Targeting of liposomes: monoclonal antibodies coupled to phospholipid vesicles provide selective transfer of trapped reagents into cultured cells.

Monoclonal antibodies were incorporated in small unilamellar vesicles by means of ultrasonic irradiation. In order to increase the incorporation efficiency, the immunoglobulins were previously treated at low pH (pH 2), following recent suggestions on the existence of a lipid soluble conformational isomer for serum IgG. The lipid to protein ratios obtained were comparable to the values obtained by other authors using covalent coupling of the antibody to the lipid matrix. Liposome-incorporated monoclonal antibodies directed towards carcinoembryonic antigen (CEA) provided increased transfer of the fluorescent dye carboxyfluorescein from liposomes into cultured human colon carcinoma cells. Another independent experiment was performed on the drug-resistant CHO cell line B30, using a monoclonal antibody to a cell surface marker of drug resistance. Selective liposome mediate drug killing was observed following incubation of the cells with liposomes containing the antitumor agent drug, daunorubicin.