PCSK9 and neoplasm: In addition, they also revealed the importance of tumor microenvironment in affecting the function of CTLs, where elevated levels of PCSK9 by tumor cells allows its binding to LDLR and prevents the LDLR/TCR complex from being recycled back to the cell surface, resulting in decreased levels of LDLR on CD8+ T cells and decreased TCR signaling, leading eventually to the inhibition of the effector function of CTLs.