Strikingly, Lck heterozygosity attenuated the enhanced antigen‐specific HER‐2 CAR T‐cell activation (as monitored by CD44, CD25, PD‐1 and LAG‐3 levels; Fig 3B) and cytotoxic potential (as measured by the antigen‐induced expression of IFNγ and TNF; Fig 3C) and the enhanced capacity of PTPN2‐deficient CAR T cells to specifically kill HER‐2‐expressing tumour cells (Fig 3D). Here, LCK is linked to neoplasm.