Abstract In contrast to patients with B cell precursor acute lymphoblastic leukemia (BCP-ALL), patients with acute myeloid leukemia (AML) have not yet benefited from recent advances in targeted immunotherapy. Repurposing immunotherapies that have been successfully used to target other hematological malignancies could, in case of a shared target antigen, represent a promising opportunity to expand the immunotherapeutic options for AML. Here, we evaluated the expression of CD19 in a large pediatric AML cohort, assessed the ex vivo AML killing efficacy of CD19-directed immunotherapies, and characterized the bone marrow immune microenvironment in pediatric AML, BCP-ALL, and non-leukemic controls. Out of 167 newly diagnosed de novo pediatric AML patients, 18 patients (11%) had CD19 + AML, with 61% carrying the translocation t(8;21)(q22;q22). Among CD19 + samples, we observed a continuum of CD19 expression levels on AML cells. In individuals exhibiting unimodal and high CD19 expression, the antigen was consistently present on nearly all CD34 + CD38 - and CD34 + CD38 + subpopulations. In ex vivo AML-T cell co-cultures, blinatumomab demonstrated substantial AML killing, with an efficacy similar to BCP-ALL. In addition, CAR T cells could effectively eliminate CD19 + AML cells ex vivo . Furthermore, our immunogenomic assessment of the bone marrow immune microenvironment of newly diagnosed pediatric t(8;21) AML revealed that T- and NK cells had a less exhausted and senescent phenotype in comparison to pediatric BCP-ALL. Altogether, our study underscores the promise of CD19-directed immunotherapies for the treatment of pediatric CD19 + AML.
