STING activation of tumor endothelial cells initiates spontaneous and therapeutic antitumor immunity

Abstract

Spontaneous CD8 T-cell responses occur in growing tumors but are usually poorly effective. Understanding the molecular and cellular mechanisms that drive these responses is of major interest as they could be exploited to generate a more efficacious antitumor immunity. As such, stimulator of IFN genes (STING), an adaptor molecule involved in cytosolic DNA sensing, is required for the induction of antitumor CD8 T responses in mouse models of cancer. Here, we find that enforced activation of STING by intratumoral injection of cyclic dinucleotide GMP-AMP (cGAMP), potently enhanced antitumor CD8 T responses leading to growth control of injected and contralateral tumors in mouse models of melanoma and colon cancer. The ability of cGAMP to trigger antitumor immunity was further enhanced by the blockade of both PD1 and CTLA4. The STING-dependent antitumor immunity, either induced spontaneously in growing tumors or induced by intratumoral cGAMP injection was dependent on type I IFNs produced in the tumor microenvironment. In response to cGAMP injection, both in the mouse melanoma model and an ex vivo model of cultured human melanoma explants, the principal source of type I IFN was not dendritic cells, but instead endothelial cells. Similarly, endothelial cells but not dendritic cells were found to be the principal source of spontaneously induced type I IFNs in growing tumors. These data identify an unexpected role of the tumor vasculature in the initiation of CD8 T-cell antitumor immunity and demonstrate that tumor endothelial cells can be targeted for immunotherapy of melanoma.M etastatic melanoma is a highly aggressive cancer with a fast increasing incidence worldwide. Unless diagnosed early and surgically resected, the disease becomes metastatic and life threatening. Both chemotherapy and irradiation are ineffective. Novel therapies that target oncogenic drivers have brought some improvements, but tumor cells escape regularly (1). Melanoma is a prototypical immunogenic tumor, as shown by the occurrence of spontaneous CD8 T-cell responses that drive tumor regressions and by the identification of CD8 T cells that recognize melanoma antigens (2, 3). Although many immunotherapeutic strategies have been developed to induce such responses, clinical efficacies have been poor. More recently, "checkpoint blockade" therapies that target T-cell-inhibitory pathways mediated by CTLA4 (4) and PD1 (5) have yielded encouraging clinical results and demonstrated that spontaneous CD8 T-cell responses in tumors can be boosted to treat melanoma.The mechanisms that drive spontaneous antitumor immune responses are poorly understood. Type I IFNs (IFN-α and IFN-β) may play a role as the expression type I IFN-related genes in primary melanoma has been associated with spontaneous tumor regressions (6) and correlated to the tumor infiltration by specific CD8+ T cells (6, 7). Furthermore, the lack of type I IFN signaling or IFN-β expression inhibited the generation of tumor-specific CD8 T cells and accelerated tumor growth in a murine melanoma mo...

The host STING pathway at the interface of cancer and immunity

“…Another mechanism that has been observed in both leukemia and glioma cells is the homozygous deletion of type I IFN genes (37,38). Consistent with these data, it has been demonstrated that the main cell types that produce IFN-β within the tumor microenvironment are innate immune cells (predominantly DCs) and endothelial cells (6,39).…”

“…A rationally designed synthetic CDN agonist, ML RR-S2 CDA, has been developed and exhibits enhanced stability, human STING activation, cellular uptake, and antitumor efficacy, as well as low reactogenicity compared with the natural STING ligands produced by bacteria or host cell cGAS (8,86). R p , R p (R,R) dithio-substituted diastereomer CDNs were resistant to digestion with phosphodiesterase, stimulated higher expression of IFN-β in cultured human (formulated with Lipofectamine) induced antitumor responses in several melanoma models and in the MC38 colon carcinoma model lends further support to an approach using intratumoraladministered CDN-based STING agonists in the clinic (39). Strategies to further enhance STING immunotherapy by combining with other immunomodulatory agents are being explored in mouse models.…”

“…These data support the notion that strategies to counteract adaptive immune resistance may enhance the potency of STING agonists in the clinic. In another study, the antitumor efficacy of cGAMP administered by intratumoral injection into B16.F10 tumors was enhanced when combined with anti-PD1 and anti-CTLA4 antibodies (39). Similarly, antitumor efficacy mediated by intratumoral injection of ML RR-S2 CDA was improved when combined with immune checkpoint inhibitors, suggesting a possible combination for future clinical development (our unpublished data).…”

Innate immune signaling and regulation in cancer immunotherapy

“…Downstream type I IFN signaling was specifically required in Batf3 DCs for T cell priming to occur, as well as for subsequent immune-mediated tumor control. Other cells in the tumor can contribute to production of type I IFNs, including tumor endothelial cells [51].…”

The role of the tumour microenvironment in immunotherapy

“…Administration of STING agonists resulted in marked increase of CD8 + T cell infiltration and upregulation of PD-L1 (Fu et al 2015). Consequently, the combined use of STING agonists and PD-1 blockade enhanced anti-tumour immunity (Demaria et al 2015) and led to regression of tumours that were resistant to PD-1 therapy (Fu et al 2015).…”