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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...

Current T cell differentiation models invoke separate T helper 2 (Th2) and Th1 cell lineages governed by the lineage-specifying transcription factors GATA-3 and T-bet. However, knowledge on the plasticity of Th2 cell lineage commitment is limited. Here we show that infection with Th1 cell-promoting lymphocytic choriomeningitis virus (LCMV) reprogrammed otherwise stably committed GATA-3(+) Th2 cells to adopt a GATA-3(+)T-bet(+) and interleukin-4(+)interferon-gamma(+) "Th2+1" phenotype that was maintained in vivo for months. Th2 cell reprogramming required T cell receptor stimulation, concerted type I and type II interferon and interleukin-12 signals, and T-bet. LCMV-triggered T-bet induction in adoptively transferred virus-specific Th2 cells was crucial to prevent viral persistence and fatal immunopathology. Thus, functional reprogramming of unfavorably differentiated Th2 cells may facilitate the establishment of protective immune responses. Stable coexpression of GATA-3 and T-bet provides a molecular concept for the long-term coexistence of Th2 and Th1 cell lineage characteristics in single memory T cells.

IMPORTANCE Immunotherapy with checkpoint inhibitors targeting the PD-1 (programmed cell death 1) axis has brought notable progress in patients with non-small cell lung cancer (NSCLC) and other cancers. However, autoimmune toxic effects are frequent and poorly understood, making it important to understand the pathophysiologic processes of autoimmune adverse effects induced by checkpoint inhibitor therapy. OBJECTIVE To gain mechanistic insight into autoimmune skin toxic effects induced by anti-PD-1 treatment in patients with non-small cell lung cancer. DESIGN, SETTING, AND PARTICIPANTS This prospective cohort study was conducted from July 1, 2016, to December 31, 2018. Patients (n = 73) with non-small cell lung cancer who received anti-PD-1 therapy (nivolumab or pembrolizumab) were recruited from 4 different centers in Switzerland (Kantonsspital St Gallen, Spital Grabs, Spital Wil, and Spital Flawil). Peripheral blood mononuclear cells, tumor biopsy specimens and biopsies from sites of autoimmune skin toxic effects were collected over a 2-year period, with patient follow-up after 1 year. MAIN OUTCOMES AND MEASURES Response to treatment, overall survival, progression-free survival, and development of autoimmune toxic effects (based on standard laboratory values and clinical examinations). RESULTS Of the cohort of 73 patients with NSCLC (mean [SD] age, 68.1 [8.9] years; 44 [60%] men), 25 (34.2% [95% CI, 24.4%-45.7%]) developed autoimmune skin toxic effects, which were more frequent in patients with complete remission or partial remission (68.2% [95% CI, 47.3%-83.6%]) than those with progressive or stable disease (19.6% [95% CI, 11.0%-32.5%]) (χ 2 = 14.02, P < .001). Nine T-cell antigens shared between tumor tissue and skin were identified. These antigens were able to stimulate CD8 + and CD4 + T cells in vitro. Several of the antigen-specific T cells found in blood samples were also present in autoimmune skin lesions and lung tumors of patients who responded to anti-PD-1 therapy. CONCLUSIONS AND RELEVANCE These findings highlight a potential mechanism of checkpoint inhibitor-mediated autoimmune toxic effects and describe the association between toxic effects and response to therapy; such an understanding will help in controlling adverse effects, deciphering new cancer antigens, and further improving immunotherapy.