US20180119192A1 - Early post-transfection isolation of cells (epic) for biologics production - Google Patents

Early post-transfection isolation of cells (epic) for biologics production Download PDF

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US20180119192A1
US20180119192A1 US15/727,272 US201715727272A US2018119192A1 US 20180119192 A1 US20180119192 A1 US 20180119192A1 US 201715727272 A US201715727272 A US 201715727272A US 2018119192 A1 US2018119192 A1 US 2018119192A1
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cells
polypeptide
population
days
selectable
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Victor R. Cairns
Christine DeMaria
Jason Vitko
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Genzyme Corp
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Genzyme Corp
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Priority to US16/683,837 priority patent/US11685943B2/en
Priority to US18/315,332 priority patent/US20240026410A1/en
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    • C—CHEMISTRY; METALLURGY
    • C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
    • C12P—FERMENTATION OR ENZYME-USING PROCESSES TO SYNTHESISE A DESIRED CHEMICAL COMPOUND OR COMPOSITION OR TO SEPARATE OPTICAL ISOMERS FROM A RACEMIC MIXTURE
    • C12P21/00—Preparation of peptides or proteins
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07K—PEPTIDES
    • C07K14/00—Peptides having more than 20 amino acids; Gastrins; Somatostatins; Melanotropins; Derivatives thereof
    • C07K14/435—Peptides having more than 20 amino acids; Gastrins; Somatostatins; Melanotropins; Derivatives thereof from animals; from humans
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07K—PEPTIDES
    • C07K14/00—Peptides having more than 20 amino acids; Gastrins; Somatostatins; Melanotropins; Derivatives thereof
    • C07K14/435—Peptides having more than 20 amino acids; Gastrins; Somatostatins; Melanotropins; Derivatives thereof from animals; from humans
    • C07K14/43504—Peptides having more than 20 amino acids; Gastrins; Somatostatins; Melanotropins; Derivatives thereof from animals; from humans from invertebrates
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07K—PEPTIDES
    • C07K14/00—Peptides having more than 20 amino acids; Gastrins; Somatostatins; Melanotropins; Derivatives thereof
    • C07K14/435—Peptides having more than 20 amino acids; Gastrins; Somatostatins; Melanotropins; Derivatives thereof from animals; from humans
    • C07K14/705—Receptors; Cell surface antigens; Cell surface determinants
    • C07K14/70592—CD52
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07K—PEPTIDES
    • C07K14/00—Peptides having more than 20 amino acids; Gastrins; Somatostatins; Melanotropins; Derivatives thereof
    • C07K14/435—Peptides having more than 20 amino acids; Gastrins; Somatostatins; Melanotropins; Derivatives thereof from animals; from humans
    • C07K14/705—Receptors; Cell surface antigens; Cell surface determinants
    • C07K14/70596—Molecules with a "CD"-designation not provided for elsewhere
    • C—CHEMISTRY; METALLURGY
    • C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
    • C12N—MICROORGANISMS OR ENZYMES; COMPOSITIONS THEREOF; PROPAGATING, PRESERVING, OR MAINTAINING MICROORGANISMS; MUTATION OR GENETIC ENGINEERING; CULTURE MEDIA
    • C12N15/00—Mutation or genetic engineering; DNA or RNA concerning genetic engineering, vectors, e.g. plasmids, or their isolation, preparation or purification; Use of hosts therefor
    • C12N15/09—Recombinant DNA-technology
    • C12N15/63—Introduction of foreign genetic material using vectors; Vectors; Use of hosts therefor; Regulation of expression
    • C12N15/79—Vectors or expression systems specially adapted for eukaryotic hosts
    • C12N15/85—Vectors or expression systems specially adapted for eukaryotic hosts for animal cells
    • C—CHEMISTRY; METALLURGY
    • C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
    • C12N—MICROORGANISMS OR ENZYMES; COMPOSITIONS THEREOF; PROPAGATING, PRESERVING, OR MAINTAINING MICROORGANISMS; MUTATION OR GENETIC ENGINEERING; CULTURE MEDIA
    • C12N5/00—Undifferentiated human, animal or plant cells, e.g. cell lines; Tissues; Cultivation or maintenance thereof; Culture media therefor
    • C12N5/0081—Purging biological preparations of unwanted cells
    • C12N5/0087—Purging against subsets of blood cells, e.g. purging alloreactive T cells
    • C—CHEMISTRY; METALLURGY
    • C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
    • C12N—MICROORGANISMS OR ENZYMES; COMPOSITIONS THEREOF; PROPAGATING, PRESERVING, OR MAINTAINING MICROORGANISMS; MUTATION OR GENETIC ENGINEERING; CULTURE MEDIA
    • C12N5/00—Undifferentiated human, animal or plant cells, e.g. cell lines; Tissues; Cultivation or maintenance thereof; Culture media therefor
    • C12N5/10—Cells modified by introduction of foreign genetic material
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume or surface-area of porous materials
    • G01N15/10—Investigating individual particles
    • G01N15/14—Optical investigation techniques, e.g. flow cytometry
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume or surface-area of porous materials
    • G01N15/10—Investigating individual particles
    • G01N15/14—Optical investigation techniques, e.g. flow cytometry
    • G01N15/149—Optical investigation techniques, e.g. flow cytometry specially adapted for sorting particles, e.g. by their size or optical properties

Definitions

  • Methods for selection of producer cell populations and cell clones are imperative for the manufacturing of biologics, such as antibodies and fusion proteins. Such methods generally rely on use of a selection agent, such as methotrexate (MTX) or methionine sulphoximine (MSX), to bias and amplify the production of biologics. Selection agent-based methods may affect the viability or growth rate of selected populations or may have a negative impact on clonal stability. Such drug-based selections can also be time consuming, often requiring multiple rounds of selection to obtain populations which contain clones that are suitable for biologic manufacturing. There remains a need for rapid and reliable methods of generating both large cell populations and clones that produce high titers of biologics with less negative impact to the host cell.
  • MTX methotrexate
  • MSX methionine sulphoximine
  • the disclosure provides methods of selecting a population of cells expressing a target polypeptide.
  • methods for selection were developed that relied upon sorting of populations shortly following their transfection.
  • the methods feature the step of isolating a sub-population of transfected cells for early detectable expression of the transfected vector.
  • the selection is based on early expression of a selectable polypeptide, which is different from the target polypeptide and detectable on the surface of the cell.
  • the methods described herein are useful, e.g., for the generation of pools of cells for screening of polypeptides of interest (such as in early clinical development and for the generation of high titer clones, which can be utilized to produce a polypeptide of interest both for small and large scale manufacturing.
  • the disclosure provides a method of producing a population of producer cells expressing a target polypeptide, the method comprising: (a) transfecting host cells with one or more vectors that encode one or more mRNAs, wherein the one or more mRNAs encode a selectable polypeptide and the target polypeptide; (b) isolating from the transfected host cells, within 2 to 15 days after transfection, a sub-population of early-expressing transfected host cells which express the selectable polypeptide; and (c) expanding the sub-population of early-expressing transfected host cells, thereby producing a population of producer cells.
  • step (b) is performed in drug-selection-free medium.
  • step (c) is performed in drug-selection-free medium.
  • step (b) and step (c) are each performed in drug-selection-free medium.
  • the method further comprises isolating the target polypeptide from the expanded sub-population.
  • the method further comprises isolating one or more single transfected host cells from the expanded sub-population and culturing the one or more single transfected host cells to produce clonal populations of the one or more single transfected host cells.
  • At least one of the clonal populations of the one or more single transfected host cells yields a 2- to 30-fold improvement in production of the target polypeptide compared to that of a stable pool of transfected but uncloned host cells obtained at step (c).
  • the transfected host cells subject to isolation in step (b) contains 80-120 ⁇ 10 6 cells.
  • the isolation in step (b) is performed less than six days after transfection. In some embodiments of any one of the methods provided, the isolation in step (b) is performed between two and four days after transfection. In some embodiments of any one of the methods provided, the isolation in step (b) is performed two days after transfection. In some embodiments of any one of the methods provided, the isolation in step (b) is performed three days after transfection.
  • the sub-population of transfected host cells contains 0.5-6.0 ⁇ 10 6 cells prior to expansion in step (c).
  • the expanding in step (c) is for between 4-31 days.
  • a first of the one or more vectors encodes the mRNA encoding the target polypeptide, and a second of the one or more vectors encodes the selectable polypeptide.
  • the mRNA encoding the target polypeptide and the mRNA encoding the selectable polypeptide are both encoded on one vector.
  • a first of the one or more vectors encodes the mRNA encoding the target polypeptide, and a second of the one or more vectors encodes the selectable polypeptide.
  • the mRNA encoding the plurality of target polypeptides and the mRNA encoding the plurality of selectable polypeptides are both encoded on one vector.
  • the isolation in step (b) employs magnetic-activated cell sorting (MACS), fluorescence-activated cell sorting (FACS), or ClonePix.
  • the selectable polypeptide is a FACS selectable polypeptide and the isolation in step (b) employs FACS.
  • the target polypeptide and the selectable polypeptide form a fusion polypeptide.
  • the mRNA is a multicistronic mRNA.
  • the multicistronic mRNA comprises a first open reading frame (ORF) that encodes the selectable polypeptide and a second ORF that encodes the target polypeptide, wherein the first ORF is 5′ to the second ORF.
  • the first ORF has a non-AUG start codon.
