A chimeric gene construct of Chlamydia trachomatis serovar E major outer membrane protein (MOMP) was designed, and expressed as a candidate vaccine antigen. The construct was based on known T and B cell epitopes located in the variable segment (VS) 2 and 4 loops of MOMP, and successfully expressed and purified in a recombinant Escherichia coli system. BALB/c mice were immunized intranasally with the chimeric MOMP antigen and Cholera toxin (CT) adjuvant, three immunizations with 10 days intervals. A final boost with the identical antigen preparation was given intravaginally. Challenge with live C. trachomatis serovar D was performed 10 days after boost. Antibodies in serum and vaginal washes were determined with the identical chimeric MOMP construct as antigen in ELISAs. All mice in vaccine groups (N=10/group and experiment) developed a strong antigen-specific IgG response in serum, and some also had detectable antigen-specific IgG in vaginal washes. An IgA response, albeit weaker, was detected in some of the mice both in serum and in vaginal washes.
After challenge with C. trachomatis, 80 and 100% of the mice became infected in two experiments, respectively. However, the vaccinated groups cleared the infection significantly faster than control groups (all vaccinated mice healthy day 24 [90% day 16], compared to day 40 for controls).
Thus, the new chimeric MOMP antigen construct gave rise to a significant immune response in mice (s-IgG). It also conferred substantial protection to infection caused by genital C. trachomatis infection of a different subtype.