US20090181423A1 - Substantially animal protein-free recombinant furin and methods for producing same - Google Patents

Substantially animal protein-free recombinant furin and methods for producing same Download PDF

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US20090181423A1
US20090181423A1 US12/339,597 US33959708A US2009181423A1 US 20090181423 A1 US20090181423 A1 US 20090181423A1 US 33959708 A US33959708 A US 33959708A US 2009181423 A1 US2009181423 A1 US 2009181423A1
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furin
cells
protein
rfurin
cell
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Barbara Plaimauer
Simone Von Fircks
Leopold Grillberger
Meinhard Hasslacher
Roland Geyer
Artur Mitterer
Manfred Reiter
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Baxter Healthcare SA
Baxter International Inc
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Baxter International Inc
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Priority to US12/339,597 priority Critical patent/US20090181423A1/en
Assigned to BAXTER INTERNATIONAL INC., BAXTER HEALTHCARE S.A. reassignment BAXTER INTERNATIONAL INC. ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: PLAIMAUER, BARBARA, HASSLACHER, MEINHARD, GEYER, ROLAND, REITER, MANFRED, VON FIRCKS, SIMONE, GRILLBERGER, LEOPOLD, MITTERER, ARTUR
Publication of US20090181423A1 publication Critical patent/US20090181423A1/en
Priority to US12/960,093 priority patent/US9127264B2/en
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    • 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
    • C12N9/00—Enzymes; Proenzymes; Compositions thereof; Processes for preparing, activating, inhibiting, separating or purifying enzymes
    • C12N9/14—Hydrolases (3)
    • C12N9/48—Hydrolases (3) acting on peptide bonds (3.4)
    • C12N9/50—Proteinases, e.g. Endopeptidases (3.4.21-3.4.25)
    • C12N9/64—Proteinases, e.g. Endopeptidases (3.4.21-3.4.25) derived from animal tissue
    • C12N9/6421—Proteinases, e.g. Endopeptidases (3.4.21-3.4.25) derived from animal tissue from mammals
    • C12N9/6424—Serine endopeptidases (3.4.21)
    • C12N9/6454—Dibasic site splicing serine proteases, e.g. kexin (3.4.21.61); furin (3.4.21.75) and other proprotein convertases
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61P—SPECIFIC THERAPEUTIC ACTIVITY OF CHEMICAL COMPOUNDS OR MEDICINAL PREPARATIONS
    • A61P43/00—Drugs for specific purposes, not provided for in groups A61P1/00-A61P41/00
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61P—SPECIFIC THERAPEUTIC ACTIVITY OF CHEMICAL COMPOUNDS OR MEDICINAL PREPARATIONS
    • A61P7/00—Drugs for disorders of the blood or the extracellular fluid
    • A61P7/02—Antithrombotic agents; Anticoagulants; Platelet aggregation inhibitors
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61P—SPECIFIC THERAPEUTIC ACTIVITY OF CHEMICAL COMPOUNDS OR MEDICINAL PREPARATIONS
    • A61P7/00—Drugs for disorders of the blood or the extracellular fluid
    • A61P7/04—Antihaemorrhagics; Procoagulants; Haemostatic agents; Antifibrinolytic agents

Definitions

  • the present invention generally relates to recombinant furin (rFurin) and methods for producing rFurin. More specifically, the invention relates to substantially animal protein-free rFurin and methods for producing substantially animal protein-free rFurin.
  • pro-proteins Active or mature proteins are usually present in very low amounts in living organisms. Therefore, their pro-proteins or pro-enzymes are preferably activated in vitro by contacting them with activation enzymes (e.g. proteases).
  • Pro-proteins or protein precursors
  • Pro-proteins are inactive proteins that become active by one or more posttranslational modifications and, in particular, by the cleavage of a pro-peptide from the pro-protein.
  • pro-proteins include, for example, pro-insulin, prothrombin, pro-von Willebrand Factor (pro-VWF), and the like.
  • VWF Von Willbrand factor
  • VWF is a blood glycoprotein involved in coagulation.
  • VWF is deficient or defective in von Willebrand disease and is involved in a large number of other diseases, including thrombotic thrombocytopenic purpura, Heyde's syndrome, and possibly hemolytic-uremic syndrome.
  • VWF is a glycoprotein circulating in plasma as a series of multimers ranging in size from about 500 to 20,000 kD. Multimeric forms of VWF are composed of 250 kD polypeptide subunits linked together by disulfide bonds.
  • VWF mediates the initial platelet adhesion to the sub-endothelium of the damaged vessel wall, and it is believed that only the larger multimers of VWF exhibit hemostatic activity.
  • VWF multimers having large molecular masses are stored in the Weibel-Pallade bodies of endothelial cells and are liberated upon stimulation. Liberated VWF is then further processed by plasma proteases to result in low molecular weight forms of VWF.
  • cell culture supernatants from such recombinant cell lines usually comprise a mixture of mature VWF and VWF precursors, like pro-VWF.
  • VWF precursors in particular pro-VWF
  • This process is usually achieved by cleaving the pro-peptide with a protease.
  • VWF and, in particular, recombinant VWF is synthesized and expressed together with recombinant Factor VIII (rFVIII) in a genetically engineered Chinese Hamster ovary (CHO) cell line.
  • the function of the co-expressed rVWF is to stabilize rFVIII in the cell culture process.
  • rVWF is synthesized in the cell in the pro-form, containing a large pro-peptide attached to the N-terminus.
  • the pro-peptide Upon maturation in the endoplasmic reticulum and Golgi apparatus, the pro-peptide is cleaved by the action of the cellular protease furin and the mature protein is secreted as a homopolymer of identical subunits, consisting of dimers of the expressed protein.
  • the maturation is typically incomplete, leading to a product comprising a mixture of pro-VWF and mature VWF.
  • Recombinant furin transforms pro-rVWF (pro-recombinant von Willebrand factor) to rVWF by cleaving the Arg741-Ser742 peptide bond.
  • This maturation step is part of a rVWF production process for the treatment of von Willebrand Disease Type B and part of the manufacturing process for recombinant Factor VIII-half life (rFVIII-HL).
  • Furin belongs to the family of the pro-protein convertases and is dependent on calcium (Ca 2+ ). Furin specifically cleaves the C-terminal peptide bond of arginine within a specific sequence, containing arginine at positions ⁇ 1 and ⁇ 4. This sequence can be found in numerous human proteins, showing that furin plays a major role in the maturation of a number of human pro-proteins.
  • activated proteins are of high clinical and diagnostic importance.
  • active or mature proteins like mature VWF, may be used to control blood coagulation.
  • the present invention provides improved recombinant furin (rFurin) which is substantially animal protein-free rFurin for the subsequent production of activated proteins. More specifically, the present invention provides substantially animal protein-free rFurin for transforming pro-VWF into mature VWF.
  • the present invention provides recombinant furin (rFurin), which is substantially animal protein-free recombinant furin (rFurin), and methods for producing same.
  • rFurin is substantially free of other proteins which may normally be associated with the production of rFurin, such as serum proteins and host cell proteins.
  • This rFurin allows for the subsequent production of mature proteins with high specific activity and high purity without side effects associated with protein contaminant in the rFurin preparation. More specifically, this rFurin allows for the production of mature VWF with high specific activity and high purity.
  • the invention provides methods for selection and adaptation of recombinant host cells to chemically-defined medium, expression of rFurin which is secreted into cell culture supernatant, and purification of rFurin after cell removal.
  • the substantially animal protein-free rFurin of the invention includes preparations or compositions of rFurin comprising host cell protein in a concentration which ranges between about 0.1 to 0.6 ng protein or less/Unit furin activity or between about 2 and 11 ⁇ g protein or less/mL and essentially lacking contaminating proteins from serum in the culture medium.
  • the substantially animal protein-free rFurin encompasses preparations of rFurin comprising contaminating host cell DNA in a concentration between about 0 to 0.4 pg DNA or less/Unit furin activity or between about 0 and 24 ng DNA or less/mL and essentially lacking contaminating proteins from serum in the culture medium.
  • compositions comprising substantially animal protein free recombinant furin at an activity of at least 10000 U furin/mL and host cell protein at a concentration less than about 11 ⁇ g protein/mL.
  • Such compositions may also comprise host cell protein at a concentration less than about 1.0 ng protein/U furin activity.
  • the host cell protein is from a CHO cell.
  • the invention includes compositions comprising substantially animal protein free recombinant furin at an activity of at least 10000 U furin/mL and host cell DNA at a concentration less than about 14 ng DNA/mL.
  • such compositions also comprise host cell DNA at a concentration less than about 0.5 pg DNA/U furin activity.
  • the host cell DNA is from a CHO cell.
  • the invention also includes compositions comprising substantially animal protein free recombinant furin at a specific furin activity of at least about 100 U/ ⁇ g and host cell protein at a concentration less than about 11 ⁇ g protein/mL. Such compositions may also comprise host cell protein at a concentration less than about 1.0 ng protein/U furin activity. In one aspect, the host cell protein is from a CHO cell.
  • the invention further includes compositions comprising substantially animal protein free recombinant furin at a specific furin activity of at least about 100 U/ ⁇ g and host cell DNA at a concentration less than about 14 ng DNA/mL.
  • Such compositions may also comprise host cell DNA at a concentration less than about 0.5 pg DNA/U furin activity.
  • the host cell DNA is from a CHO cell.
