Apoptosis in Acute Vascular Rejection of Porcine Organs Trasplanted into Primates in not an Antibody triggered Event

Apoptotic events are consistently observed in acute xenograft rejection (AHXR) of pig organs transplanted into primates. The pathogenic events responsible for these findings have yet to be identified, however. The aim of this study was to investigate the role of the humoral immune response elicited in the onset of apoptosis in the xenograft of long-term surviving primates. Methods: Four nephrectomised cynomolgus monkeys received an hDAF porcine renal xenograft (Novartis Pharma AG, Basel, Switzerland) and were immunosuppressed with cyclophosphamide (up to 4 doses), cyclosporine A, mycophenolate sodium (Novartis) and steroids. Sera from each primate were sampled pre-transplant and at the time of euthanasia. The apoptotic capacity of the sera was assessed on porcine aortic endothelial cells (PAEC) isolated from hDAF pigs. Primary cells were incubated for 18, 24 and 48 hrs with different concentrations of primate sera. Cells were stained with propidium iodide and analysed by flow cytometry for the appearance of a sub-diploid DNA peak. Swine rTNFα (50-100ng/ml), camptothecin (5-10μM) and normal human serum (NHS) were used as positive controls; normal pig serum (NPS) was used as a negative control. Results: AHRX in the xenograft was consistently observed when the animals were euthanised between 13 and 90 days after transplantation. At the doses considered, TNFα and camptothecin led to apoptosis of 14-32% of the PAEC analysed. At the concentration used, NHS was able to induce apoptosis of up to 28% of PAEC. In contrast, apoptosis was not observed when PAEC were incubated with the primate sera taken before transplantation or at the time of euthanasia in the presence of AHXR. Conclusion: The apoptosis invariably observed in AHXR of pig organs transplanted into primates is not an antibody-driven event.