Abstract 1340: The role of chemokines CCL8 and CCL12 in diffuse intrinsic pontine gliomas

Abstract Diffuse intrinsic pontine glioma (DIPG) is an aggressive pediatric brainstem glioma, which carries the deadliest prognosis of all childhood neoplasms. Despite recent advances in molecular profiling and characterization of pediatric high-grade gliomas, patient outcomes have not improved. One critical reason why current therapeutic approaches fail to provide a durable response is the adaptive nature of the highly understudied tumor microenvironment (TME). The most abundant non-neoplastic infiltrates in the DIPG TME are the tumor-associated macrophages (TAMs). There is limited data available on the role of TAMs in DIPG tumor growth and response to therapy, and the chemokines responsible for driving the infiltration of both innate and adaptive immune cells into these tumors remain unidentified.To accurately model DIPGs, we utilized immunocompetent genetically engineered mouse models (GEMMs) based on the RCAS/tv-a gene transfer system. At postnatal days 0-2, mice were injected with retrovirus-producing DF-1 cells directly in the brainstem. Tumorigenesis was driven by PDGFB overexpression and Tp53 silencing, together with human DIPG-specific mutations including: H3 histones with K27M substitution (H3.1K27M/H3.3K27M) and Acvr1R206H. Our data using these GEMMs show that mouse tumors are strikingly similar to their human counterparts as demonstrated by hallmark pathological observations including T2-contrast enhancement, highly infiltrating margins, and pseudopalisading necrosis. Loss of H3K27 trimethylation in histone mutant tumors is also observed in these tumors. Utilizing these GEMMs, we have identified CCL8 and CCL12 as important chemokines in H3.1K27M-DIPGs. Specifically, we observed longer survival in Ccl8/Ccl12 double knockout (DKO) tumor-bearing mice compared to wild-type (WT) mice. Interestingly, spectral flow cytometry analysis revealed no differences in myeloid cell infiltration but an increased number of NK cells, CD4+, and CD8+ T cells in tumors generated in Ccl8/Ccl12 DKO mice compared to WT. We also tested the efficacy of inhibiting two CCL8 receptors using a syngeneic mouse model of DIPG. Pharmacological inhibition of CCR1 and CCR5 rendered a reduction in macrophage presence in the tumors, and resulted in an extension of survival in tumor-bearing mice comparable to the effect of standard of care, radiation therapy. Our ongoing experiments aim to elucidate the mechanisms by which CCL8 and CCL12 modulate immune cell infiltration, and determine whether the effect of CCL8/CCL12 loss on survival seen in H3.1K27M-DIPG holds true for H3.3K27M-DIPG-bearing mice. Citation Format: Gonzalo M. Pinero, Montserrat Puigdelloses Vallcorba, James L. Ross, Zhihong Chen, Tanvi Joshi, Dolores Hambardzumyan. The role of chemokines CCL8 and CCL12 in diffuse intrinsic pontine gliomas [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1340.