Monoclonal antibody (MAb) and other therapeutic biologics produced by mammalian cells have the potential to introduce endogenous retroviruses and can be infected with adventitious viruses through raw materials or other parts of the biomanufacturing process (1–3). Based on regulatory guidelines, products derived from mammalian cells must contain less than one virus particle per million doses, which requires purification processes to demonstrate virus removal capabilities of about 12–18 log10 clearance of endogenous retroviruses and 6 log10 clearance for adventitious viruses (4).…