Immunity with liposome carriers

The mode of association of peptides to liposome carriers might also be critical to induce a preferential immune response either humoral or cell mediated. For example, using a human mucin MUCl 20-mer peptide, it was found that only the physical association of the peptide to liposomes (either encapsulated or surface exposed after anchoring) was necessary to observe a cell-mediated response (34). In line with this observation, it was recently shown that a soluble peptide, representing a Melan-A/MART-1 tumor-associated antigen, when encapsulated into sterically stabilized liposomes, was able to stimulate a CTL response and this construct represented a suitable formulation for a specific tumor immunotherapy (69). In contrast, and in agreement with other studies (16), only the liposome surface exposed... 

Synthetic pathways that supposedly avoid the pitfalls of viral delivery systems (see below) have been explored. Both Kaneda and coworkers (Chapter 9) and Sorgi and coworkers (Chapter 8) have been successful in designing viruslike liposomal delivery systems that provide some of the advantages of viral carriers—in other words, cell surface recognition and fusion with target cells (or intracellular compartments, i.e., endosomes, respectively)—without the detrimental immune response that viral systems generate. The efficiency of these systems is still orders of magnitude less than that of viral carriers however, cytotoxic... 

Cationic peptides have also been used as DNA carriers. For example, gramicidin S and tyrocidine are cationic peptides that will bind to plasmid DNA. When combined with DOPE, the peptide/DNA complex has been shown to transfect cells in vitro. The efficiency of the peptide compared to liposome/ DNA complexes varies by cell type, but the toxicity is equally low (65). Other types of cationic peptides have also been utilized for gene transfer, and they are most effective in combination with molecules that exhibit pH-dependent membrane perturbation effects (30,66). Presumably these helper components promote endocytic escape after cellular uptake. Cationic peptide-type carriers are not in wide usage at this time, particularly in vivo. It will be interesting to see if these peptides induce any immune response when administered to animals. 

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