  • the invention also includes methods of making a composition comprising substantially animal protein-free recombinant furin described herein. Such methods comprise the step of adapting the host cells to growth in medium with increasingly lower concentrations of serum until all serum is removed from the medium. In another aspect, the methods comprise the step of transferring the host cell from growth in medium comprising serum to growth in serum-free medium.
  • the host cell is a CHO cell.
  • the invention includes methods of using a composition comprising substantially animal protein-free recombinant furin described herein. Such uses comprise the step of contacting a pro-protein with the composition under conditions to cleave a pro-peptide from the pro-protein to form a mature protein.
  • the rFurin can be used in the formation of any mature protein from a pro-protein that is cleaved by furin.
  • the mature protein is von Willebrand Factor.
  • the mature protein is Factor VIII.
  • the invention contemplates that the rFurin of the invention is useful for both in vitro and in vivo processing of any pro-protein that it cleaves.
  • FIGS. 1-18 A further illustration of the invention is given with reference to the accompanying drawings, which are set out below in FIGS. 1-18 .
  • FIG. 1 depicts the expressed active rFurin protease construct in one embodiment of the invention.
  • the rFurin construct is truncated at the C-terminal end at AA 577 to remove the Cys-rich transmembrane and cytosol domains.
  • FIG. 2 depicts a pedigree of the generation of the CHO/rFurin clone #488-3.
  • FIG. 3 shows a pedigree of the generation of the CHO/rFurin clone #289-20.
  • FIG. 4 sets out a comparison of the graphical distribution of the rFurin producers in the cell populations of PMCB#01 and PMCB#04. 80.74% of the cells in PMCB#04 express rFurin; 74.06% of the cells in PMCB#01 express rFurin.
  • FIG. 5 shows a “Doehlert Matrix” where five temperatures were combined with three pH values, resulting in seven combinations of temperature and pH.
  • FIG. 6 shows a surface plot analysis of the data in reference to the volumetric productivity.
  • the coordinates of the data in FIG. 6 are marked as points.
  • the surface shows the assumed correlation of the single data.
  • FIG. 7 shows a contour plot which illustrates the influence of temperature and pH on the volumetric productivity.
  • the dots indicate the conditions (pH/temp.) which had been tested experimentally.
  • FIG. 8 shows a surface plot which is a three-dimensional illustration demonstrating the strong influence of the temperature and the weak influence of the pH on the volumetric productivity.
  • FIG. 9 shows a surface plot which illustrates the modeled correlation three-dimensionally; it demonstrates the quadratic relationship and shows clearly a maximum for the growth rate at 36.5° C.
  • FIG. 10 sets out an analysis of the data in reference to specific productivity. There is a similar correlation of the specific productivity with temperature and pH as seen for the volumetric productivity.
  • FIG. 11 shows that by decreasing the temperature from 37° C. to 35.1° C., the volumetric productivity could be increased from approx. 200 kU/L/d to 540 kU/L/d.
  • FIG. 12 shows SDS-page and silver-stain for rFurin.
  • the band patterns of the Capto-MMC eluates of campaign ORFU06002 and ORFU07002 correlate to a high degree; all samples show a prominent Furin band at approx. 60 kDa.
  • a trend to slightly lower molecular weight of the Furin bands is visible in samples of campaign ORFU06002 from batches MMC01 to MMC08 ( FIG. 12 , lanes 1-8).
  • FIG. 13 shows the Western blot analysis of samples using a monoclonal anti-Furin antibody.
  • FIG. 14 shows the specific band patterns for rFurin from isoelectric focusing (IEF) and subsequent Western blotting of rFurin samples of campaign ORFU06002.
  • FIG. 15 shows the specific band patterns for rFurin from isoelectric focusing (IEF) and subsequent Western blotting of rFurin samples of campaign ORFU07002.
  • FIG. 16 shows Western blot results for rFurin from isoelectric focusing (IEF) and subsequent Western blotting of rFurin samples of campaign ORFU07002.
  • FIG. 17 shows Furin Reverse Phase HPLC for samples from campaign ORFU06002 (Capto-MMC eluates). Samples were tested with C4 RP-HPLC in order to establish a fingerprint pattern for rFurin.
  • FIG. 18 shows Furin Reverse Phase HPLC for samples from campaign ORFU07002 (Capto-MMC eluates). Samples were tested with C4 RP-HPLC in order to establish a fingerprint pattern for rFurin.
  • the present invention relates to the development and production of a recombinant host cell line that is capable of growing in serum-free medium and secreting active recombinant furin (rFurin) into the cell culture supernatant.
  • the host cell line selected for transfection of a plasmid encoding recombinant furin is in one aspect the same as used for expression of recombinant Factor VIII and recombinant VWF.
  • the resulting rFurin is then purified so that is substantially free of animal protein.
  • Furin also known as PACE, PACE4, PC1/PC3, PC2, PC4 and PC5/PC6, belongs to the group of the subtilisin-like serine proteases, which play an important role in the cleavage of proproteins, especially in the secretory synthesis (Van de Ven et al., Crit. Rev. Oncogen. 4:115-136, 1993).
  • Pro-proteins are post-translationally, intracellularily processed to their mature form by the endogenous protease in the Golgi apparatus.
  • the protease cleavage site comprises a recognition sequence which is characterized by the amino acid sequence Arg-X-Lys/Arg-Arg.
  • the protease furin cleaves proproteins specifically after this consensus sequence (Hosaka et al., J. Biol. Chem. 266:12127-12130, 1991).
  • the human furin gene encodes a protein consisting of 794 amino acids, certain functions being allocatable to individual characteristic regions: a catalytic center, a middle domain, a cystine-rich region, a transmembrane domain, and a cytoplasmatic domain (Van de Ven et al., Crit. Rev. Oncogen. 4:115-136, 1993).
  • the human furin polypeptide is set out in GenBank Accession No: EAX02111 (National Center for Biotechnology Information, U.S. National Library of Medicine, Bethesda, Md.).
  • any protein having furin biological activity i.e., the ability to cleave pro-proteins (e.g., pro-VWF to produce mature VWF) can be produced by the methods described herein.
  • Intact furin is incorporated into the membrane system of the Golgi apparatus where it is functionally active (Bresnahan et al., J. Cell Biol. 111:2851-2859, 1990).
  • a truncated form of the over-expressed native furin of 75-80 kD could be detected in cell supernatant as secreted protein (Wise et al., Proc. Natl. Acad. Sci. USA 87: 9378-9382, 1990).
  • This naturally secreted furin is known as “shed furin” (Vidricaire et al., Biochem. Biophys. Res. Comm. 195:1011-1018, 1993) and is cleaved N-terminally of the transmembrane portion (Vey et al., J. Cell Biol. 127:1829-1842, 1994).
  • Furin truncated by genetic engineering in which the encoding part of the transmembrane and cytoplasmatic domains has been deleted, can also be expressed and secreted correspondingly.
  • Such N-terminal deletions have been described for amino acids 714-794 (Leduc et al., J. Biol. Chem. 267:14304-14308, 1992, Molloy et al., J. Biol. Chem. 267:16396-16402, 1992); for amino acids 716-794 (“Sol-PACE”) (Wasley et al., J. Biol. Chem.
  • Pro-vWF pro-von Willebrand factor
  • vWF mature von Willebrand factor
  • vWF is probably processed into its mature form in transfected cells, by endogenously occurring furin (Wise et al., Proc. Natl. Acad. Sci. USA 87:9378-9382, 1990, Van de Ven et al., Mol. Biol. Rep. 14:265-275, 1990).
  • pro-proteins which are cleaved by furin or by subtilisin-like enzymes, respectively, are a series of hormones and growth factors (e.g., proactivin A, hepatocyte-growth factor), plasma proteins (albumin, factor VII, factor IX, factor X), receptors (insulin pro-receptor), viral proteins (e.g. HIV-1 gp160, influenza virus haemagglutinin) as well as bacterial proteins (diphteria toxin, anthrax toxin) (Decroly et al., J. Biol. Chem. 269:12240-12247, 1994; Stieneke-Grober et al., EMBO J.
  • proactivin A hepatocyte-growth factor
  • plasma proteins albumin, factor VII, factor IX, factor X
  • receptors insulin pro-receptor
  • viral proteins e.g. HIV-1 gp160, influenza virus haemagglutinin
  • bacterial proteins diphteria tox
  • Furin deletion mutants have been demonstrated as enzymatically active when co-expressed in vivo and as secreted; the enzymatic activity of such deletion mutants could be detected inter alia in the processing of pro-factor IX (Wasley et al., J. Biol. Chem. 268:8458-8465, 1993) and pro-vWF (Rehemtulla et al., Blood 79: 2349-2355, 1992).
  • WO 91/06314 discloses the recombinant expression of furin in prokaryotic and eukaryotic cells, the preparation of furin fusion proteins, deletion mutants and fragments, the purification of recombinantly prepared furin, and the potential use of purified furin for the processing of proproteins in vitro in general.
  • WO 92/09698 describes the expression of PACE (furin), the co-expression with inactive precursors of proteins, such as, e.g., pro-vWF, as well as the preparation of fusion proteins.
  • Stieneke-Grober et al. EMBO J. 11:2407-2414, 1992
  • Decroly et al. J. Biol. Chem. 269:12240-12247, 1994
  • the rFurin of the present invention is contemplated for use in the in vivo and in vitro processing of pro-proteins as described above.