  • the second ORF has an AUG start codon.
  • the non-AUG start codon is a UUG, GUG, or CUG in a Kozak consensus sequence.
  • the ORF that encodes the selectable polypeptide is devoid of any AUG sequences.
  • the selectable polypeptide is CD52 or CD59.
  • the target polypeptide is a therapeutic agent. In some embodiments of any one of the methods provided, the target polypeptide is a secreted protein. In some embodiments of any one of the methods provided, the target polypeptide is an antibody or an Fc fusion protein.
  • the host cells are CHO cells, HEK293 cells, or HeLa cells.
  • aspects of the disclosure relate to a clonal population of transfected host cells that express a selectable polypeptide and a target polypeptide obtainable by any one of the methods described above or otherwise described herein.
  • FIG. 1A is a schematic depicting comparison between traditional transfection and selection and EPIC-based transfection and selection. Early expression refers to expression early after transfection, prior to significant genomic integration.
  • FIG. 1B is a diagram showing reporter expression of a transfected population of cells from day 3 to 21 in a nucleotide-deficient selection process (compared to mock transfected population). Transfected cells exhibited an apparent early expression shortly after transfection (e.g., day 3-4) and then transitioned to stable expression upon completion of selection (day 18-21).
  • FIG. 2 is a series of FACS histogram offsets depicting the early expression of both red fluorescent protein (RFP) and cell surface reporter CD52 expression from the same vector (pGZ729-RFP). No selection pressure was applied to the transfected cells. Peak early expression for RFP and CD52 occurs between days 2 and 3.
  • RFP red fluorescent protein
  • pGZ729-RFP cell surface reporter CD52
  • FIG. 3 is a series of FACS histogram offsets depicting the day 3 early expression of RFP and CD52 in cells transfected with pGZ729-RFP (encoding both selectable polypeptide CD52 and target polypeptide RFP) or pGZ700-RFP (encoding only target polypeptide RFP).
  • FIG. 4 is a schematic showing both the methodology of EPIC to generate a sub-population of cells for selection shortly after transfection and the beneficial effects to both the reporter expression and monoclonal antibody (mAb) titers upon isolation/expansion of the sort-enriched population.
  • Mock refers to mock transfection.
  • FIG. 5 is a graph depicting day 14 unfed batch titers for EPIC-generated pools as compared to traditional MTX methodologies. Pools generated by the rapid bulking process are also shown (RB#1 and RB#2).
  • FIG. 6 is a graph depicting day 14 unfed batch titers from EPIC-generated clones which achieved top expression ranging from 1.5-2.0 g/L. Leftmost bar (0.5 g/L) represents titer for EPIC-sorted pool prior to cloning. All other vertical bars represent titers for individual clones.
  • FIG. 7 is a series of histogram offsets depicting the comparative benefit of EPIC targeting to generate stable pools transfected with pGZ729-RFP.
  • EPIC was used to target early RFP expression at day 2 which yielded a stable pool with improved RFP (and CD52 reporter expression) as compared to traditional transfection/selection methodologies (0 nM MTX).
  • FIG. 8 is a schematic showing the 3 different methodologies for generating pools to support a clone limiting dilution (CLD) process. All methodologies use similar “pooled” recovering transfected cells to begin the process. EPIC and Rapid Bulking, which are both MTX-independent processes, also have reduced timelines compared to the traditional MTX selection process. This entire scheme was completed for each of three recombinant proteins (mAb #1, mAb #2, FcFusion #1).
  • FIG. 9 is a graph showing clonal productivity from three different molecules using from pools generated from each process shown in FIG. 8 (EPIC, Rapid Bulking, and MTX). The graph illustrates that both MTX-independent processes (EPIC and Rapid Bulking) achieved clones of similar high productivity to those produced from the MTX selection process.
  • FIG. 10 is a graph illustrating the timelines of each process from DNA to Pools and Pools to Clones for three different molecules representing each process (EPIC, Rapid Bulking, and MTX).
  • EPIC pool generations can be achieved much faster (1 month) than MTX generated pools which translates to significantly shorter overall timelines for production of clones.
  • FIG. 11A is FACS histogram overlay showing the variable sort targets of the transiently positive population which was isolated to generate an EPIC pool (compared to an unsorted control).
  • polynucleotide intends a polymeric form of nucleotides of any length, examples of which include, but are not limited to, a gene or gene fragment, exons, introns, messenger RNA (mRNA), transfer RNA, ribosomal RNA, ribozymes, complementary DNA (cDNA), recombinant polynucleotides, branched polynucleotides, plasmids, vectors, isolated DNA of any sequence, isolated RNA of any sequence, nucleic acid probes, and primers.
  • a polynucleotide may comprise modified nucleotides, such as methylated nucleotides and nucleotide analogs.
  • polypeptide intends a polymeric form of amino acids of any length, examples of which include, but are not limited to, a protein, a protein fragment, a multimeric protein, a fusion protein, an antibody (including fragments thereof), and a peptide.
  • a “selectable polypeptide” is a polypeptide that can be detected, directly or indirectly, by any suitable method including, for example and without limitation, fluorescence-activated cell sorting (FACS), magnetic-activated cell sorting (MACS), ClonePix, and affinity chromatography.
  • the selectable polypeptide is expressed on the surface of a cell, i.e., is a cell surface polypeptide.
  • selectable polypeptides include polypeptides that include an extracellular domain (e.g., CD52 or CD59) that are capable of being bound to or by a detectable binding partner (e.g., a fluorescently-labeled antibody).
  • selectable polypeptides include fluorescent proteins such as green fluorescent protein (GFP), red fluorescent protein (RFP), yellow fluorescent protein (YFP), blue fluorescent protein (BFP), and variants thereof including eGFP, Venus, mCherry, mTomato, and the like.
  • the selectable polypeptide may be conveniently detected, directly or indirectly, by flow cytometry.
  • FACS fluorescence-activated cell sorting
  • BD InfluxTM BD Biosciences
  • other equivalent cell sorters produced by other commercial vendors such as Sony, Bio-Rad, and Beckman Coulter.
  • a “FACS selectable polypeptide” is a polypeptide that can be detected, directly or indirectly, by flow cytometry.
  • FACS selectable polypeptides include polypeptides that include an extracellular domain (e.g., CD52 or CD59) that are capable of being bound to a detectable binding partner (e.g., a fluorescently-labeled antibody) for indirect detection of the polypeptide by flow cytometry.
  • FACS selectable polypeptides include fluorescent proteins such as green fluorescent protein (GFP), red fluorescent protein (RFP), yellow fluorescent protein (YFP), blue fluorescent protein (BFP), and variants thereof including eGFP, Venus, mCherry, mTomato, and the like, which may be detected directly by flow cytometry.
  • fluorescent proteins such as green fluorescent protein (GFP), red fluorescent protein (RFP), yellow fluorescent protein (YFP), blue fluorescent protein (BFP), and variants thereof including eGFP, Venus, mCherry, mTomato, and the like, which may be detected directly by flow cytometry.
  • magnetic-activated cell sorting refers to a method of separating a population of cells into one or more sub-populations based on the presence, absence, or level of one or more MACS-selectable polypeptides expressed by the cells.
  • MACS relies on magnetic susceptibility properties of tagged individual cells in order to sort the cells into sub-populations.
  • MACS cell sorters suitable for carrying out a method described herein are well-known in the art and commercially available. Exemplary MACS cell sorters include MACSQuant® flow cytometer (Miltenyi Biotec).
  • a “MACS selectable polypeptide” is a polypeptide that can be detected, directly or indirectly, by magnetic-activated cell sorting.
  • MACS selectable polypeptides include polypeptides that include an extracellular domain (e.g., CD52 or CD59) that are capable of being bound to a magnetically susceptible binding partner (e.g., an iron-, nickel-, or cobalt-labeled bead coupled to an antibody) for direct or indirect detection of the polypeptide.
  • the selectable polypeptide may be conveniently detected, directly or indirectly, by flow cytometry.
  • ClonePix refers to a method of, and device for, separating a population of cells into one or more sub-populations based on the presence, absence, or level of one or more selectable polypeptides expressed by the cells. ClonePix relies on optical properties, including white light and fluorescence detection, of individual cells or colonies of cells in order to sort the cells into sub-populations. ClonePix is described in U.S. Pat. Nos. 7,776,584; 8,034,612; 8,034,625; 8,293,520; 8,293,525; 8,293,526; and 8,293,527, each to Richmond et al., and is commercially available from Molecular Devices (Sunnyvale, Calif.).
  • target polypeptide refers to a protein, a protein fragment, a multimeric protein, a fusion protein, an antibody (including fragments thereof), or a peptide that can be produced in host cells and in the aspects exemplified herein, the target polypeptide is selected because of its potential as a therapeutic agent, e.g., an antibody (including a fragment thereof), a Fc fusion protein, a hormone or an enzyme.
  • the target polypeptide is a secreted protein.
  • the methods described herein are not limited for the selection and scale-up of therapeutic polypeptides.
  • diagnostic polypeptides or polypeptides for use in the environment are also contemplated for use as a target polypeptide in a method disclosed herein.
  • the selectable polypeptide is a cell surface polypeptide
  • the target polypeptide is a secreted polypeptide
  • antibody refers to such assemblies (e.g., intact antibody molecules, antibody fragments, or variants thereof) which have significant known specific immunoreactive activity to an antigen of interest.
