Effects of MHC-encoded TAP1 and TAP2 gene polymorphism and matching on kidney graft rejection

The products of TAP1 and TAP2 genes, recently mapped within the MHC class II region, are involved in antigen presentation by MHC class I molecules, especially in the transport of endogenous peptides. As for most MHC genes, a polymorphism has been described and the possibility that it could influence the recipient immune response by modulating antigen presentation in kidney transplantation has been tested. The aim of our study was to compare TAP1 and TAP2 gene polymorphism and matching in 53 couples of kidney donors and recipients without any rejection episodes and in 55 other couples who had experienced at least 2 acute cellular rejection episodes; 70 healthy individuals served as controls. Our results showed that allelic variant frequencies of TAP1 alleles (1A to 1C) and TAP2 alleles (2A to 2E), as assessed by amplification refractory mutation system-polymerase chain reaction, were similar among "rejection" and "no rejection" populations. Furthermore, there were no differences of TAP1 and/or TAP2 matching between donors and recipients in the 2 groups. In contrast, we showed that the recipients of the no rejection group were better matched with their corresponding donors for the HLA-DR genes than those of the rejection group. These results suggest that the currently described polymorphism in the limited coding region of TAP1 and TAP2 genes does not influence the incidence of kidney allograft rejection episodes and seems not to be a strong link to the adjacent DR/DQ subregion. Moreover, the observed increase frequency of TAP1B allele in the whole recipient's group as compared with controls (16.2% vs. 7.1% in the healthy individuals; P < 0.02) was not linked to the rejection occurrence but to the presence of glomerulonephritis as initial disease. Our study suggests that, in the clinical conditions tested, neither TAP polymorphism nor TAP matching influences the renal graft outcome.