LCK and neoplasm: To directly assess the influence of PTPN2 deficiency on T‐cell‐mediated immunosurveillance, we next isolated tumour‐infiltrating CD8+ T cells from Ptpn2fl/fl versus Lck‐Cre;Ptpn2fl/fl mice and assessed their activation by measuring IFNγ production ex vivo upon re‐challenge with tumour cells isolated from AT3‐OVA tumours that had developed in Ptpn2fl/fl mice (Fig 1F).