L-Leucyl-L-Leucine methyl ester (LLME) is a lysosomal condensation product that has been reported to be cytotoxic towards natural killer cells and CD4+ and CD8+ T lymphocytes without affecting helper T cells and B cells. It has also been shown to induce death of monocytes, polymorphonuclear leukocytes, and myeloid tumor cells. Upon entry into cells via receptor-mediated endocytosis, LLME undergoes a condensation process catalyzed by dipeptidyl peptidase I (DPPI) in lysosomes. This condensation leads to lysosomal rupture and DNA fragmentation in DPPI-expressing immune cells such as cytotoxic T cells and natural killer cells.
