate dehydrogenase, glucoamylase and acetylcholine esterase) and colorimetric labels such as colloidal gold, colored glass or plastic (e.g. polystyrene, polypropylene, latex, etc.) beads.

Commonly used fluorochromes (e.g. used in flow cytometry as further described herein) include, without being limiting. Fluorescein (FITC). Phycoerythrin (PE), PE-Texas Red Tandem. PE-CyS Tandem. PE-CyS. PE-Cy5.5. PE-C>7, Propidium Iodide. Green

Fluorescent Protein (GFP), Enhanced Green Fluorescent Protein (EGFP), enhanced yellow fluorescent protein (EYFP). Enhanced Cyan Fluorescence Protein (ECFP), DsRed. AsRed, HcRed. Allophycocyanin (APC). APC-Cy7, PerCP. Sytox Green. CFCE, CFDA-SE, Pl. Hydroxycoumarin. Y66H. Hoechst 33342. Y66F, lndo-1. DAPI. AMCA, MBB. Pacific Blue®. AmCyan, Cy5, ZsGreenl . ZsYellowl .

In one embodiment of the invention, the cell-captured secreted molecule is detected with one detector molecule carrying one label.

In another embodiment of the invention, the cell-captured secreted molecule is detected with multiple detector molecules that carry the same label. This has the benefit of yielding higher signal strength.

In yet another embodiment of the invention, the cell-captured secreted molecule is detected with multiple detector molecules that each carry a different label (e.g. different fluorochromes. magnetic beads, or combinations of fluorescent and magnetic or other types of labels as described herein). This multiparameter assessment (also referred to as "multiparameter probing^" or '"multiparameter staining") of the cell-captured secreted molecule allows the detection of different molecule variants at the same time. Combinations of specific and/or generic detector molecules may, for example, be used advantageously to determine multiple functional aspects of the cell-captured secreted molecule. Simultaneous application of different antigens, each carrying a different label, could, for example, identify and/or sort different cells at the same time, each secreting another binding agent. Simultaneous application of different immunoglobulins, antibodies, or derivatives thereof (such as Fab. scFv, dAb. Nanobody®), aptamers, affibodies®. etc. each binding a different epitope on the secreted molecule and each carrying a different label, could, for example, identify and/or sort different cells at the same time, each secreting a different variant of the same protein framework (such as secreted "display libraries"). Multiparameter probing can. for example, identify and/or sort cells secreting heavy chain antibodies from cells secreting conventional four-chain antibodies, while at the same time identifying and/or sorting the cells that secrete binders of one or more specific antigens. In yet another aspect of the present invention, one or more cell-captured secreted molecules can be detected simultaneously with one or more surface molecules and/or one or more intracellular molecules in a multiparameter set-up (i.e. a different label is used for each molecule that is detected). Many antigens that are suitable targets for therapy of diseased states, including immunoglobulin therapy, exist in membrane-bound form. Many of these antigens display only a limited portion of the molecule to the outside, where it is available for binding by an immunoglobulin drug. Importantly, the conformation of many such proteins critically depends on its close association with the cell membrane and/or subdomains of proteins (including itself) embedded into the membrane. The strong hydrophobicity of these molecules makes it impractical (if not impossible) to purify it to homogeneity and chemically label or fuse to an affinity purification tag without fundamentally altering the 3D structure. It is. however, desired that cells that secrete immunoglobulins reacting to the native conformation of the membrane antigen are isolated. Therefore, the cell captured secreted immunoglobulins should be detected with the antigen (as detector molecule) associated on the membrane of a transfected or native cell. These transfected or native cells can be labeled using fluorescent dyes without any alteration to the extracellular membrane- bound proteins. This can be performed by simple incubation of the living cells with a membrane -permeant ester derivative of a chemically activated fluorochrome. These apolar molecules migrate across the cell membrane of living cells into the cytoplasm, where a variety of enzymes with esterase activity hydrolyse the apolar molecule into two highly charged (i.e. polar) fragments. These can no longer cross the membrane, thereby effectively trapping the fluorescent dye in the cell (Molecular Probes, probes.com/handbook/sections/1402.html). Furthermore, careful engineering of dye derivatives has resulted in molecules where one of the two resulting fragments is chemically reactive and spontaneously covalently binds nearby proteins immediately after esterase-mediated hydrolysis. A short incubation of living cells with low concentrations of these dyes results in intense and highly stable fluorescent labeling of the cells, without appreciable loss of viability or altering normal cell function as only a very small portion of intracellular proteins gets modified. An early, non-limiting, example of these is the succinimidyl ester of 5-, 6-carboxyfluorescein diacetate (CFSE). where the final product is brightly green fluorescent. Many other dyes have been developed since, given rise to a panel of readily available reagents whereby one can pick which color to label a cell with. Some of these dyes have fluorescence spectra widely diverging from CFSE and the like, such as DDAO-SE, thereby minimizing potential color overlap and enabling multicolor labeling experiments (Molecular Probes, probes.com/lit/bioprobes44/7.pdf).

