BACKGROUND: The coagulation process in hyperacute and delayed xenograft rejection is essential and depends upon platelet adhesion and aggregation. The initial binding of platelets to the damaged endothelium is due to the interaction of the platelet receptor glycoprotein Ib with von Willebrand factor (vWF), which is present on activated endothelial cells and bound to the subendothelial matrix. We hypothesized that the use of organs from animals with homozygous von Willebrand disease (vWD), severely deficient in vWF, might prevent the thrombosis encountered in delayed xenograft rejection.
METHODS: Ten baboons were treated by extracorporeal immunoadsorption of xenoreactive natural antibodies (XNA) through the donor pig liver to inhibit hyperacute rejection and received heterotopic vWD or control pig kidney xenografts. XNA levels, coagulation, and platelet activation markers were studied, and specimens of rejected kidneys were analyzed histologically.
RESULTS: Although XNA depletion was comparable in both groups, neither kidney function nor survival times of control (n=5) or vWD (n=5) porcine kidneys showed any difference. Platelet and coagulation activation was evidenced in both groups after surgery and at rejection time. Immunohistochemical analysis revealed a weak endothelial vWF immunostaining in the rejected vWD kidneys, whereas it was undetectable in the nongrafted vWD kidneys, suggesting the deposition of baboon plasma vWF on the porcine vessels.
CONCLUSIONS: The use of vWD organs did not improve the survival time of grafted kidneys in this xenotransplantation model. Further studies on the use of vWD organs, in association with other therapeutic approaches, such as complement inhibition, are nevertheless necessary to evaluate the usefulness of vWF deficiency as an adjunctive therapy to decrease the coagulation process during xenograft rejection.