Dendritic cells (DC), the most potent 'professional' antigen-presenting cells, hold promise for improving the immunotherapy of cancer. In this study, we investigated the ability of normal donor DC pulsed ex vivo with 12 mer bcr-abl (b3a2) peptide to generate b3a2-specific autologous or HLA-identical sibling donor's cytotoxic T-lymphocytes (CTL). DC that were grown from normal peripheral blood adherent cells or purified DC precursors in the presence of GM-CSF and IL-4, were pulsed with b3a2-peptide then were induced to become mature and functional cells by the addition of TNF-alpha. These peptide-pulsed mature DC elicited a potent b3a2-specific CTL response in vitro. The b3a2-peptide pulsed DC-primed peripheral blood lymphocytes (PBL) displayed significantly higher cytotoxic activity compared with peptide non-pulsed DC-primed PBL against target cells, which are b3a2 positive marrow cells derived from HLA-identical sibling chronic myelogenous leukemia (CML) patient, or peptide-pulsed autologous macrophages (P < 0.001). In addition, the b3a2 peptide-pulsed DC-primed and non-pulsed DC-primed PBL showed no cytotoxic response against peptide non-pulsed autologous macrophages. These findings revealed that normal donor PBL pre-immunized with b3a2-peptide pulsed autologous DC could increase the graft-versus-leukemia effect without exaggerating graft-versus-host-disease. Both CD8+ and CD4+ T lymphocytes were shown to be involved in the effector cell populations. The b3a2 peptide-pulsed DC-primed T cells were significantly superior in their production of GM-CSF and TNF-alpha compared with peptide non-pulsed DC-primed T cells. These intriguing preclinical results imply the feasibility of developing b3a2 peptide-DC based protocol for in vitro sensitization of normal donor leukocytes before donor leukocyte transfusions for patients with CML, who relapsed after HLA-matched sibling bone marrow transplantation.