CXCL9 and breast cancer: Moreover, PTPN2 deletion in T cells expressing a chimeric antigen receptor (CAR) specific for the oncoprotein HER‐2 increased the activation of the Src family kinase LCK and cytokine‐induced STAT‐5 signalling, thereby enhancing both CAR T‐cell activation and homing to CXCL9/10‐expressing tumours to eradicate HER‐2+ mammary tumours in vivo.