Optimal bioreactor harvest time is typically determined based on maximizing product titer without compromising product quality. We suggest that ease of downstream purification (DSP) should also be considered during harvest. In this view , we studied the effect of anti-apoptosis genes on downstream performance. Our hypothesis was that more robust cells would exhibit less cell lysis and thus generate lower levels of cell debris and host-cell contaminants. We focused on the clarification unit operation , measuring post-clarification turbidity and host-cell protein (HCP) concentration as a function of bioreactor harvest time/cell viability. In order to mimic primary clarification using disk-stack centrifugation , a scale-down model consisting of a rotating disk (to simulate shear in the inlet feed zone of the centrifuge) and a swinging-bucket lab centrifuge was used. Our data suggest that in the absence of shear during primary clarification (typical of depth filters) , a 20-50% reduction in HCP levels and 50-65% lower post-centrifugation turbidity was observed for cells with anti-apoptosis genes compared to control cells. However , on exposing the cells to shear levels typical in a disk-stack centrifuge , the reduction in HCP was 10-15% while no difference in post-centrifugation turbidity was observed. The maximum benefit of antiapoptosis genes is therefore realized using clarification options that involve low shear , < 1x10^6 W/m3 and minimal damage to the cells.
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