Permissible mismatches, acceptable mismatches, and tolerance: new trends in decision making.

The identification of permissible mismatches that do not impair graft survival might open exciting new possibilities which we should follow up. The data are preliminary, but if true, 50% of the patients in Eurotransplant could get a kidney with optimal graft survival. For sensitized patients we might consider adding a CTLp test, with and without CsA, to our serological crossmatch tests. This might be beneficial especially for interpreting noncurrent crossmatches. Information on the activation status of the donor-specific cytotoxic T cells on the day of transplantation (primed or not, CsA-resistant or not) provides additional information which could facilitate the decision of whether or not to accept a mismatched graft, even in case of donor-specific antibodies in historical sera. Under certain circumstances, haplotype-shared blood transfusions can induce transplantation tolerance. Time will tell whether the determination of the level of donor-derived soluble HLA antigens might be helpful in an early diagnosis of rejection. It might become a new device to monitor homograft reactivity and to identify the patients in whom immunosuppression could be decreased or even discontinued.