Adoptive Tcell therapy uses T cell-based cytotoxic responses to attack cancer cells. T cells that have a natural or genetically engineered reactivity to a patient's cancer are generated in vitro and then transferred back into the cancer patient. This can be achieved by taking T cells that are found with the tumour of the patient, which are trained to attack the cancerous cells. These T cells are referred to astumor infiltrating lymphocytes (TIL) are then encouraged to multiply in vitro using high concentrations of IL-2 , anti-CD3 and allo-reactive feeder cells. These T cells are then transferred back into the patient along with exogenous administration of IL-2 to further boost their anti-cancer activity.

Over the past 50 years, two fundamentally different strategies to stimulate antitumor immunity have been tested in humans: therapeutic vaccination and passive immunization. Passive immunization, herein referred to as adoptive T cell therapy, is the transfusion of autologous or allogeneic T cells into tumor-bearing hosts, i.e., patients.