1.1 ,This practice assures effective inactivation of ≥,4 log10 of infectious rodent retrovirus (that is, reduction from 10 000 to 1 infectious rodent retrovirus or removal of 99.99 % of infectious rodent retroviruses) in the manufacturing processes of monoclonal antibodies or immunoglobulin G (IgG) Fc fusion proteins manufactured in rodent-derived cell lines that do not target retroviral antigens. Rodent retrovirus is used as a model for rodent cell substrate endogenous retrovirus-like particles potentially present in the production stream of these proteins.