Perfluorocarbon-mediated aeration applied to recombinant protein production by virus-infected insect cells

Abstract

Perfluorocarbon (PFC) was used as an oxygen carrier in the cultures of insect cells and virus-infected insect cells. The cell suspensions were placed on a planar layer of PFC, which was re-oxygenated in an outer aeration unit and continuously recirculated, and were agitated by two sets of impeller blades, lower one of which was set in such a way that the ridge of the blade touched the PFC layer. The maximum cell density attained in the PFC-mediated aeration culture was higher than that in surface aeration culture. On viral infection, a recombinant protein yield was significantly high in the PFC-mediated aeration culture as compared with that in the surface aeration culture, though the production was largely decreased by setting apart the lower set of the blade from the PFC–medium interface. These results showed that the PFC-mediated aeration would be a useful technique for insect cell/baculovirus expression system. Overall mass-transfer coefficient K L for oxygen was examined in both the PFC-mediated aeration and surface aeration systems, by using a flask whose dimensions were identical to those of spinner flasks used for the cultures. The K L value in the PFC-mediated system was 2.60×10 −3 cm s −1 , 1.6 times higher than that in the surface aeration system, when impeller blades were positioned at PFC–medium and medium–air interfaces, respectively. However, the K L values in both the PFC-mediated and surface aeration systems were decreased and their differences were brought so close, as the blade was set apart from the interfaces. DO behavior in the cultures was well explained by the model calculation using the determined K L values and oxygen-consumption rates of viable cells. This calculation further suggested that crucial DO, under which recombinant protein productions were unsuccessful, was 0.24–0.5 ppm (3–7%) in the insect cell/baculovirus expression system.