1.1 This practice assures 5 log10 inactivation of non-defective C-type retroviruses, which are endogenous to murine hybridoma and CHO cells and are potentially present in the production stream of biopharmaceutical processes that use rodent derived cell culture. 1.2 The process parameters specified in this practice consistently assure 5 log10 inactivation of murine retrovirus by adjusting the pH of a process solution after initial affinity capture chromatography purification. 1.3 This practice is applicable to mAb, IgG fusion, or other recombinant proteins produced from rodent cell lines (for example, CHO or murine hybridoma), which do not target retroviral proteins. Additionally, the low pH step is performed on a cell-free intermediate, post initial capture using protein A chromatography. 1.4 The 5 log10 inactivation of murine retrovirus claimed by using this practice will be utilized in conjunction with other clearance unit operations (for example, chromatography and virus retentive filtration) to assure sufficient total process clearance of murine retroviruses, which will be supportive of early phase regulatory filings. 1.5 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard. 1.6 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.