HLA-DPA1 and -DPB1 Antibodies in Kidney Transplantation

Introduction: All preformed HLA antibodies have a deleterious impact on kidney graft outcome. Moreover, HLA sensitization often shows in broad antibody patterns since antibodies bind to epitope/s of HLA molecules and these target epitopes can be shared between several molecules intra- and inter-HLA loci.Current HLA class II matching strategies for kidney transplantation only consider the DR antigens; DQ matching is sometimes considered for organ sharing program. But both ? and ? chains of DP molecules are polymorphic and can elicit a humoral immune response. DP molecules have generally low expression but are upregulated upon inflammation that may occur during transplantation. Detection of anti-DP antibodies have been difficult using complement-dependent citotoxicity but newer assays for antibody analysis, such as Luminex-Single Antigen beads (One Lambda, CA), greatly enhanced detection of anti-DP antibodies and allowed to distinguish between anti-DPB1 and -DPA1. Methods: We investigated the incidence of anti-DP alloantibodies in 248 renal transplant candidates showing production of HLA class II antibodies. Antibody characterization was performed using Luminex Single Antigen beads that contain 26 microbeads coated with DPA1/DPB1 heterodimers (4 DPA1 alleles and 19 DPB1 alleles variously combined each other).Using an online database (www.ebi.ac.uk/imgt/hla), we also analyzed the amino acid sequences of DPA1/DPB1 molecules corresponding to the detected antibodies to identify the putative epitopes for antibody formation. All the anti-DP positive patients had been typed for DPB1/DPA1 alleles by SSP methods. Results: Ninety-two (37%) of the HLA class II positive patients showed production of anti-DP antibodies; 71% of these patients had anti-DPB1, 2% had anti-DPA1 and the remaining 27% of patients had both anti-DPA1 and-DPB1.As for sensitizing events, 66 (72%) of the anti-DP positive patients had had a previous transplant, 21 (23%) had had pregnancies and 5 (5%) received transfusions only. Noteworthy, anti-DP antibodies were exclusively present in sera from 8 of the 66 (12%) patients sensitized by a previous transplant; 2 of these re-transplant patients developed anti-DPA1 only.Analyzing epitopes whose recognition determined antibody formation, we evidenced that 42 (64%) of the re-transplant patients developed a broad antibody pattern (anti-DPB1*01, *03, *05, *06, *09, *10, *11, *13, *14, *17, *19, *20) due to the recognition of 84-87DEAV epitope of the previous graft. Conclusion: This study confirms that both ? and ? chain epitopes of HLA-DP molecules are immunogenic. The most important stimulus for anti-DP antibody production was a previous transplant, but also pregnancies and transfusions may determine the development of anti-DP ?/? chain specific antibodies. The anti-DPB1 humoral response often resulted in broad antibody patterns because of the sharing of the same epitope by many DPB1 molecules.Consequently, in renal transplantation, HLA matching strategy should consider all the HLA class II molecules especially for re-transplant patients. All abstracts are available in a quotable version on the Transplantation Journal Website www.transplantjournal.com from beginning of September 2012.