Transient gene expression using valproic acid in combination with co-transfection of SV40 large T antigen and human p21^CIP /p27^KIP

Transient gene expression (TGE) in HEK293 cells was optimized by Vink et al. by co-expression of human cell cycle inhibitors p21^CIP /p27^KIP and Simian virus 40 large T antigen (SVLT). In this study, we investigated the effect of this enhancer protein complex on the TGE experiments in a cell-cycle arrested condition of HEK293F cells induced by valproic acid. Growth profiles, consumptions of nutrients, formations of waste products, and product titers of recombinant human antibodies (huAb) were monitored during the 7-day cultivation time. Our results showed that the use of enhancer proteins increased the product yields in a growth arrest condition as well. During the growth phase, no differences were detected regarding viable cell densities (VCDs), viabilities, growth rates, and cell diameters between the TGE experiments with and without enhancer proteins. However, during the declining phase VCD and viability showed slightly higher values at day 6 and 7 in the presence of enhancers. Furthermore, we could not detect any differences in glucose and glutamine metabolism during batch cultivations with co-expression of enhancer proteins. Taken together, the special complex of enhancer proteins did not contribute to further enhancement of growth arrest and shift in the main cell metabolisms, but resulted in higher cell viability during the decline phase. Our observations suggest that the human cell cycle inhibitors p21^CIP /p27^KIP together with very low amount of SVLT antigen may induce alternative functional activities than growth arrest to further improve the yield of recombinant proteins.