Enhanced Immunotherapeutic Efficacy of Anti-PD-L1 Antibody in Combination with an EP4 Antagonist.

Combination treatment approaches are increasingly considered to overcome resistance to immunotherapy targeting immunoinhibitory molecules such as programmed death (PD)-1 and PD-ligand 1 (PD-L1). Previous studies have demonstrated that the therapeutic efficacy of anti-PD-L1 Abs is enhanced by combination treatment with cyclooxygenase-2 inhibitors, through downregulation of the immunosuppressive eicosanoid PGE, although the underlying mechanism remains unclear. In this study, we show that serum PGE levels are upregulated after anti-PD-L1 Ab administration in a bovine model of immunotherapy and that PGE directly inhibits T cell activation via its receptor E prostanoid (EP) 4. Additionally, anti-PD-L1 Ab induces TNF-α production and TNF-α blockade reduces PGE production in the presence of anti-PD-L1 Ab, suggesting that anti-PD-L1 Ab-induced TNF-α impairs T cell activation by PGE upregulation. Our studies examining the therapeutic potential of the dual blockade of PD-L1 and EP4 in bovine and murine immune cells reveal that the dual blockade of PD-L1 and EP4 significantly enhances Th1 cytokine production in vitro. Finally, we show that the dual blockade decreases tumor volume and prolongs survival in mice inoculated with the murine lymphoma cell line EG7. Altogether, these results suggest that TNF-α induced by anti-PD-L1 Ab treatment is associated with T cell dysfunction via PGE/EP4 pathway and that the dual blockade of PD-L1 and EP4 should be considered as a novel immunotherapy for cancer.