Chlamydia trachomatis is the most frequently detected sexually transmitted bacterial pathogen in the world. Attempts to control these infections with screening programs and antibiotics have failed and, therefore, a vaccine is the best approach to control this epidemic. The Chlamydia major outer membrane protein (MOMP) is the most protective subunit vaccine so far tested. Protection induced by MOMP is, in part, dependent on its tertiary structure. We have previously described new recombinant antigens composed of the Neisseria lactamica PorB engineered to express the variable domains (VD) from Chlamydia muridarum MOMP. Here we tested antigens containing each individual MOMP VD and different VD combinations. Following immunization, mice were challenged intranasally with C. muridarum. Our results show that three constructs, PorB/VD1-3, PorB/VD1-4, and PorB/VD1-2-4, elicited high serum IgG titers in vivo, significant IFN-γ levels upon T cells re-stimulation in vitro, and evidence of protective immunity in vivo. PorB/VD1-3, PorB/VD1-4, and PorB/VD1-2-4 immunized mice lost less body weight, had lighter lungs, and decreased numbers of inclusion forming units (IFUs) in lungs than other PorB/VD construct tested and mock PBS-immunized mice. These results suggest that this approach may be a promising alternative to the use of MOMP in a Chlamydia vaccine.

Chlamydia trachomatis is the most frequently detected sexually transmitted bacterial pathogen in the world. Attempts to control these infections with screening programs and antibiotics have failed and, therefore, a vaccine is the best approach to control this epidemic. The Chlamydia major outer membrane protein (MOMP) is the most protective subunit vaccine so far tested. Protection induced by MOMP is, in part, dependent on its tertiary structure. We have previously described new recombinant antigens composed of the Neisseria lactamica PorB engineered to express the variable domains (VD) from Chlamydia muridarum MOMP. Here we tested antigens containing each individual MOMP VD and different VD combinations. Following immunization, mice were challenged intranasally with C. muridarum. Our results show that three constructs, PorB/VD1-3, PorB/VD1-4, and PorB/VD1-2-4, elicited high serum IgG titers in vivo, significant IFN-γ levels upon T cells re-stimulation in vitro, and evidence of protective immunity in vivo. PorB/VD1-3, PorB/VD1-4, and PorB/VD1-2-4 immunized mice lost less body weight, had lighter lungs, and decreased numbers of inclusion forming units (IFUs) in lungs than other PorB/VD construct tested and mock PBS-immunized mice. These results suggest that this approach may be a promising alternative to the use of MOMP in a Chlamydia vaccine.

Chlamydia trachomatis (Ct) is the most common cause of bacterial sexually transmitted infections (STIs) worldwide. Ct infections are often asymptomatic in women, leading to severe reproductive tract sequelae. Development of a vaccine against Chlamydia is crucial. The Chlamydia major outer membrane protein (MOMP) is a prime vaccine antigen candidate, and it can elicit both neutralizing antibodies and protective CD4+ T cell responses. We have previously designed chimeric antigens composed of immunogenic variable regions (VDs) and conserved regions (CDs) of MOMP from Chlamydia muridarum (Cm) expressed into a carrier protein (PorB), and we have shown that these were protective in a mouse model of Cm respiratory infection. Here, we generated corresponding constructs based on MOMP from Ct serovar F. Preliminary structure analysis of the three antigens, PorB/VD1-3, PorB/VD1-4 and PorB/VD1-2-4, showed that they retained structure features consistent with those of PorB. The antigens induced robust humoral and cellular responses in mice with different genetic backgrounds. The antibodies were cross-reactive against Ct, but only anti-PorB/VD1-4 and anti-PorB/VD1-2-4 IgG antibodies were neutralizing, likely due to the antigen specificity. The cellular responses included proliferation in vitro and production of IFN-γ by splenocytes following Ct re-stimulation. Our results support further investigation of the PorB/VD antigens as potential protective candidates for a Chlamydia subunit vaccine.