Abstract Optimal ex vivo expansion protocols of tumor-specific T cells followed by adoptive cell therapy must yield T cells able to home to tumors and effectively kill them. Our previous study demonstrated ex vivo activation in the presence of IL-12–induced optimal CD8+ T cell expansion and melanoma regression; however, adverse side effects, including autoimmunity, can occur. This may be due to transfer of high-avidity self-specific T cells. In this study, we compared mouse low- and high-avidity T cells targeting the tumor Ag tyrosinase-related protein 2 (TRP2). Not surprisingly, high-avidity T cells provide superior tumor control, yet low-avidity T cells can promote tumor regression. The addition of IL-12 during in vitro expansion boosts low-avidity T cell responsiveness, tumor regression, and prevents T cell exhaustion. In this study, we demonstrate that IL-12–primed T cells are resistant to PD-1/PD-L1–mediated suppression and retain effector function. Importantly, IL-12 preconditioning prevented exhaustion as LAG-3, PD-1, and TOX were decreased while simultaneously increasing KLRG1. Using intravital imaging, we also determined that high-avidity T cells have sustained contacts with intratumoral dendritic cells and tumor targets compared with low-avidity T cells. However, with Ag overexpression, this defect is overcome, and low-avidity T cells control tumor growth. Taken together, these data illustrate that low-avidity T cells can be therapeutically beneficial if cocultured with IL-12 cytokine during in vitro expansion and highly effective in vivo if Ag is not limiting. Clinically, low-avidity T cells provide a safer alternative to high-avidity, TCR-engineered T cells, as IL-12–primed, low-avidity T cells cause less autoimmune vitiligo.