ERBB2 and neoplasm: We found that the eradication of tumours by PTPN2‐deficient HER‐2 CAR T cells was not accompanied by systemic T‐cell activation and inflammation, as assessed by the unaltered number and activation of T cells in lymphoid and non‐lymphoid organs at 21 days post‐transfer (Appendix Fig S5A) and unaltered circulating pro‐inflammatory cytokines (Appendix Fig S5B) and lymphocytic infiltrates in non‐lymphoid tissues, including in the contralateral tumour‐negative mammary glands (Appendix Fig S5C).