PDCD1 and breast cancer: We examined the proliferation of blank T or anti-HER2 CAR-T cells after they were co-cultured with HER2−/PDL1+ 4T1 or HER2+/PDL1+ 4T1-Luc-HER2 breast cancer cells at effector: target ratio of 4:1 in the absence and presence of anti-PD1 antibody for 24, 48, and 72 h.