Absence of PERV infection in baboons after transgenic porcine liver perfusion

Background. Xenotransplantation offers great promise to supplement the shortage of human organs available for transplant, but cross-species infection is a substantial concern. Porcine endogenous retrovirus (PERV), in particular, is thought to pose a risk as a potential pathogen to humans. We evaluated whether PERV is capable of infecting nonhuman primates in vivo after extracorporeal porcine liver perfusion (ECLP). Methods. Livers were harvested from six human decay-accelerating factor (h-DAF) transgenic piglets and perfused with fresh baboon blood via the portal vein and the hepatic artery. Six healthy baboons underwent direct cross-circulation with the ECLP for 13 to 24 h without immunosuppression. Peripheral blood and bone marrow of baboons were sampled periodically until the baboons were euthanized for the examination of various organ tissue samples. Genomic DNA was extracted from those samples and tested for PERV and pig-specific centromeric DNA sequences by quantitative PCR. Validation showed that the assay could detect one copy of PERV in a background of 150,000 baboon cells, and it was quantitative over a range from 10 to 10 ⁶ copies of PERV. Results. PERV sequences were detected in a high number (4.4 × 10³-1.6 × 10⁴/1 μg) in peripheral leukocyte DNA during the initial phases of ECLP, but they disappeared within 1 week. Bone marrow DNA contained PERV sequences longer than peripheral blood, but PERV signals became negative within 1 month. No PERV DNA relapse was seen over the course of this study. Pig-specific centromeric sequences were also detected in the same manner. At 6 months or 1 year after ECLP, no PERV or pig-specific centromeric sequences were detected in the genomic DNA obtained from the following organs: skin, lymph nodes, spleen, liver, pancreas, kidney, heart, and lung. Conclusions. ECLP did not result in PERV infection or pig-cell microchimerism in baboons.