  • the rFurin of the invention is especially useful in the in vitro processing of pro-VWF and pro-factor IX.
  • its use is not to be construed as limited to the processing of said proteins.
  • the rFurin of the invention is particularly useful in the in vitro processing of recombinant pro-proteins.
  • a further aspect of the present invention is the co-culturing of cells which express pro-vWF and rFurin.
  • pro-vWF in the cell culture supernantant is cleaved in vitro into its active form by rFurin which is also present in the cell culture supernatant.
  • Processed vWF is subsequently isolated from the culture and purified, as discussed in U.S. Pat. No. 6,210,929, incorporated herein by reference.
  • all the common expression systems can be used, and various systems for expressing pro-vWF and rFurin may be combined with each other.
  • an expression system is used in which both pro-vWF and rFurin are expressed in host cells of the same origin.
  • host cell is used to refer to a cell which has been transformed, or is capable of being transformed with a nucleic acid sequence and then of expressing a selected gene of interest.
  • the term includes the progeny of the parent cell, whether or not the progeny is identical in morphology or in genetic make-up to the original parent, so long as the selected gene is present.
  • the invention includes any host cells or hosts known in the art for recombinant protein production. Therefore, the cells in the present invention can be derived from any source.
  • the invention includes eukaryotic and prokaryotic host cells.
  • the invention includes plant cells, animal cells, fish cells, amphibian cells, avian cells, insect cells, and yeast cells.
  • exemplary yeast cells include Pichia , e.g. P. pastoris , and Saccharomyces e.g. S. cerevisiae , as well as Schizosaccharomyces pombe, Kluyveromyces, K. zactis, K. fragilis, K. bulgaricus, K. wickeramii, K.
  • Exemplary insect cells include Autographa californica and Spodoptera frugiperda , and Drosophila.
  • the host cells are mammalian cells, including primary epithelial cells (e.g., keratinocytes, cervical epithelial cells, bronchial epithelial cells, tracheal epithelial cells, kidney epithelial cells and retinal epithelial cells) and established cell lines and their strains (e.g., 293 embryonic kidney cells, BHK cells, HeLa cervical epithelial cells and PER-C6 retinal cells, MDBK (NBL-1) cells, 911 cells, CRFK cells, MDCK cells, CHO cells, BeWo cells, Chang cells, Detroit 562 cells, HeLa 229 cells, HeLa S3 cells, Hep-2 cells, KB cells, LS180 cells, LS174T cells, NCI-H-548 cells, RPMI 2650 cells, SW-13 cells, T24 cells, WI-28 VA13, 2RA cells, WISH cells, BS-C-1 cells, LLC-MK 2 cells, Clone M-3 cells, 1-10 cells, RAG
  • Exemplary mammalian cells include varieties of CHO, BHK, HEK-293, NS0, YB2/3, SP2/0, and human cells such as PER-C6 or HT1080, as well as VERO, HeLa, COS, MDCK, NIH3T3, Jurkat, Saos, PC-12, HCT 116, L929, Ltk ⁇ , W138, CV1, TM4, W138, Hep G2, MMT, a leukemic cell, an embryonic stem cell or a fertilized egg cell.
  • an exemplary host cell is a CHO cell.
  • the medium is used to culture CHO cells in suspension.
  • Host cells can be engineered to express a protein in a variety of ways known in the art, including but not limited to insertion of exogenous nucleic acid encoding the desired protein, optionally as part of an expression vector, insertion of an exogenous expression control sequence such that it causes increased expression of the host cell's endogenous gene encoding the desired protein, or activation of the host cell's endogenous expression control sequence(s) to increase expression of endogenous gene encoding the desired protein.
  • Cultures of host cells can be prepared according to any methods known in the art, and methods of growing such host cells and recovering recombinant protein produced by the cells, whether from the cells or culture medium, are known in the art. Such culturing methods may involve addition of chemical inducers of protein production to the culture medium. Exemplary host cells and procedures are described below.
  • a nucleic acid encoding a furin polypeptide is inserted into an appropriate expression vector using standard molecular biology techniques.
  • the nucleic acid encodes the human furin polypeptide as set out in GenBank Accession No: EAX02111 (National Center for Biotechnology Information, U.S. National Library of Medicine, Bethesda, Md.), however the worker of ordinary skill in the art will appreciate that any protein having furin biological activity, i.e., the ability to cleave pro-VWF to produce mature VWF, can be produced by the methods described herein.
  • a C-terminally truncated, fully secreted rFurin was designed by deleting nucleotides encoding amino acids 578 to 794 comprising the cystine-rich, the transmembrane, and the cytoplasmic domains.
  • a tail of amino acids may be added to aid in purification processes.
  • a tail of 10 histidine residues was added after amino acid 577, with or without interjacent four glycine residues serving as a flexible linker.
  • Expression vectors optionally may include a promoter, one or more enhancer sequences, an origin of replication, a transcriptional termination sequence, a complete intron sequence containing a donor and acceptor splice site, a sequence encoding a leader or signal sequence for polypeptide secretion, a ribosome binding site, a polyadenylation sequence, a polylinker region for inserting the nucleic acid encoding the polypeptide to be expressed, and/or a selectable marker element.
  • a promoter one or more enhancer sequences
  • an origin of replication a transcriptional termination sequence
  • a complete intron sequence containing a donor and acceptor splice site a sequence encoding a leader or signal sequence for polypeptide secretion
  • a ribosome binding site a sequence encoding a leader or signal sequence for polypeptide secretion
  • a polyadenylation sequence for inserting the nucleic acid encoding the polypeptide to be expressed
  • the vector may contain a “tag”-encoding sequence, i.e., an oligonucleotide sequence located at the 5′ or 3′ end of the furin polypeptide coding sequence; the oligonucleotide molecule encodes polyHis (such as hexaHis), or another “tag” such as FLAG, HA (hemaglutinin influenza virus) or myc for which commercially available antibodies exist.
  • This tag is typically fused to the polypeptide upon expression of the polypeptide, and can serve as a means for detection or affinity purification of the furin polypeptide from the host cell.
  • Suitable vectors include, but are not limited to, cosmids, plasmids, or modified viruses, but it will be appreciated that the vector system must be compatible with the selected host cell.
  • the vector is a plasmid.
  • the plasmid is pUC-based cloning vector.
  • Other vectors that can be used in the invention include expression vectors, replication vectors, probe generation vectors, sequencing vectors, and retroviral vectors.
  • Vectors contemplated by the invention include, but are not limited to, microorganisms such as bacteria transformed with recombinant bacteriophage, plasmid, phagemid, or cosmid DNA expression vectors; yeast transformed with yeast expression vectors; insect cell systems infected with viral expression vectors (e.g., baculovirus); plant cell systems transfected with virus expression vectors (e.g., Cauliflower Mosaic Virus, CaMV; Tobacco Mosaic Virus, TMV) or transformed with bacterial expression vectors (e.g., Ti or pBR322 plasmid); or even animal cell systems.
  • microorganisms such as bacteria transformed with recombinant bacteriophage, plasmid, phagemid, or cosmid DNA expression vectors
  • yeast transformed with yeast expression vectors insect cell systems infected with viral expression vectors (e.g., baculovirus)
  • plant cell systems transfected with virus expression vectors e.g., Ca
  • Mammalian expression vectors typically comprise an origin of replication, a suitable promoter, and also any necessary ribosome binding sites, polyadenylation site, splice donor and acceptor sites, transcriptional termination sequences, and 5′ flanking nontranscribed sequences.
  • DNA sequences derived from the SV40 viral genome for example, the SV40 origin, early promoter, enhancer, splice, and polyadenylation sites may be used to provide the required expression control elements.
  • Exemplary eukaryotic vectors include pcDNA3, pWLneo, pSV2cat, pOG44, PXTI, pSG (Stratagene) pSVK3, pBPV, pMSG, pSVL, and pVITRO3.
  • Nucleic acid can be transferred into host cells by any means known in the art, e.g. through liposome-mediated transfer, receptor-mediated transfer (ligand-DNA complex), electroporation, microinjection of DNA, cell fusion, DEAE-dextran, calcium chloride, calcium phosphate precipitation, microparticle bombardment, infection with viral vectors, lipofection, transfection, or homologous recombination.
  • liposome-mediated transfer e.g. through liposome-mediated transfer, receptor-mediated transfer (ligand-DNA complex), electroporation, microinjection of DNA, cell fusion, DEAE-dextran, calcium chloride, calcium phosphate precipitation, microparticle bombardment, infection with viral vectors, lipofection, transfection, or homologous recombination.
  • transfected refers to a host cell modified to contain an exogenous polynucleotide, which can be integrated into the chromosome of the host cell or maintained as an episomal element. It is contemplated that in certain aspects of the methods provided, the host cell is transfected in a “transfection step.” The method may comprise multiple transfection steps. In addition, other methods known in the art for introducing exogenous polynucleotides into a host cell, including for example, electroporation and cell fusion which are not technically “transformation” are within the definition of the term “transformation” for purposes of this description.
  • the invention also provides methods for culturing, i.e. growing, host cells under conditions that result in rFurin protein expression. Such methods include the step of recovering the rFurin produced by the host cells from the culture medium.
  • the host cells are grown in a chemically defined, serum-free medium. Because serum is a biochemically undefined material, contains many components which have not been fully identified, differs from lot to lot, and is frequently contaminated with microorganisms, such as viruses and mycoplasma, the presence of serum in the recombinant production of rFurin is undesirable. Furthermore, the presence of animal proteins in serum in the culture media can require lengthy purification procedures.
