CD8A and metastatic melanoma: In patients who suffer from metastatic melanoma, circulating exosomal PD‐L1 levels have a positive association with IFN‐γ levels and change during anti‐PD‐1 therapy, implying that exosomal PD‐L1 may serve as a predictor of anti‐PD‐L1 therapy (Figure 2).[68] Guan et al. demonstrate that hepatocyte growth factor‐regulated tyrosine kinase substrate phosphorylation could induce the production of PD‐L1+ exosomes, thereby leading to resistance to anti‐PD‐1 treatment as a result of low infiltration of cytotoxic CD8+ T cells into tumors.[69]