Shreya Bandopadhyay

Background: Pediatric high-grade gliomas (pHGG) are the leading cause of cancer-related mortality in children¹. These tumors are uniquely characterized by an immune landscape dominated by infiltrating myeloid cells, which constitute 30% to 50% of the total tumor mass¹. Unlike adult glioblastomas, pHGGs exhibit a profound failure to mount effective T-cell responses, creating an “immune cold” environment that renders conventional therapies less effective and often leads to long-term cognitive deficits in survivors¹. Understanding this distinct microenvironment is critical for developing specialized immunotherapies for childhood malignancies.

Research Objectives: This literature review investigates how the hallmark H3K27M mutation acts as an epigenetic architect to drive immune evasion and evaluates emerging therapeutic strategies—specifically targeting the CCR1/2/5, CD47, TIM-3, and STAT3 pathways—to reprogram the myeloid microenvironment from a pro-tumoral to an anti-tumoral state^1-6.

Methods: The study synthesizes results from primary research articles published between 2023 and 2026, utilizing data from high-resolution single-cell RNA sequencing (scRNA-seq), immunocompetent de novo murine models, and a first-in-child phase I clinical trial^1-6.

Results: The H3K27M mutation alters the epigenetic profiles of surrounding immune cells, inducing a “disease-associated myeloid” (DAM) phenotype and dampening critical interferon (IFN) signaling³. Tumors exploit this by secreting chemokines (CCL8/CCL12) to recruit suppressive myeloid cells; however, pharmacological inhibition of the CCR1, CCR2, and CCR5 receptors significantly extends survival and synergizes with anti-PD-1 therapy^1-3. Furthermore, combining radiotherapy with CD47 or TIM-3 blockade reprograms macrophage plasticity and establishes long-term antitumor immune memory^4,5. Finally, clinical evaluation of the STAT3 inhibitor WP1066 successfully “unmasked” the immune system in pediatric patients, inducing a systemic shift toward pro-inflammatory T-cell activity⁶.

Conclusion: pHGGs utilize an active epigenetic program to maintain immune suppression, but this state is pharmacologically reversible. Reprogramming regulatory hubs can “flip the switch” to a pro-inflammatory state, offering a path toward successful immunotherapy⁶. Future directions include the development of precise markers to distinguish resident microglia from monocyte-derived macrophages and investigating whether direct epigenetic modifiers, such as HDAC inhibitors, can reset the myeloid transcriptome to a wild-type state.

Bibliography

1. du Chatinier A, Velilla IQ, Meel MH, Hoving EW, Hulleman E, Metselaar DS. Microglia in pediatric brain tumors: The missing link to successful immunotherapy. Cell Rep Med. Nov 21 2023;4(11):101246. doi:10.1016/j.xcrm.2023.101246
2. Pant A, Hwa-Lin Bergsneider B, Srivastava S, et al. CCR2 and CCR5 co-inhibition modulates immunosuppressive myeloid milieu in glioma and synergizes with anti-PD-1 therapy. Oncoimmunology. 2024;13(1):2338965. doi:10.1080/2162402x.2024.2338965
3. Ross JL, Puigdelloses-Vallcorba M, Piñero G, et al. Microglia and monocyte-derived macrophages drive progression of pediatric high-grade gliomas and are transcriptionally shaped by histone mutations. Immunity. Nov 12 2024;57(11):2669–2687.e6. doi:10.1016/j.immuni.2024.09.007
4. Lakshmanachetty S, Riemondy K, Sanford B, et al. Differential phagocytosis induces diverse macrophage activation states in malignant gliomas. J Immunother Cancer. Sep 5 2025;13(9)doi:10.1136/jitc-2025-012211
5. Ausejo-Mauleon I, Labiano S, de la Nava D, et al. TIM-3 blockade in diffuse intrinsic pontine glioma models promotes tumor regression and antitumor immune memory. Cancer Cell. Nov 13 2023;41(11):1911–1926.e8. doi:10.1016/j.ccell.2023.09.001
6. Castellino RC, Mumme H, Franson A, et al. First-in-child phase I trial of p-STAT3 inhibitor WP1066 in pediatric brain tumor patients. JCI Insight. Feb 9 2026;11(3)doi:10.1172/jci.insight.194823