Beyond HLA: Impact of Immunoreactive Mismatches of Minor Histocompatibility Antigens on Probability of Relapse and Graft-Versus-Host Disease after Hematopoietic Stem Cell Transplantation from HLA-Matched Unrelated Donors.

Factors contributing to relapses and GVHD following allogeneic Hematopoietic Stem Cell Transplantations (HSCT) from HLA-matched unrelated donors are not well established. We analyzed 35 patients (pts) transplanted from HLA 10/10 alleles (A, B, C, DRB1, DQB1) matched unrelated donors (URD) in the Dept. of Hematology and BMT, Katowice, Poland, with use of the same standard operating procedure from January 2004 until March 2006. Indication for HSCT was AML (13 pts), ALL (8), CML (7), MDS (2), PNH (3), CLL (1), myeloid sarcoma (1). Preparative regimen was Treosulfan+Fludarabine (23 pts), TBI+Cy (9) and Bu+Cy (3). Alleles encoding 11 minor Histocompatibility Antigens (mHA: HA-1, HA-2, HA-3, HA-8, HB-1, ACC-1, ACC-2, HwA-9, HwA-10, UGT2B17, HY) were analyzed for each donor-recipient pair with use of Dynal AllSet mHA typing kit and PCR-SSP method. Only immunogenic mHA mismatches were analyzed. Information on whether mHA mismatches might result in Host-versus-Graft or Graft-versus-Host responses was established with use of the minor Histocompatibility Knowledge Database of Leiden University Medical Center’s minor Histocompatibility Workshop.

Patients transplanted from donors with mHA mismatched in HVG direction had significantly higher probability of relapse (64⁺/₋ 8% versus 10⁺/₋ 9%, p=0.003) when compared to pairs without mHA HVG immonogenicity. Patients transplanted from donors with mHA mismatched in GVH direction had higher probability of aGVHD (88⁺/₋ 8% versus 53⁺/₋ 11%, p=0.14) and cGVHD (41⁺/₋ 16% versus 37⁺/₋ 17%, p=0.65) when compared to pairs without GVH immunogenicity. GVHD was also observed more often on day +100 (33% versus 6%, p=0.06) when mHA mismatch in GVH direction was present. Observed influence of HVG and GVH immonogenicity on probability of relapse and GVHD did not lead to significantly different survival in observed groups of pts. These results indicate that mHA immunogenic mismatches in HVG and GVH direction may be responsible for relapse and GVHD, respectively, in HSCT recipients from HLA-matched unrelated donors. The study is being continued to confirm these primary observations and to establish the associations of specific mHA mismatches with HSCT outcomes.