External factors can also influence the biogenesis of exosomes, including cell type, exposure to certain cytokines, growth factors, hypoxia, calcium signaling, drugs, etc. IFN-γ can increase the production of ExoPD-L1 by activating the JAK/STAT signaling pathway and IRF-1 [6,25,26], and transforming growth factor-beta (TGF-β) was shown to increase the expression level of PD-L1 on the exosomes released by breast cancer cells in a dose-dependent manner [27]. This evidence concerns the gene CD274 and breast cancer.