A comparative study of the bispecific monoclonal antibody,blinatumomab expression in CHO cells and E. coli

Abstract

The “bispecifics” market improved over the past decade due to the development of many technological platforms including bispecific T cell engagers (BiTEs). The approval of blinatumomab, the most advanced bispecific T-cell engager (BiTE) in clinical trials, can be a significant milestone in the development of bispecific antibodies. Both Chinese hamster ovary (CHO) cells and E. coli strain are considered as the most widely used hosts for the large-scale production of therapeutic monoclonal antibodies. Since both of the economic and qualitative aspects of protein production are important in industry, selection of a suitable protein expression system is very critical. The BsAb gene was cloned into the expression vectors FC550A-1, pcDNA3.1 (+), and PET22b and 6?×?His-tagged BsAb then purified on a Ni-NTA chromatography column. Both SDS–PAGE and Western blotting analysis of the purified protein demonstrated that blinatumomab was successfully expressed as a 55?kDa in both expression systems. The antigen-binding properties of blinatumomab were compared in the mammalian system versus Escherichia coli. The results showed that the purified antibody from a mammalian expression system has better binding activity than the one from E. coli host.     

Efficient production of bispecific IgG of different isotypes and species of origin in single mammalian cells

Bispecific IgG production in single host cells has been a much sought-after goal to support the clinical development of these complex molecules. Current routes to single cell production of bispecific IgG include engineering heavy chains for heterodimerization and redesign of Fab arms for selective pairing of cognate heavy and light chains. Here, we describe novel designs to facilitate selective Fab arm assembly in conjunction with previously described knobs-into-holes mutations for preferential heavy chain heterodimerization. The top Fab designs for selective pairing, namely variants v10 and v11, support near quantitative assembly of bispecific IgG in single cells for multiple different antibody pairs as judged by high-resolution mass spectrometry. Single-cell and in vitro-assembled bispecific IgG have comparable physical, in vitro biological and in vivo pharmacokinetics properties. Efficient single-cell production of bispecific IgG was demonstrated for human IgG₁, IgG₂ and IgG₄ thereby allowing the heavy chain isotype to be tailored for specific therapeutic applications. Additionally, a reverse chimeric bispecific IgG_2a with humanized variable domains and mouse constant domains was generated for preclinical proof-of-concept studies in mice. Efficient production of a bispecific IgG in stably transfected mammalian (CHO) cells was shown. Individual clones with stable titer and bispecific IgG composition for >120 days were readily identified. Such long-term cell line stability is needed for commercial manufacture of bispecific IgG. The single-cell bispecific IgG designs developed here may be broadly applicable to biotechnology research, including screening bispecific IgG panels, and to support clinical development.     

Evaluation of different vector design strategies for the expression of recombinant monoclonal antibody in CHO cells

Monoclonal antibodies (mAbs) have emerged as the most promising category of recombinant proteins due to their high efficiency for the treatment of a wide range of human diseases. The complex nature of mAbs creates a great deal of challenges in both upstream and downstream manufacturing processes. Proportional expression and correct folding and assembly of the light chain and heavy chain are required for efficient production of the mAbs. In this regard, expression vector design has proven to have profound effects on the antibody expression level as well as its stability and quality. Here, we have explored the efficiency of different vector design strategies for the expression of a recombinant IgG1 antibody in Chinese hamster ovary (CHO) cells. The antibody expression level was analyzed in transient expression and stable cell pools followed by expression analysis on single-cell clones. While detectable amounts of antibody were observed in all three systems, dual-promoter single-vector system showed the highest expression level in transient and stable expression as well as the highest productivity among clonal cells. Our results here show the importance of vector design for successful production of whole mAbs in CHO cells.     

Stable expression of H1C2 monoclonal antibody in NS0 and CHO cells using pFUSE and UCOE expression system

From our recent publications, it was found that the deimmunization method (Dharshanan et al. (2012) Sci Res Essays 7:2288–2299) should be applied for the development of humanized anti-C2 monoclonal antibody (H1C2 mAb). However, the overlapping-PCR mutagenesis procedure used to insert the variable regions into cloning vectors was laborious and time-consuming. Additionally, the expression of H1C2 mAb in NS0 cells was low in static culture vessels. Therefore H1C2 mAb was redeveloped by deimmunization method with the following modifications in order to optimize the production of H1C2 mAb. First, instead of the overlapping-PCR mutagenesis procedure, synthetic DNA coding the variable regions were used to express the mAb. Second, two expression vectors, pFUSE and UCOE, were used to express H1C2 mAb in NS0 cells and CHO cells in order to investigate the combination that gave the highest number of high producing stable clones. This will provide the highest chance of finding clones with the requisite high productivity and stability required for manufacturing. We found that transfection of UCOE in CHO cells generated the highest number of high producing stable clones. To our knowledge, this is the first time that H1C2 mAb has been expressed in CHO cells.     

