Conventional treatments of gastrointestinal cancers based on surgical resection and chemotherapy are not enough to eradicate potentially relapsing tumor cells and can also impair the immune system functions. Immunotherapies aim to help the body to eradicate cancer and other diseases, by modulating the immune system. They can be performed by active approaches, usually orchestrated by dendritic cell vaccines that present a specific tumor associated antigen to T cells, or passive approaches, which have the T cells as protagonist, and are based on antitumor antibodies, or adoptive cell transfer. T lymphocyte subsets can exhibit different role face to a tumor scenario, varying from an effective cellular antitumor response to a regulatory participation. Although a lot of protocols to combat cancer progression have been proposed, T cell-based immunotherapies in gastrointestinal cancers are still not approved for clinical applications mainly because of their side effects. Nowadays, promising protocols combining two or more approaches, aiming to create an efficient therapy without or with fewer side effects. In this chapter, we made a review about the role of T cells on cancer, especially focusing on gastrointestinal cancer immunotherapeutic methods.