  • the invention therefore provides a biochemically defined culture medium, essentially free from animal protein, for culturing cells recombinantly transfected with a human furin gene.
  • the components of the medium are mostly inorganic, synthetic or recombinant and as such are not obtained directly from any animal source.
  • the cell culture medium of the present invention may comprise one or more replacement compounds and can comprise one or more replacement compounds which can be metal binding compounds and/or can comprise one or more complexes comprising one or more replacement compounds.
  • the medium can comprise one or more complexes, said complex comprising one or more transition elements or salts or ions thereof complexed one or more replacement compounds which can be metal-binding compounds.
  • the medium is capable of supporting the culture of cells in vitro and permits transfection of cells cultured therein.
  • a transition element is preferably selected from the group consisting of scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, yttrium, zirconium, niobium, molybdenum, technetium, rubidium, rhodium, palladium, silver, cadmium, lanthanum, hafnium, tantalum, tungsten, rhenium, osmium, iridium, platinum, gold, mercury, and actinium, or salts or ions thereof, and is preferably an iron salt.
  • Suitable iron salts include, but are not limited to, FeCl 3 , Fe(NO 3 ) 3 or FeSO 4 or other compounds that contain Fe +++ or Fe ++ ions.
  • Metal binding compounds in the medium include any macromolecules which can interact with or bind with transition elements and facilitate their uptake by cells. Such interaction/binding can be covalent or non-covalent in nature.
  • the metal-binding compound used in this aspect of the invention is preferably selected from the group consisting of a polyol, a hydroxypyridine derivative, 1,3,5-N,N′,N′′-tris(2,3-dihydroxybenzoyl)amino-methylbenzene, ethylenediamine-N,N′-tetramethylenephosphonic acid, trisuccin, an acidic saccharide (e.g., ferrous gluconate), a glycosaminoglycan, diethylenetriaminepentaacetic acid, nicotinic acid-N-oxide, 2-hydroxy-nicotinic acid, mono-, bis-, or tris-substituted 2,2′-bipyridine, a hydroxamate derivative (e.g.
  • the metal-binding compound is a polyol such as sorbitol or dextran, and particularly sorbitol.
  • the metal-binding compound is a hydroxypyridine derivative, such as 2-hydroxypyridine-N-oxide, 3-hydroxy-4-pyrone, 3-hydroxypypyrid-2-one, 3-hydroxypyrid-2-one, 3-hydroxypyrid-4-one, 1-hydroxypyrid-2-one, 1,2-dimethyl-3-hydroxypyrid-4-one, 1-methyl-3-hydroxypyrid-2-one, 3-hydroxy-2(1H)-pyridinone, ethyl maltol or pyridoxal isonicotinyl hydrazone.
  • the metal binding compounds of the present invention can also bind divalent cations such as Ca ++ and Mg ++ .
  • the culture medium of the present invention may comprise one or more ingredients selected from the group consisting of adenine, ethanolamine, D-glucose, heparin, a buffering agent, hydrocortisone, insulin, linoleic acid, lipoic acid, phenol red, phosphoethanolamine, putrescine, sodium pyruvate, tri-iodothyronine, thymidine, L-alanine, L-arginine, L-asparagine, L-aspartic acid, L-cysteine, L-glutamic acid, L-glutamine, glycine, L-histidine, L-isoleucine, L-leucine, L-lysine, L-methionine, L-phenylalanine, L-proline, L-serine, L-threonine, L-tryptophan, L-tyrosine, L-valine, N-acetyl-cysteine, biotin,
  • the culture medium of the invention may optionally further comprise one or more supplements selected from the group consisting of one or more cytokines, soy peptone, one or more yeast peptides and one or more plant peptides (most preferably one or more of rice, aloe vera, soy, maize, wheat, pea, squash, spinach, carrot, potato, sweet potato, tapioca, avocado, barley, coconut and/or green bean, and/or one or more other plants), e.g., see international application no. PCT/US97/18255, published as WO 98/15614.
  • one or more cytokines soy peptone
  • yeast peptides and one or more plant peptides
  • plant peptides most preferably one or more of rice, aloe vera, soy, maize, wheat, pea, squash, spinach, carrot, potato, sweet potato, tapioca, avocado, barley, coconut and/or green bean, and/or one or more other plants
  • the culture medium of the present invention may also optionally include one or more buffering agents to maintain an optimal pH.
  • Suitable buffering agents include, but are not limited to, N-[2-hydroxyethyl]-piperazine-N′-[2-ethanesulfonic acid] (HEPES), MOPS, MES, phosphate, bicarbonate and other buffering agents suitable for use in cell culture applications.
  • a suitable buffering agent is one that provides buffering capacity without substantial cytotoxicity to the cells cultured. The selection of suitable buffering agents is within the ambit of ordinary skill in the art of cell culture.
  • host cells may be grown in standard media well known to one of ordinary skill in the art.
  • the media will usually contain all nutrients necessary for the growth and survival of the cells.
  • Suitable media for culturing eukaryotic cells are, Roswell Park Memorial Institute (RPMI) medium 1640 (RPMI 1640), Minimal Essential Medium (MEM), and/or Dulbecco's Modified Eagle Medium (DMEM), DMEM/F12, and ExCell 325 medium, all of which may be supplemented with serum and/or growth factors as indicated by the particular cell line being cultured.
  • RPMI Roswell Park Memorial Institute
  • MEM Minimal Essential Medium
  • DMEM Dulbecco's Modified Eagle Medium
  • DMEM/F12 Dulbecco's Modified Eagle Medium
  • ExCell 325 medium all of which may be supplemented with serum and/or growth factors as indicated by the particular cell line being cultured.
  • the invention provides that the serum in the media is then removed from the culture to obtain host cells that can grow in serum
  • the invention provides optimal media for culturing host cells under serum-free conditions for maximal production of rFurin.
  • the cells are grown in serum-free medium in suspension culture. Recipes for the various media of the invention are provided in the Examples herein.
  • an antibiotic or other compound useful for selective growth of transformed cells is added as a supplement to the media.
  • the compound to be used will be dictated by the selectable marker element present on the plasmid with which the host cell was transformed.
  • Selectable markers that confer resistance to particular drugs that are ordinarily toxic to an animal cell can be used in the methods and compositions of the invention.
  • the selectable marker element is kanamycin resistance
  • the compound added to the culture medium will be kanamycin.
  • Other compounds for selective growth include ampicillin, tetracycline, geneticin, neomycin, zeomycin (zeo); puromycin (PAC); Blasticidin S (BlaS), and GPT. Additional selectable markers are known in the art and useful in the compositions and methods of the invention.
  • Metabolic enzymes that confer cell survival or induce cell death under prescribed conditions can also be used in the methods and compositions of the inventions. Examples include, but are not limited to: dihydrofolate reductase (DHFR); herpes simplex virus thymidine kinase (TK), hypoxanthine-guanine phosphoribosyltransferase (HGPRT), and adenine phosphoribosyltransferase (APRT), which are genes which can be employed in cells lacking TK, HGPRT or APRT, respectively.
  • DHFR dihydrofolate reductase
  • TK herpes simplex virus thymidine kinase
  • HGPRT hypoxanthine-guanine phosphoribosyltransferase
  • APRT adenine phosphoribosyltransferase
  • the medium can be used to culture any host cells or hosts known in the art for recombinant protein production.
  • an exemplary host cell is a CHO cell.
  • the medium is used to culture CHO cells in suspension.
  • the medium can be harvested periodically, so that the same host cells can be used through several harvest cycles.
  • Culture medium may be added in a batch process, e.g. where culture medium is added once to the cells in a single batch, or in a fed batch process in which small batches of culture medium are periodically added. Medium can be harvested at the end of culture or several times during culture.
  • Continuously perfused production processes are also known in the art, and involve continuous feeding of fresh medium into the culture, while the same volume is continuously withdrawn from the reactor. Perfused cultures generally achieve higher cell densities than batch cultures and can be maintained for weeks or months with repeated harvests. Thus, chemostat cultures and batch reefed cultures are both suitable for the manufacturing of rFurin, as are other culture methods known in the art.
  • a variety of culture systems are known in the art, including T-flasks, spinner and shaker flasks, roller bottles and stirred-tank bioreactors.
  • Roller bottle cultivation is generally carried out by seeding cells into roller bottles that are partially filled (e.g., to 10-30% of capacity) with medium and slowly rotated, allowing cells to attach to the sides of the bottles and grow to confluency.
  • the cell medium is harvested by decanting the supernatant, which is replaced with fresh medium.
  • Anchorage-dependent cells can also be cultivated on microcarrier, e.g. polymeric spheres, that are maintained in suspension in stirred-tank bioreactors. Alternatively, cells can be grown in single-cell suspension.
  • the amount of rFurin produced by a host cell can be evaluated using standard methods known in the art. Such methods include, without limitation, Western blot analysis, SDS-polyacrylamide gel electrophoresis, non-denaturing gel electrophoresis, High Performance Liquid Chromatography (HPLC) separation, immunoprecipitation, ELISA, and/or activity assays such as DNA binding gel shift assays.
  • HPLC High Performance Liquid Chromatography
  • activity assays such as DNA binding gel shift assays.
  • specific productivity expressed as amount of protein/cell/day
  • rFurin can be evaluated using standard methods as known in the art and as described herein.
