T cells play a central role in cancer immunotherapy. They have the ability to specifically detect and selectively destroy cancer cells following recognition of a tumor antigen. We work on the mechanisms that constrain the activity of cytotoxic T cells in the tumor microenvironment. Using an in vivo shRNA screen, we have identified a series of negative regulators of T cell function in tumors. Our work focuses on the molecular mechanisms by which these genes inhibit T cell function against tumors and the development of novel cancer immunotherapies based on this insights.