Donor-recipient mismatches in MHC class I chain-related gene A in unrelated donor transplantation lead to increased incidence of acute graft-versus-host disease.

The polymorphic products of major histocompatibility complex class I-related chain A (MICA) genes are important in solid organ transplantation rejection. MICA expression is limited to gut epithelium and may play a role in triggering acute graft-versus-host disease (aGVHD). A total of 236 recipients of unrelated donor transplantation were studied. Donor-recipient human leukocyte antigen (HLA) match was 10/10 human leukocyte antigen (HLA-A, -B, -C, -DRB1, -DQB1) in 73% and MICA mismatch in 8.4%. Because of physical vicinity of the loci, MICA mismatch was significantly associated with mismatch at HLA-B and HLA-C. A higher rate of grade II-IV aGVHD was seen in MICA-mismatched patients (80% vs 40%, P = .003) irrespective of degree of HLA matching (HLA 10/10 match: 75% vs 39%, P = .02) and HLA any mismatch (83% vs 46%, P = .003). The rate of grade II-IV gastrointestinal aGVHD was also higher in MICA-mismatched patients (35% vs 17%, P = .05). We conclude that MICA may represent novel a transplantation antigen recognized by human allogeneic T cells. This study was registered at ClinicalTrials.gov (Identifier NCT00506922).