Autologous T cells are engineered ex vivo to express a chimeric antigen receptor that binds CD19 on B cells. Upon CD19 engagement, the CAR’s activation (CD3ζ) and co‑stimulatory domains (e.g., CD28 or 4‑1BB) trigger T‑cell activation, proliferation, cytokine release, and cytotoxic killing (perforin/granzyme) of CD19+ malignant and normal B cells after lymphodepleting chemotherapy enhances expansion.