We found the HLA-C allele mismatch was a significant risk factor for viral infections after CBT; thus, we hypothesized that summation of HLA class I mismatches (HLA-A, -B, and -C) can be a superior predictive marker for viral infections than that of HLA-A, -B, and -DRB1 that has long been used to select CBT graft. The gene discussed is HLA-C; the disease is viral infectious disease.