Effects of Modified Vaccinia Virus Ankara Expressing Mesothelin and the Poxvirus Immunoregulatory A35R gene in the Treatment of Murine Pancreatic Cancer

Abstract

Pancreatic cancer is the fourth leading cause of cancer-related deaths in the United States. Pancreatic tumors over-express the protein mesothelin, and therefore, it is used as a tumor target antigen for vaccine development. Our current research uses an improved Modified Vaccinia Ankara poxvirus that we developed to express mesothelin to the murine immune system to treat pancreatic tumors and create an anti-cancer vaccine. PCR, Flow Cytometry, and Western Blot confirmed virus construction, purity, and protein expression. Our hypothesis was that the A35R[delta] recombinant virus would be more efficient at stimulating the immune system and better protect against tumors caused by the Panc02 pancreatic adenocarcinoma cell line. MVA was found to both kill and replicate in Panc02 cells, showing it is an oncolytic virus. However, multiple schemes of infection/vaccination and boosts were used without any significant protection from tumor challenge in mice. Assays to determine immune response against mesothelin suggested that mice vaccinated with the mesothelin-expressing vaccine virus did not generate a strong immune response to mesothelin as expected, however the mice had robust immunity to the poxvirus. Together these results suggest that native mesothelin may not be a good vaccine target antigen for cancer treatment, possibly because immune cells responding to this self-protein are deleted and/or suppressed during development of the immune system as a protection against autoimmunity. Strategies for improving anti-mesothelin immunity are being explored.