Donor preconditioning with Carbon Monoxide (CO) in Pig-to-Primate Xenotransplantation.

Introduction: Carbon monoxide (CO) has been shown to possess both anti-inflammatory and anti-apoptotic properties. In the light of the protective role played by CO in the survival of organs and cells in concordant xenotransplantation models in rodents, we explored its potential as a protective strategy in a life-supporting pig-to-cynomolgus monkey renal xenotransplantation model. Materials and methods: CO at a concentration of 500 ppm in compressed balanced air (21% oxygen) was administered to hDAF transgenic pigs (Imutran/Novartis) to maintain a concentration of 15 ± 3% carboxyhemoglobin for 4 hours. To ascertain the biological efficacy of the regimen, we evaluated the in vitro production of TNF-α by LPS-stimulated monocytes isolated from the hDAF donor pigs before and after exposure to CO. Six bilaterally nephrectomised cynomolgus monkeys received a life-supporting kidney and were immunosuppressed with cyclophosphamide (up to 4 intravenous infusions perioperatively only), oral cyclosporine A (Neoral, Novartis), steroids, and oral mycophenolate sodium (Myfortic, Novartis). Haematology and biochemistry were closely monitored postoperatively. Results: The pigs in this group were exposed to a mean of concentration of 358.69 ± 100.7 ppm of exogenous CO. Exposure of donor pigs to this CO regimen significantly reduced the in vitro production of TNF-α in the culture media of PBMCs exposed to LPS (P=0.05). The primates in this series survived for up to 37 days (mean: 14.5 ± 14.3 days; range: 2-37 days). Four animals were euthanised due to kidney failure between day 4 and day 27 after transplantation. The two remaining animals were sacrificed for compassionate reasons. The three longest surviving animals were euthanised in the presence of grade IIIII acute humoral rejection in the graft associated with apoptotic events. Conclusions: In vivo exposure of hDAF pigs to CO at a dose capable of significantly reducing the in vitro production of the pro-inflammatory cytokine TNF-α does not extend the survival of hDAF renal xenografts transplanted into primates.