MINOR HISTOCOMPATIBILITY ANTIGENS HA-1 AND HPA-5 POLYMORPHISM IN HLA IDENTICAL RELATED BONE MARROW TRANSPLANTATION.

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MINOR HISTOCOMPATIBILITY ANTIGENS HA-1 AND HPA-5 POLYMORPHISM IN HLA IDENTICAL RELATED BONE MARROW TRANSPLANTATION.
Maria Spyropoulou-Vlachou MD , Valia Kotzampasaki Scientist , Miltiadis Papadimitropoulos Scientist and Catherine Stavropoulos-Giokas MD . Athens Greece, National Hospital of Athens G.Gennimatas, 11527, Immunology Dp.-National Tissue Typing Lab. .

The minor histocompatibility antigens (mHags) HA-1 and HPA-5 are immunogenic alloantigens shown to be responsible for graft-versus-host disease (GVHD) in HLA identical bone marrow transplantation. Both antigens have two known alleles each, resulting in a single amino acid polymorphism. The HA-1H allele encodes histidine,while the HA-1R allele encodes arginine.HLA-A*0201 molecules have high affinity for the HA-1 peptide and the formed (peptide/MHC) complex is recognized by the HA-1 specific cytotoxic T cells. The HPA-5b (Br^a) allele respectively encodes lysine,whereas the HPA-5a (Br^b) encodes glutamic acid.HLA-A*2402 and B*5201 molecules have binding motifs for the HPA-5 and the formed complex, after binding, induces immunological reactions. In this study, 49 bone marrow transplant recipients and their genetically related HLA-identical donors were evaluated for the presence of HA-1, HLA-A2 restricted mHag, while 39 recipients, different from the above mentioned ones, and their HLA identical siblings, were analyzed for the presence of HPA-5. The frequencies of the two alleles of HA-1 in the recipient population were HA-1R = 0,663 and HA-1=0,336. In the donor population, the respective frequencies were 0,704 ans 0,296. A total of 7 donors (14,5%) were mismatched with the recipients for HA-1H . On the other hand, the frequencies of the two alleles of HPA-5 in the recipient population revealed to be HPA-5a = 0,859 and HPA-5b = 0,141, whereas among donors the respective frequencies were 0,820 and 0,180. A total of 7 (17,9%) of donors were found to be mismatched with the recipients for HPA-5.Association between mHag incompatibility and transplant outcome in the above study groups is currently analyzed and will be presented.