Characterization of the immune microenvironment of diffuse intrinsic pontine glioma: Implications for development of immunotherapy

Abstract

Background

Diffuse Intrinsic Pontine Glioma (DIPG) is a uniformly fatal CNS tumor diagnosed in 300 American children per year. Radiation is the only effective treatment and extends overall survival to a median of 11 months. Due to its location in the brainstem, DIPG tumors cannot be surgically resected. Immunotherapy has the ability to target tumor cells specifically, however, little is known about the tumor microenvironment in DIPGs. We sought to characterize infiltrating immune cells and immunosuppressive factor expression in pediatric low- and high-grade gliomas and DIPG.

Methods

Tumor microarrays were stained for infiltrating immune cells. RNA was isolated from snap-frozen tumor tissue and Nanostring analysis performed. DIPG and glioblastoma cells were co-cultured with healthy donor macrophages, T cells, or NK cells, and flow cytometry and cytotoxicity assays performed to characterize the phenotype and function, respectively, of the immune cells.

Results

DIPG tumors do not have increased macrophage or T cell infiltration relative to non-tumor control, nor do they overexpress immunosuppressive factors such as PD-L1 or TGF1. H3.3-K27M DIPG cells do not repolarize macrophages, but are not effectively targeted by activated allogeneic T cells. NK cells lysed all DIPG cultures.

Conclusions

DIPG tumors have neither a highly immunosuppressive nor inflammatory microenvironment. Therefore, major considerations for the development of immunotherapy will be the recruitment, activation, and retention of tumor-specific effector immune cells.