This directed case study was written to help students learn about an innovative cancer therapy that harnesses a patient's immune system to recognize and destroy cancer cells. The critical insight underlying this therapy is to use a cancer patient's own immune cells to target and destroy cancer cells. The process involves the removal of T lymphocytes from a cancer patient's blood stream, which are then genetically engineered to express a novel cell surface protein called a chimeric antigen receptor (CAR). The approach is known as "CAR T cell therapy." Written as a conversation between a cancer patient and an oncologist, the case details the immunological protein components used to construct the CAR that permit the targeting of cancer cells and the activation of T cells. The case covers the cell biology, biochemistry, and immunology underlying CAR T cell therapies, and is appropriate for an upper-level undergraduate immunology course or a clinical course covering oncology, immunology, or therapeutics.