  • Antibodies and immunoglobulins comprise light and heavy chains, with or without an interchain covalent linkage between them. Basic immunoglobulin structures in vertebrate systems are relatively well understood.
  • antibody includes entire antibodies as well as antigen-binding fragments and variants of such antibodies.
  • Antibodies may be of any class, such as IgG, IgA or IgM; and of any subclass, such as IgG1 or IgG4.
  • the antibody can be a polyclonal or a monoclonal antibody, or it can be fragments of the polyclonal or monoclonal antibody.
  • the antibody can be chimeric, humanized, totally human, bi-specific, or bi-functional. Any antigen-binding fragment or variant of an antibody is also contemplated, such as Fab, Fab′, F(ab′) 2 , single-chain variable regions (scFv) and variations of the same.
  • an “Fc fusion protein” refers to a protein comprising an immunoglobulin Fc domain that is linked, directly or indirectly, to a polypeptide, such as a protein or peptide.
  • the linked polypeptide can be any proteinaceous molecule of interest, such as a ligand, a receptor, or an antigenic peptide.
  • a producer cell refers to a cell expressing a polypeptide of interest.
  • a producer cell is a cell expressing a target polypeptide as disclosed herein.
  • a producer cell is a cell expressing both a selectable polypeptide and a target polypeptide as disclosed herein.
  • producer cells refers to cells that are suitable for production of proteins, e.g., in a small- or large-scale manufacturing method for producing biologics.
  • producer cells are mammalian or insect cells. Producer cells are further discussed herein.
  • a “population of producer cells” is a population of cells that expresses an enhanced level of one or more polypeptides, e.g., a FACS selectable polypeptide and a target polypeptide that are encoded by the same multicistronic mRNA.
  • a “population of producer cells” is a population of cells that expresses an enhanced level of a target polypeptide.
  • the enhanced level is at least 10-fold, at least 100-fold, at least 1,000-fold, or at least 10,000-fold of the one or more polypeptides in an unselected population.
  • the enhanced level is at least 10-fold, at least 100-fold, at least 1,000-fold, or at least 10,000-fold of a FACS-selectable polypeptide in an unselected population as detected by flow cytometry (e.g., on a BD InfluxTM cell sorter). In some embodiments, the enhanced level is at least 10-fold, at least 100-fold, at least 1,000-fold, or at least 10,000-fold of a MACS-selectable polypeptide in an unselected population as detected by flow cytometry (e.g., on a MACSQuant® flow cytometer (Miltenyi Biotec)). Methods for generating populations of producer cells are described herein.
  • a “population of producer cells” is a population of cells that expresses detectable levels of one or more polypeptides, e.g., a FACS selectable polypeptide and a target polypeptide that are encoded by the same multicistronic mRNA. Methods for generating populations of producer cells are described herein.
  • a “multicistronic mRNA” is an mRNA that contains at least two open reading frames (ORFs) that are capable of encoding two or more polypeptides.
  • a “drug-selection-free medium” is a culture medium that is devoid of a drug (e.g., methotrexate (MTX)) that is used to select a population or sub-populations of cells that express a protein that confers drug resistance (e.g., dihydrofolate reductase) to the population or sub-population.
  • a drug e.g., methotrexate (MTX)
  • MTX methotrexate
  • medium-based selection is a selection process by which the culture medium is altered to include a selection agent (e.g., MTX) or to exclude a component of medium, which results in selection of a sub-population that is resistant to the selection agent or can survive in the absence of the excluded medium component.
  • a selection agent e.g., MTX
  • nucleotide-deficient medium is culture medium that is devoid of or contains low levels (e.g., less than 10 micrograms/mL) of nucleotides having one or more of the nucleobases adenine (A), cytosine (C), guanine (G), thymine (T), hypoxanthine, or thymidine.
  • nucleotide-deficient medium is medium that is devoid of hypoxanthine and thymidine.
  • Exemplary nucleotide-deficient medium includes CD CHO Medium (Gibco, Life Technologies, Catalogue numbers 10743 (liquid) and 12490 (granulated)).
  • viability marker is a cell characteristic that is indicative of cell viability and is detectable by FACS.
  • exemplary viability markers include forward scatter, side scatter, propidium iodide stain, or combinations thereof.
  • non-AUG start codon is intended to include any non-AUG polynucleotide (typically a triplet) that functions as a start site for translation initiation with reduced efficiency relative to that of an AUG start codon.
  • Naturally occurring alternate start codon usage is known in the art and described for example in Kozak (1991) J. Cell Biol. 115(4): 887-903; Mehdi et al. (1990) Gene 91:173-178; Kozak (1989) Mol. Cell. Biol. 9(11): 5073-5080.
  • non-AUG start codons have decreased translation efficiencies compared to that of an AUG; for example, the alternate start codon GUG may have 3-5% translation efficiency compared to that of an AUG (100%).
  • the translation efficiency of a non-AUG start codon can also be affected by its sequence context; for example, an optimal Kozak consensus sequence is reported to have a positive effect on translation initiation at non-AUG start codons (Mehdi et al. (1990) Gene 91:173-178; Kozak (1989) Mol. Cell. Biol. 9(11): 5073-5080).
  • the complete Kozak DNA consensus sequence is GCCRCCATGG (SEQ ID NO:1), where the start codon ATG (AUG in RNA) is bold, the A of the ATG start codon is designated as the +1 position, and “R” at position ⁇ 3 is a purine (A or G).
  • the two most highly conserved positions are a purine, preferably an A, at ⁇ 3 and a G at +4 (Kozak (1991) J Cell Biol 115(4): 887-903).
  • Alternate start codon usage is described for attenuated expression of a selectable marker in U.S. Patent Publication 2006/0172382 and U.S. Patent Publication 2006/0141577, the entire contents of which are incorporated herein by reference.
  • One of skill in the art will recognize that the sequences described herein as DNA will have correlative sequences as RNA molecules, e.g., DNA sequence ATG would correspond to RNA sequence AUG, and vice versa.
  • the terms “rapid bulk sorting” and “rapid bulking” refer to methods of fluorescence-activated cell sorting (FACS) to batch select producer cells expressing a target polypeptide.
  • the methods comprise the steps of (a) providing a heterogeneous population of producer cells, wherein the producer cells in the population express varying levels of a FACS selectable polypeptide and a target polypeptide that are encoded by the same multicistronic mRNA; (b) selecting from the heterogeneous population of producer cells a first heterogeneous sub-population of producer cells using FACS, wherein the producer cells in the first heterogeneous sub-population express the FACS selectable polypeptide at a level that is higher than the level of at least 80% of the producer cells in the heterogeneous population in (a); and (c) expanding the first heterogeneous sub-population of producer cells in drug-selection-free medium, thereby producing an expanded first heterogeneous sub-population of producer cells.
  • FACS flu
  • the rapid bulking method may further comprise the steps of (d) selecting from the expanded first heterogeneous sub-population of producer cells in step (c) a second heterogeneous sub-population of producer cells using FACS, wherein the producer cells in the second sub-population express the FACS selectable polypeptide at a level that is higher than the level of at least 80% of the producer cells in the expanded first heterogeneous sub-population of producer cells in step (c); and (e) expanding the second heterogeneous sub-population of producer cells in a drug-selection-free medium, thereby producing an expanded second heterogeneous sub-population of producer cells.
  • EPIC Early Post-transfection Isolation of Cells, as described in more detail herein.
  • FLARE refers to “FLow cytometry Attenuated Reporter Expression.” FLARE is an expression system utilizing a multicistronic mRNA that contains at least two open reading frames (ORFs), an upstream ORF containing a non-AUG start codon and encoding a FACS selectable polypeptide, and a downstream ORF containing an AUG start codon and encoding a target polypeptide. See US Patent Application Publication No. 2009/0239235 which is incorporated by reference herein in its entirety.
  • the term “about” shall refer to a range of tolerance of 10% around a stated value. Therefore, when the term “about” is used to modify a stated value, the range indicated will encompass any number within ⁇ 0.01%, 0.02%, 0.05%, 0.1%, 0.2%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10% of the stated value.
  • the disclosure relates to a method of producing a population of producer cells expressing a target polypeptide.
  • the method comprises:
  • Early-expressing transfected cells can comprise different classes of exogenous DNA, part of which has not integrated into the cells' genomic DNA, and part of which has integrated into the cells' genomic DNA. Both these types of DNA have the potential to lead to expression of the polypeptide or polypeptides they encode.
  • Host cells are transfected with one or more vectors that encode one or more mRNAs, wherein the one or more mRNAs encode a selectable polypeptide and the target polypeptide.
  • a producer cell can be generated using any cell type suitable for production of a target polypeptide from a multicistronic mRNA.
  • the host cell is a eukaryotic cell.
  • Suitable eukaryotic cells to produce a target polypeptide include, but are not limited to, a Chinese Hamster Ovary (CHO) cell line, including those designated CHO-DBX11, CHO-DG44, CHO-S, CHO-Ki, and the hamster cell line BHK-21; the murine cell lines designated NIH3T3, NS0, C127, the simian cell lines COS, Vero; and the human cell lines HeLa, HEK293 (also called 293), NIH-3T3, U-937 and Hep G2.
  • CHO Chinese Hamster Ovary
  • suitable host cells include yeast cells, insect cells (e.g., Drosophila Schneider S2 cells, Sf9 insect cells (WO 94/26087), BTI-TN-5B1-4 (High FiveTM) insect cells (Invitrogen)), plant cells, avian cells, and bovine cells.
