A platform for context-specific genetic engineering of recombinant protein production by CHO cells.

An increasing number of engineered therapeutic recombinant proteins with unpredictable manufacturability are currently filling industrial cell line development pipelines. These proteins can be "difficult-to-express" (DTE) in that production of a sufficient quantity of correctly processed recombinant product by engineered mammalian cells is difficult to achieve. In these circumstances, identification of appropriate cell engineering strategies to increase yield is difficult as constraints are cell line and product-specific. Here we describe and validate the development of a high-throughput microscale platform for multiparallel testing of multiple functional genetic components at varying stoichiometry followed by assessment of their effect on cell functional performance. The platform was used to compare and identify optimal cell engineering solutions for both transient and stable production of a model DTE IgG1 monoclonal antibody. We simultaneously tested the functional effect of 32 genes encoding discrete ER or secretory pathway components, each at varying levels of expression and utilized in different combinations. We show that optimization of functional gene load and relative stoichiometry is critical and optimal cell engineering solutions for stable and transient production contexts are significantly different. Our analysis indicates that cell engineering workflows should be cell line, protein product and production-process specific; and that next-generation cell engineering technology that enables precise control of the relative expression of multiple functional genetic components is necessary to achieve this.

Functional heterogeneity and heritability in CHO cell populations.

In this study, we address the hypothesis that it is possible to exploit genetic/functional variation in parental Chinese hamster ovary (CHO) cell populations to isolate clonal derivatives that exhibit superior, heritable attributes for biomanufacturing--new parental cell lines which are inherently more "fit for purpose." One-hundred and ninety-nine CHOK1SV clones were isolated from a donor CHOK1SV parental population by limiting dilution cloning and microplate image analysis, followed by primary analysis of variation in cell-specific proliferation rate during extended deep-well microplate suspension culture of individual clones to accelerate genetic drift in isolated cultures. A subset of 100 clones were comparatively evaluated for transient production of a recombinant monoclonal antibody (Mab) and green fluorescent protein following transfection of a plasmid vector encoding both genes. The heritability of both cell-specific proliferation rate and Mab production was further assessed using a subset of 23 clones varying in functional capability that were subjected to cell culture regimes involving both cryopreservation and extended sub-culture. These data showed that whilst differences in transient Mab production capability were not heritable per se, clones exhibiting heritable variation in specific proliferation rate, endocytotic transfectability and N-glycan processing were identified. Finally, for clonal populations most "evolved" by extended sub-culture in vitro we investigated the relationship between cellular protein biomass content, specific proliferation rate and cell surface N-glycosylation. Rapid-specific proliferation rate was inversely correlated to CHO cell size and protein content, and positively correlated to cell surface glycan content, although substantial clone-specific variation in ability to accumulate cell biomass was evident. Taken together, our data reveal the dynamic nature of the CHO cell functional genome and the potential to evolve and isolate CHO cell variants with improved functional properties in vitro.

Cell line-specific control of recombinant monoclonal antibody production by CHO cells.

In this study we compare the cellular control of recombinant human IgG(4) monoclonal antibody (Mab) synthesis in different CHO cell lines. Based on comprehensive empirical analyses of mRNA and polypeptide synthetic intermediates we constructed cell line-specific mathematical models of recombinant Mab manufacture in seven GS-CHO cell lines varying in specific production rate (qMab) over 350-fold. This comparative analysis revealed that control of qMab involved both genetic construct and cell line-specific factors. With respect to the former, all cell lines exhibited excess production of light chain (LC) mRNA and polypeptide relative to heavy chain (HC) mediated by more rapid LC transcription and enhanced LC mRNA stability. Downstream of this, cell lines differed markedly in their relative rates of recombinant mRNA translation, Mab assembly and secretion although HC mRNA abundance and the rate of HC translation generally exerted most control over qMab--the latter being directly proportional to qMab. This study shows that (i) cell lines capable of high qMab exceed a threshold functional competency in all synthetic processes, (ii) the majority of cells in parental and transfected cell populations are functionally limited and (iii) cell engineering strategies to increase Mab production should be cell line specific.