LCK and neoplasm: The ability of PTPN2‐deficient CAR T cells to suppress tumour growth and eradicate tumours was reliant on the enhanced activation of LCK, as this was significantly, albeit not completely abrogated by Lck heterozygosity (Fig 4B) that corrected the enhanced LCK activation in Lck‐Cre;Ptpn2fl/fl CAR T cells in vitro (Fig 3A).