Liposome-mediated cytosolic delivery of macromolecules and its possible use in vaccine development

In the majority of bacterial and viral infections the generation of cytotox ic T cells is of particular interest because such pathogens are able to esc ape the host defence mechanisms by surviving intracellularly within the pha gocytic cells. To generate a CD8(+) T lymphocyte response against exogenous antigens, the prerequisite is their delivery into the cytosol followed by processing and presentation along with class I major histocompatibility com plex (MHC-I) molecules. In the present study we describe the method of lipo some-based delivery of antigens and other macromolecules into the cytosol o f target cells. To develop safe and effective methods for generating CD8(+) T lymphocytes, we exploited the fusogenic character of lipids derived from lower organisms, that is baker's yeast (Saccharomyces cerevisiae). The deg ree of fusion with model membrane systems using yeast lipid liposomes varie d from 40-70%, as opposed to 1-8% observed with egg PtdCho liposomes, depen ding on the assay system used. The fusion of yeast lipid liposomes with mac rophages resulted in effective delivery of the entrapped solutes into the c ytoplasmic compartment. This was further supported by the inhibition of cel lular protein synthesis in J774 A1 cells by ricin A, encapsulated in the ye ast lipid liposomes. Interestingly, the model antigen ovalbumin, when entra pped in the yeast lipid liposomes, successfully elicited antigen reactive C D8(+) T cell responses. It may be concluded that the liposomes made of lipi ds derived from S. cerevisiae can spontaneously fuse with macrophages, deli vering a significant portion of their contents into the cytoplasmic compart ment of the cells.