The MHC gamma block matching: Impact on unrelated hematopoietic stem cell transplantation outcome

Matching for HLA-A, -B, -C, -DRB1, -DQB1 alleles is the gold standard in hematopoietic stem cell transplantation (HSCT). However, this is often not enough to prevent postransplantational complications. The HLA mismatches (MM) have been associated with higher risk of acute graft versus host disease (GvHD). Gamma block (GB) is located in central HLA region, between HLA-B/C and HLA-DRB/DQB blocks and contains many inflammatory and immune regulatory genes. Single nucleotide polymorphisms (SNPs) within that block can be considered as markers for MHC haplotype matching. Aim of the research was to test whether MM in GB impact the outcome of HSCT in 51 patients transplanted with HLA 10/10 matched unrelated donor. The recipient-donor pairs were typed using PCR SSP kit that detects 25 SNPs within GB. Fifteen out of 51 (29.41%) pairs were GT matched (GT-M) while 36 out of 51 pairs (70.59%) were mismatched (GT-MM). In a univariate analysis, GT-MM was a significant risk factor associated with aGvHD (P = 0.041), although this association was not seen in multivariate analysis. No significant difference in overall survival and relapse occurrence was seen. These results were obtained on a small sample, and it is necessary to further test the possible role of GT matching in unrelated HSCT.