Solid tumors remain a major challenge in cancer treatment, as most current T cell therapies are ineffective against them due to tumor resistance mechanisms, such as antigen loss and immune evasion. This project addresses these critical gaps by leveraging advanced CRISPR-Cas9 genome engineering to develop T cell therapies that are robust, precise, and capable of overcoming these obstacles. Our overarching goal is to engineer T cells with enhanced efficacy, safety, and specificity by focusing on three key aims: optimizing T cell receptor (TCR) sensitivity to improve therapeutic persistence, uncovering and controlling self-reactive T cells to minimize adverse effects, and creating polyclonal TCR repertoires that counteract tumor antigen loss. A key innovation is the development of a platform for scalable TCR knock-in, which eliminates the need for complex manipulation and expands the accessibility of these therapies. The expected impact of this work is transformative: it will provide new scientific insights into T cell biology and redefine engineered immunotherapies for cancer, ultimately making these treatments safer, more effective, and available to a broader range of patients.