With
tuberculosis continuing to be a major cause of global morbidity and mortality, a new
vaccine is urgently needed.
Tuberculosis subunit vaccines have been shown to induce robust immune responses in humans and are a potentially safer alternative to BCG for use in HIV-endemic areas. In this study, we investigated the protective efficacy of 16 different novel
Mycobacterium tuberculosis antigens using an aerogenic mouse model of
pulmonary tuberculosis. These
antigens were tested as
subunit vaccines formulated in
dimethyl dioctadecyl ammonium bromide (
DDA) - D(+) with
trehalose 6,6 dibenenate (TDB) (
DDA/TDB) adjuvant administered alone as monovalent
vaccines or in combination. Six of these
antigens (Rv1626, Rv1735, Rv1789, Rv2032, Rv2220, and Rv3478) were shown to consistently and significantly reduce bacterial burdens in the lungs of mice relative to nonvaccinated controls. Three of these six (Rv1789, Rv2220, and Rv3478) induced levels of protective immunity that were essentially equivalent to protection induced by the highly immunogenic
antigen 85B (>0.5 log₁₀CFU reduction in the lungs relative to naïve mice). Importantly, when these three
antigens were combined, protection essentially equivalent to that mediated by BCG was observed. When either Rv1626 or Rv2032 were combined with the highly protective E6-85 fusion
protein (
antigen 85B fused to ESAT-6), the protection observed was equivalent to BCG-induced protection at one and three months post-
aerosol infection and was significantly greater than the protection observed when E6-85 was administered alone at 3 months post-
infection. Using multiparameter flow cytometry, monofunctional IFNγ CD4T cells and different multifunctional CD4T cell subsets capable of secreting multiple
cytokines (IFNγ, TNFα and/or IL-2) were shown to be induced by the three most protective
antigens with splenocyte CD4T cell frequencies significantly greater than observed in naïve controls. The identification of these highly immunogenic TB
antigens and
antigen combinations should allow for improved immunization strategies against
tuberculosis.