Recent advances in the development of live, attenuated bacterial vectors.

Over the last quarter century, scientific advances have created new tools and technologies to improve the safety and efficacy of vaccines. These improvements are spurred by social and commercial needs to enhance existing vaccines or to create new ones against an expanding spectrum of diseases. Vaccines based on live, attenuated, pathogenic bacteria were originally developed to prevent infection by homologous pathogens. More recently, strategies have been developed to use these bacterial vaccines as vectors to deliver a variety of protective, vaccine antigens via the mucosal route. These approaches are being developed to protect not only against heterologous microbial infections, but also against non-traditional threats such as biowarfare and cancer. These strategies and their application to the recent development of delivery systems for use in humans will be discussed.