Perfusion CHO cell culture applied to lower aggregation and increase volumetric productivity for a bispecific recombinant protein.

Secreted recombinant proteins can aggregate during cell culture. We studied a poorly-behaved bispecific scaffold that increasingly aggregated (up to 62% high molecular weight species, HMW) as a function of culture time in a fed-batch and intensified cell culture processes. We identified that protein aggregates increased with accumulated protein concentration inside the bioreactor. Furthermore, results indicated that a maximum product concentration was reached beyond which no additional soluble protein accumulated in culture even when doubling the integrated viable cell density with the intensified process, suggesting additional secreted protein was precipitating. To overcome this limitation and maintain the cell-specific productivity (q) in culture, we explored a perfusion process where recombinant protein was continuously removed from the bioreactor to maintain low product concentration and consequently, minimize protein aggregation. We studied different viable cell densities (VCDs) inside the bioreactor (one to five-fold) and found a corresponding two-fold modulation of monomer levels. In all VCD conditions, q was maintained. On the contrary, the previous intensified process showed an "apparent" 2.5-fold decrease in q at the end of culture because of the presumed limited protein solubility at higher concentrations. The combination of lower aggregate levels and constant q resulted in up to four to five-fold increase in recoverable product (i.e., monomer) with the improved perfusion process.