PCSK9 (a key protein that regulates cholesterol metabolism) was found to promote the re-localization and degradation of MHC-I in lysosomes to disrupt MHC-I recycling at the cell surface, while inhibition of PCSK9 induced a significant increase in MHC-I expression on tumor cells and enhanced the efficacy of anti-PD1 therapy [197]. Here, PDCD1 is linked to neoplasm.