Liu et al. (2021) confirmed that by increasing the expression of melanoma exosomes PD-L1, the M2 polarization of macrophages can be induced, which ultimately leads to resistance to anti-PD-1/PD-L1 treatment. In addition, this method is consistent with the results of tumor immune escape and anti-PD-L1 treatment caused by directly upregulating PD-L1 in macrophages (Zhang et al., 2017; Wen et al., 2018). Here, PDCD1 is linked to melanoma.