PDCD1 and melanoma: Poggio et al. (2019) found that exosome PD-L1 seems to be resistant to anti-PD-L1 treatment. At the same time, inhibiting exosome PD-L1 helps maintain long-lasting anti-tumor immunity (Zhang et al., 2017). A study by Del Re et al. (2018) explored the relationship between exosome PD-L1 mRNA expression and response to anti-PD-1 treatment in melanoma (n = 18) and non-small cell lung cancer (n = 8). They emphasized that exosome PD-L1 should be considered when predicting the outcome of anti-PD-1 treatment (Siegel et al., 2012).