PCSK9 and neoplasm: Furthermore, we found that the tumor microenvironment (TME) downregulates CD8<sup>+</sup> T cell LDLR level and TCR signaling via tumor cell-derived proprotein convertase subtilisin/kexin type 9 (PCSK9) which binds to LDLR and prevents the recycling of LDLR and TCR to the plasma membrane thus inhibits the effector function of CTLs.