Regulatory T cells (Tregs) are a vital component of the T cell immune system by their ability to control T cell responses that would lead to autoimmune disease. Tregs also protect damaged normal cells that are healing from T cells programmed to kill any abnormal cells in the body. Cancer (tumor) develops from normal cells and can express normal self-antigens. Tregs protect precancerous cells as if they were healing damaged cells and inhibit the anti-tumor T cell response by the use of advanced effector mechanisms, which stop the T cell immune system from effectively removing the tumor. The function of cells involved in this process is controlled by the cell membrane activation of intracellular translational pathways interacting with the nucleus that produces transcriptional proteins, which control cellular behavior such as secretion of lymphokines or cell proliferation. This book examines the function and related translational pathways of Tregs, anti-tumor T cells, and cancer cells. It relates that information to the treatment of cancer by examining human clinical trials of new immune cell-based treatments (immunotherapy). The book also proposes ways to improve those treatments by manipulating the translational pathways of immunotherapeutic cells. The hope is that these new treatment proposals stimulate positive thought about the future of cancer immunotherapy.