Background: Immune checkpoint inhibitors (ICI) are highly effective in select cancers. Novel predictors of T cell-inflammation may identify a broader subset of tumors with ICI responsiveness. Our group has identified four chemokines (CCL4, CCL5, CXCL9, CXLC10) able to predict a T cell-inflamed phenotype in primary and metastatic pancreatic tumors. Here, we test whether this 4-chemokine signature can predict T cell-inflammation across additional tumor types and response to ICI. Methods: Using matched genomic and transcriptomic data from 6,455 patients spanning 25 tumor types from The Cancer Genome Atlas, we searched for associations between the 4-chemokine signature and metrics of antitumor immunity. Further, we tested the association of this signature with markers of DNA damage repair deficiency. We also investigated the ability of this signature to predict response to immunotherapy using real-world data from a pan-cancer cohort of 82 patients in the Personalized OncoGenomics Program who had received ICI. Results: The majority of tumor types displayed sub-populations with high expression of the 4-chemokines (4-chemokine^hi) and transcriptional hallmarks of the cancer-immunity cycle. Testicular germ cell tumors, cervical squamous cell carcinomas, and head and neck squamous cell carcinomas were the strongest expressors of the signature. Immunomodulatory genes, including PD-L1, PD-1, TIM3, LAG3, TIGIT, CTLA-4, and FASLG, were significantly overexpressed (p<0.05) in the 4-chemokine^hi cohorts. Genesets of processes involved in the cancer-immunity cycle, including MHC I expression and cytolytic activity, were upregulated in the 4-chemokine^hi cohorts (p<0.05). While a global relationship between tumor mutation burden (TMB) and 4-chemokine expression across tumor histological type was seen (rho=0.42, p=0.02), high TMB was associated with only a subset of 4-chemokine^hi tumors. Among patients treated with ICIs, those with 4-chemokine^hi tumors had a longer median time to progression (104 versus 71 days, p=0.013) and overall survival (391 versus 195 days, p=0.016). The 4-chemokine signature outperformed TMB for overall survival prediction. Conclusions: Sub-populations of T cell-inflamed patients exist across tumor types and may therefore respond favourably to ICI. The 4-chemokine signature has the potential to select a wider spectrum of patients that may benefit from ICIs.

HR = Hazard Ratio. OS = Overall survival from ICI initiation. TTP = Time to progression from ICI initiation.