Single-dose Ag85B-ESAT6-loaded poly(lactic-<i>co</i>-glycolic acid) nanoparticles confer protective immunity against tuberculosis

Background Bacillus Calmette-Guérin, the attenuated strain of Mycobacterium bovis , remains the only available vaccine against tuberculosis (TB). However, its ineffectiveness in adults against pulmonary TB and varied protective efficacy (0-80%) speak to an urgent need for the development of an improved and efficient TB vaccine. In this milieu, poly(lactic- co -glycolic acid) (PLGA), is a preferential candidate, due to such properties as biocompatibility, targeted delivery, sustained antigen release, and atoxic by-products. Methods In this study, we formulated PLGA nanoparticles (NPs) encapsulating the bivalent H1 antigen, a fusion of Mycobacterium tuberculosis (Mtb) Ag85B and ESAT6 proteins, and investigated its role in immunomodulation and protection against Mtb challenge. Using the classical water-oil-water solvent-evaporation method, H1-NPs were prepared, with encapsulation efficiency of 86.1%±3.2%. These spherical NPs were ~244.4±32.6 nm in diameter, with a negatively charged surface (ζ-potential -4±0.6 mV). Results Under physiological conditions, NPs degraded slowly and the encapsulated H1 antigen was released over a period of weeks. As a proof-of-concept vaccine candidate, H1 NPs were efficiently internalized by the THP-1 human macrophages. Six weeks after a single-dose vaccination, H1 NP-immunized C57BL/6J mice showed significant increase in the production of total serum IgG ( P 2a being the predominant one, followed by IgG 1 . Further, the cytokine-release profile of antigen-stimulated splenocyteculture supernatant indicated a strong T H 1-biased immunoresponse in H1 NP-vaccinated mice, with ~6.03- and ~2.8-fold increase in IFNγ and TNFα cytokine levels, and ~twofold and 1.6 fold increase in IL4 and IL10 cytokines, respectively, compared to H1 alone-immunized mice. In protection studies, H1 NP-vaccinated mice displayed significant reductions in lung and spleen bacillary load ( P Conclusion Altogether, our findings highlight the significance of the H1-PLGA nanoformulation in terms of providing long-term protection in mice with a single dose.