Recent studies have detected Wilms tumor antigen (WT1)-specific cytotoxic T lymphocytes (CTLs) in patients with acute myelogenous leukemia (AML) and chronic myelogenous leukemia (CML) and demonstrated that most of these CTLs were low avidity. Although HLA-mismatched donors can mount high-avidity CTLs against HLA-A2-presented peptides of WT1, a dominant anti-alloimmune response usually obscures detection of peptide-specific CTLs. Here we explored the feasibility of using recombinant HLA-A2 monomers containing single peptide epitopes as immunogens to generate peptide-specific CTLs from allogeneic donors. We demonstrate that the coating of HLA-A2(-) B lymphocytes with A2/peptide monomers provides a strong stimulus for autologous peptide-specific CTLs. After 3 to 5 rounds of stimulation a population of CD8(+) T cells binding A2/peptide tetramers is easily detectable by fluorescence-activated cell sorting analysis. Furthermore, sorted A2/WT1 tetramer-positive CTLs display strong cytotoxic activity against leukemia cells expressing WT1 endogenously but not against WT1(-) human tumor cells. Thus, HLA/peptide monomers may be useful to isolate peptide-specific donor lymphocytes for treatment of patients with leukemia after HLA-mismatched transplantation.