IMMU-16. ANTI-VEGF TREATMENT EFFECT AGAINST GLIOMA IS IMMUNE DEPENDENT AND MEDIATED BY ENHANCED T CELL ACTIVITY

Abstract Immunotherapy trials in glioblastoma patients increasingly avoid immunosuppressive steroids and consider bevacizumab as alternative anti-edema treatment. Since VEGF is also a potent immunosuppressive factor, we explored the dimension and mechanisms of immune-mediated effects of anti-VEGF treatment. Murine glioma cells were injected intracerebrally into C57BL/6 wild-type mice or immunodeficient Pfp/Rag2 knockout mice and animals were treated with B20 (anti-murine VEGF) or dexamethasone. Immune cells were profiled by flow cytometry, and RNAseq was performed on sorted tumor and immune cells at different timepoints. B20 prolonged the survival of immunocompetent mice but not of Pfp/Rag2 knockout mice, indicating that the immune system is essential for its effect. At an early timepoint when controls became symptomatic, B20 “early” tumors (B20-ea) showed increased infiltration with T cells and myeloid cells, and decreased vascularization, whereas B20 tumors at the survival endpoint resembled IgG-controls. Gene expression in B20-ea tumor cells was dominated by hypoxia, neural development, invasion, TGF-β, Notch and Wnt signatures as well as concerted upregulation of Kmt2 H3K4 methyltransferases. In CD11b+ myeloid cells from B20-ea tumors, M1 hallmark genes and T cell activation genes were upregulated, while M2 genes were downregulated. Deconvolution revealed a transient shift towards pro-immune microglia/macrophages as well as increased NK cells and DCs. In CD8+ and CD4+ T cells, B20 increased the expression of S1pr1 and α/β TCR genes. The proportion of progenitor-like exhausted CD8+ cells, which are responsive to PD-1 blockade, was increased in B20-ea. In CD4+ cells, B20 caused skewing towards TFH, while dexamethasone increased TH2 cytokine expression. Depletion experiments demonstrated that CD8+ and CD4+ T cells but not NK cells were necessary for the survival-prolonging effect of B20. To conclude, anti-VEGF therapy has significant immunostimulatory effects which are, however, largely transient, so that an early treatment window of opportunity may exist during which it could actively support immunotherapy.