Further staining techniques will be clear to the skilled person and are. for example described in WO 06/079372 (e.g. on pages 25 to 32). As indicated above, detector molecules and/or labels can be used with a variety of physical and/or chemical properties which provide the basis for detection of the cell-captured secreted molecule. Means for detecting labels are well known in the art. The method for detection will depend on the detector molecule and possible label used, and include, without being limiting, optical properties (e.g. selected from the group consisting of light scattering, light absorbance or colorimetry. fluorescence, time-delayed fluorescence, phosphorescence and chermluminescence). mass density properties, acoustic properties, magnetic properties, electrical properties (e.g. electrical resistance measurements (see. for example. Kachel in Flow Cytometry and Sorting, Melamed et al. (Eds), Wiiey, New York, pp. 61 -104), and dielectric property measurement (see. for example, Harris et al, Enzyme Microb. Technol. 9: 181-186, 1987). and the like, well know to the skilled person and thermal properties.

Thus, for example, where the label is a radioactive label, means for detection include a scintillation counter or photographic film as in autoradiography. Where the label is a fluorescent label, it may be detected by exciting the fluorophore with the appropriate wavelength of light and detecting the resulting fluorescence. The fluorescence may be detected visually, by means of a photographic film, by the use of electronic detectors such as charge coupled devices (CCDs) or photomultipliers and the like.

Cells secreting a specific molecule can also be physically isolated (sorted) based on the detection of the cell-captured secreted molecule. Examples of physical isolation include, without being limiting, removing cells from a suspension and placing then in another suspension, sorting the cells using a flow cytometry or cell sorter, identifying the ceils by microscopy and utilizing micromanipulation to remove the cells. For the purpose of isolation, also physical forces (e.g. magnetic forces) which interact with the cell-captured secreted molecule, the detector molecule and/or the label can be used.

Suitable techniques for sorting cells include, for example, without being limiting, contacting the cells with a suitably detector molecule, such as a fluorescently labeled or magnetically labeled detector molecule, and then subjecting the cells to a separation technique in which the cells that bind the detector molecule are separated from the cells that do not bind said detector molecule. This may be performed in any suitable manner known per se, such as with a FACS apparatus or another suitable cell sorter. Suitable labels and methods for preparing labeled molecules will also be clear to the skilled person and are described further herein. The cells that bind the detector molecule are then collected, optionally- separated from the detector molecule, and optionally separated into individual cells. This may be again performed in a manner known per se, as will be clear to the skilled person.

Other techniques may involve the use of a surface or carrier on or to which the detector molecule is bound. The cells that do not bind to the detector molecule/carrier are then washed away, upon which the cells that bind to the carrier or surface are released from the carrier or surface, collected, and optionally separated into individual cells. Alternatively, the carrier with the cells attached to it may be separated from the medium, after which the cells that bind to the carrier or surface are released from the carrier or surface, collected, and optionally separated into individual cells. In case small particulate carriers such as magnetic microbeads are used, the carriers may be left attached to the carrier binding cells after separation of carrier binding and non-binding cells. Suitable caiτiers and techniques will be clear to the skilled person, and for example include panning with a surface coated with the detector molecule, the use of a polymeric matrix or gel to which the detector molecule is attached (i.e. covalently or otherwise), or the use of beads coated with the detector molecule or to which the detector molecule is attached (i.e. covalently or otherwise), such as Dynabeads™ (Invitrogen, Paisley, UK: Dynal Biotech, Oslo, Norway), MACS beads (Miltenyi Biotech, Bergisch Gladbach. Germany), EasySep (Stemceil Technologies, Vancouver. BC, Canada), iMag (BD, Franklin Lakes, NJ) or other types of magnetic beads. The detector molecule may also be bound to and/or present on a suitable membrane, including but not limited to a cell membrane or cell membrane fraction. In case detachment of carrier- or surface-bound cell is called for. bound cells may be removed from the carrier or surface by enzymatic treatment such as trypsin or other proteases, addition of bivalent cation chelating agents such as EDTA to the medium, addition of agents breaking down the physical link between antigen and carrier or surface such as DTT when reduceabϊe linkers were used, competitive displacement with another antigen binding ligand, or combinations thereof.

One of the advantages of the methods of the invention for identification and/or sorting of cells by their secreted molecule is the high speed at which the methods can be performed with and the possibility for significant automation of the method to medium and high throughput formats, for example, using suitable robotics. Suitable assays can be carried out automatically at high speed, or forces providing separation can be used within a short time interval to accomplish identification and isolation, such that this method provides identification and/or sorting of desirable cells more rapidly than conventional processes. High throughput assays suitable for use with the method of the present invention are any assay which accomplishes the identification and/or sorting of cells, and more particularly, the assays used for the detection and sorting of cells based on cell associated (i.e. displayed on the cell surface or intracellular) molecules.

