(1) A type of white blood cell that can directly destroy specific cells. T cells can be separated from other blood cells, grown in the laboratory, and then given to a patient to destroy tumor cells. Certain cytokines can also be given to a patient to help form cytotoxic T cells in the patient's body.
(2) Any of various large differentiated T cells that recognize and lyse target cells bearing a specific foreign antigen, usually by infection with a virus, and that also function in defense against cancer cells. Also called cytotoxic T cell, killer T cell.