Histologic characterization of the immune infiltrate in IDH wild type and mutant WHO grade 2 and 3 gliomas

Aim: This study aims to describe the immune infiltrations in low-grade glioma (LGG) with respect to their histological classification, isocitrate dehydrogenase 1 and 2 (IDH1/2) mutation status and survival. Materials and Methods: The IDH1/2 status (mutant or wild-type) of 66 World Health Organization Grade II and III gliomas were defined using next-generation sequencing or multiplex ligation-dependent probe amplification. The immune infiltrates of these tumors (46 mutant IDH, 20 wild-type IDH) were assessed immunohistochemically using a panel of antibodies (CD3, CD4, CD8, FOXP3, CD20, CD68, and CD163). Confirmatory analyses were performed on a cohort of lower grade gliomas from the Cancer Genome Atlas (TCGA). Statistical analyses were performed with Mann–Whitney U-tests and Kaplan–Meier survival estimates. Results: There was no relation between the amount of CD3+, CD4+, CD8+, or CD20+ lymphocyte infiltration and IDH mutation status in the tumors. FOXP3+ T regulatory cell infiltrates were rare, but more frequent in IDH1/2 wild-type tumors (P = 0.046). While the presence of these cells did not correlate with overall survival, FOXP3 messenger RNA expression was associated with survival in a distinct cohort of LGG from the TCGA (P < 0.05). CD4+ lymphocyte infiltrates, on the other hand, tended to prevail in astrocytic tumors as compared to oligodendrogliomas (P = 0.056). While CD68 (M1) microglial/monocytic cells were equally abundant in IDH mutant and wild-type tumors, the presence of round, activated M1 CD68+ microglia significantly associated with a mutant IDH status (P = 0.015). Conclusion: FOXP3+ expression and activated CD68+ M1 cells associated with IDH status in LGG, and might contribute to their differential evolution