  • yeast useful for expression include, but are not limited to Saccharomyces, Schizosaccharomyces, Hansenula, Candida, Torulopsis, Yarrowia, and Pichia. See e.g., U.S. Pat. Nos. 4,812,405; 4,818,700; 4,929,555; 5,736,383; 5,955,349; 5,888,768 and 6,258,559.
  • producer cells can be prokaryotic, including bacterial cells such as E. coli (e.g., strain DH5 ⁇ TM) (Invitrogen, Carlsbad, Calif.), PerC6 (Crucell, Leiden, NL), B. subtilis and/or other suitable bacteria.
  • E. coli e.g., strain DH5 ⁇ TM
  • PerC6 Cell, Leiden, NL
  • B. subtilis Bacillus subtilis
  • the cells can be purchased from a commercial vendor such as the American Type Culture Collection (ATCC, Rockville, Md.) or cultured from an isolate using methods known in the art.
  • Vectors that encode one or more mRNAs include DNA vectors.
  • Vectors that may be used include plasmids, viruses, phage, transposons, and minichromosomes of which plasmids are a typical embodiment.
  • Such vectors further include a signal sequence, origin of replication, one or more marker genes, a promoter and transcription termination sequences operably linked to the gene encoding the multicistronic mRNA so as to facilitate expression.
  • DNA viral vectors examples include adenovirus (Ad) and adeno-associated virus (AAV).
  • Ads adenovirus-based vectors for the delivery of polynucleotides are known in the art and may be obtained commercially or constructed by standard molecular biological methods.
  • Adenoviruses (Ads) are a group of viruses, including over 50 serotypes. See, e.g., International Patent Application No. WO 95/27071.
  • Other viral vectors for use in the present disclosure include vectors derived from vaccinia, herpesvirus (e.g., herpes simplex virus (HSV)), and retroviruses.
  • Gene delivery vehicles also include several non-viral vectors, including DNA/liposome complexes, and targeted viral protein-DNA complexes.
  • circular vectors may be pre-linearized, i.e., linearized prior to introduction into the host cell, for example by restriction at one or more restriction endonuclease sites. Linearization is believed to be necessary for integration into the genome, and this can be effected by pre-linearization or in a random fashion by endonucleases naturally present within the host cell. Pre-linearization has the potential advantage of introducing a degree of control into the site of restriction.
  • circular vectors, including supercoiled circular vectors may be introduced into the host cell.
  • the one or more vectors are linear at the time of transfection.
  • Vectors that contain both a promoter and a cloning site into which a polynucleotide can be operatively linked are known in the art and available from commercial vendors. Such vectors are capable of transcribing RNA in vitro or in vivo, and are commercially available from sources such as Agilent Technologies and Promega Corporation. In order to optimize expression and/or in vitro transcription, it may be necessary to remove, add or alter 5′ and/or 3′ untranslated portions to eliminate extra, potentially inappropriate alternative translation initiation codons or other sequences that may interfere with or reduce expression, either at the level of transcription or translation. Alternatively, consensus ribosome binding sites can be inserted immediately 5′ of the start codon to enhance expression.
  • a promoter can be provided for expression in the producer cell. Promoters can be constitutive or inducible. For example, a promoter can be operably linked to a nucleic acid encoding a multicistronic mRNA such that it directs expression of the encoded polypeptides.
  • a variety of suitable promoters for prokaryotic and eukaryotic hosts are available. Prokaryotic promoters include lac, tac, T3, T7 promoters for E.
  • 3-phosphoglycerate kinase or other glycolytic enzymes e.g., enolase, glyceraldehyde 3-phosphate dehydrogenase, hexokinase, pyruvate decarboxylase, phosphofructokinase, glucose 6 phosphate isomerase, 3-phosphoglycerate mutase, and glucokinase.
  • Eukaryotic promoters include inducible yeast promoters such as alcohol dehydrogenase 2, isocytochrome C, acid phosphatase, metallothionein, and enzymes responsible for nitrogen metabolism or maltose/galactose utilization; RNA polymerase II promoters including viral promoters such as polyoma, fowlpox and adenoviruses (e.g., adenovirus 2), bovine papilloma virus, avian sarcoma virus, cytomegalovirus (CMV, in particular, the immediate early gene promoter), retrovirus, hepatitis B virus, actin, Rous sarcoma virus (RSV) promoter, and the early or late Simian virus 40 (SV40) and non-viral promoters such as EF-1 alpha (Mizushima and Nagata (1990) Nucleic Acids Res. 18(17):5322). Those of skill in the art will be able to select
  • enhancer elements can be included instead of or as well as those found located in the promoters described above.
  • suitable mammalian enhancer sequences include enhancer elements from globin, elastase, albumin, fetoprotein, metallothionein, and insulin.
  • an enhancer element from a eukaryotic cell virus such as SV40 enhancer, cytomegalovirus early promoter enhancer, polyoma enhancer, baculoviral enhancer or murine IgG2a locus (see, WO 2004/009823).
  • enhancers are often located on the vector at a site upstream to the promoter, they can also be located elsewhere, e.g., within the untranslated region or downstream of the polyadenylation signal.
  • the choice and positioning of enhancer may be based upon compatibility with the host cell used for expression.
  • the vectors may comprise a selectable marker for selection of host cells carrying the vector, and, in the case of a replicable vector, an origin of replication.
  • Genes encoding products which confer antibiotic or drug resistance are common selectable markers and may be used in prokaryotic (e.g., f3-lactamase gene (ampicillin resistance), tet gene (tetracycline resistance) and eukaryotic cells (e.g., neomycin (G418 or geneticin), gpt (mycophenolic acid), ampicillin, or hygromycin B resistance genes).
  • the dihydrofolate reductase (DHFR) gene permits selection with methotrexate or nucleotide-deficient medium in a variety of hosts.
  • the glutamine synthetase (GS) gene permits selection with methionine sulphoximine.
  • Genes encoding the gene product of auxotrophic markers of the host e.g., LEU2, URA3, HIS3 are often used as selectable markers in yeast.
  • Use of viral (e.g., baculovirus) or phage vectors, and vectors which are capable of integrating into the genome of the host cell, such as retroviral vectors, are also contemplated.
  • polyadenylation and termination signals may be operably linked to a polynucleotide encoding the multicistronic mRNA as described herein. Such signals are typically placed 3′ of an open reading frame.
  • polyadenylation/termination signals include those derived from growth hormones, elongation factor-1 alpha and viral (e.g., SV40) genes or retroviral long terminal repeats.
  • polyadenylation/termination signals include those derived from the phosphoglycerate kinase (PGK) and the alcohol dehydrogenase 1 (ADH) genes.
  • PGK phosphoglycerate kinase
  • ADH alcohol dehydrogenase 1
  • polyadenylation signals are typically not required and it is instead usual to employ shorter and more defined terminator sequences.
  • the choice of polyadenylation/termination sequences may be based upon compatibility with the host cell used for expression.
  • other features that can be employed to enhance yields include chromatin remodeling elements, introns and host cell specific codon modification.
  • the producer cells of the disclosure contain a recombinant polynucleotide (e.g., a recombinant cDNA) that encodes a multicistronic mRNA molecule from which the target and selectable polypeptides are separately translated from different ORFs.
  • the selectable polypeptide is a cell surface polypeptide.
  • the producer cells of the disclosure contain a plurality of recombinant polynucleotides, each of which encodes a multicistronic mRNA molecule from which a target polypeptide and a selectable polypeptide are separately translated from different ORFs. Each target polypeptide can thus be associated with a particular selectable polypeptide.
  • the selectable polypeptide is a cell surface polypeptide.
  • cell surface polypeptides include, but are not limited to CD2, CD20, CD52, and CD59.
  • Exemplary, non-limiting, amino acid sequences for CD52 and CD59 cell surface polypeptides are provided below.
  • a first ORF which encodes a selectable polypeptide, such as CD52 or CD59.
  • a selectable polypeptide such as CD52 or CD59.
  • Exemplary, non-limiting ORF sequences for CD52 and CD59 are provided below.
  • a second ORF which encodes a target polypeptide, such as an antibody, enzyme, or Fc fusion protein.
  • a target polypeptide such as an antibody, enzyme, or Fc fusion protein.
  • separate translation is accomplished by use of a non-AUG start codon for translation initiation of the selectable polypeptide and the use of an AUG start codon for translation initiation of the target polypeptide.
  • the polynucleotide encoding the target polypeptide is located downstream of the polynucleotide encoding the selectable polypeptide.
  • Separate translation can also be achieved using an internal ribosome entry site (IRES).
  • the IRES element is located upstream of the polynucleotide encoding the target polypeptide and downstream of the polynucleotide encoding the selectable polypeptide. In some embodiments, the IRES element is located upstream of the polynucleotide encoding the selectable polypeptide and downstream of the polynucleotide encoding the target polypeptide.
  • a non-AUG start codon is located within the DNA encoding the selectable polypeptide in such a way that translation of the selectable polypeptide is less efficient than translation of the target polypeptide.
  • the AUG start codon of the selectable polypeptide may be changed to an alternate non-AUG start codon, examples of which include but are not limited to: CUG, GUG, UUG, AUU, AUA, and ACG.
  • a selectable polypeptide when using an alternate non-AUG start codon, expression of a selectable polypeptide can be attenuated relative to that of a co-expressed target polypeptide.
