LIPOSOMAL MURAMYL TRIPEPTIDE UP-REGULATES ADHESION MOLECULES ON THE SURFACE OF HUMAN MONOCYTES

We previously demonstrated that liposome-encapsulated muramyl tripepti de phosphatidylethanolamine (L-MTP-PE), a biologic response modifier n ow undergoing phase III clinical trial in osteosarcoma, upregulated mo nocyte expression of several cytokines' mRNA and the subsequent produc tion of these proteins. In the present work, we investigated whether L -MTP-PE upregulated adhesion molecules on the surface of normal human monocytes. Flow-cytometric analysis showed that several subunits of th e integrins, including alpha L, alpha 5, and beta 1 subunits, and inte rcellular adhesion molecule-1 on the monocytes were upregulated follow ing their stimulation with 2 mu g/ml L-MTP-PE for 24 h. Anti-alpha L a ntibodies blocked monocyte-mediated tumor cell killing stimulated by L -MTP-PE. We conclude that L-MTP-PE also stimulates the increase of sev eral molecules on the monocyte cell surface. These adhesion molecules may contribute to the increased activation of monocyte-mediated tumor cell killing seen following L-MTP-PE exposure.