Live attenuated bacteria, such as the Lactobacillus [Turner & Giffard, 1999], Salmonella and Listeria systems [Gentschev et al., 2000], are promising delivery vehicles that could be explored in chlamydial vaccine. In addition, non-living bacterial delivery systems, such as recombinant bacterial ghosts, have potential to direct immune response against multiple antigens [Eko et al., 1999]. Bacterial ghosts are devoid of cytoplasmic contents while maintaining their native surface antigenic structures and cellular morphology. In the novel recombinant bacterial ghost vaccine strategy, an appropriate bacterium is transformed with the gene of interest to express high levels of the antigen in a targeted location on the cell, and ghosts are produced by controlled lysis of the cells. Certain bacterial ghost preparations possess intrinsic adjuvant properties that boost immune responses against the antigen expressed. Since multiple genes can be expressed on ghosts in a deliberately controlled manner, high levels of an antigen or different antigens from the same or different pathogens can be presented to the immune system simultaneously to produce effective combination vaccines against multiple agents [Eko et al., 1999]. Recent efforts in designing multi-subunit experimental ghost vaccines, by expressing select chlamydial proteins on the epitheliotropic Vibrio cholerae ghosts (VCG), are showing promise in a mouse genital infection model . The immunologic and strategic advantages of using VCG in the development of multi-component vaccines against mucosal pathogens, such as Chlamydia, include: first, the mucosal tropism of V. cholerae likely to promote mucosal immunity; second, the ability to induce both protective mucosal humoral and CMI responses [Eko et al., 1999], which is important for chlamydial immunity; third, the capacity to accommodate large doses of antigens in their native conformations that ensures efficient antigen processing for immune activation, and fourth, the ability to present multiple antigenic determinants from the same or different pathogens simultaneously as a combination vaccine. Besides, VCG are safe, with relatively easy and cheap production cost, which offers a technological and manufacturing advantage for a vaccine needed on a global scale.

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