  • the DNA encoding the selectable polypeptide may be modified at all internal ATG triplets to prevent internal initiation of translation.
  • the selectable polypeptide has a short amino acid sequence ( ⁇ 200 amino acids) and is encoded by a polynucleotide with few ( ⁇ 10) ATG triplets.
  • ribosomes begin scanning at the 5′ cap structure of the mRNA with the majority scanning past the alternate start codon (for example, UUG) and instead initiating translation at the downstream AUG start codon.
  • alternate start codon for example, UUG
  • translation initiation can occur at the alternate start codon, albeit with very low frequency, so that a low level of the selectable polypeptide is also expressed.
  • transfected host cells From the transfected host cells is selected a sub-population of early-expressing transfected host cells which express detectable levels of the selectable polypeptide.
  • individual host cells take up different amounts of exogenous polynucleotide, e.g., DNA, in an essentially random manner. Some cells will take up many copies of the exogenous polynucleotide, others will take up fewer copies, and some will take up none.
  • the amount of DNA taken up into a given cell affects the fate of the DNA, including its early expression and its integration into the genome.
  • the polynucleotide that has been introduced into the cell is translocated into the nucleus where it is transcribed into mRNA.
  • expression of the introduced DNA may be driven off one or more classes of DNA, some of which has not yet been integrated into the genome of the host cell, and some of which has been integrated into the genome of the host cell.
  • the extent of expression is believed to be principally proportional to the “dose” of DNA introduced into the host cell and its nucleus. The greater the amount of exogenous DNA taken up by the host cell the greater the degree of early expression.
  • a small amount of DNA that has been introduced into the host cell particularly once it is linear, can become integrated into the genome of the host cell.
  • the first 2 to about 15 days there are early-expressing transfected host cells which express detectable amounts of the selectable polypeptide.
  • this early expression is believed to be largely, but not necessarily exclusively, driven off exogenous DNA that has not yet been integrated into the genome of the host cell.
  • this early period following transfection there may be some degree of integration of exogenous DNA into the host cell genome.
  • transfected host cells include sub-populations of cells expressing different amounts of polypeptide encoded by the exogenous DNA. Also during this early period the sub-populations of cells expressing greater amounts of polypeptide encoded by the exogenous DNA presumably took up greater amounts of exogenous DNA and therefore have a greater chance of incorporating the DNA into their genome.
  • the term “early-expressing” or “early expression”, as used herein, refers to detectable expression in the first 2 to about 15 days (e.g., 2-15 days, 2-14 days, 2-13 days, 2-12 days, 2-11 days, 2-10 days, 2-9 days, 2-8 days, 2-7 days, 2-6 days, 2-5 days, 2-4 days, 2-3 days, 3-15 days, 3-14 days, 3-13 days, 3-12 days, 3-11 days, 3-10 days, 3-9 days, 3-8 days, 3-7 days, 3-6 days, 3-5 days, 3-4 days, 4-15 days, 4-14 days, 4-13 days, 4-12 days, 4-11 days, 4-10 days, 4-9 days, 4-8 days, 4-7 days, 4-6 days, 4-5 days, 5-15 days, 5-14 days, 5-13 days, 5-12 days, 5-11 days, 5-10 days, 5-9 days, 5-8 days, 5-7 days, 5-6 days, 6-15 days, 6-14 days, 6-13 days, 6-12 days, 6-11 days, 6-10 days, 6-9 days, 6-8
  • the term “early-expressing” or “early expression” refers to detectable expression in the first 2 to about 10 days following transfection. In certain embodiments, the term “early-expressing” or “early expression” refers to detectable expression in the first 2 to about 6 days following transfection. In certain embodiments, the term “early-expressing” or “early expression” refers to detectable expression in the first 2 to about 5 days following transfection. In certain embodiments, the term “early-expressing” or “early expression” refers to detectable expression in the first 2 to about 4 days following transfection. In certain embodiments, the term “early-expressing” or “early expression” refers to detectable expression in the first 2 to about 3 days following transfection.
  • an antibody or other cell surface marker-specific binding agent is contacted directly or indirectly with the transfected host cells under conditions that permit or favor binding of antibody to the selectable polypeptide and thereby select a sub-population of early-expressing transfected host cells.
  • the selection of the antibody or other binding agent is determined by: 1) its ability to selectively bind the selectable polypeptide that is expressed on the host cell; and 2) its ability to be labeled with a detectable label or bind to a detectable label, for example, for use in flow cytometry or FACS.
  • a first agent can be a protein or peptide that binds to the selectable polypeptide, which first agent also in turn binds to a second agent that is capable of being detectably labeled (e.g., incorporating a fluorescent, enzymatic, colorimetric, magnetically susceptible, or other detectable label).
  • a second agent that is capable of being detectably labeled (e.g., incorporating a fluorescent, enzymatic, colorimetric, magnetically susceptible, or other detectable label).
  • the antibody or other binding agent binds directly to the cell surface marker and comprises a fluorescent label.
  • fluorescent labels include, but are not limited to, fluorescein isothiocyanate (FITC), rhodamine, tetramethylrhodamine, eosin, phycoerythrin (PE), erythrosin, allophycocyanin (APE), coumarin, methyl-coumarins, pyrene, Malachite green, stilbene, Lucifer Yellow, Cascade Blue, and Texas Red.
  • FITC fluorescein isothiocyanate
  • PE phycoerythrin
  • APE erythrosin
  • coumarin methyl-coumarins
  • pyrene Malachite green
  • stilbene Lucifer Yellow
  • Lucifer Yellow Cascade Blue
  • Texas Red Texas Red
  • the fluorescent label is functionalized to facilitate covalent attachment to the antibody or other agent.
  • Suitable functional groups include, but are not limited to, isothiocyanate groups, amino groups, haloacetyl groups, maleimides, succinimidyl esters, and sulfonyl halides, all of which may be used to attach the fluorescent label to a second molecule.
  • the choice of the functional group of the fluorescent label will depend on the site of attachment to the antibody or other binding agent, the selectable polypeptide, or the second labeling agent.
  • Attachment of the fluorescent label may be either direct or via a linker to the antibody or other binding agent.
  • the linker is a relatively short coupling moiety that generally is used to attach molecules.
  • attachment of the first labeling moiety to the candidate agents will be done as is generally appreciated by those in the art, and may include techniques outlined above for the incorporation of fluorescent labels.
  • Suitable binding pairs for use in indirectly linking the label to the agent include, but are not limited to, antigens/antibodies, including digoxigenin/antibody, dinitrophenol (DNP)/anti-DNP, dansyl-X/anti-dansyl, fluorescein/anti-fluorescein, lucifer yellow/anti-lucifer yellow, rhodamine/anti-rhodamine; and biotin/avidin (or biotin/streptavidin).
  • the binding pairs should have high affinities for each other, sufficient to withstand the shear forces during cell sorting or other detection system used in connection with the disclosure.
  • first labeling moieties include, but are not limited to, haptens such as biotin.
  • Biotinylation of target molecules is well known, for example, a large number of biotinylation agents are known, including amine-reactive and thiol-reactive agents, for the biotinylation of proteins, nucleic acids, carbohydrates, and carboxylic acids.
  • haptens such as biotin.
  • Biotinylation of target molecules is well known, for example, a large number of biotinylation agents are known, including amine-reactive and thiol-reactive agents, for the biotinylation of proteins, nucleic acids, carbohydrates, and carboxylic acids.
  • haptenylation reagents are also known.
  • the antibodies used in a method described herein can be produced in cell culture, in phage, or in various animals, including but not limited to mice, rats, hamsters, guinea pigs, rabbits, sheep, goats, horses, cows, camelids, monkeys, chimpanzees, etc., so long as the antibodies retain specificity of binding for the selectable polypeptide.
  • Antibodies can be tested for specificity of binding by comparing binding to appropriate antigen to binding to irrelevant antigen or antigen mixture under a given set of conditions.
  • the antibody or binding agent for the selectable polypeptide preferably also contains and retains the ability to bind a secondary agent which is detectable after binding to the cell via the selectable polypeptide.
  • the selectable polypeptide when the selectable polypeptide is CD52, the selectable polypeptide may be detected using an anti-CD52 antibody.
  • Anti-CD52 antibody refers to an antibody that specifically recognizes and binds CD52. Anti-CD52 antibodies can be generated by methods well known in the art. See for example, Current Protocols in Molecular Biology (F. M. Ausubel, et al. eds., 1987 to present versions) and Antibodies: A Laboratory Manual, Second edition (Greenfield, ed. 2013). Additionally, several anti-CD52 antibodies are commercially available (e.g., antibodies conjugated to a fluorescent label, such as those sold by the commercial vendors AbCam, SeroTec, and BioLegend).
  • the selectable polypeptide when the selectable polypeptide is CD59, the selectable polypeptide may be detected using an anti-CD59 antibody.
  • Anti-CD59 antibody refers to an antibody that specifically recognizes and binds CD59. Anti-CD59 antibodies can be generated by methods well known in the art. Additionally, several anti-CD59 antibodies are commercially available (e.g., antibodies conjugated to a fluorescent label, such as those sold by the commercial vendors AbCam, SeroTec, and BioLegend).
  • the selectable polypeptide when the selectable polypeptide is CD20, the selectable polypeptide may be detected using an anti-CD20 antibody.