  • substantially animal protein-free rFurin is defined as encompassing preparations of rFurin comprising host cell protein in a concentration which ranges from between about 0.1 to 0.6 ng protein or less/Unit furin activity or between about 2 and 11 ⁇ g protein or less/mL and essentially lacking contaminating proteins from serum in the culture medium.
  • the substantially animal protein-free rFurin encompasses preparations of rFurin comprising host cell DNA in a concentration which ranges from between about 0 to 0.4 pg DNA or less/Unit furin activity or between about 0 and 24 ng DNA or less/mL and essentially lacking contaminating proteins from serum in the culture medium.
  • host cells expressing rFurin are grown in a chemically-defined, serum-free medium. Alternatively, the cells may be grown in medium with serum and purified according to methods provided herein.
  • Host cells expressing rFurin are cultured in suspension in a medium free of animal (including human) derived substances under chemostat conditions.
  • the cells are removed by filtration and the rFurin containing cell culture supernatant is concentrated by ultrafiltration and purified by ion exchange chromatography to result in a solution of rFurin with an activity of at least about 1000 Units/ml, of at least about 2000 Units/ml, of at least about 3000 Units/ml, of at least about 4000 Units/ml, of at least about 5000 Units/ml, of at least about 6000 Units/ml, of at least about 7000 Units/ml, of at least about 8000 Units/ml, of at least about 9000 Units/ml, of at least about 10000 Units/ml, of at least about 15000 Units/ml, of at least about 20000 Units/ml, of at least about 25000 Units/ml, of at least about 30000 Units
  • the purified solution of recombinant furin of the invention has a specific activity of at least about 10 U/ ⁇ g protein, at least about 20 U/ ⁇ g protein, at least about 30 U/ ⁇ g protein, at least about 40 U/ ⁇ g protein, at least about 50 U/ ⁇ g protein, at least about 60 U/ ⁇ g protein, at least about 70 U/ ⁇ g protein, at least about 80 U/ ⁇ g protein, at least about 90 U/ ⁇ g protein, at least about 100 U/ ⁇ g protein, at least about 120 U/ ⁇ g protein, at least about 140 U/ ⁇ g protein, at least about 160 U/ ⁇ g protein, at least about 180 U/ ⁇ g protein, at least about 200 U/ ⁇ g protein, at least about 250 U/ ⁇ g protein, at least about 300 U/ ⁇ g protein, at least about 350 U/ ⁇ g protein, at least about 400 U/ ⁇ g protein, at least about 450 U/ ⁇ g protein, at least about 500 U/ ⁇ g protein, at least about 550 U/ ⁇ g protein, at least about 600 U/ ⁇ g protein
  • the purified solution of rFurin in the invention contains host cell protein at a concentration of less than about 20.0 ⁇ g/ml, less than about 19.0 ⁇ g/ml, less than about 18.0 ⁇ g/ml, less than about 17.0 ⁇ g/ml, less than about 16.0 ⁇ g/ml, less than about 15.0 ⁇ g/ml, less than about 14.0 ⁇ g/ml, less than about 13.0 ⁇ g/ml, less than about 12.0 ⁇ g/ml, less than about 11.0 ⁇ g/ml, less than about 10.5 ⁇ g/ml, less than about 10.0 ⁇ g/ml, less than about 9.5 ⁇ g/ml, less than about 9.0 ⁇ g/ml, less than about 8.5 ⁇ g/ml, less than about 8.0 ⁇ g/ml, less than about 7.5 ⁇ g/ml, less than about 7.0 ⁇ g/ml, less than about 6.5 ⁇ g/ml, less
  • the purified solution of rFurin in the invention contains host cell protein at a concentration of less than about 1.0 ng protein/U rFurin, less than about 0.95 ng protein/U rFurin, less than about 0.90 ng protein/U rFurin, less than 0.85 ng protein/U rFurin, less than about 0.80 ng protein/U rFurin, less than about 0.75 ng protein/U rFurin, less than about 0.70 ng protein/U rFurin, less than about 0.65 ng protein/U rFurin, less than about 0.60 ng protein/U rFurin, less than about 0.55 ng protein/U rFurin, less than about 0.50 ng protein/U rFurin, less than about 0.45 ng protein/U rFurin, less than 0.40 ng protein/U rFurin, less than about 0.35 ng protein/U rFurin, less than about 0.30 ng
  • CHO cells have been widely used in the production of recombinant proteins, and engineered CHO cells (those in which a CHO cell line is transfected with a product gene and a selectable marker gene) are routinely grown in culture medium containing serum.
  • engineered CHO cells (those in which a CHO cell line is transfected with a product gene and a selectable marker gene) are routinely grown in culture medium containing serum.
  • serum poses a number of problems. Serum is an expensive commodity, which is not readily available in amounts required for commercial production. Serum is also a biochemically undefined material and contains many components which have not been fully identified nor their actions determined. Thus serum will differ from batch to batch, possibly requiring testing to determine levels of the various components and their effect on the cells.
  • bovine antibodies in bovine serum albumin (BSA) makes purification of the desired antibodies expressed by the recombinant CHO cell line extremely difficult. Removal of bovine antibody from medium prior to use is possible, but this removal and the additional product testing required after removal adds greatly to the cost of production of the product. Consequently, there are benefits in using a culture medium devoid of animal components which will support cellular growth, especially of CHO cells. While CHO cells do not readily grow in serum-free conditions, the present invention provides rFurin grown in CHO cells under serum-free conditions.
  • Engineered CHO cells are also difficult to grow in suspension. It is highly desirable to achieve growth in suspension when using the cells to express a product like rFurin. For the production of such a biological protein on a commercial scale, it is desirable to be able to support growth in fermenters of a considerable size. A suitable medium is also required to support the cells so that they may grow in large production conditions. Such suitable media are set out in the Examples herein. The worker of ordinary skill in the art will appreciate that any methods of culturing cells in the art can be used in culturing the host cells comprising rFurin as set out in the invention. Non-limiting examples of culture methods are provided in the Examples herein.
  • the invention also provides purification methods that are carried out after cells are grown in serum-free medium to remove CHO cell proteins from rFurin.
  • the worker of ordinary skill in the art will appreciate that any methods of protein purification known in the art can be used in the purification of rFurin from the culture medium. Non-limiting examples of purification methods are provided in the Examples herein. Accordingly, rFurin which is essentially substantially free from all animal source protein can be produced. The substantially animal protein-free rFurin is optionally stored frozen until use.
  • Example 1 describes the construction of a rFurin expression plasmid and host cell transfection;
  • Example 2 describes the processes of adapting the rFurin-expressing CHO cell clones to growth in serum-free conditions;
  • Example 3 describes a process of optimization for manufacturing rFurin in animal-protein free medium;
  • Example 4 describes the purification of rFurin;
  • Example 5 sets out the downstream processing (concentration and purification) and analysis of the large scale production of rFurin; and
  • Example 6 demonstrates the safety, sterility, and stability testing that is performed to determine and maintain the quality of the host cell bank.
  • furin progenitor plasmids used to construct a rFurin expression plasmid designated #556 is set out in Table 1. Expressed under control of a constitutive cytomegalovirus (CMV) promoter, the mature rFurin contains the catalytic domain, the P domain, and a small portion of the cystine-rich domain whereas regions located C-terminal to amino acid 577 are removed leading to a fully secreted active protease.
  • CMV cytomegalovirus
  • DHFR-vector used as the selection plasmid is depicted in Table 2.
  • Table 2 A description of the construction of the DHFR-vector used as the selection plasmid is depicted in Table 2.
  • CHO cells lacking a functional endogenous DHFR gene were co-transfected with plasmids # 556 and # 73 employing calcium phosphate co-precipitation. Clones secreting high levels of rFurin were selected in several rounds of subcloning and amplification using the DHFR/MTX selection system.
  • the plasmid amongst other restriction sites provides a human cytomegalovirus also the unique sites for SmaI immediate early (CMV IE) gene and AvrII. promoter and enhancer, the RNA splicing signals from the SV40 genome consisting of the late viral protein gene 16s/19s splice donor and acceptor sequences, and the SV40 polyadenylation signal.
  • the original vector pCMV ⁇ is a pUC19 derivative containing the E. coli ⁇ 3.4 kbp ⁇ - galactosidase cDNA inserted into the NotI site.
  • DHFR plasmid generation Plasmid Description Comments # 29
  • pAdD26SV(A)-3 was obtained from H. J. Hauser (GBF, Braunschweig, Germany).
  • This plasmid contains the full length murine dihydrofolate reductase (DHFR) cDNA behind an adenovirus major late promoter.
  • DHFR murine dihydrofolate reductase
  • # 73 Murine DHFR-cDNA under control of the The PstI fragment comprising SV40 early promoter.
  • the DHFR cDNA and the SV40 polyadenylation signal of plasmid # 29 was cloned into the PstI site of plasmid # 53.
  • plasmid # 73 contains two polyadenylation signals.
  • # 53 Eukaryotic expression vector from The ⁇ -galactosidase NotI- Clontech (Palo Alto, CA, USA) which has cassette was removed and a been modified to contain a multiple multiple cloning site was inserted cloning site instead of the ⁇ - instead having amongst other galactosidase cDNA.
  • the plasmid restriction sites also a unique provides a simian virus 40 (SV40) early site for PstI.
