Apoptosis-resistant NS/0 E1B-19K myelomas exhibit increased viability and chimeric antibody productivity under cell cycle modulating conditions.

Lymphoid cells expressing sufficient levels of Bcl-2 or E1B-19K are known to resist to induction of apoptosis in glutamine-free or nutrient-limited batch cultures. However, despite the increased viability and prolonged stationary phase achieved in batch culture, product yields are not necessarily improved. Here we have found that expression of E1B-19K in NS/0 myeloma cells cultivated in the presence of certain cell cycle modulators could result in a significant increase in MAb productivity as compared to untransfected control cells. The use of E1B-19K significantly enhanced cell survival in the presence of osmolytes (sorbitol, NaCl), DNA synthesis inhibitors (hydroxyurea, excess thymidine), and the cell culture additive OptiMAbtrade mark. E1B-19K myelomas cultivated in the presence of NaCl or OptiMAbtrade mark accumulated in the G1 phase, while those arrested with excess thymidine were blocked in all phases. Interestingly, control NS/0 cells treated with these agents were found to die in a cell-cycle specific manner. Thus, while all G1 and most S phase cells quickly underwent apoptosis, G2/M cells remained alive and maintained MAb secretion for more than 10 days if supplied with adequate nutrients. For both control and E1B-19K cells, incubation with sorbitol or hydroxyurea was detrimental for MAb secretion, while addition of NaCl, excess thymidine and OptiMAbtrade mark resulted in an increased specific MAb productivity as compared to the batch culture. However, this increase resulted in an improvement of final MAb yields only in the case of OptiMAbtrade mark. The extension of viability conferred by E1B-19K allowed to further improve the final MAb yield obtained using OptiMAbtrade mark with a 3.3-fold increase for E1B-19K cells as compared to 1.8-fold for control NS/0 cells.