Population analysis of a recombinant Chinese hamster ovary cell line expressing recombinant human protein cultured in the presence and absence of methotrexate selective pressure

Abstract

We have examined recombinant CHO cell populations expressing a recombinant human protein and mouse dihydrofolate reductase after extended passage in the presence and absence of MTX selective pressure. Population analysis was carried out by methods that generated frequency distribution profiles of cell subpopulations with respect to the relative expression of recombinant human protein and DHFR. Population analysis of recombinant CHO cells after extended culture in MTX showed an increase in heterogeneity with respect to expression of recombinant human protein. In contrast, the same cell populations became more homogeneous with respect to the relative DHFR content per cell. The data suggests that expression of recombinant human protein diverged from expression of DHFR. Implications of changes in the cell population with respect to recombinant human protein product consistency are discussed. Finally, population analysis of recombinant CHO cells continuously cultured in the absence of MTX showed a decrease in the homogeneity of the frequency distribution profiles and an enrichment for lower-producing subpopulations.