Allogeneic bone marrow transplantation (BMT) has been associated with a graft-vs.-leukemia (GVL) reactivity. Since T cell depletion of the bone marrow graft has decreased the risk of graft-vs.-host disease (GVHD), but has been associated with higher rates of leukemia relapse, GVL reactivity is probably caused by donor-derived T lymphocytes. Previously, we demonstrated that minor histocompatibility (mH) antigen-specific cytotoxic T lymphocyte (CTL) clones, generated from patients after BMT, are capable of major histocompatibility complex-(MHC) restricted lysis of (clonogenic) myeloid leukemic cells. Here, we investigated whether donor-derived leukemia-specific CTL clones can be generated in vitro, before BMT, using irradiated leukemic cells from a patient with acute myeloid leukemia as stimulator cells, and peripheral blood or bone marrow from the HLA genotypically identical sibling donor as responder cells. Several CTL lines were generated that showed specific lysis (> 50%) of the recipient leukemic cells in a 51Cr-release assay. Two of these CTL lines were cloned by limiting dilution in the presence of the irradiated recipient cells. Multiple leukemia-reactive, HLA class I and II-restricted clones with various specificities could be established. These alloreactive, antileukemic CTL clones may cause GVL reactivity after BMT, and may be used as adjuvant immunotherapy in the treatment of leukemia.