CD274 and melanoma: In breast cancer cells, this unshielded RN7SL1 activates the pattern recognition receptor (PRR) RIG-I, thereby augmenting tumor progression, metastasis, and resistance to therapy.241 Furthermore, tumor-derived exosomes can modulate macrophages towards an immunosuppressive phenotype, furthering tumor metastasis.183 In melanoma, exosomes, which constitute the majority of EVs from metastatic melanomas, exhibit PD-L1 on their surfaces.