  • the original vector pSV40 ⁇ is a pUC19 derivative containing the E. coli ⁇ 3.4 kbp ⁇ - galactosidase cDNA inserted into the NotI site.
  • FIG. 2 A pedigree of the generation of the CHO/rFurin clone # 488-3 is depicted in FIG. 2 .
  • Clone CHO/rFurin # 488-3 was obtained from initial clones which underwent two rounds of subcloning in 10% DHFR selection medium before entering amplification in selection medium supplemented with 100 nM MTX in which one round of subcloning in medium containing unchanged MTX concentration was performed.
  • Clone # 448-3 was expanded for freezing.
  • the CHO/rFurin clone # 289-20 was likewise prepared and expanded. However, clone #289-20 is a successor clone derived from clone #488-3.
  • a pedigree of the generation of the CHO/rFurin clone # 289-20 is depicted in FIG. 3 .
  • Furin activity was measured in the conditioned medium of clones, which were cultured for 24 hrs in serum-free DHFR medium. Cell clones which showed high furin activity (U/10 6 cells per 24 hrs) were selected. Selected high producer clones were expanded for the preparation of freeze stock ampules, and used for splitting for the next cloning round. Isolation and identification of high producer cell clones was performed. Cell densities were analyzed using the Casy cell-counter. Furin expression levels of up to 200-300 U/10 6 cells per 24 hrs were achieved for clone # 488-3. Furin expression levels of up to 400 U/10 6 cells per 24 hrs were achieved for clone # 289-20.
  • the strategy for cell line adaptation and selection is to adapt the cell line to a serum- and protein-free cell line in either gradually in a step-wise dilution or abruptly.
  • the purpose of this study was to find a CHO cell population growing under serum-free conditions, which was stably producing rFurin.
  • the CHO cell clone #488-3 was used as starting material.
  • the rFurin expressing cell clone CHO #488-3 was changed over to serum-free conditions in three parallel conducted adaptations as set out in detail below.
  • the serum depletion process started in spinner flasks with use of microcarriers to find a means to hold back cells in the phase of adaptation, since in that phase cells usually show slow growth. By using this method, it was possible to avoided, during subsequent media changes, diluting the cells to such concentrations where growth could be inhibited.
  • BAP Three variants of an in-house developed medium, BAP, BAS, and BCS, (as shown in Table 3) were used during the course of this study.
  • Table 5 summarizes media and reagents which were used for the establishment of the pre-master cell bank clones PMCB#01 and the PMCB#04.
  • Table 6 summarizes media and reagents which were used in the course of sub-cloning and establishing of the corresponding evaluation cell banks (ECBs) of the sub-clones #488-3/CJ06-19/5F10 (5F10) and #488-3/CJ06-19/1E8 (1E8).
  • Adaptation to serum-free conditions was performed in T-flasks or in spinner flasks in conjunction with cell retention (centrifugation and the like) by weaning off the cells from fetal bovine serum (FBS).
  • FBS fetal bovine serum
  • the clones were expanded in 24-well plates, then in T25 flasks, then in T75 flasks, and then in T175 flasks.
  • IPC in process controls
  • the supernatants of the cell cultures were used to determine the amount and activity of expressed rFurin. Fluorescence activated cell sorting (FACS) analysis was used to see the ratio of producer to non-producer cells in a given cell population. Morphology and growth behavior of cells were determined by optical control. Additionally, the supernatant of the cell cultures was also examined to monitor medium conditions, such as the determination of the pH value and the residual concentration of glucose, glutamine, lactate, and ammonium. These analyses were performed by means of a NOVA instrument.
  • FACS Fluorescence activated cell sorting
  • Cells were prepared in 150 ml growth medium (BAS with Put, Glut, Synp and Fe) containing 5% FBS, 0.2 g/l. Cytopore 2 carriers were used for the adaptation to serum-free conditions. Having inoculated the 5-day old cell suspension resulting in a starting cell density of about 2.0 ⁇ 10 5 cells/ml, the cells attached to the porous carriers within the first hours. Thus, the cells were kept in the spinner flask, while the growth medium was exchanged to reduce the serum concentration in two steps, from 5% to 3.8% to 0% on day 05. During the following culture period the cells got adapted to the serum-free medium conditions. The cells detached from the surface of the carriers and continued their growth in suspension. The cell density and the viability of the suspension cells increased continuously. Every two to three days the suspension cells were split in a ratio of 1:2.
  • An evaluation cell bank (ECB) was then prepared. On culture day 28, cells having a viability of greater than 60% were transferred to a new experiment. The culture was grown in 200-300 ml BAS medium (with Put, Glut, Synp and Fe) in a Bellco spinner without carriers. According to the determined CASY cell density, the suspension culture was split every two to three days to a starting cell density of about 2.0 ⁇ 10 5 cells/ml. After 16 days, when the cell culture reached a viability of greater than 80%, the evaluation cell bank (ECB) consisting of six vials of cells was produced.
  • BAS medium with Put, Glut, Synp and Fe
  • One vial of the ECB was thawed in a new experiment.
  • the cells were grown for four days in a T175 in BAS medium with Put, Glut, Synp, Fe and Zn. Cells were then transferred to a Bellco spinner containing up to 600 ml BAS medium with Put, Glut, Synp, Fe and Zn. Again, every two to three days the suspension culture was split to a starting cell density of about 2.0 ⁇ 10 5 cells/ml. On culture day 13, 143 ml of the cell suspension were removed for the preparation of the PMCB#01, consisting of 20 vials. The cells were expanded and quality control tests were performed on PMCB#01.
  • a Bellco spinner flask was prepared with BAS medium (with addition of Put, Glut, Synp and Fe) containing no FBS and no carriers.
  • the cells were inoculated with a starting cell density of about 2.5 ⁇ 10 5 cells/ml. Due to the sudden serum-free conditions, the doubling time of the cells decreased to a rather low level. To avoid diluting the cells to such a concentration where growth could be possibly inhibited, the medium was changed by spinning down the cell suspension. The cell pellet was resuspended in fresh growth medium. Culture splits were performed when the cell density was greater than 4.0 ⁇ 10 5 cells/ml.
  • the cells After having reached a minimum viability of about 50% at culture day 15, the cells started to recover and, from culture day 32 and on, their viability increased to between 85-90%. On culture day 61, the adapted cells were frozen as an ECB consisting of 15 vials.
  • One vial of the ECB was thawed in a new experiment in serum-free BAS medium comprising Put, Glut, Synp and Fe. After the culture was cultured in T175 flasks for seven days, it was transferred to a Bellco Spinner, where the cells grew for two further days. Then, the addition of Zn was tested. About 100 ml of the centrifuged cell suspension were resuspended in serum-free BAS medium containing Put, Glut, Synp, Fe and Zn. The suspension was cultured in a Bellco Spinner. According to the determined CASY cell density, every two to three days the suspension culture was split to a starting cell density of about 2.0 ⁇ 10 5 cells/ml.
  • the cell culture was scaled up to 1000 ml in a Bellco Spinner. On culture day 02, 465 ml of the cell suspension were used to produce the PMCB#04, consisting of 20 ampules. The cells were expanded and quality control tests were performed on PMCB#04.
  • FIG. 4 sets out a comparison of the graphical distribution of the rFurin producers in the cell populations of PMCB#01 and PMCB#04. 80.74% of the cells in PMCB#04 express rFurin. 74.06% of the cells in PMCB#01 express rFurin.
  • CHO/rFurin #488-3 subclones CJ06-19/5F10 and CJ06-19/1E8 were then generated.
  • An ampule of the CHO/rFurin clone #488-3 was thawed and the culture was passaged in a T175 flask.
  • BAP medium developed by Baxter
  • CD-CHO provided by Gibco
  • ExCell 325 PF CHO provided by JRH
  • the cells were weaned off from serum in small steps. The whole procedure ranged over three experiments.
  • the anchorage-dependent cells were initially cultured in T175 flasks in ExCell 325 PF CHO containing 5% FBS. The serum was then slowly reduced to 0.5% on culture day 13. During the next 13 culture days two splits were performed, wherein the serum concentration was further reduced to 0.25% and the viability decreased to lesser than 70%. The cells lost their anchorage-dependent behavior, showed more and more spherical shape, and started to grow in suspension.
  • the cells were then subcloned.
  • a cell suspension was diluted with preconditioned ExCell 325 PF CHO in such a way, that 100 ⁇ l of the suspension theoretically contained 0.5-1.0 cells.
  • five 96-well plates were filled with 100 ⁇ l of this cell suspension per well. The day after the seeding of the cells, the wells were searched for single cells under the microscope. Wells containing one cell were marked and observed further. Addition and exchange of preconditioned ExCell 325 PF CHO were performed when necessary. When the cell died or in the absence of cell division during the next two weeks, the relevant well was excluded from the experiment.
  • the evolved clones having reached an appropriate size, were transferred into a well of a 24-well plate.
  • the exchange of preconditioned ExCell 325 PF CHO was also performed according to the growth and the requirements of the culture.
  • the subclones CJ06-19/5F10 and CJ06-19/1E8 were transferred into a T25 flask on culture day 07 and day 10, respectively.
  • the ECBs were prepared in ExCell medium. These ECBs present the source material for further investigations concerning the two subclones, such as a re-adaptation from expensively purchased media to a more economical formulation, self-developed by Baxter.
