Duplication of a chromosome 2 segment in production CHO cell lines correlates with age-related growth improvement

Monitoring the stability of recombinant Chinese Hamster Ovary (CHO) cell lines is essential to ensure the selection of production cell lines suitable for biomanufacturing. It has been frequently observed that recombinant CHO cell lines develop phenotypic changes upon aging, such as accelerated cell growth in late generation cultures. However, the mechanism responsible for age-correlated changes is poorly understood. In this study, we investigated the molecular mechanisms underlying the age-correlated cell growth improvement in Pfizer's platform fed-batch production process, by examining multiple cell lines derived from different CHO expression systems, expressing a variety of monoclonal antibodies (mAbs). Comprehensive whole-genome resequencing analysis revealed duplication of a continuous 50.2 Mbp segment in chromosome 2 (Chr2) specific to clones that showed age-correlated growth change as compared to clones that did not exhibit age-correlated growth change. Moreover, such age- and growth-related Chr2 duplication was independent of the presence or type of recombinant monoclonal antibody expression. When we compared transcriptome profiles from low-growth and high-growth cell lines, we found that >95% of the genes overexpressed in high-growth cell lines were in the duplicated Chr2 segment. To the best of our knowledge, this is the first report of large genomic duplication, specific to Chr2, being associated with age-correlated growth change. Investigation of the cause-and-effect relationship between the genes identified in the duplicated regions and age-correlated growth change is underway. We are confident that this effort will lead to improved cell line screening and targeted rational cell line engineering efforts to develop cell lines with improved stability performance.