Flow cytometry instruments are exquisitely suited for this purpose, as these are designed to automatically detect and quantitate binding of fluorescently labeled molecules to very large numbers of individual cells. Furthermore, their ability to detect multiple fluorescent labels per cell as well as cell morphology derived parameters enables the user to include various negative controls to exclude binding to irrelevant cells in the sample (such as polymorphonuclear cells, macrophages, T-cells, or dead cells), as well as positive markers (such as general markers identifying all B-cells in the sample). Finally, modern flow cytometric sorter devices offer the user the option to physically sort individual cells based on any arbitrarily user-chosen combination of such parameters and dispense them all together into either one bulk collection vessels (such as a centrifuge tube) or one by one into many individual vessels (such as the wells from a microtiter plate).

A specialized type of flow cytometry is Fluorescence-activated cell-sorting (FACS) which provides a method for sorting a heterogenous mixture of biological cells into two or more containers, one cell at a time, based upon specific light scattering and fluorescent characteristics of each cell (Hertzenberg, Med. Clin. Exp. 27: 240, 2004). Other FACS techniques that are suitable in the context of the present invention (e.g. in an analogous manner which will be clear to the skilled person based on the disclosure herein) are for example described in J. Immunol. Meth. 1989, 1 17: 275 or are known in the art {such as BD' s FACS 440). and include the presently available high-speed sorters (such as Beckman- Coulter^"s Altra and MoFIo: BD^'s Vantage. FACSaria. FACSaria II; or Cytopeia's InFlux; reference is also made to J. Immunol. Meth., 2000. 243: 13); also. Daughterly el al. {J.

Immunol. Meth.. 2000. 243: 21 1) give a review of eel! display library selection using flow cytometry sorters, which techniques can also be used in the context of the present invention (e.g. in an analogous manner which will be clear to the skilled person based on the disclosure herein). Other methods for single cell measurement include, without being limiting, flow- through-microfluorimetry. an optical particle analysis (see. for example. Shapiro H.M., Practical Flow Cytometry. A.R. Liss, New York. 1985: Stewart. Current Protocols in Cytometry. 1997. John Wiley & Sons; Shapiro H.M., Practical 1 low Cvfometπ . Fourth hdiiion. & Sons. Sklar L.A., Flow Cytometry for Biotechnology. 2005. Oxford University Press).

A number of alternative approaches exist as well, whereby one immobilizes the detector molecule to a solid support or magnetic particle (using absorption, covalent binding, fusion to affinity purification tags) and uses washing steps or a magnet to rinse away unbound cells.

In addition, or alternatively, techniques known per se other than high throughput flow cytometry can be used in the context of the present invention to identify and/or sort cells with the desired cell captured secreted molecule from cell not having the desired cell captured secreted molecule. Immobilizing the detector molecule on magnetic microbeads (such as those from Miltenyi Biotech (Bergisch Gladbach. Germany) and Dynal Biotech (Oslo. Norway), to name only two major suppliers) or on another solid phase such as standard disposable tissue culture plasticware allows "panning^" of tens of millions of cells against the detector molecule simultaneously, using generally available equipment well-known in the art. Subsequently washing away non-binding cells from the plastic, or holding the cells plus beads suspension to a magnet and pipetting off all non-bound cells, separates the vast majority of irrelevant cells (cells not having the desired cell captured secreted molecule on their surface) from the cells of interest. The procedure takes only a lew hours in total, with most of the time required actually consisting of the incubation steps. The publication series from H. Leyendeckers et al. (for instance. Eur. J. Immunol.. 2002. 32: 3126 and Eur. J. Immunol. 1999, 29: 1406) describe such methods for obtaining cell populations of high purity, as well as near-perfect preservation of viability after panning.

Also, one or more of the above techniques can be suitably combined. For example, solid phase cell panning can be combined with the use flow cytometers or vice versa. The publication from N. N. Gaπgopadhyay et al. (J. Immunol. Meth.. 2004, 292: 73) vividly illustrates the power of combining two such methodologies to get highly specific isolation (using flow cytometry sorting) of very rare cells (pre-enriched before FACS using cell panning techniques).

Specific fluorescent and magnetic staining reagents can, for example, be used for cytometric analysis and cell sorting. They can be used in a multiparameter set up with simultaneous staining with specific fluorescent and magnetic staining reagents.

All techniques described above or any suitable combination thereof can be used in the context of the present invention (e.g. in an analogous manner which will be clear to the skilled person based on the disclosure herein).

The Figures and the Experimental Part/Examples are only given to further illustrate the invention and should not be interpreted or construed as limiting the scope of the invention and/or of the appended claims in any way. unless explicitly indicated otherwise herein.

FIGURE LEGENDS

Figure I: Coomassie stained SDS-PAGE as described in Example 1. Lane 3 : Precision

Plus Prot™ All Blue standard (Bio-Rad; Cat No: 161-0373); lanes 3-6: PD-10 gel elution fractions 3-6: lanes 7-10: fractions 10-13; lane 1 ] : mouse anti human monoclonal antibody (Jackson Immunoreserach; Cat. No. 209-005-098).

