HMHB1 encodes a minor histocompatibility antigen (mHag) that functions as an immunogenic target for donor-derived cytotoxic T lymphocytes (CTLs) after HLA-matched allogeneic bone marrow transplantation 1. The HB-1 antigen is presented on cell surfaces via MHC class I HLA-B44 molecules, where it displays a polymorphic peptide (EEKRGSLHVW) with a critical His-to-Tyr substitution at position 8 that enables T-cell recognition 1. Notably, HMHB1 expression is restricted to B-cell acute lymphoblastic leukemia (B-ALL) cells and Epstein-Barr virus-transformed B cells, with minimal expression in normal tissues 1. This restricted expression pattern allows HB-1-specific CTL responses to target B-ALL without triggering graft-versus-host disease (GVHD) 1. Clinically, HB-1 gene expression serves as a sensitive biomarker for B-ALL detection and minimal residual disease monitoring, with expression levels specifically elevated in newly diagnosed and relapsed B-ALL patients compared to remission cases and healthy donors 2. The antigen generates both CD8+ cytotoxic and CD4+ helper T-cell responses, establishing HB-1 as a candidate for dendritic cell-based immunotherapy in B-ALL 3. These properties position HB-1 as a tumor-associated antigen with therapeutic potential in hematological malignancies 4.