Microglia Depletion Modulates the Immune Profile and Survival in Diffuse Midline Glioma Mice Model

Introduction: Diffuse midline glioma (DMG) is a highly aggressive pediatric brain tumor characterized by a poor prognosis and a cold immune profile. Understanding the tumor microenvironment (TME), particularly microglial function, is therefore crucial. This study investigates the TME and the role of microglia in DMG development and progression.

Methods: Syngeneic mouse models of DMG with H3K27M and ATRX mutation, TP53 loss, and PDGFRA overexpression were used. Microglia were first depleted with Pexidartinib (PLX), a CSF1R inhibitor, and allowed to repopulate. Spectral cytometry and immunofluorescence were used to analyze immune profiles. Next, PLX was administered at different stages of DMG development in mice (pre-, during, or post-tumor formation). Kaplan-Meier survival analysis and pairwise log-rank tests evaluated survival.

Results: Microglia depletion was confirmed by flow cytometry (N = 3) and immunofluorescence (N = 5, p < 0.0001). Following PLX removal, microglia repopulated above baseline levels, persisting until day 24 (flow cytometry, N = 3, p < 0.001; immunofluorescence, N = 5, p < 0.0001). Leukocyte populations increased significantly from day 0 to day 10 (N = 3, p < 0.001), along with sustained elevations in CD3+ and CD3+CD8+ populations by day 7 (NS, p < 0.05) and day 24 (p < 0.001, p < 0.05).

When investigating differential microglia depletion during tumor formation, mice treated with PLX pre- and during DMG tumor formation had significantly shorter survival compared to post-tumor PLX treatment (p < 0.05) and tumor alone (p < 0.01). The tumor, confirmed by H3K27M and GFP expression, showed Iba1+ microglia infiltration, which was reduced in PLX-treated mice. CD3+ cells were present in the tumor in both microglia depleted and control groups.

Conclusion : Microglial depletion and repopulation markedly reshape immune cell dynamics, with potential implications for DMG progression. These findings highlight the need to further investigate how modulating the TME might influence tumor development and survival.