Mifamurtide (muramyl tripeptide phosphatidyl ethanolamine, MTP-PE) is a fully synthetic derivative of muramyl dipeptide (MDP), the smallest naturally-occurring immune stimulatory component of cell walls from Mycobacterium sp. It has similar immunostimulatory effects as natural MDP with the additional advantage of a longer half-life in plasma. Mifamurtide liposomal formulation is specifically designed for in vivo targeting to macrophages by intravenous infusion. MTP-PE is a specific ligand of NOD2, a receptor found primarily on monocytes, dendritic cells and macrophages. MTP-PE is a potent activator of monocytes and macrophages. Activation of human macrophages by mifamurtide is associated with production of cytokines, including tumour necrosis factor (TNF-alfa), interleukin-1 (IL-1beta), IL-6, IL-8, and IL-12 and adhesion molecules, including lymphocyte function-associated antigen-1 (LFA-1) and intercellular adhesion molecule-1 (ICAM-1). In vitro-treated human monocytes killed allogeneic and autologous tumour cells (including melanoma, ovarian, colon, and renal carcinoma), but had no toxicity towards normal cells.