CD28 and non-Hodgkin lymphoma: 28 simultaneously administered autologous anti‐CD19 CAR T cells both without (first‐generation) and with (second‐generation) an intracellular CD28 costimulatory domain to six patients with relapsed or refractory (r/r) B‐cell non‐Hodgkin's lymphoma (B‐NHL) without prior lymphodepleting chemotherapy. The CAR T cells lacking a CD28 costimulatory domain showed limited expansion and poor persistence, whereas the T cells expressing a CAR incorporating the CD28 domain underwent a greater degree of expansion and persisted for longer in all six patients.28