Programmed cell death is required for normal development and tissue homeostasis, but can also occur as a defensive response to pathogen infection. We now understand that cells can undergo distinct forms of programmed cell death: in addition to apoptosis, necroptosis is a recently-described form of cell suicide that can be induced by viral infection. Necroptosis involves cellular swelling and rupture, and has been hypothesized to trigger inflammatory and immune responses when it occurs in vivo, but the determinants of immune responses to necroptosis are not well understood. We have found that activation of the key necroptosis-inducing kinase, RIPK3, can trigger transcriptional responses in addition to inducing cell death. Furthermore, our preliminary data indicate that chemokine expression induced by RIPK3 activation accompanies RIPK3-induced cell death, and that this transcriptional response is required to render necroptosis immunogenic. This leads to the central hypothesis of this proposal: That necroptosis represents a uniquely immunogenic form of cell death, because it couples the production if immune-attractant chemokines with lytic cell death. An important extension of this idea, which we will test, is that induction of necroptosis within the tumor microenvironment will promote beneficial tumor immunity. To test this idea, we will focus on three Aims. First, we will use novel high-content imaging approaches to compare the way the immune system traffics, presents, and reacts to antigens derived from apoptotic, necroptotic, or necrotic cells. We will then use flank tumor models, in combination with a newly developed system for the rapid induction of different forms of cell death in vivo, assess the immune response to the necroptotic death of tumor cells. We will apply these findings to clinically-relevant tumor models, by testing the ability of the immune signature created by tumor cell necroptosis to synergize with immune checkpoint inhibitors and to promote immune clearance of metastatic lesions. Finally, we will create and test a system allowing rapid induction of necroptosis in unmodified tumor cells in vivo. Together, the experiments proposed here will determine what makes necroptosis immunogenic, then apply these findings to models of tumor immunotherapy.