The downregulation of MHC class-I by treatment with PD-1 or PD-L1 antibodies is one of the mechanisms of tumor resistance to drugs [31], and the fact that the expression of MHC class-I is almost unchanged by PD-1 antibody alone suggests that the MHC class-I expression was once upregulated due to the resistance mechanism. This evidence concerns the gene PDCD1 and neoplasm.