Two chimeric human/murine monoclonal antibodies were constructed by substitution of the murine constant regions with human gamma 1 and kappa constant regions for heavy and light chains, respectively. The chimeric human/murine molecules are anti-idiotypic antibodies, meaning that they were directed against the antigen binding site in the variable region of another antibody. Antibody batches were produced under identical production conditions, using two selected SP2/0 myeloma cell subclones, which produce chimeric antibodies with different variable regions, but identical constant regions. Several samples were collected during the production of the antibodies in hollow-fibre reactors. The heavy chain, but not the light chain, of the two different chimeric IgG1 antibodies is glycosylated. Structural analysis of the enzymically released N-linked carbohydrate chains by 1H-NMR spectroscopy, as well as by chromatographic profiling, demonstrated that the collection of N-glycans comprises a small amount of monoantennary, and for the greater part diantennary structures. The N-glycans are completely (alpha 1-->6)-fucosylated at the innermost GlcNAc residue. The antennae of the neutral diantennary N-glycans are built up from GlcNAc beta 1-->2, Gal beta 1-->4GlcNAc beta 1-->2 or Gal alpha 1-->3G alpha 1 beta 1-->4GlcNAc beta 1-->2 elements, whereas the antennae of the neutral monoantennary carbohydrate chains have only (beta 1-->2)-linked GlcNAc residues. Galactosylation of the GlcNAc beta 1-->2Man alpha 1-->6 branch occurs four times more frequently than that of the GlcNAc beta 1-->2Man alpha 1-->3 branch, independently of the production batch. A small amount of the diantennary N-glycans are mono- or disialylated, carrying N-acetylneuraminic acid (Neu5Ac) or N-glycolylneuraminic acid (Neu5Gc), exclusively (alpha 2-->6)-linked to beta Gal. Analysis of the different production batches demonstrates that the structures of the N-linked carbohydrate chains are identical in the two chimeric antibodies, but that the relative amounts of the major oligosaccharide components, the degree of sialylation and the molar ratio of Neu5Ac to Neu5Gc varies with the SP2/0 cell subclone, and only slightly with cell age.
Methods for the selection of transfectoma cells that express large quantities of mouse-human chimeric antibodies have been develped. SP2/0 mouse myeloma cells were transfected with pSV2-gpt and pSV2-neo based immunoglobulin expression vectors. Double transfectants were selected using the xanthine-guanine phosphoribosyl transferase (gpt)and the neomycin (neo) selection marker genes. ELISA-based screening of transfectoma clones resulted in the isolation of IgG-producing transfectomas. Introduction of the kappa light-chain 3'-enhancer into the light-chain expression vector significantly increased immunoglobulin expression, but only when the enhancer was located at its physiological site, 9 kb downstream of the kappa constant region exon. With some of the transfectomas, final yields of up to 80 mg/L of chimeric IgG were obtained in conventional flask cultures using serum-free growth medium. A pilot-scale AcuSyst Maximizer hollow fiber cell culture system was used for the production of gram amounts of chimeric IgG. Results obtained with different transfectoma clones in conventional culture were not fully predictive for yields in the hollow fiber system. In contrast, differences in productivity between individual clones in the laboratory-scale Tecnomouse cell culture unit were comparable with those in the Maximizer system. Up to 200 mg of chimeric IgG were produced per day in one Maximizer bioreactor. (c) 1995 John Wiley & Sons, Inc.
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