PDCD1 and melanoma: Loss of the MHC class I complex and antigen peptide transporters (TAP1/TAP2), which leads to defective antigen presentation, has also been reported in lung cancer.77 Finally, a clinical study of four melanoma patients investigating acquired checkpoint resistance identified that the loss of the MHC class I complex due to the mutation of β2M led to an impaired immune response to PD-1-based therapy (pembrolizumab).78