Vector-mediated immunization with naked DNA has received an enormous attention in recent times [Brunham et al., 2000; Brunham & Zhang, 1999; Dong-Ji et al., 2000; Gurunathan et al., 2000; Svanholm et al., 2000],  with delivery of MOMP and HSP60 genes showing some of the most significant promise [Brunham & Zhang, 1999; Stagg, 1998], however, this approach has been mostly successful in the murine lung model, but not genital tract [Pal et al., 1999]. It is uncertain whether immunity to chlamydiae at different anatomical sites could involve distinct mechanisms, but it might reflect differences in infection targets (macrophages versus epithelial cells) in these locations, and emphasizes the use of appropriate models in studying immunity and designing vaccines particularly against a pathogen with multiple infection targets. The use of DNA vectors in a prime-boost strategy, which MOMP was delivered sequentially with DNA and ISCOMS, was also promising [Dong-Ji et al., 2000]. Using a DNA or vector delivery strategy, genes encoding candidate vaccines can be fused with Th1 enhancers, such as immunostimulatory CpG motifs [Klinman et al., 1999] or specific APC-targeting domains such as the ligands for the co-stimulatory B7 [Iwasaki et al., 1997], CD40 [Garunathan et al., 1998], or genes expressing specific chemokines. At the present phase of the technology, the DNA vaccine strategy constitutes a highly useful tool for rapid screening for potential vaccine candidates in experimental models [Murdin et al., 2000] pending the alleviation of DNA integration and toxicity concerns. At this stage, the use of recombinant viral vectors as delivery systems for chlamydial vaccines deserves serious consideration beyond earlier reports of recombinant poliovirus hybrid constructs harboring chlamydial sequences [Murdin et al., 1995]. Non-infectious adenovirus [Babiuk & Tikoo, 2000] , canarypox virus [Hewson, 2000], vaccinia virus [Bennink & Yewdell, 1990], and alphavirus replicons [Schlesinger & Dubensky, 1999] are some of the well characterized viral delivery systems with potential in chlamydial vaccine design. In addition, experimental mucosal adjuvants, including cholera toxin (CT), heat-labile enterotoxin (LT), mutant toxin (LTK63 and LTR7), polymerized liposomes, microparticles and interleukins, are other potential strategies for chlamydial vaccine research [Singh & O'Hagan, 1999].

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