Enhancement of the protective efficacy of a Chlamydia trachomatis recombinant vaccine by combining systemic and mucosal routes for immunization

Chlamydia trachomatis causes respiratory and sexually transmitted infections. Here, we tested a vaccine formulated with the recombinant major outer membrane protein from C. trachomatis mouse pneumonitis (CT-MoPn) for its ability to protect mice against an intranasal (i.n.) challenge. The adjuvants CpG and Montanide were used for systemic routes, intramuscular (i.m.) and subcutaneous (s.c.), and cholera toxin for mucosal routes, sublingual (s.l.) and colonic (c.l.). Mucosal immunizations were performed either alone or in combination with systemic routes. Mice inoculated i.n. with 104 inclusion-forming units (IFU) of CT-MoPn served as a positive control and the Neisseria gonorrhoeae recombinant porin B (Ng-rPorB) as the negative antigen control. Immunized animals were challenged i.n. with 104 IFU of CT-MoPn. Following immunization the combination groups showed high chlamydial serum IgG titers (s.l. + i.m. + s.c. 25,600; c.l + i.m. + s.c. 102,400) and the IgG2a/IgG1 ratios indicated a Th1 response. Following the i.n. challenge the s.l. + i.m. + s.c. group showed the best protection as demonstrated by an increase in body weight of 0.3% over the 10 day course of infection. A statistically significant difference was found when compared with the Ng-rPorB immunized animals that had lost 20% of their original body weight (P < 0.05). In addition, the repeated measures ANOVA test showed significant difference in body weight change for the combined immunized groups vs their mucosal counterparts and also the systemic immunized group. A statistically significant difference (P < 0.05) was also observed in the number of IFUs recovered from the lungs when the s.l. + i.m. + s.c. (2.8 × 106) and c.l. + i.m. + s.c. (3.4 × 106) groups were compared to their respective mucosal only groups (s.l.: 61.9 × 106 and c.l: 136.2 × 106) and the control Ng-rPorB immunized mice (198.2 × 106) (P < 0.05). In conclusion, a combined systemic plus mucosal vaccination provides better protection against a respiratory challenge with C. trachomatis than either systemic or mucosal immunizations alone.