Non-inflammatory tumor microenvironment of diffuse intrinsic pontine glioma

Mario L. Suvà,Surya Nagaraja,Hannes Vogel,Grant L. Lin,Mariella G. Filbin,Michelle Monje

doi:10.1186/s40478-018-0553-x

Abstract

Diffuse intrinsic pontine glioma (DIPG) is a universally fatal malignancy of the childhood central nervous system, with a median overall survival of 9–11 months. We have previously shown that primary DIPG tissue contains numerous tumor-associated macrophages, and substantial work has demonstrated a significant pathological role for adult glioma-associated macrophages. However, work over the past decade has highlighted many molecular and genomic differences between pediatric and adult high-grade gliomas. Thus, we directly compared inflammatory characteristics of DIPG and adult glioblastoma (GBM). We found that the leukocyte (CD45+) compartment in primary DIPG tissue samples is predominantly composed of CD11b + macrophages, with very few CD3+ T-lymphocytes. In contrast, T-lymphocytes are more abundant in adult GBM tissue samples. RNA sequencing of macrophages isolated from primary tumor samples revealed that DIPG- and adult GBM-associated macrophages both express gene programs related to ECM remodeling and angiogenesis, but DIPG-associated macrophages express substantially fewer inflammatory factors than their adult GBM counterparts. Examining the secretome of glioma cells, we found that patient-derived DIPG cell cultures secrete markedly fewer cytokines and chemokines than patient-derived adult GBM cultures. Concordantly, bulk and single-cell RNA sequencing data indicates low to absent expression of chemokines and cytokines in DIPG. Together, these observations suggest that the inflammatory milieu of the DIPG tumor microenvironment is fundamentally different than adult GBM. The low intrinsic inflammatory signature of DIPG cells may contribute to the lack of lymphocytes and non-inflammatory phenotype of DIPG-associated microglia/macrophages. Understanding the glioma subtype-specific inflammatory milieu may inform the design and application of immunotherapy-based treatments.

Highlights

Diffuse intrinsic pontine glioma (DIPG) is a devastating tumor that arises in the ventral pons, during childhood, and is universally fatal
We have previously demonstrated that human DIPG samples demonstrate substantial immunoreactivity for the macrophage/microglial markers CD68 and CD163 [6], illustrating that Glioma-associated microglia/macrophages (GAMs) are a large fractional component of the DIPG microenvironment
We demonstrate that while DIPG-associated macrophages exhibit some gene expression programs similar to adult GBM-associated macrophages, they express substantially fewer inflammatory cytokines and chemokines compared to adult GAMs

Summary

Introduction

Diffuse intrinsic pontine glioma (DIPG) is a devastating tumor that arises in the ventral pons, during childhood, and is universally fatal. The standard of care is radiotherapy, which offers temporary stabilization or reduction of symptoms and extends median survival by approximately 3 months [21]. Overall median survival remains 9–11 months with less than 10% of children surviving beyond 2 years [7, 20]. GBM samples exhibit a muted immune functional phenotype compared to pediatric pilocytic astrocytomas and ependymomas [15], but the immune state of DIPG has not been analyzed to date. DIPG exhibits a unique mutational profile and transcriptional state [27, 29], raising the question of a unique immune microenvironment. As interest in the clinical application of immunotherapeutic approaches for DIPG grows, it is critically important to understand how potential differences in the DIPG immune microenvironment could influence treatment efficacy. The presence or absence of lymphocytes would inform the consideration of strategies such as checkpoint inhibition

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Conclusion