Activation of the antitumor immune response using programmed death receptor-1 (PD-1) blockade showed benefit only in a fraction of patients with hepatocellular carcinoma (HCC). Combining PD-1 blockade with antiangiogenesis has shown promise in substantially increasing the fraction of patients with HCC who respond to treatment, but the mechanism of this interaction is unknown.

We recapitulated these clinical outcomes using orthotopic-grafted or induced-murine models of HCC. Specific blockade of vascular endothelial receptor 2 (VEGFR-2) using a murine antibody significantly delayed primary tumor growth but failed to prolong survival, while anti-PD-1 antibody treatment alone conferred a minor survival advantage in one model. However, dual anti-PD-1/VEGFR-2 therapy significantly inhibited primary tumor growth and doubled survival in both models. Combination therapy reprogrammed the immune microenvironment by increasing cluster of differentiation 8-positive (CD8 ) cytotoxic T cell infiltration and activation, shifting the M1/M2 ratio of tumor-associated macrophages and reducing T regulatory cell (Treg) and chemokine (C-C motif) receptor 2-positive monocyte infiltration in HCC tissue. In these models, VEGFR-2 was selectively expressed in tumor endothelial cells. Using spheroid cultures of HCC tissue, we found that PD-ligand 1 expression in HCC cells was induced in a paracrine manner upon anti-VEGFR-2 blockade in endothelial cells in part through interferon-gamma expression. Moreover, we found that VEGFR-2 blockade increased PD-1 expression in tumor-infiltrating CD4 cells. We also found that under anti-PD-1 therapy, CD4 cells promote normalized vessel formation in the face of antiangiogenic therapy with anti-VEGFR-2 antibody.

We show that dual anti-PD-1/VEGFR-2 therapy has a durable vessel fortification effect in HCC and can overcome treatment resistance to either treatment alone and increase overall survival in both anti-PD-1 therapy-resistant and anti-PD-1 therapy-responsive HCC models.