(499c) Sterile Filtration of Oncolytic Viruses Using Novel Nanoporous Silicon Nitride Membranes

Oncolytic viruses (OVs) are a growing class of bio-therapeutics that have attracted significant interest for cancer immunotherapy and are expected to be worth over $1B by 2026. In 2016 alone, there were over 40 clinical trials (phase I, II, and III) conducted, both with OVs on their own and in combination with other cancer therapies. Current Good Manufacturing Practice (GMP) standards for the manufacturing of OVs rely on sterile filtration processes using microporous polymeric membranes to remove microbial contaminants. While this is necessary to ensure the purity and safety of the formulation, sterile filtration can also lead to reduced yield and increased process costs due to entrapment of viruses within the high internal surface area and broad pore distributions of the membrane; new process technologies are required to help optimize the production of OVs.

Nanoslit silicon nitride (NSN) membranes are an emerging technology of considerable potential to address this gap. Fabricated using advanced silicon processing techniques, these ultrathin (<400 nm) membranes have precisely controlled pore size (200-500 nm) and geometry (slit or circular). It is hypothesized that the unique properties of NSN membranes will allow it to significantly reduce the titer loss during sterile filtration while also being amenable to filtration at higher fluxes and lower pressures as compared to traditional membranes. We set out to demonstrate that the novel NSN membranes would enable sterile filtration of viruses while also having titer loss less than 10% (given starting load of ~10¹⁰ PFU/mL) and filtration capacity greater than or equal to commercial membranes (PVDF, PES). The NPN membranes were integrated into custom-built dead-end micro-scale filtration cells and studied under constant flux filtration, while a wide range of variables were monitored and characterized for their effect on performance including membrane properties, operational parameters, and feed composition. The filtration studies were performed using an attenuated strain of the oncolytic Maraba virus, a Rhabdovirus with a unique bullet shape (170 nm x 70 nm) which is currently undergoing clinical trails and shows promise as both an immunotherapy vaccine vector and oncolytic agent. Appropriate theoretical frameworks were used to analyze the experimental results in terms of the underlying bio-physical properties of the OVs and associated impurities (e.g. DNA, host cell proteins).