Mutant IDH Modulates Suppressive Myeloid Populations in Malignant Glioma

Mutations in the isocitrate dehydrogenase (IDH) genes IDH1 and IDH2 have critical diagnostic and prognostic significance in diffuse gliomas. Neomorphic mutant IDH activity has been previously implicated in T-cell suppression; however, the effects of IDH mutations on intratumoral myeloid populations remain underexplored. In this study, we investigate the influence of IDH status on the myeloid compartment using human glioma specimens and preclinical models.

We performed RNA sequencing and quantitative immunofluorescence on newly diagnosed, treatment-naive IDH-mutant grade 4 astrocytoma and IDH-wild-type (IDH-WT) glioblastoma (GBM) specimens. We also generated a syngeneic murine model, comparing transcriptomic and cell-level changes in paired isogenic glioma lines that differ only in IDH mutational status.

Among patient samples, IDH-mutant tumors displayed an underrepresentation of suppressive myeloid transcriptional signatures, which was confirmed at the cellular level with decreased numbers of intratumoral M2-like macrophages and myeloid-derived suppressor cells. Introduction of the mutant IDH enzyme into murine glioma was sufficient to recapitulate the transcriptomic and cellular shifts observed in patient samples.

We provide transcriptomic and cellular evidence that mutant IDH is associated with a quantitative reduction of suppressive myeloid cells in gliomas and that introduction of the mutant enzyme is sufficient to result in corresponding cellular changes using an in vivo preclinical model. These data advance our understanding of high-grade gliomas by identifying key myeloid cell populations that are reprogrammed by mutant IDH and may be targetable through therapeutic approaches.