  • Anti-CD20 antibody refers to an antibody that specifically recognizes and binds CD20. Anti-CD20 antibodies can be generated by methods well known in the art. Additionally, several anti-CD20 antibodies are commercially available from vendors such as BD Pharmingen; Beckman Coulter, Inc. (Fullerton, Calif., numerous clones including Catalog No. 6604106 Clone H299 (B1); Isotype IgG2a and Catalog No.
  • a labeled or unlabeled primary antibody or other binding agent e.g., Fc fusion protein
  • Fc fusion protein e.g., Fc fusion protein
  • Miltenyi Biotec sells CD20 microbeads and anti-mouse IgG microbeads, but neither CD52 nor CD59 microbeads; anti-mouse IgG microbeads could be used to label primary mouse IgG anti-human CD52 or mouse IgG anti-human CD59.
  • a population of transfected host cells as described herein is contacted with an agent that recognizes and directly or indirectly binds the selectable polypeptide, if present, on the surface of the cells.
  • the contacting is performed under conditions that favor or are suitable for specific binding (directly or indirectly) of the agent or antibody with the selectable polypeptide.
  • the cells that are bound to the agent or antibody are then selected for using a suitable method such as FACS (e.g., by gating for cells that express the FACS-selectable polypeptide at a high level such as a level that is at least 80% of the level of the population) and used to select a sub-population of early-expressing transfected host cells.
  • the cells that are bound to the agent or antibody are then selected for using a suitable method such as MACS (e.g., by gating for cells that express the MACS-selectable polypeptide at a high level such as a level that is at least 80% of the level of the population) and used to select a sub-population of early-expressing transfected host cells.
  • a suitable method such as MACS (e.g., by gating for cells that express the MACS-selectable polypeptide at a high level such as a level that is at least 80% of the level of the population) and used to select a sub-population of early-expressing transfected host cells.
  • the selected sub-population of early-expressing transfected host cells is then grown under conditions that result in expansion of the sub-population to produce a population of producer cells expressing the target polypeptide.
  • the step of isolating from the transfected host cells, within 2 to 15 days of transfection, a sub-population of early-expressing transfected host cells which express the selectable polypeptide is performed in drug-selection-free medium.
  • the step of isolating from the transfected host cells, within 2 to 15 days of transfection, a sub-population of early-expressing transfected host cells which express the selectable polypeptide is performed in 0 nM MTX (i.e., MTX-free) medium.
  • the step of expanding the selected sub-population of transfected host cells is performed in drug-selection-free medium.
  • the step of expanding the selected sub-population of transfected host cells is performed in 0 nM MTX (i.e., MTX-free) medium.
  • both the step of (b) isolating from the transfected host cells, within 2 to 15 days of transfection, a sub-population of early-expressing transfected host cells which express the selectable polypeptide, and the step of (c) expanding the isolated sub-population of transfected host cells are performed in drug-selection-free medium.
  • both the step of (b) isolating from the transfected host cells, within 2 to 15 days of transfection, a sub-population of early-expressing transfected host cells which express the selectable polypeptide, and the step of (c) expanding the isolated sub-population of transfected host cells are performed in 0 nM MTX (i.e., MTX-free) medium.
  • Cells including producer cells, may be cultured in spinner flasks, shake flasks, roller bottles, wave reactors (e.g., System 1000 from wavebiotech.com) or hollow fiber systems, or for large scale production, stirred tank reactors or bag reactors (e.g., Wave Biotech, Somerset, N.J. USA) are used particularly for suspension cultures.
  • Stirred tank reactors can be adapted for aeration using e.g., spargers, baffles or low shear impellers. For bubble columns and airlift reactors, direct aeration with air or oxygen bubbles may be used.
  • the medium can be supplemented with a cell protective agent such as poloxamer 188 (Pluronic® F-68) to help prevent cell damage as a result of the aeration process.
  • a cell protective agent such as poloxamer 188 (Pluronic® F-68) to help prevent cell damage as a result of the aeration process.
  • microcarriers may be used as growth substrates for anchorage-dependent cell lines, or the cells may be adapted to suspension culture.
  • the culturing of host cells, particularly vertebrate host cells may utilize a variety of operational modes such as batch, fed-batch, repeated batch processing (see, Drapeau et al. (1994) Cytotechnology 15:103-109), extended batch process or perfusion culture.
  • recombinantly transformed producer cells may be cultured in serum-containing media such media comprising fetal calf serum (FCS), in some embodiments, such host cells are cultured in serum-free media such as disclosed in Keen et al. (1995) Cytotechnology 17:153-163, or commercially available media such as ProCHO-CDM or UltraCHOTM (Cambrex, N.J., USA), supplemented where necessary with an energy source such as glucose and synthetic growth factors such as recombinant insulin.
  • FCS fetal calf serum
  • serum-free media such as disclosed in Keen et al. (1995) Cytotechnology 17:153-163, or commercially available media such as ProCHO-CDM or UltraCHOTM (Cambrex, N.J., USA), supplemented where necessary with an energy source such as glucose and synthetic growth factors such as recombinant insulin.
  • the serum-free culturing of host cells may require that those cells are adapted to grow in serum-free conditions.
  • One adaptation approach is to culture such host cells in serum containing media and repeatedly exchange 80% of the culture medium for the serum-free media so that the host cells adapt to serum-free conditions (see, e.g., Scharfenberg, K. et al. (1995) In: Animal Cell Technology: Developments Towards the 21 st Century (Beuvery, E. C. et al., eds), pp.619-623, Kluwer Academic publishers).
  • the method further comprises isolating the target polypeptide from the population of producer cells.
  • the target polypeptide can be isolated using any method known in the art and may be further purified, e.g., according to Current Good Manufacturing Practice (CGMP) for recombinant proteins and antibodies, to a purity level of at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, at least 99.5%, or more.
  • CGMP Current Good Manufacturing Practice
  • a target polypeptide according to the described embodiments may be secreted into the medium and recovered and purified therefrom using any of a variety of techniques to provide a degree of purification suitable for the intended use.
  • a target polypeptide e.g., an antibody or Fc fusion protein
  • the use of a target polypeptide for the treatment of human subjects typically mandates at least 95% purity as determined by reducing SDS-PAGE, more typically 98% or 99% purity, when compared to the culture media comprising the target polypeptide.
  • cell debris from the culture media can be removed using centrifugation followed by a clarification step of the supernatant using e.g., microfiltration, ultrafiltration and/or depth filtration.
  • a target polypeptide can be harvested by microfiltration, ultrafiltration or depth filtration without prior centrifugation.
  • HA hydroxyapatite
  • affinity chromatography optionally involving an affinity tagging system such as polyhistidine
  • HIC hydrophobic interaction chromatography
  • a target polypeptide such as an antibody or Fc fusion protein, following various clarification steps, is captured using Protein A or G affinity chromatography followed by further chromatography steps such as ion exchange and/or HA chromatography, anion or cation exchange, size exclusion chromatography and ammonium sulphate precipitation.
  • virus removal steps may also be employed (e.g., nanofiltration using, e.g., a DV-20 filter). Following these various steps, a purified preparation comprising at least 10 mg/mL or greater, e.g., 100 mg/mL or greater of the target polypeptide described herein is provided.
  • the methods of the invention further include the step of isolating one or more single transfected host cells from the expanded sub-population and culturing the one or more single transfected host cells to produce clonal populations of the one or more single transfected host cells.
  • the methods of the invention further include the step of isolating one or more single transfected host cells from the expanded sub-population and culturing the one or more single transfected host cells to produce one or more clonal populations of producer cells expressing the target polypeptide. Preparation of a clonal population can be performed by any method known in the art.
  • the selected cells may be plated into 96-well (or other size) plates at a density of one cell per well and permitted to grow for a period of time (e.g., typically 7-28 days) which permits the single cell to grow into a multi-cell colony of daughter cells (i.e., a clonal population).
  • the method may next comprise analyzing one or more of the clonal populations by detecting the level of the selectable polypeptide and/or target polypeptide expression on said clonal population and selecting one or more clonal populations with a high expression level of the selectable polypeptide and/or target polypeptide, thereby selecting one or more clonal populations stably expressing the target polypeptide.
  • the clonal population is cultured for 7-28 days after plating at a single cell density before the clonal populations are analyzed.
  • the method may further include contacting the clonal population with a detectable antibody or other binding agent that recognizes and directly or indirectly binds the selectable polypeptide, if present, on the surface of the clonal cell under conditions that permit or favor binding of the antibody or other binding agent with the selectable polypeptide; and selecting or detecting one or more cells that are directly or indirectly bound to the antibody or other binding agent. These cells so selected also can be isolated and cultured.
  • the method may further include analyzing target polypeptide expression of the one or more clones, e.g., using protein A screening (such as when the target polypeptide is an antibody or Fc fusion protein), Western blot, SDS polyacrylamide gel electrophoresis (PAGE) with Coomassie Blue or silver stain, or an enzyme activity assay.
  • protein A screening such as when the target polypeptide is an antibody or Fc fusion protein
  • Western blot such as when the target polypeptide is an antibody or Fc fusion protein
  • SDS polyacrylamide gel electrophoresis PAGE
  • Coomassie Blue Coomassie Blue
  • silver stain or an enzyme activity assay.
  • the sub-population of transfected host cells subject to isolation in step (b) comprises at least 80-120 ⁇ 10 6 cells.