Figure 2: FACS analysis of CHO-Kl cells with BAM-antibody conjugate as described in Example 2. Left panel: histogram display of goat-anti-mouse PE stained untreated CHO- Kl cell population. Right panel: histogram of PE fluorescence intensity of BAM-mouse antibody-conjugate treated CHO cells. Mean fluorescence intensity values of 44 and 52097 were obtained, respectively, demonstrating the very high degree of membrane incorporation of the BAM-antibody conjugate without inducing cell death. Figure 3: Density of BAM-capture reagent conjugate on cell surface of BAM-capture reagent conjugate labeled CHO cells, as a function of post-labeling 37°C incubation time. Cell surface exposed BAM-capture reagent conjugate is detected using a fluorescently labeled anti -capture reagent polyclonal. Relative density per cell is expressed as mean fluorescence intensity channel number.

Figure 4: Untransfected CHO cells, an Fc/IgE receptor 1 fusion protein secreting transfected CHO cell clone, or a 50/50 mixture of both populations were labeled with BAM- mouse-anti-human ϊgG conjugate as described in Example 4. Once labeled, all three cell populations were incubated for 45 minutes at 37°C to allow for secretion of Fc fusion protein. All three cell populations were subsequently stained using fluorescently labeled IgE, washed and analyzed separately on FACS. An overlay of all three separate histograms is shown.

EXAMPLES

Example 1: Conjugation of mouse anti human IgGl monoclonal antibody to BAM

A fresh 6.6 mM solution of BAM (NOF Corporation, Tokyo. Japan; Product name: SUNBRΪGHT® OE-080CS) was made by dissolving 67.2 mg in 1.27 ml of anhydrous DMSO. 910 μl of mouse anti -human IgG (Jackson Immunoresearch, Suffolk, UK: Cat. No. 209-005-098), supplied at 1 .8 mg/ml (=12 μM), was mixed with 91 ml of 6.6 mM reactive BAM in DMSO and allowed to react overnight or longer. Conjugated antibody was then separated from free unreacted BAM by passing the mixture over a PD-IO gel filtration column (GE Healthcare, Chalfont St. Giles. UK: Product code 17-0851-01). pre-equilibrated with 2x30ml Dulbecco^'s PBS (Invitrogen. Carlsbad, CA, US; Cat. No. 20012-068). Optical density at 260 and 280 nin wavelengths were determined by NanoDrop® ND-] 000 (NanoDrop Technologies. Wilmington. DE. US) from all 15 fractions collected from the column (Table 1). Aliquots of selected fractions (marked with asterisk in Table 1) were further analyzed by Coomassie stained SDS-PAGE gel electrophoresis (Invitrogen. Carlsbad. CA. US: NuP AGE® 10% Bis-Tris gel 1.0 mm, 15 well) (Figure 1 ). Fraction 4. the fraction with the highest OD280 of the first series of fraction having an OD280 over background, was the only one showing a clearly staining high MW band on gel. Fraction 4 was therefore selected for further experiments. The high MW versus unconjugated reference rnAb (Figure 1 , lane 11) indicated the monoclonal antibody had been successfully conjugated. The low staining intensity was attributed to the PEG moiety of the conjugate, which has been described elsewhere as diminishing protein Coomassie staining. Table ϊ :

Example 2: Incorporation of BAM-mαuse anti human IgGl monoclonal antibody conjugate in live CHO cell membrane

To evaluate whether BAM-mouse anti human IgGl monoclonal antibody conjugate (BAM-antibody conjugate) integrates into mammalian cell membranes, we incubated the conjugate prepared such as described in Example 1 with CHO-Kl cells (ATCC CCL-61™). To this end. 3 x 10^ live cells were devided in microliter plate wells, centrifuged down, and cell culture supernatant was removed. Next, cell pellets were resuspended in 60 μl of BAM- antibody conjugate (in PBS or PBS + fetal calf serum) or PBS and incubated for 30 minutes at 37°C. Cells were washed twice with 250μl per well of FACS buffer (10% FCS in D-PBS) before being resuspended in the same buffer holding a 1/50 dilution of phycoerytrmn conjugated goat-anti-mouse IgG (Jackson Immunoresearch. Suffolk, UK; Cat No: 1 15-115- 164). After 30 minutes incubation at 4°C, cells were washed another five times as above, resuspended in FACS buffer containing 5μM of the TOPRO3 viability dye (Molecular Probes/Invitrogen Cat. No. T3605) and analyzed on a BD FACSarray flow cytometer (BD Biosiences ϊmmuno cytometry, San Jose. CA). Dead (TOPRO3 positive) cells were virtually absent from treated or control wells (<5% of total events), but were gated out of further PE fluorescence histrogram analysis. As is shown in Figure 2, only BAM-antibody conjugate incubated CHO cells bind high amounts of PE labeled goat-anti-mouse antiserum.

Clearly, very high levels of BAM-antibody conjugate were able to integrate into the CHO cell membrane without making the antibody inaccessible to goat immunoglobulin conjugate binding, or resulting in cell death.

