Intriguingly, cytokine profiling from on-chip tests demonstrated that 4-1BBζ-CAR secreted more interleukin (IL)-13 (a TH2 cytokine), and CD28ζ-CAR and ICOSζ-CAR secreted more IL-10, which may not be clearly observed in simple 2D tests with respective co-cultures of CAR T cells and leukaemia blasts (Extended Data Fig. 4c–e and Supplementary Fig. 8). This evidence concerns the gene IL10 and leukemia.