PDCD1 and breast cancer: Since PD-1, PD-L1 and LAG-3 were also found to be expressed on different types of tumor cells, such as breast cancer cells [33,35,36], and the parental mAbs PD-L1_1 and PD-1_1 have previously shown the ability to bind to IC-positive tumor cells by inhibiting their growth, even in the absence of immune cells, we investigated the effects of the novel tribodies on tumor cell viability in the absence of lymphocytes.