  • the sub-population of transfected host cells subject to isolation in step (b) comprises at least about 80 ⁇ 10 6 cells; in certain embodiments, the sub-population of transfected host cells subject to isolation in step (b) comprises at least about 90 ⁇ 10 6 cells; in certain embodiments, the sub-population of transfected host cells subject to isolation in step (b) comprises at least about 100 ⁇ 10 6 cells; in certain embodiments, the sub-population of transfected host cells subject to isolation in step (b) comprises at least about 110 ⁇ 10 6 cells; and in certain embodiments, the sub-population of transfected host cells subject to isolation in step (b) comprises at least about 120 ⁇ 10 6 cells.
  • the sub-population of transfected host cells subject to isolation in step (b) comprises about 80 ⁇ 10 6 to about 800 ⁇ 10 6 cells, about 100 ⁇ 10 6 to about 800 ⁇ 10 6 cells, about 200 ⁇ 10 6 to about 800 ⁇ 10 6 cells, about 300 ⁇ 10 6 to about 800 ⁇ 10 6 cells, about 400 ⁇ 10 6 to about 800 ⁇ 10 6 cells, about 500 ⁇ 10 6 to about 800 ⁇ 10 6 cells, about 80 ⁇ 10 6 to about 600 ⁇ 10 6 cells, about 100 ⁇ 10 6 to about 600 ⁇ 10 6 cells, about 200 ⁇ 10 6 to about 600 ⁇ 10 6 cells, about 300 ⁇ 10 6 to about 600 ⁇ 10 6 cells, about 400 ⁇ 10 6 to about 600 ⁇ 10 6 cells, about 500 ⁇ 10 6 to about 600 ⁇ 10 6 cells, about 80 ⁇ 10 6 to about 500 ⁇ 10 6 cells, about 100 ⁇ 10 6 to about 500 ⁇ 10 6 cells, about 200 ⁇ 10 6 to about 500 ⁇ 10 6 cells, about 300 ⁇ 10 6 to about 500 ⁇ 10 6 cells, about 400 ⁇ 10 6 to about 500 ⁇ 10 6 cells, about 80 ⁇ 10 6 to about 500 ⁇ 10 6 cells,
  • the isolation in step (b) is performed less than 6 days after transfection.
  • the isolation in step (b) is performed between two and four days after transfection.
  • the isolation in step (b) is performed two days after transfection.
  • the isolation in step (b) is performed three days after transfection.
  • the sub-population of transfected host cells comprises about 0.5-6.0 ⁇ 10 6 cells prior to expansion in step (c).
  • the sub-population of transfected host cells comprises about 0.5 ⁇ 10 6 cells, about 1.0 ⁇ 10 6 cells, about 2.0 ⁇ 10 6 cells, about 3.0 ⁇ 10 6 cells, about 4.0 ⁇ 10 6 cells, about 5.0 ⁇ 10 6 cells, or about 6.0 ⁇ 10 6 cells prior to expansion in step (c).
  • the sub-population of transfected host cells comprises about 0.5 ⁇ 10 6 to about 1.0 ⁇ 10 6 cells, about 0.5 ⁇ 10 6 to about 2.0 ⁇ 10 6 cells, about 0.5 ⁇ 10 6 to about 3.0 ⁇ 10 6 cells, about 0.5 ⁇ 10 6 to about 4.0 ⁇ 10 6 cells, about 0.5 ⁇ 10 6 to about 5.0 ⁇ 10 6 cells, about 0.5 ⁇ 10 6 to about 6.0 ⁇ 10 6 cells, about 1.0 ⁇ 10 6 to about 2.0 ⁇ 10 6 cells, about 1.0 ⁇ 10 6 to about 3.0 ⁇ 10 6 cells, about 1.0 ⁇ 10 6 to about 4.0 ⁇ 10 6 cells, about 1.0 ⁇ 10 6 to about 5.0 ⁇ 10 6 cells, about 1.0 ⁇ 10 6 to about 6.0 ⁇ 10 6 cells, about 2.0 ⁇ 10 6 to about 3.0 ⁇ 10 6 cells, about 2.0 ⁇ 10 6 to about 4.0 ⁇ 10 6 cells, about 2.0 ⁇ 10 6 to about 5.0 ⁇ 10 6 cells, about 2.0 ⁇ 10 6 to about 6.0 ⁇ 10 6 cells, about 3.0 ⁇ 10 6 cells, about 2.0 ⁇ 10 6 to about 4.0 ⁇ 10 6 cells, about
  • the sub-population of transfected host cells contains greater than 6.0 ⁇ 10 6 cells prior to expansion in step (c).
  • the sub-population of transfected host cells comprises about 7.0 ⁇ 10 6 cells, about 8.0 ⁇ 10 6 cells, about 9.0 ⁇ 10 6 cells, or about 10.0 ⁇ 10 6 cells, prior to expansion in step (c).
  • the expanding in step (c) is for between 4-31 days.
  • the expanding is for 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, or 31 days.
  • a first of the one or more vectors encodes the mRNA encoding the target polypeptide
  • a second of the one or more vectors encodes the mRNA encoding the selectable polypeptide.
  • the vectors are independently selected from plasmids, viruses, phage, transposons, and minichromosomes.
  • the mRNA encoding the target polypeptide and the mRNA encoding the selectable polypeptide are both encoded on one vector.
  • a single vector encodes a polycistronic mRNA encoding both the target polypeptide and the selectable polypeptide.
  • the mRNA encoding the selectable polypeptide can be upstream (i.e., 5′) of the mRNA encoding the target polypeptide.
  • the mRNA encoding the target polypeptide can be upstream (i.e., 5′) of the mRNA encoding the selectable polypeptide.
  • the target polypeptide and the selectable polypeptide are encoded by a single multicistronic mRNA.
  • the multicistronic mRNA comprises a first open reading frame (ORF) that encodes the selectable polypeptide and a second ORF that encodes the target polypeptide, wherein the first ORF is 5′ to the second ORF.
  • the first ORF has a non-AUG start codon.
  • the non-AUG start codon is a UUG, GUG, or CUG in a Kozak consensus sequence.
  • a non-AUG start codon can be installed using standard molecular biology techniques such as are well known in the art.
  • the second ORF has an AUG start codon.
  • the first ORF has a non-AUG start codon
  • the second ORF has an AUG start codon
  • the ORF that encodes the selectable polypeptide is devoid of any AUG sequences.
  • AUG sequences can be converted to other triplet sequences, other than stop codons, using standard molecular biology techniques such as are well known in the art; for example, and without limitation, AUG sequences can be converted independently to CUG (L), GUG (V), UUG (L), AAG (K), ACG (T), AGG (R), AUA (I), AUC (I), AUU (I), GCA (A), GCC (A), GCG (A), or GCU (A).
  • the target polypeptide and the selectable polypeptide form a fusion protein.
  • the fusion protein is membrane-bound.
  • the selectable polypeptide is present in a detectable form, i.e., the target polypeptide portion of the fusion protein does not prohibit detection of the selectable polypeptide portion of the fusion protein.
  • the target polypeptide is present in a functional form, i.e., the selectable polypeptide portion of the fusion protein does not prohibit function of the target polypeptide portion of the fusion protein.
  • the fusion protein is released from the host cell as a soluble protein.
  • the fusion protein is expressed as a surface protein but can be cleaved to release the target polypeptide in a soluble, functional form.
  • the target polypeptide is a therapeutic agent, e.g., an antibody, an antigen-binding fragment of an antibody, an Fc fusion protein, a hormone, or an enzyme.
  • Polypeptide hormones include, without limitation, adrenocorticotropic hormone (ACTH), antidiuretic hormone (vasopressin), atrial natriuretic peptide (ANP), cholecystokinin, follicle stimulating hormone (FSH), gastrin, glucagon, growth hormone, insulin, leptin, leuteinizing hormone (LH), oxytocin, prolactin, somatostatin, and thyroid stimulating hormone (TSH).
  • ACTH adrenocorticotropic hormone
  • vasopressin antidiuretic hormone
  • ABP atrial natriuretic peptide
  • FSH cholecystokinin
  • FSH follicle stimulating hormone
  • gastrin gastrin
  • glucagon growth hormone
  • Enzymes include, without limitation, acid alpha-glucosidase, adenosine deaminase, alpha-galactosidase, alpha-L-iduronidase, arylsulfatase B, beta-galactosidase, beta-glucuronidase, galactose-6-sulfate sulfatase, glucocerebrosidase, heparan sulfamidase, heparan-alpha-glucosaminide N-acetyltransferase, hyaluronidase, iduronate-2-sulfatase, N-acetylgalactosamine-4-sulfatase, N-acetylglucosamine 6-sulfatase, and N-acetylglucosaminidase.
  • the target polypeptide is a secreted protein.
  • the host cells are mammalian cells.
  • the host cells are selected from the group consisting of CHO cells, BHK-21 cells, NIH/3T3 cells, HEK293 cells, HeLa cells, SP2/0 cells, NS0 cells, C127 cells, COS cells, Vero cells, and U937 cells. All of these cells (cell lines) are commercially available from sources such as American Type Culture Collection (ATCC, Manassas, Va.).
  • the host cells are selected from the group consisting of CHO cells, HEK293 cells, and HeLa cells.
  • An aspect of the invention is a clonal population of transfected host cells that express a selectable polypeptide and a target polypeptide obtainable by the method the invention.
  • the clonal population of transfected host cells expresses a FACS-selectable polypeptide and a target polypeptide obtainable by the method the invention.
