Growth Rate Changes in CHO Host Cells Are Associated with Karyotypic Heterogeneity

Chinese hamster ovary (CHO) cell line instability and clonality issues can affect cell culture phenotypes such as cell growth, productivity, or product quality and remain challenges for biopharmaceutical manufacturing. While there have been efforts for characterizing cell line instability in CHO production cell lines, a pre-existing level of cell line instability in CHO host cells has not been determined. In this study, cell line instability and chromosomal heterogeneity of the host, CHO-DUK cell line, is reported by using a karyotyping approach. Long-term cultures and karyotype analysis of CHO-DUK cells revealed that the growth rate was higher in later passage cultures, correlating with an increase in the population ratio containing the mar3 chromosome. To further investigate a correlation between growth rate and karyotype, CHO-DUK cells are subcloned by limiting dilution and the growth rate and karyotype of each subclone are determined. Subclones containing the mar3 chromosome exhibit higher cell growth rates than subclones without the mar3 chromosome. Finally, karyotype analysis indicate that CHO-DUK cells, as well as limiting-diluted subclones, exhibit a karyotypically heterogeneous population, suggesting that chromosomal rearrangements occur spontaneously and frequently even in non-engineered host cells. These results demonstrate CHO host cell line instability and suggest that chromosomal instability and karyotypic changes are associated with compromised clonality (heterogeneity), affecting cell line (in)stability in CHO host cells.