Chlamydia muridarumT-Cell Antigens Formulated with the Adjuvant DDA/TDB Induce Immunity against Infection That Correlates with a High Frequency of Gamma Interferon (IFN-γ)/Tumor Necrosis Factor Alpha and IFN-γ/Interleukin-17 Double-Positive CD4+T Cells

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Abstract
Major impediments to developing a Chlamydia vaccine lie in identifying immunologically relevant T-cell antigens and delivery in a manner to stimulate protective immunity. Using an immunoproteomic approach, we previously identified three immunodominant Chlamydia T-cell antigens (PmpG-1, PmpE/F-2, and RplF). Because RplF has high homology to a human ortholog, it may not be suitable for human vaccine development. Therefore, in this study, we evaluated protection against Chlamydia infection in the genital tract in C57BL/6 mice immunized with Chlamydia-specific membrane proteins PmpG-1, PmpE/F-2, and major outer membrane protein (MOMP; as a reference) or a combination of them formulated with one of three adjuvants, CpG oligodeoxynucleotide (CpG-ODN), AbISCO-100 (AbISCO), or DDA/TDB (dimethyldioctadecylammonium bromide/d-(+)-trehalose 6,6′-dibehenate). The results show that immunization with the CpG-ODN formulation failed to provide protection against Chlamydia infection; the AbISCO formulation conferred moderate protection, and the DDA/TDB formulation showed the highest degree of protective efficacy. The combination of PmpG-1, PmpE/F-2, and MOMP proteins formulated with DDA/TDB exhibited the greatest degree of protection among all vaccine groups studied. Moreover, this vaccine combination also engendered significant protection in BALB/c mice, which have a different major histocompatibility complex (MHC) background. We measured cell-mediated immune cytokine responses in mice immunized with PmpG-1 mixed with each of the three adjuvants. The results demonstrate that mice immunized with the DDA/TDB formulation induced the strongest gamma interferon (IFN-γ) and interleukin-17 (IL-17) responses, characterized by the highest frequency of IFN-γ/tumor necrosis factor alpha (TNF-α) and IFN-γ/IL-17 double-positive CD4+ T cells. In conclusion, a Chlamydia vaccine based on the recombinant proteins PmpG-1, PmpE/F-2, and MOMP delivered in a DDA/TDB adjuvant conferred protection against infection that correlated with IFN-γ/TNF-α and IFN-γ/IL-17 double-positive CD4+ T cells.

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