28-OR

Abstract

Aim A 53 year- old female with therapy-related myelodysplasia was a candidate for unrelated double-cord transplant. She had already received an autologous transplant, followed by a haploidentical transplant from her son. Multiple transfusions were required. STR analysis indicated that her cells were now 90-100% of patient origin. Anti-HLA antibodies were characterized to avoid cord-specific antigens. Methods Solid phase HLA antibody detection technology (One Lambda) was applied to screen and identify Class I and II anti-HLA. Results The patient was highly sensitized as shown by hemolysis after the haploidentical transplant. Further testing also detected anti Class I and II HLA antibodies, with very high MFI values starting at 14000. Specific antibodies to self antigens (A3, B51, 52) were not detected, except for an anti-HLA-A∗68. Raw data from single antigen beads (One Lambda), clearly showed the presence of the A68 antibody, however, the corresponding molecular specificity was not the patient’s A∗68:01, but A∗68:02, with high MFI values of 8500 and 3800, detected on 2 different samples 5 months apart. In both cases, anti A∗68:01 was negative. Conclusions There are 5 amino acid differences between A∗68:01 and A∗68:02, affecting the CDEF pockets, which may result in distinctly different peptide binding specificities. While the A∗68:01 allele is present everywhere, the A∗68:02 allele occurs mostly in Africa. A disease association with one, but not the other allele of the A68 group has been reported, and could result in functional differences. The previous transplant donor, the haploidentical son, was negative for A∗68:02 and therefore the presence of the A68 antibody would not have influenced the transplant outcome. Our institution uses HLA-A, B antigen and DRB1 allele matching for cords. In this particular case, our recommendation was to only mismatch antigens if the patient has no cord specific anti-HLA antibodies and to avoid mismatches for HLA-A∗68 alleles.