Vaccines against intracellular bacterial pathogens

There is a long history of remarkable success in developing vaccines against bacteria that are extracellular pathogens. In general, the development of vaccines against intracellular bacterial pathogens has proven to be more challenging. Typically, such vaccines need to induce a range of immune responses, including antibody, CD4(+) and CD8(+) T cell responses. These responses can be induced by live attenuated vaccines, but eliciting these responses with non-living vaccines has proven to be difficult. The difficulties appear to be related partly to the problems associated with the identification of protective antigens and partly with the difficulties associated with inducing CD8(+) T cell responses.