Background: HLA matching improves the outcome of cadaveric renal transplantation. However, many allografts function well even in the presence of one or more HLA mismatches, which raises the question of whether some mismatches are better recognised by the recipient's immune system than others. We aimed to identify mismatched HLA donor-recipient combinations that were associated with increased graft loss.
Methods: We selected 2877 first, unrelated renal transplants with a single HLA A, B, or DR mismatch, undertaken between 1982 and 1992, from the Eurotransplant database. To enhance statistical power the analysis was restricted to mismatches of an HLA antigen that occurred in 100 or more donors. 1342 transplants met this criterion and were grouped into a definition set (n = 873) and a validation set (n = 469). In the definition set, we studied further only those recipient HLA antigens that occurred in at least 30 cases within each donor antigen mismatch subset. By a Cox proportional hazards model, donor-recipient combinations that led to significantly higher graft loss than in the whole group were defined. Such combinations were classified as taboo; the remaining combinations were classified as indifferent.
Findings: 106 individual recipient antigens were found at least 30 times with a corresponding donor mismatch in the definition set; 11 of the 106 had a significant effect on graft survival. Seven combinations were classified as taboo. Taboo combinations, confirmed as such in the validation set, were associated with graft survival of 81% at one year and 50% at 5 years, significantly lower than the rates in the group with indifferent combinations (89% and 69%; p = 0.04) or among 1190 recipients with no mismatches (89% and 72%; p = 0.03). The findings were substantiated by a multivariate analysis that included the effect of patient immunisation, cold ischaemia time, age, and sex.
Interpretation: Mismatched donor antigens are differentially recognised depending on the HLA phenotype of the recipient. The findings may have important clinical consequences for graft survival after transplantation.