Immune deconvolution and temporal mapping identifies stromal targets and developmental intervals for abrogating murine low-grade optic glioma formation.

Background: Brain tumor formation and progression are dictated by cooperative interactions between neoplastic and non-neoplastic cells. This stromal dependence is nicely illustrated by tumors arising in the Neurofibromatosis type 1 (NF1) cancer predisposition syndrome, where children develop low-grade optic pathway gliomas (OPGs). Using several authenticated -OPG murine models, we previously demonstrated that murine -OPG growth is regulated by T cell function and microglia Ccl5 production, such that their inhibition reduces tumor proliferation . While these interactions are critical for established -OPG tumor growth, their importance in tumor formation has not been explored.

Methods: A combination of bulk and single-cell RNA mouse optic nerve sequencing, immunohistochemistry, T cell assays, and pharmacologic and antibody-mediated inhibition methods were used in these experiments.

Results: We show that T cells and microglia are the main non-neoplastic immune cell populations in both murine and human LGGs. Moreover, we demonstrate that CD8 T cells, the predominant LGG-infiltrating lymphocyte population, are selectively recruited through increased Ccl2 receptor () expression in CD8, but not CD4, T cells, in a NF1/RAS-dependent manner. Finally, we identify the times during gliomagenesis when microglia Ccl5 production (3-6 weeks of age) and Ccl2-mediated T cell infiltration (7-10 weeks of age) occur, such that temporally-restricted Ccl2 or Ccl5 inhibition abrogates tumor formation >3.5 months following the cessation of treatment.

Conclusions: Collectively, these findings provide proof-of-concept demonstrations that targeting stromal support during early gliomagenesis durably blocks murine LGG formation.