HMHB1 encodes one of the minor histocompatibility antigens, which play an important role in the induction of cytotoxic T lymphocyte (CTL) reactivity against leukemia after human histocompatibility leukocyte antigen (HLA)-identical allogeneic bone marrow transplantation (BMT). This gene is only expressed in B cell acute lymphoblastic leukemia cells and Epstein-Barr virus-transformed B cells. The translation of this mRNA initiates at a non-AUG (CUG) codon. HB-1 gene expression in transformed B cells and B-cell acute lymphoblastic leukemia patient cells, but not in T-cell leukemias, myelomas, myeloid leukemias, or solid tumors. Recognition of the HB-1 peptide by cytotoxic T cells in association with HLA-B44 resulted from a C-to-T change at nucleotide 153, leading to a his8-to-tyr (H8Y) substitution in the HB-1 peptide (H16Y in the mature protein).