Background: The xenotransplantation of organs and tissues, in particular those from pigs, is viewed as a means to alleviate the shortage of human donor organs and cells available for transplantation and also as a therapy for other diseases. The potential microbiological hazards of xenotransplantation have recently attracted much attention. One concern is over pig endogenous retroviruses (PERV). Until the possible consequences of infection by PERV are better understood it is unlikely that a significant number of porcine xenotransplants will proceed. However, a small number of patients have already been treated with or exposed to living porcine cells or tissue, and investigation of these patients may provide valuable information.
Methods: We took serial blood samples from two renal dialysis patients whose circulation had been linked extracorporeally to pig kidneys and tested them for pig DNA and PERV DNA by nested PCR. The patients' plasma was also tested for neutralising antibodies to two anthropotropic PERV strains.
Findings: Having established that the nested PCRs could detect single molecules of target sequence, we analysed DNA isolated from patients' peripheral blood mononuclear cells. We found no evidence of pig or PERV DNA in either patient, even in samples taken as early as 6 h after the perfusion. Furthermore, we found no evidence of seroconversion for PERV-specific antibodies.
Interpretation: The absence of porcine cells in the circulation of both patients, even in the samples taken soon after the perfusion experiment, suggests that any porcine cells dislodged from the kidney became rapidly sequestered from the circulation. Since cell-to-cell contact increases the efficiency of infection of PERV this removal of porcine cells may increase the risk of transmission of PERV to the xenograft recipient. We did not, however, detect indications of infection by PERV by PCR or neutralisation assay. The genetic and serological methods described here will be useful for detection of possible PERV infection in other patients.