A 2-amino acid compound with immunomodulatory activity. L-leucyl-L-leucine methyl ester (LLME) is a lysosomotropic agent entering cells via receptor-mediated endocytosis. LLME undergoes a condensation process catalyzed by dipeptidyl peptidase I (DPPI) in lysosomes. Condensation of LLME leads to lysosomal rupture and DNA fragmentation in DPPI-expressing immune cells such as cytotoxic T-cells and natural killer cells. Therefore, this agent may be able to decrease the incidence of graft versus host disease (GVHD) via cytotoxic T-cell depletion. Furthermore, LLME has the potential for augmenting antibody production when used in pretreatment of peripheral blood mononuclear cells (PBMCs), possibly by interfering with gene expression of inflammatory factors.