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20 BioPharm International eBook July 2021 www.biopharminternational.com Detecting Residual HCPs Demands a Holistic Approach Gene therapy products present a unique set of challenges for the control of host cell protein impurities. R esidual host cell proteins (HCP) are inevitable impurities in any biopharmaceutical product. In contrast to traditional recombinant proteins like monoclonal antibodies (mAbs) manufac- tured in Chinese hamster ovary (CHO) cells, viral vector-based gene therapy products present additional HCP control challenges from a strategic process develop- ment perspective. Such viral vectors are t y pically manufactured using human cell lines such as HEK293, which present a poten- tially complex proteome background. Contrasting with recombinant proteins purif ied from cell culture superna- tant, the harvest of viral vectors typically relies on cell lysis, meaning the entire proteome may contribute to the HCP load presented to the downstream purification process. Additionally, instead of the chemically def ined media used in CHO production processes, virus production relies on protein growth factors and protein-containing additives including serum originated from other non-host cell species. Finally, the purification steps used for viral vectors may be more limited in number, impacting their overall capacity to separate the virus product from other proteinaceous impurities. Adding to these technical challenges, gene therapy programs are often intended for severe indications and, therefore, are more likely to be placed on an accelerated development pathway. This time pressure conf licts with the OLAF STAMM, PhD, is scientific advisor, biologics testing; ANDREW HANNEM AN, Ph D, is sc ientif ic ad v isor, biologic s te s ting; AR T CANSIZOGLU, PhD, is senior scientist, and THORSTEN STRAHL is supervisor protein and scientific officer, all with Charles River. OLAF STAMM, ANDREW HANNEMAN, ART CANSIZOGLU, AND THORSTEN STRAHL Biopharmaceutical Analysis Impurity Analysis eplisterra - Stock.adobe.com