PRF1 and leukemia: Upon interaction with CD19+ targets on-chip, CAR T cell significantly enhanced surface expression of T cell activation markers, CD25 (Fig. 2e) and CD69 (Fig. 2f), secretion of cytotoxicity-related cytokines, interferon-γ (IFNγ; Fig. 2g), granzyme B (Extended Data Fig. 3d) and perforin (Extended Data Fig. 3e), and intracellular expression of proliferation marker Ki67 (Supplementary Fig. 3), relative to on-chip CAR T cells either interacting with CD19− leukaemia or without any leukaemia.