External factors can also influence biogenesis of exosomes including cell type, cell confluency, serum conditions, cytokines, growth factors, the sites of exosomes, protein sorting, physico-chemical aspects, etc. (69) PD-L1 on cell surface can be upregulated by IFN-γ and it has been reported that exoPD-L1 from melanoma cells can be also augmented upon IFN-γ treatment (4, 52). Here, CD274 is linked to melanoma.