Established T Cell-Inflamed Tumors Rejected after Adaptive Resistance Was Reversed by Combination STING Activation and PD-1 Pathway Blockade.

Patients with head and neck squamous cell carcinoma harbor T cell-inflamed and non-T cell-inflamed tumors. Despite this, only 20% of patients respond to checkpoint inhibitor immunotherapy. Lack of induction of innate immunity through pattern-recognition receptors, such as the stimulator of interferon (IFN) genes (STING) receptor, may represent a significant barrier to the development of effective antitumor immunity. Here, we demonstrate robust control of a T cell-inflamed (MOC1), but not non-T cell-inflamed (MOC2), model of head and neck cancer by activation of the STING pathway with the synthetic cyclic dinucleotide RP, RP dithio-c-di-GMP. Rejection or durable tumor control of MOC1 tumors was dependent upon a functional STING receptor and CD8 T lymphocytes. STING activation resulted in increased tumor microenvironment type 1 and type 2 IFN and greater expression of PD-1 pathway components in vivo. Established MOC1 tumors were rejected and distant tumors abscopally controlled, after adaptive immune resistance had been reversed by the addition of PD-L1 mAb. These findings suggest that PD-1 pathway blockade may reverse adaptive immune resistance following cyclic dinucleotide treatment, enhancing both local and systemic antitumor immunity. (C) 2016 AACR.