Antibody Targeting of Liposomes : Cell Specificity Obtained by Conjugation of F ( ab ' ) 2 to Vesicle Surface

A method devisedfor conjugating liposomes with protein resulted in the binding of up to 200 micrograms of immunoglobulin G per micromole of lipid. The coupling of antibody to human erythrocyte F(ab')2 in vesicles (140 molecules per vesicle) by this method caused a 200-fold increase in the binding ofvesicles to human erythrocytes and resulted in about 80 percent of the vesicle lipid and contents being 539 o n D ec em be r 7, 2 01 1 w w w .s ci en ce m ag .o rg D ow nl oa de d fr om mole of lipid and no prior protein modification is required. In this report we describe experiments on the interaction of antibody-linked liposomes with human erythrocytes in which about 80 percent of the targeted vesicles were associated with the cells. For these experiments, reverse-phase evaporation vesicles (11) were prepared from galactocerebroside, phosphatidylglycerol, and cholesterol (in a 45:5:50 mole ratio) or from gangliosides, phosphatidylcholine, and cholesterol (in a 10:45:45 mole ratio) in 10 mM borate, and 60 mM NaCl buffer, pH 8.4. Before the vesicles were coupled to protein they were oxidized by periodate (8 mM, pH 8.5) for 2 hours at 25°C to produce aldehydes on the liposome surface. Under these conditions, approximately 40 percent of the oxidizable lipid is oxidized (10) whereas encapsulated markers, such as sucrose or glycerol-l-phosphate, are neither oxidized nor induced to leak out of the vesicles during the periodate treat-