A genetic off-target event in a site-specific integration cell line expressing monoclonal antibody has no impact on commercial suitability

Site-specific integration (SSI) cell line systems are gaining popularity for biotherapeutic development and production. Despite the proven advantages for these expression hosts, the SSI system is still susceptible to rare off-target events and potential vector rearrangements. Here we describe the development process of an SSI cell line for production of an IgG1 monoclonal antibody (mAb-086). During cell line generational studies to assess suitability of clone C10 for commercial purposes, restriction fragment lengths of genomic DNA harboring the light chain (LC) were not in agreement with the predicted size. We first confirmed that the SSI landing-pad achieved occupancy of the desired expression plasmid. Additional investigation revealed that random integration had occurred, resulting in the acquisition of a partial copy of the LC and a full-length copy of the heavy chain (HC) at a different locus in the host genome. This off-target event had no impact on the genotypic consistency and phenotypic stability of the cell line, the production process, or the drug substance product quality. Given the genetic, phenotypic, and process consistency of the cell line, clone C10 was deemed suitable as a manufacturing cell line.

Automated summary

Site-specific integration (SSI) cell line systems have advantages for biotherapeutic development and production, but they can still experience rare off-target events and vector rearrangements. In this study, we developed an SSI cell line for producing an IgG1 monoclonal antibody. While evaluating the suitability of clone C10 for commercial use, we found unexpected genomic rearrangements but determined that they had no impact on the cell line's genetic consistency, phenotypic stability, production process, or product quality. Based on the consistent genetic, phenotypic, and process characteristics, clone C10 was considered suitable as a manufacturing cell line.