Intracellular Delivery of Proteins and Nucleic Acids to Mammalian Cells with Invaplex Isolated from Shigella Flexneri

The invasion plasmid antigens (Ipa) of Shigella spp, are effector molecules necessary for the invasion of colonic epithelial cells. Recently, we have isolated an invasin protein-LPS complex from intact, virulent Shigella (Invaplex). In vitro observations suggest that Invaplex interacts with host-cell membranes, is internalized, and is released into the cytoplasm via a process similar to the activity expressed by virulent shigellae. It was therefore hypothesized that if heterologous molecules (DNA or protein) were present at the time of Invaplex-induced endocytosis, the heterologous molecule would also be taken up by the host cell. Using plasmid DNA encoding either GFP, βgalactosidase or scrub typhus Sta56 protein, Invaplex was found to induce the uptake of plasmids into host cells resulting in intracellular expression. Invaplex also mediated the transport of purified proteins (GFP, βgalactosidase) across mammalian cell membranes while retaining protein functionality. In vivo experiments demonstrated that Invaplex enhanced the immune response to co-delivered proteins and DNA.