ERBB2 and breast cancer: In order to determine the efficacy of effector cells together with anti-PD1 antibody on target cells in vitro, anti-HER2 CAR-T cells were co-cultured with HER2-positive breast cancer cells (4T1-Luc-HER2) at effector: target ratios of 16:1, 8:1, 4:1 and 2:1 for 18 h in the absence or presence of anti-PD1 antibody.