Analytical subcloning of a clonal cell line demonstrates cellular heterogeneity that does not impact process consistency or robustness.

During development of a cell line intended to support production of an IgG2 monoclonal antibody, a sequence variant caused by a genetic mutation was identified in the bulk drug substance. Gene copy number analysis together with the level of the observed variant in genomic DNA indicated that the master cell bank was a mixed population of cells; some harboring the variant copy and some mutation free. Since the cell bank had been single-cell cloned, this variant could be used as a biomarker to demonstrate either that the bank was not derived from a single cell, or that the variant was a result of a post-cloning genetic event, leading to a mixed population of cells.