Example 3: Persistence of BAM-πiouse anti human IgGl monoclonal conjugate in live CHO cell membrane

To determine whether the incorporation of BAM-antibody conjugate remains sufficiently stable over time to allow for secreted protein capture, BAM-antibody conjugate was allowed to integrate into CHO-Kl cell membrane as described in Example 2. Next, cells were washed as above, but resuspended in 37⁰C prewarmed cell culture medium and placed in a 37°C/5%CO2 incubator. Aliquots were removed from this culture at 0, 20. 40. 60, 80, 100 and 120 minutes. All aliquots were washed with cold FACS buffer at the time of sampling, stained with goat-anti-mouse PE and resuspended in FACS buffer with TOPRO 3 as described in Example 2. Figure 3 shows the mean fluorescence intensity of histograms obtained from these samples, plotted against the time of cell culturing after BAM-antibody conjugate incorporation. Although levels of detectable cell surface exposed BAM-antibody conjugate can be seen to deteriorate over time, fluorescence intensities far above background level are still present after 2 hours of incubation at 37^CC. Thus, at physiological temperatures, CHO cells gradually lose cell membrane surface associated BAM-antibody conjugate, but at a rate which still leaves high levels of the molecule intact after two hours or more of incubation.

Thus, sufficient levels of capture reagent will remain available on the cell surface even after more than 2 hours of incubation of BAM-capture reagent conjugate (i.e. BAM- antibody conjugate) labeled CHO cells under circumstances conducive to secretion of the soluble product of interest. Example 4: Capture of CHO cell secreted protein b> membrane-bound BAM-mouse anti human IgGl monoclonal conjugate

To determine whether cell surface exposed BAM-capture reagent conjugate can retain detectable levels of secreted protein on the cell surface, a CHO cell clone stably transfected with a construct coding for a secreted fusion protein was labeled with BAM-rnouse-anti- human IgG conjugate according to the procedure described in Example 2. The fusion protein expressed and secreted by the transfected CHO cells consisted of the extracellular domain of the human high affinity IgE receptor alpha chain, genetically fused to human IgGl Fc. essentially as described in Haak-Frendscho et al. (J. Immunol. 1993, 151 : 351). Thus. CHO cells secreting this protein should be able to bind fluorescently labeled human IgE if the BAM capture reagent conjugate is incorporated into the cell membrane and remains functional (that is. binds the IgGl Fc moiety of the fusion protein and presents the IgE receptor moiety). As controls, untransfected CHO cells or a 50/50 mixture of transfected clone and untransfected CHO cells were labeled with BAM-mouse-anti-human IgG conjugate in parallel. All three BAM-antibody conjugate labeled cell populations were then washed with and resuspended in 37°C warm cell culture medium and incubated for 45 minutes at 37°C on a head -over-head rotator to allow for secretion (and cell surface capture) of fusion protein by positive cells. Continuous agitation of the eel! suspension was performed to prevent cells from settling down at the bottom of the tube, which would increase the chance of non-secreting cells capturing free secreted protein as all cells come in closer contact in the cell pellet. After this incubation step, cells from all three tubes were washed with cold FACS buffer and stained using either a commercial goat anti mouse PE conjugate as described in Examples 2 and 3. or Alexa fluor 488 fluorescently labeled human IgE (prepared in-house at Ablynx. using purified clone HEl monoclonal human IgE (Diatec, Oslo. Norway; Cat. No. 7050 - Al 0) and pre-activated Alexa 488 (Invitrogen; Cat, No. A20000). according to the manufacturer^'s instructions). Analysis of PE fluorescence histograms clearly demonstrated integration of BAM-mouse-anti-human mAb capture reagent in the cell membrane of all cell populations, confirming earlier results (data not shown). Analysis of Alexa 488 fluorescence histograms clearly showed that non-transfected CHO cells do not bind human IgE. In contrast, all cells of the IgE receptor/Fc fusion protein secreting CHO cell clone bound high levels of fluorescent human IgE. and a 50/50 mixed population of untransfected and transfected cells showed a broad distribution pattern spanning the fluorescence intensity range of both pure populations. Figure 4 shows the overlay of all three histograms. We therefore conclude that membrane bound BAM-caplure reagent conjugate is present in all cells incubated with the BAM-capture reagent conjugate. The BAM-capture reagent conjugate was capable of capturing the secreted molecule by the Fc moiety in a fashion which also preserved the function of the IgE receptor domain of the fusion protein. The relative amount of captured fusion protein detected per cell reflects the production (or lack of production) of fusion protein of the individual cells. The latter implies the fluorescence intensity of a detector molecule, in this case receptor/Fc fusion protein Hgand, can be used to identify which individual cells of a given mixed secretor/non-secretor population actually produce significant levels of secreted protein.

