Retransplant candidates have donor-specific antibodies that react with structurally defined HLA-DR,DQ,DP epitopes.

This report describes a detailed analysis how donor-specific HLA class II epitope mismatching affects antibody reactivity patterns in 75 solid organ transplant recipients with an in situ allograft and who were considered for retransplantation. Sera were tested for antibodies in a sensitive antigen-binding assay (Luminex) with single class II alleles. Their reactivity was analyzed with HLAMatchmaker, a structural matching algorithm that considers so-called eplets to define epitopes recognized by antibodies. Only 24% of the patients showed donor-specific anti-DRB1 antibodies and there was a significant correlation with a low number of mismatched DRB1 eplets. This low detection rate of anti-DRB1 antibodies may also be due to allograft absorption. In contrast, antibodies to DRB3/4/5 mismatches were more common. Especially, 83% of the DRB4 (DR53) mismatches resulted in detectable antibodies against an eplet uniquely found on DR53 antigens. Donor-specific DQB mismatches led to detectable anti-DQB antibodies with a frequency of 87%. Their specificity correlated with eplets uniquely found on DQ1-4. The incidence of antibodies induced by 2-digit DQA mismatches was 64% and several eplets appeared to play a dominant role. These findings suggest that both alpha and beta chains of HLA-DQ heterodimers have immunogenic epitopes that can elicit specific antibodies. About one-third of the sera had anti-DP antibodies; they reacted primarily with two DPB eplets and an allelic pair of DPA eplets. These data demonstrate that HLA class II reactive sera display distinct specificity patterns associated with structurally defined epitopes on different HLA-D alleles.

Serum analysis after transplant nephrectomy reveals restricted antibody specificity patterns against structurally defined HLA class I mismatches.

This study deals with HLA-mismatched kidney transplants that have been removed following rejection. Sera from 27 patients were screened for HLA-specific antibodies by direct complement-dependent lymphocytotoxicity with HLA-typed cell panels. Circulating donor-specific antibodies were detected in 3 cases (11%) before and in 26 cases (97%) after allograft nephrectomy. These findings demonstrate the production of donor-specific antibodies in patients with rejected transplants, but in most cases, they were undetectable before nephrectomy, because the graft had adsorbed them. With an HLAMatchmaker-based serum analysis program, we observed restricted antibody specificity patterns against amino acid triplet-defined epitopes on donor HLA-A,B antigens. Many donor triplets were non-reactive while others were apparently recognized by antibodies. In some patients, the donor triplet specific antibodies persisted for a long time whereas in many other patients, they became undetectable after a few months. The characterization of the antibody specificity profiles of post-allograft nephrectomy sera is clinically useful in defining criteria of HLA mismatch acceptability for sensitized patients awaiting another transplant. It provides also opportunities for determining the relative immunogenicity of mismatched triplets.

HLA mismatching increases the risk of BK virus nephropathy in renal transplant recipients.

BK virus (BKV) nephropathy is a serious complication in kidney transplant recipients that may lead to irreversible graft failure. We have analyzed the degree of donor/recipient HLA compatibility and HLA antigen association in 40 kidney transplant patients with BKV nephropathy in comparison with a control group of 404 unaffected transplant recipients who were on tacrolimus-based immunosuppression with no induction. HLA compatibility was assessed by determining the number of HLA-A, -B, -DR-mismatched antigens. BK virus nephropathy was diagnosed histologically and confirmed by immunochemistry. Univariate and multiple logistic regression statistical analyses have shown a significant association between BKV nephropathy and HLA mismatching. This analysis showed also that BKV nephritis is associated with a greater number of rejection episodes and a higher incidence of steroid-resistant rejection requiring antilymphocyte treatment. There was no association between BKV nephropathy and any specific HLA allele. We propose that HLA mismatching promotes the development of BKV nephropathy through rejection-related inflammatory processes and heavy immunosuppression which cause virus reactivation and injury of the tubular epithelium.