  • the clonal population yields a 2- to 30-fold improvement in production of the target polypeptide compared to that of a stable pool of transfected but uncloned host cells obtained at step (c).
  • the clonal population yields a 2- to 30-fold, 3- to 30-fold, 5- to 30-fold, 10- to 30-fold, 15- to 30-fold, 20- to 30-fold, 25- to 30-fold, 2- to 25-fold, 3- to 25-fold, 5- to 25-fold, 10- to 25-fold, 15- to 25-fold, 20- to 25-fold, 2- to 20-fold, 3- to 20-fold, 5- to 20-fold, 10- to 20-fold, 15- to 20-fold, 2- to 15-fold, 3- to 15-fold, 5- to 15-fold, 10- to 15-fold, 2- to 10-fold, 3- to 10-fold, 5- to 10-fold, 2- to 5-fold, 3- to 5-fold, or 2- to 3-fold improvement in production of the target polypeptide compared to that of a stable pool of transfected but uncloned host cells obtained at step (c).
  • the clonal population yields a greater than 30-fold improvement in production of the target polypeptide compared to that of a stable pool of transfected but uncloned host cells obtained at step (c).
  • the clonal population yields an up to 40-fold, up to 50-fold, up to 60-fold, up to 70-fold, up to 80-fold, up to 90-fold, or up to 100-fold improvement in production of the target polypeptide compared to a stable pool of transfected but uncloned host cells obtained at step (c).
  • a heterogeneous population of producer cells is provided.
  • the heterogeneous population of producer cells can be produced using any method known in the art or described herein.
  • the heterogeneous population of producer cells is produced by transfecting cells with a vector that encodes the multicistronic mRNA and subjecting the transfected cells to less than or equal to one round of medium-based selection to select cells expressing varying levels (e.g., a variation of at least 10-, 100-, 1,000-, or 10,000-fold) of the multicistronic mRNA.
  • the vector further contains a drug-selectable marker, e.g., a dihydrofolate reductase (DHFR) gene, and the medium-based selection is methotrexate (MTX, e.g., 1 nM-100 nM MTX), nucleotide-deficient medium, or a combination thereof.
  • the vector further contains a glutamine synthetase (GS) gene and the medium-based selection is methionine sulphoximine (MSX, e.g., 25-100 ⁇ M MSX).
  • the vector lacks a drug-selectable marker, e.g., lacks a DHFR gene or GS gene.
  • FACS is used to select cells expressing varying levels of the multicistronic mRNA, e.g., by using the FACS selectable polypeptide level to select the cells.
  • FIG. 1A depicts a general scheme for EPIC.
  • FIG. 1B shows the early expression of the reporter gene during the nucleotide-deficient selection process.
  • EPIC can be executed by transfecting a population and allowing early expression to develop, which can be targeted for isolation using flow cytometry or other means of cell sorting. These sort-isolated early-expression sub-populations can then be placed in a selection media to establish a stable expression pool. Isolation of these post-transfection early expression sub-populations prior to selection yields improved productivity over standard transfection/selection methodologies alone (e.g., as shown in FIG. 1A ).
  • CD52 red fluorescent protein
  • CD52 pGZ729-RFP
  • RFP red fluorescent protein
  • the pGZ729 vector backbone sequence (including sequence encoding CD52 but not RFP) is shown below, followed by annotations of the sequence.
  • CHO cells transfected with pGZ729-RFP produced early expression of both CD52 and RFP that peaked around days 2 and 3, with signal deteriorating out to day 7 post-transfection. Therefore, EPIC targeting on or near days 2-3 is suitable for isolation of early-expressing sub-populations of transfected host cells.
  • EPIC targeting on or near days 2-3 is suitable for isolation of early-expressing sub-populations of transfected host cells.
  • CHO cells transfected with either pGZ729-RFP or pGZ700-RFP were analyzed for RFP and CD52 expression. As shown in FIG.
  • both CHO cells transfected with pGZ729-RFP and CHO cells transfected with pGZ700-RFP robustly expressed RFP (top left and bottom left, respectively), whereas while CHO cells transfected with pGZ729-RFP had modest expression of CD52 (top right), CHO cells transfected with pGZ700-RFP expressed essentially no detectable CD52 (bottom right).
  • early RFP expression was targeted for EPIC from a transfected population using pGZ729-RFP to then generate a stable pool.
  • Early RFP expression was targeted for sort isolation and collection two days after transfection (peak transience).
  • the EPIC generated RFP positive sub-population was then used to establish a stable pool via selection in 0 nM MTX nucleotide deficient media.
  • a standard transfection/selection pool was also generated to serve as comparative control.
  • the EPIC generated pool (which targeted early RFP expression) yielded a stable pool (EPIC pool) with greater RFP and CD52 reporter expression than traditional transfection/selection methodology alone (0 nM pool).
  • Results demonstrate a FLARE independent proof of principle supporting the claim that EPIC generated pools are more productive than traditional transfection/selection methodologies.
  • EPIC was initially attempted using mAb#1 in which CHO cells were transfected and given 2 days to recover, after which 0 nM MTX selection was initiated to establish early expression.
  • FIG. 4 by day 8 sorting for EPIC yielded a slightly enriched population as seen by CD52 reporter expression as compared to standard selection.
  • the EPIC and standard selected pools were both used to establish unfed batch cultures to determine mAb#1 titers. As shown in FIGS. 4 and 5 , the EPIC-generated pool yielded a titer of 502 mg/L, far outpacing any pools generated by MTX amplification, again using no MTX throughout the processes. Comparatively, the pool generated by standard selection yielded a titer of 150 mg/L, which was 3-fold lower than that of the EPIC-generated pool.
  • Example 2 The EPIC-generated pool of Example 2 was next used to generate clones using FLARE as previously described (see, e.g., Cairns, V. et al. (2011) Utilization of Non-AUG Initiation Codons in a Flow Cytometric Method for Efficient Selection of Recombinant Cell Lines, Biotechnol Bioeng 108(11):2611-2622). Briefly, FLARE was used to isolate and single cell plate the top 3-5% of reporter-expressing cells from each pool using FACS. Expanded clones were then screened (taking top 30% positive expressers), again using FLARE, to identify only the top tier clones to expand for target polypeptide titer evaluation. As shown in FIG.
  • top expressing EPIC-generated clones achieved similar titers to those of best clones from traditional methods, e.g., using MTX-amplified pools (near 2.0 g/L).
  • EPIC offers a MTX-independent methodology to achieve clone titers similar to those from traditional MTX methodologies, resulting in potentially more robust and stable clones.
  • EPIC is also amenable to MTX introduction during selection/expansion of EPIC-generated sub-populations, with the potential to drive even higher expression in these enriched populations.
  • FIG. 8 depicts the general scheme for the comparative study, with each of the three processes being initiated from a single source pool of transfected cells.
  • one portion of the pooled transfected cells was allowed to continue recovery for two additional days prior to sort isolation of the cell surface reporter positive expression population.
  • the sort isolated cells were placed in nucleotide deficient media (no MTX) for expansion to generate a stable EPIC pool.
  • nucleotide deficient media no MTX
  • Rapid Bulking Process one portion of the pooled transfected cells was placed in nucleotide deficient media (no MTX) to generate a population which was then bulk enriched two times (targeting top 10%), by sort isolation based on cell surface reporter expression levels ending with the rapid bulk #2 pool.
  • the “Direct Selection Process” one portion of the pooled transfected cells was placed in media with MTX for a standard selection procedure. The resulting pool was passaged in nucleotide deficient media prior to clone generation. Each arm represents an independent method to prepare a stably transfected population of cells (pools) suitable for clone generation.
  • the pool generated at the end of the process was used to generate clones using FLARE as previously described (see, e.g., Cairns, V. et al. (2011) Utilization of Non-AUG Initiation Codons in a Flow Cytometric Method for Efficient Selection of Recombinant Cell Lines, Biotechnol Bioeng 108(11):2611-2622). Briefly, FLARE was used to isolate and single cell plate the top 3-5% of reporter-expressing cells from each pool using FACS. Expanded clones were then screened (taking the top 30% of positive expressers), again using FLARE, to identify only the top tier clones to expand for target polypeptide titer evaluation.
  • FIG. 9 shows the distribution of target polypeptide (mAb#1, mAb#2, or Fc Fusion#1) titers for the clones generated using the three independent processes.
  • Fc fusion protein clones from the rapid bulking process achieved titers as high as those from the MTX selection process. While there is a greater frequency of higher producers associated with the MTX selection process, this may indicate that the MTX process results in a less diverse group of clones, perhaps being of similar genetic origin with similar transgene integrations.
  • the EPIC and rapid bulking methods which are sort enrichment processes rather than a drug selection/cell death process, may yield a more diverse group of clones with different transgene integration sites and therefore a greater range of productivity. A greater degree of clone diversity is often preferable when identifying cell lines that are suitable for a manufacturing process.
  • FIG. 10 shows the number of days from transfection to the pool used for cloning (black) and from the pool to the final clones (gray).
  • the EPIC process generates the pools one month faster than the standard MTX selection process. It is at this pool generation step that the most significant time savings is realized, and the faster generation of pools with this MTX-independent methodology translates to an overall CLD process timeline reduced by 1 month.
  • EPIC Variable Sort Targeting for Early Post-Transfection Isolation of Cells
  • variable sort targeting for EPIC was performed at 2 days post-transfection, with the aim of isolating an increasingly positive transient expression population to, in turn, yield a further enriched EPIC pool.

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