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In France, organ retransplantation represents a small proportion of all organ transplantations, but becomes a significant difficulty when considering the allocation of a limited number of organs. In fact, the results of organ retransplantations are grosso modo inferior to those of first transplantations. Failures of retransplantations have many causes including surgical complications, immunosuppression, rejection, and often the bad consequences of a long standing disease. Little place is specifically devoted to retransplantation in organ allocation rules. The impact of retransplantation on organ allocation is in fact very largely linked to the medical decision of the transplant team, a decision which certainly would gain to be better analysed.

For several years, our group has been interested in experimental models of discordant xenografts. The pig-to-human donor-recipient combination could have some clinical relevance in the future but experimentation is limited to in vitro and ex vivo models. In contrast, the guinea pig-to-rat combination also allows in vivo experimentation, but the data provided by such transplantations cannot easily be extrapolated to any clinical condition. In these experimental models, hyperacute rejection occurs within several minutes or hours, according to the combination or organ considered [2, 14]. This rejection is primarily mediated by the activation of the recipient’s complement through its direct and alternative pathways which are simultaneously involved [4, 11]. The graft endothelial cells are the first targets encountered by the recipient’s blood as soon as it bursts into the graft. Natural (preformed) antibodies [17, 18] bind to xenoantigens borne by the graft endothelium and engage the direct pathway [3, 6, 8], while the alternative pathway is activated by the contact with some unknown foreign molecules present on the endothelial surface [10, 15].

The first xenotranspiantations were performed at the beginning of the twentieth century. Actually, only 46 xenotransplantations were published between 1906 and 1970, with poor results as the grafts, which were mostly harvested from non human primates. were all rejected w ithin hours or days.