Use of lectins and polyethylene glycol for fusion of glycolipid-containing liposomes with eukaryotic cells.

Efficient fusion of phospholipid vesicles with monolayer cultures of eukaryotic cells was accomplished by attaching glycolipid-containing vesicles to the cell surface by using a lectin displaying binding for both the cell surface and the glycolipid, followed by treatment with polyethylene glycol. Fusion was inferred from the transfer of fluorescent lipid analog probes embedded in the vesicle membrane over the entire cell surface and of fluoresceinated proteins from the aqueous space of the vesicle to the cytoplasm of the cell. Fluorescence recovery after photobleaching showed that both the injected membrane and the cytoplasmic markers were mobile. Two different lectin--glycolipid combinations [Ricinus communis agglutinin I-lactosylcerebroside and concanavalin A-tetradecyl- (or hexadecyl-) maltobionamide] were used to promote attachment of lipid vesicles before polyethylene glycol-induced fusion with BG-9 human fibroblasts, NIL-8M2 hamster cells, or L-929 mouse cells. In the absence of lectin or polyethylene glycol, fusion was negligible. However, when both the lectin and the glycol were used, a dramatic increase in the transfer of both vesicle membrane and aqueous space markers from the liposomes to the cells occurred.