We have interrogated a 12-chemokine gene expression signature (GES) on genomic arrays of 14,492 distinct solid tumors and show broad distribution across different histologies. We hypothesized that this 12-chemokine GES might accurately predict a unique intratumoral immune reaction in stage IV (non-locoregional) melanoma metastases. The 12-chemokine GES predicted the presence of unique, lymph node-like structures, containing CD20⁺ B cell follicles with prominent areas of CD3⁺ T cells (both CD4⁺ and CD8⁺ subsets). CD86⁺, but not FoxP3⁺, cells were present within these unique structures as well. The direct correlation between the 12-chemokine GES score and the presence of unique, lymph nodal structures was also associated with better overall survival of the subset of melanoma patients. The use of this novel 12-chemokine GES may reveal basic information on in situ mechanisms of the anti-tumor immune response, potentially leading to improvements in the identification and selection of melanoma patients most suitable for immunotherapy.

Lack or loss of tumor antigenicity represents one of the key mechanisms of immune escape and resistance to T cell–based immunotherapies. Evidence suggests that activation of stimulator of interferon genes (STING) signaling in tumor cells can augment their antigenicity by triggering a type I IFN-mediated sequence of autocrine and paracrine events. Although suppression of this pathway in melanoma and other tumor types has been consistently reported, the mechanistic basis remains unclear. In this study, we asked whether this suppression is, in part, epigenetically regulated and whether it is indeed a driver of melanoma resistance to T cell–based immunotherapies. Using genome-wide DNA methylation profiling, we show that promoter hypermethylation of cGAS and STING genes mediates their coordinated transcriptional silencing and contributes to the widespread impairment of the STING signaling function in clinically-relevant human melanomas and melanoma cell lines. This suppression is reversible through pharmacologic inhibition of DNA methylation, which can reinstate functional STING signaling in at least half of the examined cell lines. Using a series of T cell recognition assays with HLA-matched human melanoma tumor-infiltrating lymphocytes (TIL), we further show that demethylation-mediated restoration of STING signaling in STING-defective melanoma cell lines can improve their antigenicity through the up-regulation of MHC class I molecules and thereby enhance their recognition and killing by cytotoxic T cells. These findings not only elucidate the contribution of epigenetic processes and specifically DNA methylation in melanoma-intrinsic STING signaling impairment but also highlight their functional significance in mediating tumor-immune evasion and resistance to T cell–based immunotherapies. Significance Although cancer immunotherapies have shown potential in inducing durable tumor regression in patients with metastatic melanoma, their efficacy remains highly variable and patient specific. Here, we present one strategy to overcome resistance to T cell–based immunotherapies by pharmacologically modulating the STING pathway, a relatively common suppressed DNA-sensing pathway in human melanomas. We show that rescue of this pathway in human melanoma cells using a clinically available DNA methylation inhibitor can augment their antigenicity and recognition by tumor-infiltrating lymphocytes. These findings have important clinical implications for the development of optimal therapeutic protocols that consider the status of tumor-intrinsic STING activity and provide a strategy to design clinical interventions using T cell–based immunotherapies with appropriate patient selection in melanoma.

A unique 12-chemokine gene expression score (CS) accurately predicted the presence of tumor-localized, ectopic lymph node-like structures (TL-ELNs) and improved overall survival (OS) in primary colorectal cancer and metastatic melanoma. We analyzed the correlation between CS, clinicopathological variables, molecular data, and 366 survival in Moffitt Cancer Center’s Total Cancer Care (TCC) patients with non-metastatic breast cancer. Affymetrix gene expression profiles were used to interrogate the CS by the principal component method. Breast tumors were classified as high or low score based on median split, and correlations between clinicopathologic variables, PAM50 molecular subtype, and ELN formation were analyzed using the TCC dataset. Differences in overall survival (OS) and recurrence-free survival (RFS) in the larger KM Plot breast cancer public datasets were compared using Kaplan-Meier curves. We divided the Total Cancer Care (TCC) breast cancer patients into two groups of high or low CS. Mean CS was 0.24 (range, 2.2–2.1). Patients with higher CS were more likely to be white (172 vs. 159; p = 0.03), had poorly differentiated tumors (112 vs. 59; p <0.0001), ER/PR negative (41 vs. 26) and HER2 positive (36 vs. 19; p = 0.001), and contain TL-ELNs. Higher CS scores were also seen in the basal and HER2+ molecular subtypes. In the KM Plot breast cancer datasets higher CS patients demonstrated superior OS (HR = 0.73, p = 0.008) and RFS (HR 0.76, p = <0.0001), especially in basal and HER2+ patients. High CS breast tumors tend to be higher grade, basal or HER2+, and present more frequently in Caucasians. However, this group of patients also shows the presence of TL-ELNs within the tumor microenvironment and has better survival outcomes. The CS is a novel tool that can identify breast cancer patients with tumors of a unique intratumoral immune composition and better prognosis. Whether or not the CS is a predictive response marker in breast cancer patients undergoing immunotherapy remains to be determined.

STING (stimulator of IFN genes) signaling is an innate immune pathway for induction of a spontaneous antitumor T-cell response against certain immunogenic tumors. Although antigen-presenting cells are known to be involved in this process, insight into the participation of tumor cell–intrinsic STING signaling remains weak. In this study, we find diversity in the regulation of STING signaling across a panel of human melanoma cell lines. We show that intact activation of STING signaling in a subset of human melanoma cell lines enhances both their antigenicity and susceptibility to lysis by human melanoma tumor-infiltrating lymphocytes (TIL) through the augmentation of MHC class I expression. Conversely, defects in the STING signaling pathway protect melanoma cells from increased immune recognition by TILs and limit their sensitivity to TIL lysis. Based on these findings, we propose that defects in tumor cell–intrinsic STING signaling can mediate not only tumor immune evasion but also resistance to TIL-based immunotherapies.

While STING-activating agents have shown limited efficacy in early-phase clinical trials, multiple lines of evidence suggest the importance of tumor cell-intrinsic STING function in mediating antitumor immune responses. Although STING signaling is impaired in human melanoma, its restoration through epigenetic reprogramming can augment its antigenicity and T cell recognition. In this study, we show that reversal of methylation silencing of STING in murine melanoma cell lines using a clinically available DNA methylation inhibitor can improve agonist-induced STING activation and type-I IFN induction, which, in tumor-bearing mice, can induce tumor regression through a CD8⁺ T cell-dependent immune response. These findings not only provide mechanistic insight into how STING signaling dysfunction in tumor cells can contribute to impaired responses to STING agonist therapy, but also suggest that pharmacological restoration of STING signaling through epigenetic reprogramming might improve the therapeutic efficacy of STING agonists.