Peritoneal resident macrophages in mice with MLL-AF9-induced acute myeloid leukemia show an M2-like phenotype.

Background: Acute myeloid leukemia (AML) is a devastating disease with a poor prognosis. Innate and adaptive immunity is closely related to the progression of leukemia. Macrophages within the leukemic microenvironment have a tendency toward a leukemia-permissive phenotype. However, the characteristics of macrophages in leukemia, including their kinetics, gene expression, and functional roles have not been fully illuminated.

Methods: In the current study, the characteristics of peritoneal resident macrophages, which were large peritoneal macrophages (LPM), from mice with mixed lineage leukemia (MLL)-AF9-induced AML were investigated. AML-associated large macrophages (AML-LPM) were gated as F4/80 MHC-II by flow cytometry. To further investigate the relationship between the leukemic microenvironment and macrophage characteristics, RNA sequencing was performed. Meanwhile, apoptosis, killing ability, and phagocytic function of peritoneal resident macrophages in MLL-AF9-induced AML were assessed.

Results: The results suggested that AML microenvironment was found to affect the kinetics and morphology of peritoneal resident macrophages. The results of RNA sequencing suggested that the gene expression of AML-LPMs differed significantly from that of normal LPMs. The AML microenvironment also had effects on the apoptosis, killing ability, and phagocytic function of peritoneal resident macrophages.

Conclusions: These data suggest that peritoneal resident macrophages in mice with AML induced by MLL-AF9 show an M2-like phenotype. The reversal of macrophage polarization in the leukemic microenvironment may potentially enhance the immunotherapeutic effect in AML.