B4GALT1 and breast carcinoma: Knockdown of B4GALT1 could indeed reduce PD-L1 glycosylation in multiple breast cancer cells in the absence or presence of IFN-γ (Figs. 4D, S4E and S7), whereas overexpression of B4GALT1 elevated the glycosylation of PD-L1 (Figs. S4F and S7).