The complement receptor C3AR constitutes a novel therapeutic target in NPM1-mutated AML

Mutated nucleophosmin 1 (NPM1) is the most common genetic alteration in acute myeloid leukemia (AML), found in ∼30% of cases. Although mutations in this gene are considered favorable according to current risk stratification guidelines, a large fraction of patients will experience relapse, demonstrating the urgent need for new treatment options. Therefore, we aimed to identify cell surface proteins specifically expressed on NPM1-mutated AML cells, allowing for potential targeting with antibody-based therapies. Herein, we report on an arrayed flow cytometry-based screen directed to 362 cell surface markers. In comparing the cell surface expression on NPM1-mutated AML cells with primitive (CD34+ CD38-) normal bone marrow cells, we identified the complement receptor C3AR as being specifically expressed in NPM1-mutated AML. By flow cytometry and single-cell RNA sequencing, we further show that normal hematopoietic stem and progenitor cells lack detectable C3AR gene and protein expression, making it particularly suitable as a target for antibody therapy. We also demonstrate that C3AR in combination with GPR56 distinguishes the leukemic stem cells (LSCs) in NPM1-mutated AML from the normal hematopoietic stem cells, defining the LSC population, as shown by transplantation into immunodeficient mice. Mechanistically, the stimulation of C3AR-expressing cells with C3a, the ligand of C3AR, leads to the activation of ERK1/2 and increased survival of AML cells, suggesting that this is an important signaling axis in this subtype of AML. Finally, we show that antibodies directed against C3AR efficiently elicit natural killer cell-mediated killing of primary AML cells ex vivo, highlighting C3AR as a candidate therapeutic target in NPM1-mutated AML.