Example 5: Identification and isolation of individual CHO cells that secrete high levels of soluble protein from a given heterogeneous population

Having established that a BAM-capture antibody conjugate integrates in the cell membrane, and that secreted protein can be captured and detected on the cell membrane of soluble protein producing cells by virtue of the capture moiety, we will use this method to identify and selectively isolate clones of a mixed population wherein individual cells produce levels of soluble protein ranging from very low to very high. To accomplish this, we transfect CHO-Kl cells with an expression vector encoding both heavy and light chains of a recombinant antibody having a human IgGl Fc. and the neomycin antibiotic selection marker. Transfection is performed using linearized endotoxin free purified plasmid DNA and the commercially available Fugene reagent (Roche Applied Science, Basel. Switzerland) using the method recommended by the transfection reagent manufacturer. Cells are submitted to G418 antibiotic selection 48 hours after transfection. using a concentration of antibiotic known to be cytotoxic to non-transfected CHO-Kl host cells. Once cells have been under selective pressure for a sufficiently long period to allow for non-transfected cells to have died (which is determined by observation of parallel cell cultures of non-transfected CHO-Kl cultures put under identical selection pressure), the remaining viable cells are incubated with BAM-human IgGI capture agent conjugate as described in Example 2. Such labeled cells are then incubated in fresh cell culture medium at 37⁰C for 2 hours under continuous gentle agitation to prevent cells from settling at the bottom of the tube. After this incubation step, cells are pelleted by centrifugation. washed with cold FACS buffer, and stained with fluorescently labeled antigen which the secreted recombinant antibody is known to bind. After removal of free labeled antigen, the cells are resuspended in cold FACS buffer containing a live/dead cell discriminating dye and analyzed on a cell sorter, i.e. a BD FACSAria instrument with ACDU option fitted. Live cells are identified based on forward/side scatter profile and live/dead discrimination dye fluorescence. Within the live cell subpopulation. fluorescence intensity in the channel corresponding to the antigen label is plotted as a histogram. The most intensely fluorescent 1% of the total histogram population are marked by a gate, and the instrument is set up to sort individual cells within that gate into individual wells of 96-well microtiter plates, using the instrument^'s ACDU subsystem. Such plates are prefilled with cell culture medium containing selective antibiotic.

Alternatively, control plates receive live cells not having been pre-selected in the top 1% fluorescence intensity gate set as described above. These represent a random selection of single transfectant clones, to be used as reference for selection efficiency.

Plates having received individual cells are placed in a humidified CO2 incubator until cells grow out to multicellular clones, as observed under microscope. Conditioned supernatants from plates having been seeded with the top 1% fluorescence intensity gated cells are analyzed by quantitative antigen binding ELISA. alongside conditioned supernatant of control plates having received individual transfectants not preselected for high levels of transgene expression. Analysis will show a higher percentage of clones producing high levels of transgene encoded recombinant antibody in the 1 % top fluorescence intensity preselected cell plates than in the random sampled total population (control plates). Thus, this experiment demonstrates the method is capable of identifying which individual cells of a given heterogeneous population secrete high levels of soluble protein, and that physical isolation of cells away from the pool based on the measured parameter leads to isolation of high soluble protein producer cell clones.

As a further refinement of the method, cells labeled with BAM-capture reagenl conjugate and allowed to secrete soluble protein as described above can be stained with fluorescent antigen and a reagent detecting the total level of cell surface associated BAM- capture reagent conjugate, which is itself conjugated to a second fluorescent label. Such a second detection reagent could consist for instance of a polyclonal or monoclonal antibody reactive to the capture agent moiety of the BAM-capture reagent conjugate. This reagent is selected so as not to interfere with secreted protein/BAM-capture reagent conjugate interaction. The fluorescence intensity of both reagents can be determined simultaneously in the cell sorter. By plotting the fluorescence intensity of both against one another in a two- dimensions dot plot, one can correlate the fluorescence intensity of the antigen bound to individual cells in the cell population to the total amount of BAM-capture reagent still associated with the same cells. That is. cells having larger amounts of BAM-capture reagent associated with them will have higher fluorescent antigen binding capacity versus cells having less BAM-capture reagent associated with them at similar protein production ratios. However, cells having such similar production ratios at different BAM-capture agent loading levels will be located on the diagonal of a two-dimensional dot plot. Thus, by sorting individual cells off the diagonal axis on such a plot (having a higher than average antigen fluorescence intensity associated with them than other cells at the same BAM-capture reagent loading), one will be able to preferentially identify and isolate clones producing higher levels of soluble protein even if BAM-capture reagent loading is non-homogenous across the overall cell population.

The terms and expressions which have been employed are used as terms of description and not of limitation, and there is no intention in the use of such terms and expressions of excluding any equivalents of the features shown and described or portions thereof, it being recognized that various modifications are possible within the scope of the invention.

All of the references described herein are incorporated by reference for the purposes described herein.

Claims

1. Method for the identification and/or sorting, from a cell population, of cells that secrete one or more specific molecules said method comprising the step of capturing said one or more specific molecules onto the cell membranes of said cell population and detecting said one or more specific molecules captured on the cell membrane, wherein said one or more specific molecules are captured by a lipid coupled capture reagent.

