Checkpoint blockade immunotherapy is favored in patients having a T cell-inflamed tumor microenvironment at baseline. Therefore, absence of a T cell-inflamed phenotype represents a first approximation of immunotherapy resistance. Investigation of molecular features of tumor genomics, host genetics, and commensal microbiota that correlate with the degree of spontaneous T-cell infiltration has revealed multiple layers of pathways that impact on relative response versus resistance to immunotherapeutic interventions. The first tumor-intrinsic oncogene pathway demonstrated mechanistically to mediate T-cell exclusion from the tumor microenvironment and lack of checkpoint blockade efficacy is the Wnt/β-catenin pathway. Additional molecular aberrations correlated with deficient immune infiltration in various cancers include loss of function mutation or absence of PTEN, LKB1, or p53 and activation of FGFR3 or PPAR-γ. Mouse modeling has revealed that tumor cell-intrinsic β-catenin pathway activation also mediates downstream resistance to adoptive T-cell therapy, due to defective expression of key chemokines. In one patient case analyzed, transition from a β-catenin-negative to a β-catenin-positive phenotype has been associated with secondary resistance to immunotherapy. TCGA and other large genomic datasets have been an invaluable tool for identifying such molecular correlates, through availability of tumor RNAseq and exome sequencing data as well as germline SNP analysis. Host germline polymorphisms also have been identified that correlate with the degree of T-cell infiltration in the tumor, and mouse models are being utilized to investigate mechanisms. Specific commensal bacteria associated with the degree of T-cell infiltration also have been identified in animal models, and similar analyses are ongoing with human stool samples in patients undergoing checkpoint blockade therapy. A common feature of non-T cell-inflamed tumors is a relative lack of Batf3-dendritic cells and absence of a type I IFN gene signature. Thus, regulation at the level of innate immunity seems to be a key determining factor. Strategies aimed at boosting innate immune activation in the tumor microenvironment represent a major category of therapeutic intervention to convert non-T cell-inflamed tumors to T cell-inflamed, and STING agonists and probiotics are beginning to be investigated clinically.

Citation Format: Thomas Frank Gajewski. Tumor and host factors regulating immunotherapy responsiveness [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr SY25-04. doi:10.1158/1538-7445.AM2017-SY25-04