The use of site-specific recombination and cassette exchange technologies for monoclonal antibody production in Chinese Hamster ovary cells: retrospective analysis and future directions

Chinese hamster ovary (CHO) cell-based platforms are the most widely used for the biomanufacturing of complex therapeutic proteins, such as monoclonal antibodies (mAbs). The development of high-producing clones that are stable and amenable to large-scale cultures is essential to advance a molecule toward clinical evaluation. Nevertheless, the generation of such clones generally relies on random integration of an expression plasmid encoding the therapeutic protein gene into the host genome. The ensuing clone selection relying on empirical screens and cell line characterization is extensive and time-consuming. An emerging paradigm in CHO cell line development is the use of site-specific recombinases to enable the integration of therapeutic transgenes into pre-marked chromosomal locations with defined expression characteristics. Recombinase-mediated cassette exchange (RMCE) provides a sophisticated alternative to conventional CHO cell line development, leading to the generation of more consistent and reliable clones and may ultimately shorten the "time-to-clinic" of recombinant therapeutics. Herein, we review the recent advances in the use of site-specific recombination systems and their associated cassette exchange technologies for the rapid generation of stable CHO clones with predictable growth, stability, quality and productivity characteristics. Particular emphasis is placed on cassette exchange technologies currently used in the industry. We also discuss the technical hurdles associated with uses of site-specific recombinase systems in CHO cells, illustrate how these problems can be mitigated and provide a perspective on future work concerning these systems.