Liposomally activated macrophages; subsequent interaction with L1210 leukemic cells.

The coincubation of liposomes with mouse leukemia cells or fibroblasts can cause a wide of effects on their viability. These effects are not particular specific in terms of destroying the leukemic cells. However, it was observed that the combination of phosphorylcholine-cholesterol (PC-CHOL)1-liposomes, which are not toxic by themselves, with alkyl-lysophospholipids as components of the liposome, can produce the desired specific cytotoxicity for leukemic cells. In this report we show that the cytotoxic effect of vinca alkaloid entrapped in PC-CHOL-liposomes was enhanced by syngeneic mouse bone marrow macrophages. In addition, alkyl-lysophospholipids, which are known to be potent macrophage activators, augment the cytotoxicity. Thus, the macrophage could act as a carrier for liposome-entrapped drug and, on the other hand, the liposomes partly composed of macrophage activating alkyl-lysophospholipids and loaded with chemotherapeutic drug seem to be ideal carriers of two effector mechanisms for attacking leukemic cells.