Immunization with the Chlamydia trachomatis major outer membrane protein, using adjuvants developed for human vaccines, can induce partial protection in a mouse model against a genital challenge

To test several vaccines for Chlamydia trachomatis we vaccinated BALB/c and C3H/HeN female mice with a purified preparation of the native mouse pneumonitis (MoPn) major outer membrane protein (MOMP). The MOMP was formulated with anyone of three different adjuvants MF59, LT-K63 or LT-R72. As a negative control the animals were immunized with ovalbumin. Positive controls were inoculated intranasally (i.n.) with 104 inclusion-forming units (IFU) of C. trachomatis MoPn. High levels of Chlamydia-specific antibodies were detected in the serum and vaginal washes of the mice immunized with MOMP. Using a lymphoproliferative assay (LPA) a significant response was obtained in splenocytes from most of the groups of mice vaccinated with MOMP. Two weeks after the last immunization the mice were challenged in the left ovarian bursa with 105 IFU of C. trachomatis MoPn and vaginal cultures were collected for a period of 6 weeks. Overall, BALB/c and C3H/HeN mice immunized with MOMP showed a decrease in the severity and length of the infection but the difference with the controls was not statistically significant. Following mating the percentage of mice with bilateral fertility was not significantly different between mice vaccinated with MOMP and their respective ovalbumin-immunized controls. However, the C3H/HeN mice immunized with MOMP using MF59 or LTR72 as adjuvants had significantly more embryos per mouse than the control groups. In conclusion, mice immunized with native MOMP and adjuvants developed for human vaccines showed significant Chlamydia-specific immune response and a limited protection against infection and long-term sequelae.