In reverse experiments, CRISPR–Cas9-mediated targeting of FOXO1 in human Lewis Y (LeY) CAR T cells led to a loss of CD62L expression and a reduction in CAR T cell expansion upon extended culture (Extended Data Fig. 9a–d), and impaired production of IFNγ upon co-culture with tumour cells (Extended Data Fig. 9e). This evidence concerns the gene FOXO1 and neoplasm.