Tumor-associated microglia/macrophages (TAMs) are the main innate immune effector cells in
malignant gliomas and have both pro- and anti-
tumor functions. The plasticity of TAMs is partially dictated by oncogenic mutations in
tumor cells. Heterozygous IDH1 mutation is a
cancer driver gene prevalent in grade II/III
gliomas, and IDH1 mutant
gliomas have relatively favorable clinical outcomes. It is largely unknown how IDH mutation alters TAM phenotypes to influence
glioma growth. Here we established clinically relevant isogenic
glioma models carrying monoallelic IDH1 R132H mutation (IDH1R132H/WT) and found that IDH1R132H/WT significantly downregulated immune response-related pathways in
glioma cells, indicating an
immunomodulation role of mutant IDH1. Co-culturing IDH1R132H/WT
glioma cells with human macrophages promoted anti-
tumor phenotypes of macrophages and increased macrophage migration and phagocytic capacity. In orthotopic xenografts, IDH1R132H/WT decreased
tumor growth and prolonged animal survival, accompanied by increased TAM recruitment and upregulated phagocytosis markers, suggesting the induction of anti-
tumor TAM functions. Using human
cytokine arrays that query 36
proteins, we identified significant downregulation of ICAM-1/CD54 in IDH1R132H/WT
gliomas, which was further confirmed by ELISA and immunoblotting analyses. ICAM1 gain-of-function studies revealed that ICAM1 downregulation in IDH1R132H/WT cells played a mechanistic role to mediate the
immunomodulation function of IDH1R132H/WT.
ICAM-1 silencing in IDH1 wild-type
glioma cells decreased
tumor growth and increased the anti-
tumor function of TAMs. Together, our studies support a new TAM-mediated phagocytic function within IDH1 mutant
gliomas, and improved understanding of this process may uncover novel approaches to targeting IDH1 wild type
gliomas.