Anti-VEGF treatment enhances antitumor responses by targeting regulatory T cells

Cholangiocarcinoma (CCA) shows limited response to systemic treatments including immunotherapy. We initiated an open-label phase II clinical trial testing bevacizumab (anti-VEGF-A) plus tremelimumab (anti-CTLA-4) and durvalumab (anti-PD-L1) in patients with primary liver cancer. Exceptional responses were observed in patients with CCA that were accompanied with moderate to severe, yet manageable immune-related events in the majority of patients. Correlative studies using paired PBMC and serum samples demonstrated a proinflammatory cytokine profile, reinvigoration of precursor exhausted CD8+ T cells, and expansion of regulatory T cell and non-classical monocyte subsets. We utilized subcutaneous, orthotopic as well as plasmid-induced murine CCA models to better understand how anti-VEGF-A enhances anti-tumor immunity induced by anti-CTLA4 plus anti-PD-L1. We describe a novel multi-modal mechanism of how anti-VEGF-A therapy enhances immune checkpoint inhibitor-induced immune responses. The treatment effect was dependent on an increase in tumor infiltrating B cells and IL-12 causing Treg rewiring towards fragile and unstable states. Using a mouse model that genetically ablates VEGFR2 expression on Tregs, we show that the VEGF /VEGFR2 axis on Tregs contributes to the pro-tumoral function of Tregs and supports tumor progression in a syngeneic CCA model. This study provides clinical evidence that simultaneously targeting three immunosuppressive axes, namely VEGF-A, CTLA-4 and PD-L1, can elicit strong anti-tumor immunity to potentiate CCA regression and merits broader evaluation in other cancers.