Because HLA-A*02:06 versus HLA-A*02:01 is known as a high risk HLA allele mismatch combination for graft-versus-host disease (GVHD) in hematopoietic stem cell transplantation,22,23 it is likely that the 4-1 CTL clone had an alloreaction against HLA-A*02:06. Here, HLA-A is linked to graft versus host disease.