Figure 2. The scheme of ACT using CD8+ Tm cells. ACT is a type of treatment in which T cells isolated from patients are modified and expanded in the laboratory, so that T cells can recognize and kill cells expressing Ags after re-infusion into patients. These cells are prepared using three major protocols: (A) in vitro-activated T cells, (B) T cells isolated from tissues, and (C) T cells engineered by genetic modification. (A) Tn cells derived from a patient’s blood can be activated in vitro with the desired Ags for clonal expansion. (B) T cells harvested from tissues, especially from tumors, promptly expand in vitro with homeostatic cytokines including IL-7, IL-15, IL-21, and IL-2 and refuse to eliminate tumor cells. (C) After collection from a patient’s blood, CD8+ T cells can be genetically engineered to become CAR-T cells that have Ag receptors that recognize cancer. These CAR-T cells can also be expanded in vitro in the laboratory and then reinfused into patients for use in immunotherapy.