Prevention of relapse of juvenile myelomonocytic leukemia (JMML) by inhibition of immune checkpoint CD47

Juvenile myelomonocytic leukemia (JMML) is an aggressive childhood myeloid malignancy driven by RAS pathway mutations, marked by clonal expansion and tissue infiltration of myeloid cells, including macrophages. This study investigated the role of macrophage polarization, phagocytic function, and CD47-mediated immune evasion in JMML pathogenesis. Analysis of human PTPN11-mutated JMML spleen samples revealed an enrichment of pro-inflammatory M1-like macrophages compared to KRAS-mutated cases and controls. Both human JMML macrophages and murine Ptpn11-mutant macrophages retained phagocytic capacity, with M1-like subsets exhibiting the highest activity. CD47, an immune checkpoint ligand that inhibits phagocytosis, was overexpressed in JMML cells, and its blockade enhanced macrophage-mediated clearance in vitro. In a patient-derived xenograft model, CD47 inhibition with magrolimab reduced splenic leukemia burden but showed limited efficacy in the bone marrow, with no synergistic effect observed when combined with azacitidine. These findings demonstrate that JMML macrophages remain functionally active and contribute to disease-associated inflammation, while CD47 blockade offers partial therapeutic benefit. Our study underscores the complex interplay between macrophage polarization, immune evasion, and inflammatory signaling in JMML, providing insights for future targeted therapies.