Droplet digital PCR: A comprehensive tool for genetic analysis and prediction of bispecific antibody assembly during cell line development

Molecular biological methods have emerged as inevitable tools to accompany the process of cell line development for the generation of stable and highly productive manufacturing cell lines in the biopharmaceutical industry. PCR-based methods are especially useful for screening and characterization of cell lines due to their low cost, scalability, precision and propensity for multidimensional read-outs. In this study, the diverse applications of droplet digital PCR (ddPCR) as a molecular biological tool for cell line development are demonstrated. Specifically, it is shown that ddPCR can be used to enable precise, sensitive and reproducible absolute quantification of genomically integrated transgene copies during cell line development and cell bank characterization. Additionally, an amplitude multiplexing approach is applied to simultaneously run multiple assays on different genetic targets in a single reaction and advance clonal screening by measuring gene expression profiles to predict the assembly and homogeneity of difficult-to-express (DTE) proteins. The implementation of ddPCR-based assays during cell line development allows for early screening at a transcriptional level, particularly for complex, multidomain proteins, where balanced polypeptide chain ratios are of primary importance. Moreover, it is demonstrated that ddPCR-based genomic characterization improves the robustness, efficiency and comparability of absolute transgene copy number quantification, an essential genetic parameter that must be demonstrated to regulatory authorities during clinical trial and market authorization application submissions to support genetic stability and consistency of the selected cell substrate.