  • ECB of sub clone CJ06-19/5F10, CJ06-42 was expanded in ExCell 325 PF CHO medium from a T25, to a T75, to a T175, and then into a Bellco Spinner.
  • the ECB/CJ06-63 consisting of 10 vials were frozen from a culture out of the T175 on day 21.
  • ECB of subclone CJ06-19/1E8, CJ06-43 was also expanded in ExCell 325 PF CHO medium.
  • the culture was expanded from a T25, to a T75, to a T175, and then into a Bellco Spinner.
  • the ECB/CJ06-64 consisting of 10 vials were frozen from a culture out of the T175 on day 18.
  • the ECBs (Subclones 5F10 and 1E8) were adapted to BCS medium as set out below.
  • the subclone CJ06-19/5F10 of ECB clone CJ06-19 was thawed in experiment CJ06-66, and then by adding BCS medium to ExCell medium in an increasing volume, the cells were weaned from ExCell medium and acquired the ability to grow in BCS medium.
  • the subclone CJ06-19/1E8 of ECB clone CJ06-19 was simultaneously adapted to BCS medium in a similar manner.
  • Table 8 shows all serum-free cell banks which were prepared in the course of this study.
  • the cell populations cultured in the experiments CJ06-69 as well as SK06-49 and SK06-63 represent the precursor cultures of the cell lines for the PMCBs. These cells were grown in BAS medium (with the addition of Put, Glut, Synp, Fe and Zn), and were frozen as PMCB#01 and PMCB#04, respectively.
  • the subclones 5F10 and 1E8 were grown in the commercially available medium ExCell 325 PF CHO provided by JRH. Because the ability of growing in medium based on the BAS formulation was preferred, PMCB#01 and PMCB#04 were chosen for further production of rFurin.
  • the cells of PMCB#04 showed better growth behavior in comparison to PMCB#01. Viabilities and growth rates were greater in PMCB#04, and generation doubling times were lower. The cell-specific as well as the volumetric production ratio of rFurin was also greater throughout the evaluated period of time. In a further experiment, the data concerning the viabilities was confirmed. One ampule of each of the PMCBs was thawed into a T175 flask containing BCS medium with Zn as additive. As shown in Table 10 the viability of PMCB#04 was again greater than that of PMCB#01.
  • PMCB#04 was chosen as the source material for the future production of a rFurin Master Cell Bank (MCB) and all further working cell banks (WCBs).
  • MBCB Master Cell Bank
  • WBs further working cell banks
  • the PMCB#04 consisting of 20 vials was established in compliance with the current Good Tissue Practice regulations. Quality Control (QC) testing was performed in accordance to requests of the ICH-Guideline Q5D.
  • PMCB#04 was chosen for producing rFurin in manufacturing processes.
  • the growth medium is free of human or animal derived substances and is self-developed. Having the cells removed by filtration, the rFurin containing supernatant is concentrated by ultrafiltration. After purification by exchange chromatography, the activity of the rFurin solution is aimed to be at least 200 Units rFurin/ml.
  • the criteria for selection are high Furin activity (e.g., Furin protein, ELISA) and homogeneity of the cell population in immunoflourescence (FACS), performed on different subclones in comparison to initial clones #488-3 and #289-20, respectively.
  • FACS immunoflourescence
  • the impurity profiles have to be compared qualitatively (e.g. by UV-peak patterns after RP HPLC or by SDS-PAGE/Coomassie techniques).
  • This example describes the development and optimization process for the culture of the rFurin expressing CHO clone #488-3.
  • Specific medium optimization with regard to amino acids, glucose, and NaHCO3 concentration was carried out, which resulted in increased cell growth rates and higher productivities of the fermentation process.
  • Optimization for inline controlled process parameters was carried out with the optimized medium formulation for pO2 (10%, 20% and 50%), and a factorial experiment was carried out to determine optimum pH (range 7.1-7.3) and temperature (range 35.1° C.-37.9° C.), which resulted in a significant yield improvement for CHO clone #488-3 when fermentation was carried out at lower temperatures between 35°-36° C.
  • a subclone # 488-03 was developed in-house which was adapted to a serum- and insulin-free medium.
  • the following experiments were carried out in a FBS-free and insulin-free medium (BACD-medium) as the basic medium formulation (see Table 11).
  • glutamine was added to the medium (300 mg/L) to give a final concentration of glutamine at 900 mg/L. After the addition of glutamine to the medium the growth rate increased from 0.55 d ⁇ 1 to 0.67 d ⁇ 1 (see Tables 13 and 14).
  • these three amino acids mentioned above namely methionine (10 mg/L), leucine (40 mg/L) and phenylalanine (10 mg/L)
  • the growth rate of the cells could be increased again (0.69 d ⁇ 1 ) (see Table 15).
  • the supplementation of the medium with glutamine, methionine, leucine and phenylalanine showed a positive effect on cell growth, and volumetric and specific activity, and was therefore retained for further medium preparation.
  • a growth rate of 0.52 d ⁇ 1 was reached at a cell count of 1.49 ⁇ 10 6 cells/mL and a dilution rate of 0.53 d ⁇ 1 in the same interval.
  • the viability was reduced to 86.1%, compared to 95.9% at 7.5% CO 2 .
  • volumetric productivity was reduced to approximately 36% and the specific productivity to 50%. Due to the high CO 2 concentration, the specific glucose uptake rate was decreased as well ( ⁇ 39%). The negative influence of an increased CO 2 concentration (11-12%) on cell growth and productivity was quite obvious and, therefore, it is optimal to carry out the fermentation at 7.5% CO 2 .
  • the concentration of dissolved CO 2 during fermentation was adjusted to 7-8% in the fermenter with 2 g/L NaHCO 3 and to 6-7% in the fermenter with 1.5 g/L NaHCO 3 by constant CO 2 gassing in the head space.
  • the growth rates of both cultures were similar (0.58 and 0 56 d ⁇ 1 ) and the cultures showed comparable volumetric productivities and viabilities.
  • the specific glucose uptake rate was slightly higher in the culture with a lower NaHCO 3 concentration (0.83 mg/10 6 cells/d vs. 0.67 mg/10 6 cells/d). Therefore, a glucose concentration of 4.65 g/L was considered to be reasonable and was retained in further medium preparation.
  • the regular concentration of Synperonic F68 in the cell culture medium was set at 0.25 g/L.
  • the purpose of Synperonic F68 in the medium is to protect the cells from damage due to submerged oxygenation. Therefore, one experiment was carried out in 2 ⁇ 10 L bioreactors, where an increased Synperonic F68 concentration of 1.0 g/L vs. the regular concentration of 0.25 g/L was investigated.
  • the fermentation was carried out at 35.8° C. at a pH of 7.30 and with a pO 2 of 20%.
  • RSM Response Surface Methodology
  • FIG. 6 Analysis of the data in reference to the volumetric productivity.
  • a surface plot was created ( FIG. 6 ).
  • the coordinates of the data in FIG. 6 are marked as points.
  • the surface shows the assumed correlation of the single data.
  • the surface plot supposes a linear correlation between the parameters temperature/pH and the responding volumetric productivity.
  • the chart indicates an increase of the volumetric productivity with decreasing temperature.
  • the influence of the pH is considered to be weak.
  • Subsequent calculations showed a linear correlation of the data (calculation not shown).
  • an equation was generated which describes the correlation between pH, temperature and volumetric productivity:
  • FIG. 7 Based on the mathematical model a contour plot was generated ( FIG. 7 ) which illustrates the influence of temperature and pH on the volumetric productivity. The dots indicate the conditions (pH/temp.) which had been tested experimentally.
  • the contour plot shows that the area, where maximum volumetric productivity can be expected, is at 35.1° C. and a pH of approx. 7.10. Both values are at the edge of the experimental design which means that the real maximum could be found even below those values. Furthermore the Contour plot shows that the influence of the pH on the volumetric productivity is marginal and slightly higher at low pH values.
  • the surface plot ( FIG. 8 ) which is a three-dimensional illustration of the mathematical model, gives the same result as the contour plot: the strong influence of the temperature and the weak influence of the pH on the volumetric productivity.
  • the surface plot ( FIG. 9 ) illustrates the modeled correlation three-dimensionally, demonstrates the quadratic relationship, and shows a maximum growth rate at 36.5° C.
  • the chemostat- and the batch reefed-fermentations were run in parallel, using the same cell culture as inoculum.
  • the cells were cultured in the chemostat mode until day 6.
  • one fermentation run was switched to the batch refeed mode (FUR — 06 — 50-F03) while the other one was continued in the chemostat mode (FUR — 06 — 51-F04).
  • Culture in the batch refeed mode resulted in a mean cell count of 2.22 ⁇ 10 6 cells/mL at the end of the batch, with a growth rate of 0.64 d ⁇ 1 (Table 20).
  • a growth rate of 0.50 d ⁇ 1 was obtained with an average cell count of 1.67 ⁇ 10 6 cells/mL. Due to the higher cell count and growth rate in the batch refeed mode, the volumetric productivity was greater as well (238 vs. 197 kU/L/d).
  • the batch refeed mode harvest- and further downstream processes are restricted to certain intervals, while in the chemostat mode, harvesting can be performed continuously.
  • each method has its advantages. No optimization experiments for the parameters of the batch reefed mode were performed like for the optimal cell counts at the end of a batch or for the best split ratio.
  • Table 21 gives an overview of the bioreactor set-ups.
  • the agitation rate of 60 rpm with ball impellers gave a similar tip speed as the rushton impeller at 90 rpm (see Table 21).
