ID #911 Preclinical models of pediatric high-grade glioma (pHGG) for dissecting tumor-host interactions and evaluating novel therapeutic strategies

Abstract

Pediatric high-grade gliomas are malignant, fast-growing brain tumors that develop in children. A hallmark of pHGGs is mutations in histone coding genes, which, along with other oncogenic alterations, promote tumor initiation and progression. In the absence of curative therapy, complete surgical resection is unattainable due to their diffusive nature, and radiotherapy remains the primary option, offering transient benefits. These tumors exhibit an immunosuppressive ‘cold’ tumor microenvironment (TME), despite substantial recruitment of macrophages and resident microglia. This study aims to investigate how histone mutations contribute to this immunosuppressive phenotype and influence recruited immune cells.

To address this, we are developing pre-clinical syngeneic mouse models for pHGG through two approaches: 1) infecting embryonic neural stem cells with lentiviral particles carrying the oncogenic mutations, and 2) isolating primary tumor cells from tumors induced in neonatal mice injected with these lentiviruses. We are establishing murine cell lines expressing genetic alterations specific to midline and hemispheric pHGGs, each engineered with or without the histone mutation. These cell lines are stereotactically injected into the brains of immunocompetent mice.

Once fully characterized, our mouse models can serve as valuable tools for studying the TME, dissecting poorly understood tumor-host interactions, and evaluating the efficacy of emerging therapies. Transplanted tumors are harvested before animals reach endpoint, processed into single-cell suspensions, and enriched for CD45+ cells, followed by multiplex flow cytometry to characterize lymphoid and myeloid populations. Fixed brains are sectioned and immunostained to assess the spatial distribution and morphology of specific immune cells within the TME. Therapies targeting pHGG-microglia interactions are being investigated, alone or in combination with immunotherapy, to determine their effects on survival and TME across histone mutant and WT models.

Integrating insights into tumor immunobiology and advanced immunotherapeutic strategies may ultimately pave the way for more effective clinical trials and improved treatment outcomes for pHGG.