Liposomes as a means to introduce fragment A of diphtheria toxin into cells.

The incorporation of fragment A of diphtheria toxin into liposomes is described. The intracellular delivery of the entrapped toxin, as evidenced by the inhibition of protein synthesis by a human lymphoblastoid cell line could be demonstrated with liposomes that contained phosphatidylethanolamine or phosphatidylserine in addition to phosphatidylcholine and cholesterol. Free fragment A, either alone or added to empty liposomes of any composition, did not affect protein synthesis, even when present in considerably higher concentrations than the liposome-entrapped form.