Treatment of murine CD8+ HER‐2 CAR T cells with compound 8 in vitro increased their antigen‐specific cytotoxic potential to levels seen in Lck‐Cre;Ptpn2fl/fl HER‐2 CAR T cells, but had no additional effect on Lck‐Cre;Ptpn2fl/fl HER‐2 CAR T cells, consistent with the inhibitor acting specifically to inhibit PTPN2 and thereby activate CAR T cells upon engagement with specific tumour antigen (Fig EV5A). This evidence concerns the gene LCK and neoplasm.