Rapid monitoring of recombinant antibody production by mammalian cell cultures using fourier transform infrared spectroscopy and chemometrics

Fourier transform infrared (FT‐IR) spectroscopy combined with multivariate statistical analyses was investigated as a physicochemical tool for monitoring secreted recombinant antibody production in cultures of Chinese hamster ovary (CHO) and murine myeloma non‐secreting 0 (NS0) cell lines. Medium samples were taken during culture of CHO and NS0 cells lines, which included both antibody‐producing and non‐producing cell lines, and analyzed by FT‐IR spectroscopy. Principal components analysis (PCA) alone, and combined with discriminant function analysis (PC‐DFA), were applied to normalized FT‐IR spectroscopy datasets and showed a linear trend with respect to recombinant protein production. Loadings plots of the most significant spectral components showed a decrease in the C–O stretch from polysaccharides and an increase in the amide I band during culture, respectively, indicating a decrease in sugar concentration and an increase in protein concentration in the medium. Partial least squares regression (PLSR) analysis was used to predict antibody titers, and these regression models were able to predict antibody titers accurately with low error when compared to ELISA data. PLSR was also able to predict glucose and lactate amounts in the medium samples accurately. This work demonstrates that FT‐IR spectroscopy has great potential as a tool for monitoring cell cultures for recombinant protein production and offers a starting point for the application of spectroscopic techniques for the on‐line measurement of antibody production in industrial scale bioreactors. Biotechnol. Bioeng. 2010; 106: 432–442. © 2010 Wiley Periodicals, Inc.     

Identification and characterization of a -1 reading frameshift in the heavy chain constant region of an IgG1 recombinant monoclonal antibody produced in CHO cells

Frameshifts lead to complete alteration of the intended amino acid sequences, and therefore may affect the biological activities of protein therapeutics and pose potential immunogenicity risks. We report here the identification and characterization of a novel -1 frameshift variant in a recombinant IgG1 therapeutic monoclonal antibody (mAb) produced in Chinese hamster ovary cells during the cell line selection studies. The variant was initially observed as an atypical post-monomer fragment peak in size exclusion chromatography. Characterization of the fragment peak using intact and reduced liquid chromatography-mass spectrometry (LC-MS) analyses determined that the fragment consisted of a normal light chain disulfide-linked to an aberrant 26 kDa fragment that could not be assigned to any HC fragment even after considering common modifications. Further analysis using LC-MS/MS peptide mapping revealed that the aberrant fragment contained the expected HC amino acid sequence (1-232) followed by a 20-mer novel sequence corresponding to expression of heavy chain DNA sequence in the -1 reading frame. Examination of the DNA sequence around the frameshift initiation site revealed that a mononucleotide repeat GGGGGG located in the IgG1 HC constant region was most likely the structural root cause of the frameshift. Rapid identification of the frameshift allowed us to avoid use of a problematic cell line containing the frameshift as the production cell line. The frameshift reported here may be observed in other mAb products and the hypothesis-driven analytical approaches employed here may be valuable for rapid identification and characterization of frameshift variants in other recombinant proteins.     

Enhanced cell culture performance using inducible anti-apoptotic genes E1B-19K and Aven in the production of a monoclonal antibody with Chinese hamster ovary cells

Mammalian cells are used for the production of numerous biologics including monoclonal antibodies. Unfortunately, mammalian cells can lose viability at later stages in the cell culture process. In this study, the effects of expressing the anti-apoptosis genes, E1B-19K and Aven, separately and in combination on cell growth, survival, and monoclonal antibody (MAb) production were investigated for a commercial Chinese Hamster Ovary (CHO) mammalian cell line. CHO cells were observed to undergo apoptosis following a model insult, glucose deprivation, and at later stages of batch cell culture. The CHO cell line was then genetically modified to express the anti-apoptotic proteins E1B-19K and/or Aven using an ecdysone-inducible expression system. Stable transfected pools induced to express Aven or E1B-19K alone were found to survive 1-2 days longer than the parent cell line following glucose deprivation while the expression of both genes in concert increased cell survival by 3 days. In spinner flask batch studies, a clonal isolate engineered to express both anti-apoptosis genes exhibited a longer operating lifetime and higher final MAb titer as a result of higher viable cell densities and viabilities. Interestingly, survival was increased in the absence of an inducer, most likely as a result of leaky expression of the anti-apoptosis genes confirmed in subsequent PCR studies. In fed-batch bioreactors, the expression of both anti-apoptosis genes resulted in higher growth rates and cell densities in the exponential phase and significantly higher viable cell densities, viabilities, and extended survival during the post-exponential phase. As a result, the integral of viable cells (IVC) was between 40 and 100% higher for cell lines engineered to express both Aven and E1B-19K in concert, and the operational lifetime of the fed-batch bioreactors was increased from 2 to 5 days. The maximum titers of MAb were also increased by 40-55% for bioreactors containing cells expressing Aven and E1B-19K. These increases in volumetric productivity arose primarily from enhancements in viable cell density over the course of the fed-batch culture period since the specific productivities for the cells expressing anti-apoptosis genes were comparable or slightly lower than the parental hosts. These results demonstrate that expression of anti-apoptosis genes can enhance culture performance and increase MAb titers for mammalian CHO cell cultures especially under conditions such as extended fed-batch bioreactor operation.