Porcine endogenous retroviruses (PERVs) are integrated into the genome of all pigs and can infect human cells in culture. However, no PERV infections have been reported in recipients following preclinical or clinical xenotransplantation or deliberate infection experiments. Detection of PERV infection in transplanted recipients is challenging due to microchimerism, such as the presence of pig cells containing PERV proviruses in the recipient. Based on our previous publications on PERV detection in xenotransplant recipients, particularly from the first clinical trials, we developed a comprehensive strategy to screen for PERV infections. Recipients can be monitored for increasing levels of viral genomic RNA and mRNA using real-time reverse transcriptase (RT)-PCR, which can indicate PERV expression and replication. To test this strategy, explanted pig hearts and organs from baboons after pig heart transplantation were analyzed. No PERV genomic RNA or mRNA was detected in these tissues, although both were found in PERV-producing human control cells. Screening for antibodies against PERV as indirect evidence of infection is the method of choice. Recombinant viral proteins were prepared for use in Western blot assays. Animal antisera generated through immunization with recombinant PERV proteins served as positive controls. No antibodies against PERV were detected in transplanted baboons, even though microchimerism was observed in many of the animals' organs. For effective antibody screening, at least two PERV proteins should be used as antigens.
