CD274 and metastatic melanoma: While it has been reported that metastatic melanoma patients with CD14+CD16−HLA-DRhi monocytes in the peripheral blood prior to treatment respond poorly to anti-PD-1 immune checkpoint therapy [9,187,188], other studies demonstrated that the frequency of PD-L1+ CD14+ monocytes in the peripheral blood is inversely associated with patient responses to anti-PD-1 immunotherapy [189,190].