Identification of exogenous forms of human-tropic porcine endogenous retrovirus in miniature Swine.

The replication of porcine endogenous retrovirus subgroup A (PERV-A) and PERV-B in certain human cell lines indicates that PERV may pose an infectious risk in clinical xenotransplantation. We have previously reported that human-tropic PERVs isolated from infected human cells following cocultivation with miniature swine peripheral blood mononuclear cells (PBMC) are recombinants of PERV-A with PERV-C. Here, we report that these recombinants are exogenous viruses in miniature swine; i.e., they are not present in the germ line DNA. These viruses were invariably present in miniature swine that transmitted PERV to human cells and were also identified in some miniature swine that lacked this ability. These data, together with the demonstration of the absence of both replication-competent PERV-A and recombinant PERV-A/C loci in the genome of miniature swine (L. Scobie, S. Taylor, J. C. Wood, K. M. Suling, G. Quinn, C. Patience, H.-J. Schuurman, and D. E. Onions, J. Virol. 78:2502-2509, 2004), indicate that exogenous PERV is the principal source of human-tropic virus in these animals. Interestingly, strong expression of PERV-C in PBMC correlated with an ability of the PBMC to transmit PERV-A/C recombinants in vitro, indicating that PERV-C may be an important factor affecting the production of human-tropic PERV. In light of these observations, the safety of clinical xenotransplantation from miniature swine will be most enhanced by the utilization of source animals that do not transmit PERV to either human or porcine cells. Such animals were identified within the miniature swine herd and may further enhance the safety of clinical xenotransplantation.

Identification of receptors for pig endogenous retrovirus.

Xenotransplantation of porcine tissues has the potential to treat a wide variety of major health problems including organ failure and diabetes. Balanced against the potential benefits of xenotransplantation, however, is the risk of human infection with a porcine microorganism. In particular, the transmission of porcine endogenous retrovirus (PERV) is a major concern [Chapman, L. E. & Bloom, E. T. (2001) J. Am. Med. Assoc. 285, 2304-2306]. Here we report the identification of two, sequence-related, human proteins that act as receptors for PERV-A, encoded by genes located on chromosomes 8 and 17. We also describe homologs from baboon and porcine cells that also are active as receptors. Conversely, activity could not be demonstrated with a syntenic murine receptor homolog. Sequence analysis indicates that PERV-A receptors [human PERV-A receptor (HuPAR)-1, HuPAR-2, baboon PERV-A receptor 2, and porcine PERV-A receptor] are multiple membrane-spanning proteins similar to receptors for other gammaretroviruses. Expression is widespread in human tissues including peripheral blood mononuclear cells, but their biological functions are unknown. The identification of the PERV-A receptors opens avenues of research necessary for a more complete assessment of the retroviral risks of pig to human xenotransplantation.

Porcine endogenous retrovirus transmission characteristics of an inbred herd of miniature swine.

Here we report the identification of inbred miniature swine that failed to produce human-tropic replication-competent porcine endogenous retroviruses (HTRC PERVs), using in vitro coculture assays. When HTRC PERVs were isolated from transmitting animals, all were recombinant viruses, with the receptor-binding domain of PERV-A combining with PERV-C-related sequences.