2. Method for the identification and/or sorting, from a large cell population, of cells that secrete one or more molecules, said method comprising the following steps: a) providing a eel] population, wherein said cell population comprises at least one cell that expresses and secretes or is capable of expressing and secreting one or more molecules; b) incubating the cell population with a Hpid-coupled capture reagent under conditions allowing the anchoring of the lipid-coupled capture reagent into the membrane of the cells in the cell population and subsequently capturing the one or more secreted molecules by the capture reagent; c) detecting the one or more secreted molecules captured on the cell membrane of the at least one cell that expresses and secretes or is capable of expressing and secreting one or more molecules.

3. Method according to any of claims 1 or 2, wherein the lipid-coupled capture reagent comprises or essentially consists of a lipid based membrane-integrating entity coupled to a capture reagent.

4. Method according to claim 3, wherein the lipid based membrane-integrating entity as the following structure: lipid - [PEG]_n - reactive group wherein: - the polyethylene glycol (PEG) chain can be of variable length, wherein n represents the average number of the ethylene oxide unit repeats present in the membrane integrating entity; - the reactive group is capable of binding the capture reagent.

5. Method according to claim 4, wherein the lipid is a fatty acid or a fatty acid derivative, composed of fatty acid chains between 14 and 24 carbon atoms.

6. Method according to claim 5, wherein the fatty acid is selected from laurate, myristate, palmitate. stearate, arachidate, behenate. lignocerate, palmitoleate, oleate, linoleate, linolenate, arachidonate, palmitate (Cl 6, saturated) and oleate (C 18, one double bond).

7. Method according to claim 4, wherein the lipid is a phospholipid.

8. Method according to claim 7, wherein the lipid is a phosphoglyceride selected from phosphatidyl choline, phosphatidyl serine, phosphatidyl ethanolamine, phosphatidyl choline, phosphatidyl inositol, phosphatidyl glycerol and sphingomyelin.

9. Method according to claim 4, wherein the lipid is dioleylphosphatidylethanolamine.

10. Method according to claim 4, wherein the PEG chain has an average number of ethylene oxide unit repeats between 20 and 250,

11. Method according to claim 4, wherein the reactive groups is selected from N- hydroxysuccinimide (NHS), isothiocyanate (ITC), maleimide-, iodoacetamide- or hydrazide derivatives.

12. Method according to claim 4, wherein the membrane-integrating entity is selected from BAM40, BAM90, BAMl 80 and DOPE-BAM80.

13. Method according to claim 3, wherein the capture reagent is an immunoglobulin or antibody (monoclonal, polyclonal) or derivative (such as e.g. scFv, Fab, dAb or Nanobody) or artificial entity (aptamer, affibody, etc.), reactive to the secreted molecule or to a tag attached to it.

14. Method according to claim 3, wherein the capture reagent is an antigen for which the secreted molecule is a binder.

15. Method according to any of claims 1 to 14, wherein the cell population contains prokaryotic cells, eukaryotic cells, native cells, mortal cells, immortalized cells, transformed cells and/or transfected cells.

16. Method according to claim 15, wherein the cell population contains transfected cell that produce one or more recombinant proteins and the high transgene expressing cells are selected and/or sorted from non-transfected cells and/or from low transgene expressing cells.

17. Method according to claim 15. wherein the cell population contains microorganisms that secrete one or more molecules and the high expressing and secreting microorganisms are selected and/or sorted from the non-producing microorganisms and/or from the low expressing and/or secreting microorganisms.

18. Method according to claim 15. wherein the cell population contains a functionally discrete subset of cells defined (at least partially) by the pattern of secreted soluble proteins.

19. Method according to claim 15, wherein the cell population contains hybridoma cells that secrete a monoclonal antibodies and the hybridoma cells that secrete a specific monoclonal antibody at high rate and/or at high levels are selected and/or sorted from the hybridoma cells that do not produce and secrete the specific monoclonal antibody and/or from the hybridoma cells that produce and/or secrete the specific monoclonal antibody at lower levels.

20. Method according to claim 15, wherein the cell population contains B-cells that produce and secrete immunoglobulins and the B-cells that produce and secrete immunoglobulins at high levels are selected and/or sorted from other cells.

21. Method according to claim 20, wherein said B-cells are activated B lymphocytes and/or plasma cells.

22. Method according to any of claims 20 or 21, wherein the immunoglobulins are heavy chain antibodies and/or four-chain antibodies.

