ABSTRACT While checkpoint immunotherapy has transformed the treatment of metastatic melanoma over the past decade, this therapy fails to provide durable responses for the majority of patients. Immunotherapy resistance in solid tumors is often driven by the immunosuppressive tumor microenvironment (TME), which dampens the anti-tumor capacity of incoming T cells. In this proposal, I aim to genetically engineer T cells to overcome a key pathway of immunosuppression which I identified using an unbiased bioinformatics screen. I aim to improve the function of adoptively transferred T cells by using CRISPR to knockout the expression of this key immune inhibitory receptor expressed on the T cell surface. I have already developed a method to knockout this gene efficiently in murine and human T cells, and through this proposal, I will determine the effect of gene knockout on intrinsic T cell fitness and function (Aim 1), T cell accumulation and function in the melanoma microenvironment (Aim 2), and T cell anti-tumor efficacy (Aim 3). I expect that this research will yield a translational method to improve the function of adoptively transferred T cells in the immunosuppressive melanoma TME. Our team has demonstrated the ability to take novel T cell therapies from the lab to the clinic, and our established program to treat patients with genetically-engineered T cells will ease translation.