Bacterial ghosts as novel efficient targeting vehicles for DNA delivery to the human monocyte-derived dendritic cells

Recombinant bacterial ghosts loaded with plasmids were tested as an antigen delivery system and as a potential mediator of maturation for human monocyte-derived dendritic cells (DCs). Bacterial ghosts are cell envelopes derived from Gram-negative bacteria; the intracellular content is released by the controlled expression of plasmid-encoded lysis gene E of PhiX174. All the cell surface structures of the native bacteria, including the outer membrane proteins, adhesins, LPS, lipid A, and peptidoglycans, are preserved. Co-incubation of immature DCs with ghosts resulted in decreased expression of CD1a, CD80, and CD83 molecules, while addition of maturation mix (TNF-alpha, IL-1 beta, IL-6, and PGE2) to the cultures enhanced expression of these molecules. No marked changes were observed in the expression of the CD11c, CD40, and CD86 surface molecules. The exposure of DCs to ghosts in combination with maturation mix resulted in a nonsignificant increase in their ability to activate T cells. DCs co-incubated with bacterial ghosts carrying plasmids encoding GFP in combination with maturation mix exhibited high expression levels of GFP (up to 85%). These results indicate that in addition to their well-established use as vaccines, bacterial ghosts can also be used as carriers of nucleic acid-encoded antigens.