Moreover, in an adoptive transfer setting, Ptpn2-deficient T cells inhibit tumor growth, and in CAR-T cells a lack or inhibition of PTPN2 fosters the production, antigen-specific activation, and cytotoxicity of CD8+ HER2 CAR-T cells ex vivo, while reducing HER2+ E0771 mammary tumor growth. The gene discussed is ERBB2; the disease is breast cancer.