Simple SummaryNearly 30% of adult acute myeloid leukemias (AML) harbor mutations of thenucleophosmin(NPM1) gene. These forms have a favorable outcome but, despite notable treatment advances, about 50% of patients still die of progressive disease. Thus, identification of new therapeutic opportunities is important to improve the prognosis. The aim of our study was to assess the feasibility of obtaining a cell therapy medicinal product specific for the mutated NPM1 protein from patients or healthy donors that could be employed to control leukemia and prevent hematologic relapse. We demonstrated that cytotoxic T cells specific for the mutated antigen can be reproducibly expanded, and these cells efficiently recognize and lyse leukemia blasts or other cell types carrying the NPM1-mutated antigen, without causing damage to normal hematopoietic cells. We believe that these T cells may integrate other therapy options in the treatment of patients with refractory or relapsed AML.AbstractAcute myeloid leukemia (AML) with nucleophosmin (NPM1) genetic mutations is the most common subtype in adult patients. Refractory or relapsed disease in unfit patients or after allogeneic hematopoietic stem cell transplantation (allo-HSCT) has a poor prognosis. NPM1-mutated protein, stably expressed on tumor cells but not on normal tissues, may serve as an ideal target forNPM1-mutated AML immunotherapy. The study aim was to investigate the feasibility of producing mutated-NPM1-specific cytotoxic T cells (CTLs) suitable for somatic cell therapy to prevent or treat hematologic relapse in patients withNPM1-mutated AML. T cells were expanded or primed from patient or donor peripheral blood mononuclear cells by NPM1-mutated protein-derived peptides, and tested for leukemia antigen-targeted cytotoxic activity, cytokine production and hematopoietic precursor inhibitory effect. We found that mutated-NPM1-specific CTLs, displaying specific cytokine production and high-level cytotoxicity against patients’ leukemia blasts, and limited inhibitory activity in clonogenic assays, could be obtained from both patients and donors. The polyfunctional mutated-NPM1-specific CTLs included both CD8+ and CD4+ T cells endowed with strong lytic capacity. Our results suggest that mutated-NPM1-targeted CTLs may be a useful therapeutic option to control low-tumor burden relapse following conventional chemotherapy in olderNPM1-mutated AML patients or eradicate persistent MRD after HSCT.