Tumor Ripk1 Signaling Regulates Intrinsic And Extrinsic Mechanisms Of Resistance To Immune Checkpoint Blockade Therapy
Immune checkpoint blockade therapy (ICB) can result in impressive clinical responses of multiple cancer types, however most patients fail to respond. Mechanisms of resistance include both tumor-intrinsic evasion of immune mediated killing and tumor-extrinsic features in the immune-microenvironment, such as poor infiltration of tumor reactive T cells and accumulation of immunosuppressive cells. Understanding the signaling pathways that can govern resistance to ICB can help with the development of novel combination therapies and improve patient responses. Our lab has previously shown that cancer cells upregulate a subset of interferon stimulated genes (ISGs) in response to chronic interferon signaling that are associated with resistance to immune checkpoint blockade, which ISGs regulate resistance to immune checkpoint blockade are unknown. Here, I show that cancer cells utilize the receptor interacting protein kinase 1 (RIPK1), which is an interferon stimulated gene, to orchestrate resistance to immune checkpoint blockade. RIPK1 can integrate signals down-stream of innate immune receptors, such as the death receptors, to facilitate either pro-survival signals and inflammation or cell death. Based on the multiple roles of RIPK1, I hypothesized that RIPK1 expression in the cancer cells may influence both intrinsic and extrinsic mechanisms regulating response to ICB. To test this hypothesis, I genetically deleted RIPK1 in murine cancer cell lines, this resulted in improved overall survival and tumor control upon ICB treatment compared to tumors expressing RIPK1. Mechanistically, signaling through RIPK1 orchestrates NF-kB and MAPK dependent pro-survival signals and inflammation that is regulated by its ubiquitin scaffolding function. Cancer-intrinsic RIPK1-dependent inflammatory chemokine production facilitates accumulation of immunosuppressive myeloid cells that are associated with ICB resistance in murine tumor models and human melanoma patients. In addition, RIPK1-dependent pro-survival signals directly impede the formation of a secondary signaling complex down-stream of the death receptors, and associated Caspase-8 (CASP8) dependent cell death. Blocking cancer-intrinsic survival and inflammatory signals through RIPK1 deletion can disable the development of immunosuppressive myeloid cells while promoting cytotoxic T and NK cells to eradicate tumors through death receptor mediated CASP8-dependent cell death. This work provides grounds for novel combinatorial treatment with immune checkpoint blockade therapy.