Purification of Oncolytic Viruses - a New Challenge for Membrane Processes

Oncolytic viruses (OVs) are a class of cancer therapies that are currently going through clinical trials on their way to full approval. They are attractive given their inherent specificity for disease targets. The upstream production procedure of these bio-therapeutic molecules vectors results in a high amount of cell debris, host cell proteins, and nucleic acids that must be removed to meet the guidelines of regulatory authorities.  Thus, there is a need for robust, high-yielding manufacturing downstream processes (DSP) to improve the speed of production, along with the yields and purity of OV products.  One of the primary challenges during production is the final sterile filtration step – some recent studies have reported an over 80% loss in the vector titer.  The objective of this study is to develop new filtration processes that can achieve the required purity requirements but at the higher throughputs and lower losses that are needed for full-scale production of OVs.

For this work, a purified lot of the Maraba virus (MG1) was provided by the Mulcahy Family Manufacturing Facility (at the Ottawa Hospital Research Institute) to study the filtration performance in a dead-end (i.e. normal flow) configuration. The Maraba virus is from the rhabdovirus family and features a unique bullet-shaped, enveloped structure.  The effects of formulation buffer conditions (salt concentrations, buffer type, buffer concentrations, and pH values), membrane type, and the length of the holding time before the filtration step were studied.  Our hypothesis is that virus aggregation is the dominant reason for the high losses reported in recent studies.  The transmembrane pressure (TMP) profile was used to monitor for membrane fouling and the number of plaque forming units (PFUs) was used to assess the virus concentration.  Future work will use unpurified lots of the same Maraba virus solution to assess the performance of different membrane filters under actual DSP conditions.