Autologous T cells are genetically engineered to express a chimeric antigen receptor that recognizes a tumor antigen (e.g., CD19). CAR engagement activates CD3ζ and costimulatory domains (such as CD28 or 4‑1BB), leading to T‑cell expansion, cytokine release, and perforin/granzyme‑mediated cytotoxic killing of antigen‑expressing malignant cells; this immune activation can cause toxicities including ICANS.