The HLA-A *0201-restricted minor histocompatibility antigen HA-1^H peptide can also be presented by another HLA-A2 subtype, A *0206

HA-1^H is one of the most attractive minor histocompatibility antigens (mHA) as a target for immunotherapy of hematopoietic malignancies, but HLA-A*0201 and HLA-B60 molecules capable of presenting HA-1^H-derived peptides are less common in eastern Asian populations when compared with Caucasian populations. Therefore, an attempt was made to search for novel epitopes presented by HLA alleles other than those previously reported by generating CTL lines from patients undergoing HLA-identical, HA-1 disparate hematopoietic stem cell transplantation (hematopoietic SCT) by stimulation with a 29-mer HA-1^H peptide spanning a central polymorphic histidine (His). Two CTL clones established were found to be restricted by HLA-A*0206, which is the second or third most common HLA-A2 subtype worldwide. Epitope mapping revealed that the clones recognized the same nonameric peptide as A*0201-restricted HA-1^H, VLHDDLLEA. This epitope was unexpected, since it does not contain any preferred anchor motifs for HLA-A*0206. However, an HLA peptide binding assay revealed stronger binding of this peptide to A*0206 than to A*0201. Interestingly, HLA-A* 0206-restricted CTL clones could lyse both HLA-A*0206⁺ and HLA-A*0201⁺ targets (including leukemic blasts) that express HA-1^H peptide endogenously, whereas an HLA-A*0201-restricted, HA-1^H-specific CTL clone failed to lyse HLA-A*0206⁺ targets. This finding will expand the patient population who can benefit from HA-1^H -based immunotherapy.