The discussion about the clinical risk of
zoonoses in
xenotransplantation has recently culminated in the demand for a moratorium on clinical
organ transplantation using pig donors. The basis for this discussion was a recent report showing a possible trans-species transmission of pig endogenous retrovirus (PERV) by in vitro transfer to human cell lines. At present, it remains unclear if this could also happen in vivo or in the setting of
xenotransplantation. Potential in vivo transfer of PERV after
xenotransplantation was investigated in an experimental pig-to-baboon
cell transplantation model. Baboons were immunosuppressed with high-dose
cyclophosphamide (total 45-150 mg/kg) and transplanted with primary porcine aortic endothelial cells (PAEC). Tissue samples (skin, lymph nodes, lung) and peripheral blood leukocytes of 15 baboons, taken about 12-24 months after
transplantation of PAEC, were then analyzed by PCR and showed no PERV
infection. PERV expression in PAEC was also analyzed: PERV
mRNA and
reverse transcriptase in the culture supernatant could be detected. In spite of the release of retroviral particles from cultured PAEC,
transplantation of these cells into baboon recipients did not result in virus transmission, not even under heavy immunosuppression.