Repolarizing heterogeneous leukemia-associated macrophages with more M1 characteristics eliminates their pro-leukemic effects.

Macrophages exhibit phenotypic heterogeneity under both physiological and pathological conditions. Applications targeting M2-like tumor-associated macrophages (TAMs) improve outcome in solid tumors. Considerable differences are detected between leukemia-associated macrophages (LAMs) and TAMs. However, application to induce M1 characteristics in heterogeneous LAMs has not been established. Here we analyzed clinical relevance of macrophage phenotypes in human acute myeloid leukemia (AML), studied phenotypic evolution of bone marrow (BM) and spleen (SP) LAMs in mouse AML and T cell acute lymphoblastic leukemia (T-ALL) models, explored mechanism leading to different LAM phenotypes and tried to eliminate pro-leukemic effects by inducing M1 characteristics. The results showed that more M2-like LAMs but not total LAMs correlated with worse prognosis in AML patients. Heterogeneity of LAM activation in tissue-specific leukemic microenvironments was observed in both AML and ALL models, i.e. SP LAMs evolved with more M2 characteristics while BM LAMs with more M1 characteristics. Furthermore, IRF7 contributed to M1 characteristics through the activation of SAPK/JNK pathway. Moreover, targeting IRF7-SAPK/JNK pathway to induce M1 characteristics in LAMs contributed to prolonged survival in leukemia mice. Our study provides the potential target for macrophage based immuno-therapy strategy against leukemia.