HLA-A, B, C, DRB1, DQB1 matching heterogeneity in ‘favourably matched’ kidney recipients

Antibody-defined epitopes on HLA-DQ alleles reacting with antibodies induced during pregnancy and the design of a DQ eplet map

The concept that HLA antibodies recognize epitopes is leading to new approaches of HLA matching at the epitope level. HLA-DQ plays an important role and many studies have identified structurally defined DQ epitopes specifically recognized by antibodies; they have been recorded in the International HLA Epitope Registry http://www.epregistry.com.br but the list is still incomplete. Pregnancy offers an attractive model to study antibody responses to HLA epitopes. The current analysis was done on 42 DQ-reactive post-pregnancy sera tested in binding assays with a panel of DQ heterodimers. The reactivity of 29 sera corresponded fully to the presence of antibody-verified DQA and DQB epitopes recorded in the Registry. Analysis of the remaining 13 sera led to the identification of additional antibody-defined DQB and DQA epitopes. We have designed the first version of an eplet map for DQ alleles which includes antibody-defined DQA and DQB epitopes and shows sequence positions with polymorphic residues which can be used in HLA epitology studies to identify new antibody-defined DQ epitopes.

Generation of donor-specific anti-human leukocyte antigen antibodies after the transplantation of a fully matched kidney allograft and its impact on the selection of a subsequent renal regraft: a case report

Detection of anti-human leukocyte antigen (HLA) antibodies and identification of their specificities represent important tasks for patients awaiting kidney allografts. Regarding patients immunized by pregnancies, transfusions, or previous transplantations of solid organs, the immunization status must be observed carefully because grafting them with HLA phenotypes recognized by their antibodies represents the main cause for hyper-acute or acute rejection episodes, often leading to transplant loss. A 10-year-old patient with end-stage renal insufficiency of HLA type A3, 25; B8, 18, (Bw6); Cw7,12; DR15,17; DR51,52; DQ2,6 received a deceased donor graft showing no HLA mismatch in 1998. It lost function after 8 years, resulting in the patient's re-entry onto the waiting list for kidney transplantation in 2006. Antibody screening detected anti-HLA-A25, A26, A34, and A66 (broad A10) antibodies using various techniques (DynaChip, Single Antigen enzyme-linked immunosorbent assay [ELISA]). Additionally, a kidney offer expressing the HLA-A25 phenotype was not acceptable for the patient due to a positive complement-dependent cytotoxicity assay (CDC)-based cross-match. The question arose whether this reactivity might be due to auto-reactive antibodies directed against the HLA-A25 phenotype. However, no auto-reactive antibodies were detectable using either the CDC-based or the antibody monitoring system-ELISA-based cross-match assays. Consequently the patient was re-examined at high resolution showing the rare HLA-A*25:14 genotype. This case showed that rare alleles may result in allele-specific antibodies directed against the common variants, thus leading to unexpected positive cross-match results against apparently matched allografts.

Assessment of differences in HLA-A, -B, and -DRB1 allele mismatches among African-American and non-African-American recipients of deceased kidney transplants

Among recipients of deceased donor kidney transplants, African-Americans experience a more rapid rate of kidney allograft loss than non-African-Americans. The purpose of this study was to characterize and quantify the HLA-A, -B, and -DRB1 allele mismatches and amino acid substitutions at antigen recognition sites among African-American and non-African-American recipients of deceased donor kidney transplants matched at the antigen level. In recipients with zero HLA antigen mismatches, the degree of one or two HLA allele mismatches for both racial groups combined was 47%, 29%, and 11% at HLA-DRB1, HLA-B, and HLA-A, respectively. There was a greater number of allele mismatches in African-Americans than non-African-Americans at HLA-A (P < .0001), -B (P = .096), and -DRB1 loci (P < .0001). For both racial groups, the HLA allele mismatches were predominantly at A2 for HLA-A; B35 and B44 for HLA-B; but multiple specificities for HLA-DRB1. The observed amino acid mismatches were concentrated at a few functional positions in the antigen binding site of HLA-A and -B and -DRB1 molecules. Future studies are ongoing to assess the impact of these HLA mismatches on kidney allograft loss.

Single-Antigen-Expressing Cell Lines Are Excellent Tools for Detecting Human Leukocyte Antigen-C???Reactive Antibodies in Kidney Transplant Recipients

BACKGROUND

Human leukocyte antigen (HLA)-C is expressed on nucleated cells and platelets in lower levels than HLA-A,B, and its antigens are in linkage disequilibrium with HLA-B antigens. Therefore, HLA-C antibody detection is difficult. The authors questioned whether HLA-C could serve as a target in clinical kidney transplantation using a newly developed assay.

METHODS

Flow cytometry was performed with sera from patients (n=34) awaiting a kidney retransplant using nine cell lines expressing a single HLA-C antigen (single-antigen lines [SAL]).

RESULTS

The SAL were validated with HLA-C-specific alloantisera and human monoclonal antibodies against HLA-A, -B, and -C. The results were in agreement with the specificities previously reported. Exceptions, because of new HLA-C specificities used here, could be explained by epitope sharing between the antigens. With respect to patient sera, 15 of the 34 patients tested (44%) showed serum reactivity toward one or more HLA-C SAL.

CONCLUSIONS

In contrast to peripheral blood lymphocytes, SAL are excellent targets for detecting HLA-C-reactive alloantibodies by flow cytometry. This preliminary analysis revealed that HLA-C-reactive antibodies are frequently present in sera of retransplant patients, serving as possible targets in clinical transplantation.