Sterile filtration of oncolytic viruses: An analysis of effects of membrane morphology on fouling and product recovery

Oncolytic viruses (OVs) are an emerging class of bio-therapeutics that have attracted significant interest due to their inherent specificity for targeting malignant tissues in cancer immunotherapy. One of the main challenges in many OVs manufacturing processes is the dead-end sterile filtration step that is highly desirable from a safety and regulatory perspective. The primary issue is the severe membrane fouling, as indicated by a dramatic and uncontrollable transmembrane pressure (TMP) increase in constant flux experiments, and low recovery of the desired final product. While previous studies have mostly focused on selective retention or removal of viruses during the production of smaller biologics, this study is the first to obtain quantitative data for the fouling propensity of microfiltration filters and recovery of viral vectors in a sterile filtration process. The performance of four either 0.2 or 0.22 mu m commercial sterile filters was evaluated in constant flux filtration tests with a promising OV candidate (Rhabdovirus Maraba). Among the tested sterile filters, two-layered sterile filters (i.e. Fluorodyne EX EDF and MiniSart Plus) demonstrated slower transmembrane pressure (TMP) increase along with a higher filtered viral volume. For all four filters, the total viral recovery was quite low (less than 25%) - this significant amount of loss of a valuable therapeutic product is of particular concern. These results provide important insights into the development of new sterile filtration membranes and processes that are critically needed for the large-scale production of OVs.