The current administration of many vaccines requires several injections of a given amount of antigen at specified time interval to achieve a booster immune response. In some cases, frequent immunization is necessary because of short-lived immunological memory is necessary because of short-lived immunological memory coupled with a long interval between the initial vaccination and the subsequent natural challenge. In addition, the painful and inconvenience associated with multiple injections can make compliance a problem. The broad long-term objectives of this project are to use cholera and influenza antigens to formulate single injection multiple dose biodegradable controlled release booster delivery system to provide not only the priming antigen, but one or more booster challenges at specified time intervals. The specific aims of the project are: (1) to use agents that could stabilize the cholera and influenza antigens while encapsulated for prolonged periods of time; (2) to design controlled released microcapsules of cholera and influenza antigens in conjunction with stabilizers by the solvent evaporation/extraction procedure; (3) to conduct in vitro release of antigens from the microcapsules by following the pulsed nature of the release and stability of the antigens; (4) to evaluate the immune response in rabbits following intramuscular or subcutaneous administration of encapsulated antigens. Cholera, influenza types A and B antigens, and stabilizers will be encapsulated in biodegradable poly (D,L-lactide-co-glycolide), poly-dl- lactic acid, and poly (epsilon-caprolactone) of different molecular weights by the solvent evaporation/extraction technique. The microcapsules containing the antigens will be characterized morphologically, biochemically, and immunochemically. The stability and pulsed delivery of the antigens from the microcapsules of carefully selected polymer compositions will be followed in vitro. For in vivo studies, microcapsules containing antigens, and control microcapsules without antigens, will be administered by a single intramuscular or subcutaneous injection into rabbits. At specific time intervals, blood samples will be collected, and analyzed for the presence of specific antibodies of the immunoglobulin G (IgG), M (IgM), and A (IgA) classes, respectively.