Protective efficacy of a parenterally administered MOMP-derived synthetic oligopeptide vaccine in a murine model of Chlamydia trachomatis genital tract infection: serum neutralizing IgG antibodies do not protect against chlamydial genital tract infection.

The protective efficacy of an alum-adsorbed, parenterally administered synthetic oligopeptide immunogen corresponding to antigenically common T-helper and neutralizing B-cell epitopes of the Chlamydia trachomatis major outer membrane protein was studied in a murine model of chlamydial genital tract infection. Mice produced high levels of anti-chlamydial serum IgG neutralizing antibodies following subcutaneous immunization with the alum-adsorbed oligopeptide. Lower but detectable levels of chlamydial specific IgG antibodies were found in vaginal washes. IgG1 was the predominant isotype present in sera and vaginal washes. Chlamydial-specific IgA was not present in either the sera or vaginal washes of immunized mice. Vaccinated and control mice were challenged intravaginally or intrauterinally with low, medium, or high doses of C. trachomatis serovar D challenge inocula. Protection was assessed by performing quantitative chlamydial cervico-vaginal cultures over the course of the infection period. There were no statistically significant differences between groups of immunized and control mice in either colonization, shedding, or duration of infection. These findings demonstrate that parenteral immunization with the oligopeptide (serum-neutralizing antibodies) is ineffective in preventing chlamydial genital tract infection. It is possible, since chlamydial infection is restricted to the genital tract mucosae, that a more accurate evaluation of the oligopeptide vaccine potential will require local rather than systemic immunization.