Allogeneic stem cell transplantation following reduced-intensity conditioning is being evaluated in patients with advanced B-cell chronic lymphocytic leukemia (B-CLL). The curative potential of this procedure is mediated by donor-derived alloreactive T cells, resulting in a graft-versus-leukemia effect. However, B-CLL may escape T-cell-mediated immune reactivity since these cells lack expression of costimulatory molecules. We examined the most optimal method to transform B-CLL cells into efficient antigen-presenting cells (APC) using activating cytokines, by triggering toll-like receptors (TLRs) using microbial pathogens and by CD40 stimulation with CD40L-transfected fibroblasts. CD40 activation in the presence of IL-4 induced strongest upregulation of costimulatory and adhesion molecules on B-CLL cells and induced the production of high amounts of IL-12 by the leukemic cells. In contrast to primary B-CLL cells as stimulator cells, these malignant APCs were capable of inducing the generation of B-CLL-reactive CD8(+) CTL lines and clones from HLA class I-matched donors. These CTL lines and clones recognized and killed primary B-CLL as well as patient-derived lymphoblasts, but not donor cells. These results show the feasibility of ex vivo generation of B-CLL-reactive CD8(+) CTLs. This opens new perspectives for adoptive immunotherapy, following allogeneic stem cell transplantation in patients with advanced B-CLL.