Risk posed by porcine encephalomyocarditis virus in xenotransplantation

Recent advances toward using pig tissues in human transplantation have made it necessary to determine the risk of transmitting zoonotic viruses from pigs to humans. Encephalomyocarditis virus (EMCV) is a cardiovirus in the family of picornaviruses that causes endemic infection in pigs worldwide and infects many other species, including non-human primates and humans. We demonstrated that pigs inoculated with EMCV developed infection that persisted for up to 90 days in the heart and brain that was accompanied by virus-induced pathologic changes, and that EMCV seronegative pigs harbored viral RNA in their heart tissues. Further, EMCV productively infected primary human cardiomyocytes and persistently infected the heart and central nervous system of cynomolgus macaques, indicating that the virus may pose a risk in pig-to-human transplantation. Transplantation of heart and pancreas tissues from acutely EMCV-infected pigs transmitted the virus to recipient C57BU6-RAG-1-/- (lacking B and T lymphocytes) and C57BU6 mice, resulting in acute fatal EMCV encephalitis, with faster onset and more severe disease in C57BU6-RAG-1 -/- recipients. Transplantation of tissues from chronically EMCV-infected pigs resulted in transmission of viral RNA primarily to the brains of recipient RAG-1-/- mice. EMCV productively infected pig islet cells (PICs), which are being investigated as a treatment for Type I diabetes in humans, resulting in a 1,500-fold increase in infectious virus by 5 hours post-infection, and cytolysis that destroyed up to 50% of cells within 96 hours. As long as cells remained viable, however, infected PICs produced insulin at levels comparable with uninfected PICs. Intra-abdominal transplantation of EMCV-infected PICs resulted in transmission of the virus to C57BU6 recipient mice, resulting in EMCV-induced fatal encephalitis. Moreover, transplantation of EMCV-infected PICs under the kidney capsule of diabetic C57BU6 mice clinically reversed diabetes similarly to uninfected PICs, until the onset of acute EMCV disease 5 days following transplantation. Altogether, the data indicate that EMCV represents a zoonotic risk in xenotransplantation, and is an ideal and reproducible viral xenozoonosis model for the development of vaccination and anti-viral therapies that will prevent disease and preserve xenograft function in transplant recipients.