Almost one century after the discovery of the BCG vaccine, tuberculosis remains a major cause of global mortality and morbidity, emphasizing the urgent need to design more efficient vaccines. The heparin-binding haemagglutinin (HBHA) appears to be a promising vaccine candidate, as it was shown to afford protection to mice against a challenge infection with Mycobacterium tuberculosis when combined with the strong adjuvant DDA/MPL (dimethyldioctadecyl-ammonium bromide/monophosphoryl lipid A), a TLR4 ligand. In this study, we investigated the immunological response and protection of mice immunized with HBHA formulated in lipid-containing nanoparticles and adjuvanted with CpG, a TLR9 ligand. Subcutaneous immunization with this HBHA formulation led to a marked Th1 response, characterized by high IFN-γ levels, but no significant IL-17 production, both in spleen and lung, in contrast to DDA/MPL MPL-formulated HBHA, which induced both IFN-γ and IL-17. This cytokine profile was also observed in BCG-primed mice and persisted after M. tuberculosis infection. No significant protection was obtained against challenge infection after vaccination with the nanoparticle-CpG formulation, and this was associated with a failure to mount a memory immune response. These results suggest the importance of both Th1 and Th17 immune responses for vaccine-induced immunity.
Keywords: CpG; HBHA; Nanoparticle; Th17 response; Tuberculosis.
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