HLA-DP epitope typing using monoclonal antibodies

Antibodies against HLA-DP recognize broadly expressed epitopes

HLA matching and avoidance of pre-transplant donor-specific antibodies are important in selection of donors for solid organ transplant. Solid phase testing with single antigen beads allows resolution of antibody reactivity to the level of the allele. Single antigen bead testing results at a large transplant center were reviewed to identify selective reactivity patterns of anti-HLA antibodies. Many HLA-DP antibodies were identified in the context of other HLA antibodies, but some sera had antibodies against only HLA-DP. B cell flow crossmatch testing was positive for 2 out of 9 sera with HLA-DP antibodies. Many patterns of reactivity corresponded to epitopes in hypervariable regions C and F of DPB1, but some matched epitopes in other regions or DPA1. Through analysis of single antigen bead testing from a large number of patients, we report that anti-HLA-DP antibodies predominantly recognize broadly cross-reactive epitopes. The United Network for Organ Sharing has mandated HLA-DP typing on all deceased kidney donors, and HLA-DP epitopes should be considered as the major antigens for avoidance of pre-transplant donor-specific antibodies.

Unexpected anti-HLA-DR and -DQ alloantibodies after nephrectomy of an HLA-DR and -DQ identical first renal transplant

The development of the single antigen beads assay by Luminex technology enables accurate identification of allele-specific antibodies. Herein, we report the identification of donor-specific HLA-DR and -DQ antibodies in a first kidney transplant recipient who received a DR and DQ identical kidney transplant. The recipient was a non-sensitized, non-transfused male patient suffering from an end-stage renal failure due to focal and segmental glomerulosclerosis. Two weeks after graft nephrectomy, anti-class I (donor-specific and non-donor specific) and class II antibodies were detected. The single antigen beads technique identified class II antibodies directed against DRB3*0202 and HLA-DQB1*0603 alleles. High-resolution class II typing revealed five allelic incompatibilities between donor and recipient. Amino-acid sequence alignment showed why this post-transplant highly immunized patient developed only these two allele-specific antibodies. Minimizing HLA mismatches between donor and recipient is important, but it is also useful to consider the combination of all HLA molecules present in the donor and recipient in order to define the antibody epitopes responsible for alloantibody responses.

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.

Beryllium binding to HLA-DP molecule carrying the marker of susceptibility to berylliosis glutamate beta 69

Berylliosis is a chronic granulomatous disorder caused by inhalation of Be dusts that is driven by the accumulation of Be-specific CD4+ Th1-cells at disease sites. Susceptibility to berylliosis has been associated with the supratypic variant of HLA-DP gene coding for glutamate at position beta69 (HLA-DPbetaGlu69). The aim of this study was to test the hypothesis that the HLA-DPbetaGlu69 residue plays a role in the interaction with Be. To this end, soluble HLA-DP2 molecule (carrying betaGlu69) and its mutated form carrying lysine at position beta69 (HLA-DP2Lys69) were produced in Drosophila melanogaster and then used in a Be binding assays. BeSO4 (1-1000 microM) was used to compete for the binding of the biotinilated invariant chain-derived peptide CLIP (50 microM). BeSO4 was capable of compete out biotin-CLIP binding from the HLA-DP2 (IC50%: 4.5 microM of BeSO4 at pH 5.0 and 5.5 microM of BeSO4 at pH 7.5), but not from the HLA-DP2Lys69 molecule (IC50%: 480 microM of BeSO4 at pH 5.0 and 220 microM of BeSO4 at pH 7.5). Moreover, the binding of NFLD.M60, a MoAb recognizing an epitope in the HLA-DP peptide binding region, to the HLA-DP2, but not to the HLA-DP2Lys69 soluble molecules was inhibited BeSO4. NFLD.M60 binding to HLA-DP2, but not to HLA-DP2Lys69 stably transfected murine cells was also inhibited by Be both at pH 5.0 and at pH 7.5. The data indicate a direct interaction of Be with the HLA-DPGlu69 molecule, in the absence of antigen processing.

The biological significance of HLA-DP gene variation in haematopoietic cell transplantation

Although it has been over 25 years since HLA-DP was mapped to the major histocompatibility complex (MHC), its biological functions remain ill-defined. We sought to test the hypothesis that HLA-DP functions in a manner similar to that of other class II genes by measuring the risk of clinically severe grades III-IV acute graft-vs.-host disease (GVHD) associated with recipient HLA-DP disparity after haematopoietic cell transplantation. HLA-DPB1 exon 2 was sequenced in 205 patients who underwent transplantation from HLA-A, -B, -C, -DRB1 and -DQB1 allele-matched unrelated donors. HLA-DPB1 mismatched recipients experienced a significantly increased risk of acute GVHD compared with HLA-DP-identical transplants. Patients who were mismatched for a single HLA-DPB1 allele had an odds ratio (OR) of 1.0 (0.5, 2.2; P = 0.99) and patients who were mismatched for two alleles had an OR of 2.2 (1.0, 4.9; P = 0.06) for developing acute GVHD. Compared with matched and single-allele mismatched transplants, patients who were mismatched for two DPB1 alleles had an OR of 2.2 (1.2, 4.1; P = 0.01). HLA-DP plays an important role in the alloimmune response. A threshold effect of multiple HLA-DP disparities is evident in determining the risk of acute GVHD after haematopoietic cell transplantation from unrelated donors.