Evaluating the impact of ionic strength on retention of minute virus of mice during small virus‐retentive filtration

Abstract Small virus‐retentive filtration (VRF) is a critical unit operation utilized in the viral clearance package to ensure the viral safety of biotherapeutics. This step is relied upon to provide effective parvovirus retention of ≥4 log reduction value (LRV) (e.g., minute virus of mice; MVM), and robust retention of larger viruses. Biomolecules, including multispecific antibodies and recombinant proteins, present purification challenges that require multiple chromatography columns to achieve final purity specifications. These additional polishing steps may utilize high ionic strength solution conditions to meet purity targets, and it is critical to assess if those process conditions impact the viral retention performance of the subsequent VRF operations. In one instance, retention performance was lower than expected (≤4 LRV) and was attributed to the use of a high ionic strength buffer. Two possible mechanisms were investigated, that is, reduction in the effective size of the MVM virus (~25 nm) and/or an increase in the membrane filter pore size, as observed with increase in the virus filter permeability. Based on modeling and experimental data presented here, at high ionic strength solution conditions the hydrodynamic size of MVM is reduced while virus‐retentive membrane effective pore size is larger, as compared to low ionic strength conditions. Additionally, MVM LRV and membrane permeability of multiple commercial‐grade virus filters were impacted by high ionic strength and process interruptions. These results demonstrate that high ionic strength solution conditions could impact parvovirus retention performance, and these findings may guide process development for biotherapeutics operating under similar atypical solution conditions.