  • the tip speeds cannot be equated with each other due to the different geometry of the impellers (shape, diameter).
  • the fermentation conditions were as follows: 37° C., pH 7.15, pO 2 of 20% and pCO 2 of 6-7%. (Medium: 4.65 g/L Glc, 1.5 g/L NaHCO 3 ). Comparison of the fermentation data showed that the performance in the bioreactor with the standard set-up, i.e. equipped with the rushton impeller and agitated at a rate of 170 rpm, was higher than in the bioreactors with the other set-ups (Table 22). The use of ball impellers at 60 rpm resulted in a somewhat lower growth rate (0.57 vs. 0.61d-1), a lower volumetric (197 vs.
  • a similar batch reefed process was carried out, where a 2-3 consecutive two day batch cycles were started with a starting cell density of 0.5 ⁇ 10E06 cells/mL. The experiment was carried out at 2 different agitation rates, i.e. 55 rpm and 120 rpm). Culture conditions were identical with the culture conditions used in the PP1: pH-SP 7.15, Temp-SP 35.5° C., pO2-SP 20%. Data from the last batch were compared after adaptation to the respective agitation conditions.
  • This example provides methods for the filtering and purifying rFurin.
  • the collected cell culture supernatants were first filtered on depth filters (Cuno Zetaplus filters) to get them cell-free and particle-free, followed by membrane filtration at 0.45 ⁇ m PVDF filters (PALL Fluorodyne II).
  • the filtered cell culture supernatant containing the rFurin was then concentrated by ultrafiltration on 10 K PES UF cassettes from Sartorius (Sartocon PESU 10 kDa) with concentration factors ranging from 10-50.
  • the furin concentrates (with furin activity ranging from 290-1700 Units/ml) were then stored in aliquots at ⁇ 60° C.
  • a purification procedure on an anion exchange resin was developed that required a loading conductivity of ⁇ 5 mS/cm (RT) for efficient binding of rFurin.
  • the elution was then performed as a step procedure at an ionic strength of approximately 500-300 mM NaCl and during the screening phase, a gradient elution up to 300 mM NaCl was applied (see overview in Table 24).
  • the original pH of the buffers of 6.7 (RT) was increased to 7.5 to improve binding of rFurin during loading, in particular at high protein loading and high liner flow rates (see summary of relevant buffers in Table 25).
  • the purification experiments were performed on EMD TMAE (Merck) and CaptoQ (GE Healthcare) anion exchange resins that differed in the stability of the packed and the maximum flow rate to operate.
  • the analytical data summarized in Table 26 show that rFurin can be concentrated from the cell culture supernatant up to 362 fold with yields ranging from 20-71%.
  • the rFurin activities in the eluate pools was between 639 Units/ml and 27651 Units/ml depending on the load applied.
  • the CHO impurity level in the eluate was found in a range between 10-134 ng CHO protein/Unit rFurin and reduction rates up to 12.3 with a slightly better performance for CHO reduction found for the CaptoQ resin.
  • This example describes other methods used in the concentration and purification (i.e., downstream processing) of large-scale rFurin. Such processing methods include ultrafiltration, diafiltration, and capto-MMC chromatography, that was carried out in the production of substantially animal protein-free rFurin. It also describes methods of analyzing protein concentration, specific activity, and contamination by host cell protein and DNA.
  • the supernatant (approx. 800-1200 kg in the Chemostat campaigns, and approx. 550-700 kg in the RFB-campaigns) was separated from the cells and concentrated to a final volume of 3545 L by ultrafiltration.
  • the parameters and setpoints of the Ultrafiltration/Diafiltration System (UFS) during the concentration step are listed in Table 27.
  • Diafiltration Immediately after finishing the concentration step, diafiltration of the retentate was initiated.
  • the parameters and setpoints of the UFS during the diafiltration step are listed in Table 28.
  • Capto-MMC Chromatography The Capto-MMC gel, a multimodal cation exchanger, was used to bind rFurin and to eliminate the vast majority of contaminants from the diafiltrated product. After equilibration of the chromatography gel, the diafiltered product is loaded to the column. A 0.22 ⁇ m filter capsule was installed to perform an online filtration of the diafiltered product. The further chromatographic steps are listed and detailed in Table 29.
  • the mean values of all three campaigns for the Host Cell Protein and Host Cell DNA content reveal rather low mean maximum values of 8.55 ⁇ g/ml (ranging from 2.2-10.4 ⁇ g/ml) and 13.48 ng/ml (ranging from 0.0-23.9 ng/ml), respectively (see Table 30).
  • the chromatographic step was able to reduce the specific contamination to low mean maximum values of 0.35 ng CHO Protein/U rFurin Activity (ranging from 0.13-0.52 ng CHO Protein/U) and 0.148 pg Host Cell DNA/U rFurin Activity (ranging from 0.0-0.365 pg DNA/U rFurin Activity).
  • Furin Activity Assay The purified rFurin batches (Capto-MMC eluate pools) were tested for enzymatic activity of Furin.
  • the substrate is a short synthetic peptide containing the dibasic recognition sequence attached to a fluorescent amino-methyl coumarin (AMC) group, that is released after cleavage (BOC-RVRR-AMC).
  • AMC fluorescent amino-methyl coumarin
  • BOC-RVRR-AMC fluorescent amino-methyl coumarin
  • the released fluorogenic group can be detected by excitation at 380 nm and subsequent measurement of the emitted light at 435 nm.
  • One activity unit is defined as the release of 1 pMol of AMC per minute at 30° C.
  • rFurin activity was in the range of about 10000 U/ml up to more than about 100000 U/ml, with a mean value of approx. 69000 U/ml (Table 32, Table 32, and Table 34).
  • An increase of rFurin activity for the RFB mode campaigns was noticed, especially when comparing the mean values of the Chemostat campaign ORFU06002 (47737 U/ml) with the mean values of RFB campaigns ORFU07001 (77653 U/ml) and ORFU07002 (93178 U/ml). (Overall, rFurin activity ranged from about 10000 to greater than 100000 U/ml; all data not shown).
  • the specific activity of Furin is expressed as the activity U/ ⁇ g protein (see Tables 32-34).
  • the mean specific activity for campaign ORFU06002 was 269 U/ ⁇ g protein, increasing to 500 U/ ⁇ g for ORFU07001 and 563 U/ ⁇ g for ORFU07002, respectively. (Overall, specific activity ranged from 124-620 U/ ⁇ g protein; data not shown).
  • specific activity doubled for the two RFB campaigns a result of the higher enzymatic activity of the RFB rFurin compared to the batches produced in Chemostat mode.
  • the Furin-Use-Test is designed to quantify the efficacy of rFurin to process pro-VWF to mature rVWF.
  • the maturation efficacy is expressed as the amount of Furin units required for the maturation of 1 VWF Antigen unit (U Furin/U VWF).
  • the substrate is a proVWF/VWF preparation that has been purified at Pilot scale according to the current manufacturing procedure but omitting the Furin maturation and the final purification step on Superose 6.
  • the rVWF substrate concentration was 100 U Ag/ml (F8HL — 24 — 01UF02-R).
  • SDS-PAGE Western Blot Western blot analysis for all samples was performed using a monoclonal anti-Furin antibody ( FIG. 13 ). The prominent band at ⁇ 60 kDa can be identified as the Furin band and is found in all samples. Comparability of the samples is very high. Slight variations in band intensity are due to the different Furin concentration in the samples. Overall, SDS-PAGE analysis underlines the comparability of rFurin produced in Chemostat and RFB mode.
  • IEF Isoelectric Focusing
  • IEF of samples of campaign ORFU07002 was carried out using Coomassie staining and Western blot analysis for visualization.
  • Coomassie staining reveals the specific band pattern with all samples showing at minimum five separate bands in the range of pH 4.5 to pH 5.5, and up to eight bands can be identified (see FIG. 15 , Lane 3).
  • Chromatograms of all tested samples show a characteristic main peak at a retention time of approx. 13 min., which can be assigned to Furin. The peak heights correlate well with the Furin concentration in the samples. Other protein impurities can be seen as minor peaks in the range of 8 min to 17 min. All samples from campaign ORFU07002 show significantly less and smaller peaks from impurities than those from ORFU06002. This fact is well in accordance with the results of SDS-PAGE, as in the RFB mode campaign ORFU07002 a smaller number and decreased amount of impurities were found.
  • This example describes the safety, sterility, and stability testing that is performed to determine and maintain the quality of the CHO cell bank. Testing on sterility/mycoplasma has to be performed in accordance to requests of the ICH-Guideline Q5D. The quality of the cell bank has to be checked by determination of average viability and cell density of the thawed cells and subsequent growth rate of the cultures.
  • Cells were tested for viral safety (Table 38), genetic stability (Table 39), and identity (Table 40). Cells were found to be sterile, free of mycoplasma, free from extraneous agents, free from retroviruses, negative for MVM virus, negative for adventitious viruses, negative for rodent viruses, free from porcine and bovine viruses, and free from Cache Valley virus (CVV).
  • CVV Cache Valley virus
  • Cells from the MCB/WCB should show stable growth and Furin expression over the entire production process.

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TWI666319B (zh) * 2014-08-12 2019-07-21 美商巴克斯歐塔公司 在分泌ｆｕｒｉｎ之哺乳動物表現系統中生產經完全加工且具功能性之因子Ｘ
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