A
vaccine is likely the most effective strategy for controlling human chlamydial
infections. Recent studies have shown immunization with Chlamydia muridarum major outer
membrane protein (MOMP) can induce significant protection against
infection and disease in mice if its native trimeric structure is preserved (nMOMP). The objective of this study was to investigate the immunogenicity and
vaccine efficacy of Chlamydia trachomatis nMOMP in a nonhuman primate
trachoma model. Cynomolgus monkeys (Macaca fascicularis) were immunized systemically with nMOMP, and monkeys were challenged ocularly. Immunization induced high serum
IgG and
IgA ELISA Ab titers, with Abs displaying high strain-specific neutralizing activity. The PBMCs of immunized monkeys produced a broadly cross-reactive, Ag-specific IFN-gamma response equivalent to that induced by experimental
infection. Immunized monkeys exhibited a significant decrease in infectious burden during the early peak shedding periods (days 3-14). However, at later time points, they exhibited no difference from control animals in either burden or duration of
infection. Immunization had no effect on the progression of ocular disease. These results show that systemically administered nMOMP is highly immunogenic in nonhuman primates and elicits partially protective immunity against ocular chlamydial challenge. This is the first time a
subunit vaccine has shown a significant reduction in ocular shedding in nonhuman primates. A partially protective
vaccine, particularly one that reduces infectious burden after primary
infection of children, could interrupt the natural
trachoma reinfection cycle. This would have a beneficial effect on the transmission between children and sensitized adults which drives blinding inflammatory disease.