A Novel LNP-Based Chlamydia Subunit Vaccine Formulation That Induces Th1 Responses without Upregulating IL-17 Provides Equivalent Protection in Mice as Formulations That Induced IL-17 and Th1 Cytokines

Sexually transmitted Chlamydia infections can lead to the development of debilitating diseases such as chronic pelvic pain, ectopic pregnancy, pelvic inflammatory disease, and infertility. It has been proposed that immunity against Chlamydia infection and disease may be determined by a balance of IL-17 signaling. We sought to evaluate novel formulations for a candidate Chlamydia vaccine, consisting of Chlamydia major outer membrane protein (MOMP) alone or in combination with polymorphic membrane protein D (PmpD) and polymorphic membrane protein G (PmpG) as target immunogens. Native MOMP (nMOMP) isolated from C. muridarum elementary bodies (EBs) and recombinant PmpD and PmpG proteins were adjuvanted with Monophosphoryl lipid A (MPLA), in one of two formulations containing either lipid nanoparticles (LNPs) or the cationic lipid dimethyldioctadecylammonium bromide (DDA). Antibody titers to C. muridarum, nMOMP, and EBs were evaluated by ELISA, and T-cell responses by intracellular cytokine staining (ICS). Protection from challenge was determined by qPCR and gross pathology. All mice immunized with the new vaccine formulations showed significantly higher antibody titers to nMOMP (P<0.001) and C. muridarum EBs (P<0.001), when compared to the negative control group (adjuvant alone). Antibody titers in vaccine groups with Monophosphoryl lipid A (MPLA)+LNP were higher as compared to the MPLA+DDA group (P<0.001) except for groups 6 (Cm nMOMP+PmpG+PmpD p73+PmpD p82+MPLA+DDA) vs 7 (Cm nMOMP+PmpG+PmpD p73+PmpD p82+MPLA+LNP) for both C. muridarum EBs and PmpG; the groups were not statistically significant. ICS analysis showed more robust CD4+ T-cell responses (IFN-γ/IL-2/TNF-α) in the dimethyldioctadecylammonium bromide (DDA) and LNP groups compared to the adjuvant alone group. The combination of DDA and MPLA gave robust Th17 responses in comparison to MPLA and LNP group. Immunized groups also showed protection from challenge with C. muridarum , as evidenced by a reduction in bacterial shedding from the vagina for all groups (P<0.003) compared to shedding from the adjuvant control, Group 1. Both vaccine formulations generated robust immunological responses and both vaccine formulations were protective by reducing bacterial shedding after challenge. This data indicates equal protection can be achieved without the induction of Th17 responses.