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 t o resist to induction of apoptosis in glutamine-free or nutrient-limited ba tch cultures. However, despite the increased viability and prolonged statio nary phase achieved in batch culture, product yields are not necessarily im proved. 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 i n a significant increase in MAb productivity as compared to untransfected c ontrol cells. The use of E1B-19K significantly enhanced cell survival in th e presence of osmolytes (sorbitol, NaCl), DNA synthesis inhibitors (hydroxy urea, excess thymidine), and the cell culture additive OptiMAb(TM). E1B-19K myelomas cultivated in the presence of NaCl or OptiMAb(TM) accumulated in the G(1) phase, while those arrested with excess thymidine were blocked in all phases. Interestingly, control NS/0 cells treated with these agents wer e found to die in a cell-cycle specific manner. Thus, while all G(1) and mo st S phase cells quickly underwent apoptosis, G(2)/M cells remained alive a nd 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, exc ess thymidine and OptiMAb(TM) resulted in an increased specific MAb product ivity as compared to the batch culture. However, this increase resulted in an improvement of final MAb yields only in the case of OptiMAb(TM). The ext ension of viability conferred by E1B-19K allowed to further improve the fin al MAb yield obtained using OptiMAb(TM) with a 3.3-fold increase for E1B-19 K cells as compared to 1.8-fold for control NS/0 cells.