23. Method according to any of claims 20 to 22. additionally comprising the step of isolating a nucleic acid or nucleotide sequence that encodes an immunoglobulin or that encodes an antigen-binding fragment thereof,

24. Methods according to claim 23. wherein nucleic acid or nucleotide sequences are generated or cloned that encode an immunoglobulin or an antigen-binding fragment thereof directed against a specific antigen, said method comprising the steps of: a) providing a cell population from an animal, such as a mammal immunized with said antigen, or a population of cells from a non-immune animal, wherein said cell population comprises at least one cell that expresses and secretes or is capable of expressing and secreting an immunoglobulin directed against said antigen; b) incubating the cell population with a Jipid-coupled capture reagent under conditions allowing the anchoring of the lipid-coupled capture reagent into the membrane of the cells in the cell population and subsequently capturing the immunoglobulin by the capture reagent; c) detecting the immunoglobulin captured on the cell membrane of the at least one cell that expresses and secretes or is capable of expressing and secreting an immunoglobulin; d) isolating from said cell population said at least one cell that expresses and secretes or is capable of expressing and secreting an immunoglobulin directed against said antigen; e) obtaining from said at least one cell a nucleic acid or nucleotide sequence that encodes an immunoglobulin directed against the specific antigen or that encodes an antigen-binding fragment thereof directed against said specific antigen.

25. Method according to any of claims 20 to 24, wherein nucleic acid or nucleotide sequences are generated that encode a heavy chain antibody or an antigen-binding fragment thereof directed against a specific antigen, said method comprising the steps of: a) providing a cell population from a Canielid immunized with said antigen, or cell population from a non-immune Camelid, wherein said cell population comprises at least one cell that expresses and secretes or is capable of expressing and secreting a heavy chain antibody directed against said antigen; b) incubating the cell population with a lipid-coupled capture reagent under conditions allowing the anchoring of the lipid-coupled capture reagent into the membrane of the cells in the cell population and subsequently capturing the heavy chain antibody by the capture reagent; c) detecting the heavy chain antibody captured on the cell membrane of the at least one cell that expresses and secretes or is capable of expressing and secreting a heavy chain antibody: d) isolating from said cell population said at least one cell that expresses and secretes or is capable of expressing and secreting a heavy chain antibody directed against said antigen; e) obtaining from said at least one cell a nucleic acid or nucleotide sequence that encodes a heavy chain antibody directed against the specific antigen or that encodes an antigen-binding fragment thereof directed against said specific antigen.

26. Method according to claim 25. wherein step d) comprises at least one of the following steps: d-1) separating cells that express antibodies from cells that do not express antibodies; d-2) separating cells that express antibodies against the desired antigen from cells that express antibodies directed against other antigens; d-3) separating cells that express heavy chain antibodies from cells that express conventional four-chain antibodies;

27. Method according to any of claims 20 to 22, wherein the cell population contains B-cells from a transgenic non-human animal that expresses and secretes human or human-like four-chain antibodies against a desired antigen.

28. Kit for the identification and/or sorting of cells that secrete one or more molecules based on their secreted molecule, said kit at least comprising a lipid coupled capture reagent.

29. Kit for performing a method according to any of claims 1 to 27, said kit at least comprising a lipid coupled capture reagent.

30. Kit according to any of claims 28 or 29, further comprising a detector molecule, a label and/or a buffer.

31. Kit according to any of claims 28 to 30, wherein the lipid-coupled capture reagent comprises or essentially consists of a lipid based membrane-integrating entity coupled to a capture reagent.

32. Kit according to claim 31 , wherein the lipid based membrane-integrating entity as the following structure: lipid - [PEG]_n - reactive group wherein:

- the polyethylene glycol (PEG) chain can be of variable length, wherein n represents the average number of the ethylene oxide unit repeats present in the membrane integrating entity;

- the reactive group is capable of binding the capture reagent.

33. Kit according to claim 32, wherein the lipid is a fatty acid or a fatty acid derivative, composed of fatty acid chains between 14 and 24 carbon atoms.

34. Kit according to claim 33, wherein the fatty acid is selected from laurate, myristate, palmitate. stearate, arachidate, behenate, lignocerate, palmitoleate, oleate. linoleate, linolenate. arachidonate, palmitate (C16, saturated) and oleate (C18, one double bond).

35. Kit according to claim 32, wherein the lipid is a phospholipid.

36. Kit according to claim 35, wherein the lipid is a phosphoglyceride selected from phosphatidyl choline, phosphatidyl serine, phosphatidyl ethanolamine, phosphatidyl choline, phosphatidyl inositol, phosphatidyl glycerol and sphingomyelin.

37, Kit according to claim 32, wherein the lipid is dioleylphosphatidylethanolamine.

38. Kit according to claim 32, wherein the PEG chain has an average number of ethylene oxide unit repeats between 20 and 250.

39. Kit according to claim 32, wherein the reactive groups is selected from N- hydroxysuccinimide (NHS), isothiocyanate (ITC), maleimide-, iodoacetamide- or hydrazide derivatives.

40. Kit according to claim 32, wherein the membrane-integrating entity is selected from BAM40, BAM90, BAMl 80 and DOPE-BAM80.

41. Kit according to claim 31 , wherein the capture reagent is an immunoglobulin or antibody (monoclonal, polyclonal) or derivative (such as e.g. scFv, Fab, dAb or Nanobody) or artificial entity (aptamer, affibody, etc.), reactive to the secreted molecule or to a tag attached to it.

42. Kit according to claim 31, wherein the capture reagent is an antigen for which the secreted molecule is a binder.