Concurrent transfection of randomized transgene configurations into targeted integration CHO host is an advantageous and cost-effective method for expression of complex molecules

Development of a 10 g/L process for a difficult-to-express multispecific antibody format using a holistic process development approach

Ichnos has developed a multi-specific antibody platform based on the BEAT® (Bispecific engagement by antibodies based on the T-cell receptor) interface. The increased complexity of the bi- and multi-specific formats generated with this platform makes these molecules difficult-to-express proteins compared to standard monoclonal antibodies (mAbs). This report describes how expression limitations of a bi-specific bi-paratopic BEAT antibody were improved in a holistic approach. An initial investigation allowed identification of a misbalance in the subunits composing the BEAT antibody as the potential root cause. This misbalance was then addressed by a signal peptide optimization, and the overall expression level was increased by the combination of two vector design elements on a single gene vector. Further improvements were made in the selection of cell populations and an upstream (USP) platform process was applied in combination with a cell culture temperature shift. This allowed titer levels of up to 6 g/L to be reached with these difficult-to-express proteins. Furthermore, a high-density seeding process was developed that allowed titers of around 11 g/L for the BEAT antibody, increasing the initial titer by a factor of 10. The approach was successfully applied to a tri-specific antibody with titer levels reaching 10 g/L. In summary, a platform process for difficult-to-express proteins was developed using molecular biology tools, cell line development, upstream process optimization and process intensification.

Gene copy number, gene configuration and LC/HC mRNA ratio impact on antibody productivity and product quality in targeted integration CHO cell lines

The augmentation of transgene copy numbers is a prevalent approach presumed to enhance transcriptional activity and product yield. CHO cell lines engineered via targeted integration (TI) offer an advantageous platform for investigating the interplay between gene copy number, mRNA abundance, product yield, and product quality. Our investigation revealed that incrementally elevating the gene copy numbers of both IgG heavy chain (HC) and light chain (LC) concurrently resulted in the attainment of plateaus in mRNA levels and product titers, notably occurring beyond four to five gene copies integrated at the same TI site. Furthermore, maintaining a fixed gene copy number while varying the position of genes within the vector influenced the LC/HC mRNA ratio, which subsequently exerted a substantial impact on product titer. Moreover, manipulation of the LC/HC gene ratio through the introduction of surplus LC gene copies led to heightened LC mRNA expression and a reduction in the levels of high molecular weight species. It is noteworthy that the effects of excess LC on product titer were dependent on the specific molecule under consideration. The strategic utilization of PCR tags enabled precise quantification of transcription from each expression slot within the vector, facilitating the identification of highly expressive and less expressive slots. Collectively, these findings significantly enhance our understanding of stable antibody production in TI CHO cell lines.

The impact of expression vector position on transgene transcription allows for rational expression vector design in a targeted integration system

Site-specific integration (SSI) technology has emerged as an effective approach by the pharmaceutical industry for the development of recombinant Chinese hamster ovary (CHO) cell lines. While SSI systems have been demonstrated to be effective for the development of CHO cell lines, they can be limiting in terms of both transgene expression and in the case of multi-specifics, the ability to generate the correct product of interest. To maximize the performance of Pfizer's dual SSI expression system for expressing monoclonal and multi-specific antibodies, we used a novel approach to investigate the positional effect of transgenes within expression vectors by engineering nucleotide polymorphisms (NP)s to use as biomarkers to track the level of transcript output from each expression vector position. We observed differences in transcript level for two different transgenes across all four expression vector positions interrogated. We then applied these learnings to rationally design expression vectors for six different mAbs and a multi-specific antibody. We showed enhanced productivity and optimal product quality when compared to a conventional expression vector topology. The learnings gained here can potentially aid in the determination of optimal vector topologies for several IgG-like multi-specific formats.

Reshaping cell line development and CMC strategy for fast responses to pandemic outbreak

The global pandemic outbreak COVID-19 (SARS-COV-2), has prompted many pharmaceutical companies to develop vaccines and therapeutic biologics for its prevention and treatment. Most of the therapeutic biologics are common human IgG antibodies, which were identified by next-generation sequencing (NGS) with the B cells from the convalescent patients. To fight against pandemic outbreaks like COVID-19, biologics development strategies need to be optimized to speed up the timeline. Since the advent of therapeutic biologics, strategies of transfection and cell line selection have been continuously improved for greater productivity and efficiency. NGS has also been implemented for accelerated cell bank testing. These recent advances enable us to rethink and reshape the chemistry, manufacturing, and controls (CMC) strategy in order to start supplying Good Manufacturing Practices (GMP) materials for clinical trials as soon as possible. We elucidated an accelerated CMC workflow for biologics, including using GMP-compliant pool materials for phase I clinical trials, selecting the final clone with product quality similar to that of phase I materials for late-stage development and commercial production.