The AIDS pandemic and associated generation of multiple antibiotic resistance among pathogens, in addition to recalcitrant endemic diseases such as malaria, all indicate that innovative approaches to vaccine development are needed. As a step toward this goal, we are developing an antigen delivery system for HIV-1 and HIV-2 clad viruses using a novel, particulate virus-like organelle called the gas vesicle, which is naturally used for flotation by aquatic prokaryotes. We have extensively studied the gas vesicles of salt-loving halophilic archaebacteria both genetically and biochemically, and found that these extremely stable proteinaceous structures are encoded by a cluster of 13 or 14 genes, including two genes, gvpA and gvpC, encoding major structural proteins. When we cross-linked TNP to gas vesicles and injected mice, we found high-level and long-term immune response in the absence of any adjuvant. When a peptide-encoding sequence was genetically engineered into gvpC, it was effectively presented to the mouse immune system. In order to facilitate the production of recombinant gas vesicles displaying HIV antigenic epitopes, we incorporated four unique restriction sites in gvpC and one site in the C-terminal coding region of gvpA. During the period of this proposal, we plan to (1) evaluate the best sites for genetic engineering of gas vesicles using selected SIV and HIV sequences, (2) produce epitope libraries of SIV and HIV Env and Gag proteins in gas vesicles and possible other sequences, and (3) evaluate the magnitude, duration, and memory of systemic response, and stimulation of mucosae and of a cell mediated response in mice. The use of SIV will permit subsequent testing of antigen delivery in a primate model. We hope to establish the feasibility of antigen presentation using halobacterial gas vesicles and lay the groundwork for the development of an HIV vaccine delivery system. If successful, this system would permit extremely large-scale production of a sale, inexpensive, and stable vaccine.