Screening pigs for xenotransplantation: prevalence and expression of porcine endogenous retroviruses in Gottingen minipigs

Background To establish the safety of xenotransplantation when cells, tissues, or organs of pigs are used, an effective screening for potential zoonotic microorganisms has to be performed. In doing so, special attendance has to be paid to porcine endogenous retroviruses (PERVs) that are widely distributed as proviruses in the genome of pigs. PERV-A and PERV-B are present in all pigs, they infect human cells in vitro and therefore represent a direct risk. PERV-C infects only pig cells; however, recombinant PERV-A/C infecting human cells and replicating at a higher rate were found in pigs indicating an indirect risk. To prevent the transmission of PERV, it was suggested to use animals characterized by a low expression of PERV-A and PERV-B that are free of PERV-C and cannot generate recombinants. Gottingen minipigs are used for numerous biomedical investigations and they are well characterized; however, the prevalence and the expression of PERV in these animals were not yet investigated. Methods The presence and expression of all PERVs including a new variant (nv) of PERV-C and PERV-A/C were analyzed using PCR and real-time PCR methods. Altogether, 15 animals belonging to different families were analyzed. To make a low expression better measurable, peripheral blood mononuclear cells (PBMCs) of the animals were stimulated with phytohaemagglutinin generally increasing the expression of PERV and allowing a better classification into animals with high and low expression. As a major end point, the release of virus particles able to infect susceptible human 293 cells was investigated. Results PERV-A, PERV-B, PERV-C, and PERV-Cnv were found in the genome of all investigated Gottingen minipigs, but recombinant PERV-A/Cs were not found. When the expression of PERV was compared with that in previously analyzed pig strains, it was higher than in German landrace and some other pigs, but lower than in Yucatan miniature pigs. Virus particles able to infected human 293 cells were not detected even after mitogen treatment of the PBMCs. Conclusion The Gottingen minipigs are well defined concerning their physiologic parameters, their health status, and their genetics, and therefore, they may be considered as donor animals for at least cell xenotransplantation. When the prevalence and the expression of PERVs were analyzed in these animals, it was demonstrated that although PERV-A, -B, and -C proviruses were found in all animals, their expression was low. Additional investigations are required to assess the suitability of Gottingen minipigs and other animals for xenotransplantation in terms of microbiological safety.