An unbiased genome-wide Mycobacterium tuberculosis gene expression approach to discover antigens targeted by human T cells expressed during pulmonary infection.

Mycobacterium tuberculosis is responsible for almost 2 million deaths annually. Mycobacterium bovis bacillus Calmette-Guérin, the only vaccine available against tuberculosis (TB), induces highly variable protection against TB, and better TB vaccines are urgently needed. A prerequisite for candidate vaccine Ags is that they are immunogenic and expressed by M. tuberculosis during infection of the primary target organ, that is, the lungs of susceptible individuals. In search of new TB vaccine candidate Ags, we have used a genome-wide, unbiased Ag discovery approach to investigate the in vivo expression of 2170 M. tuberculosis genes during M. tuberculosis infection in the lungs of mice. Four genetically related but distinct mouse strains were studied, representing a spectrum of TB susceptibility controlled by the supersusceptibility to TB 1 locus. We used stringent selection approaches to select in vivo-expressed M. tuberculosis (IVE-TB) genes and analyzed their expression patterns in distinct disease phenotypes such as necrosis and granuloma formation. To study the vaccine potential of these proteins, we analyzed their immunogenicity. Several M. tuberculosis proteins were recognized by immune cells from tuberculin skin test-positive, ESAT6/CFP10-responsive individuals, indicating that these Ags are presented during natural M. tuberculosis infection. Furthermore, TB patients also showed responses toward IVE-TB Ags, albeit lower than tuberculin skin test-positive, ESAT6/CFP10-responsive individuals. Finally, IVE-TB Ags induced strong IFN-γ(+)/TNF-α(+) CD8(+) and TNF-α(+)/IL-2(+) CD154(+)/CD4(+) T cell responses in PBMC from long-term latently M. tuberculosis-infected individuals. In conclusion, these IVE-TB Ags are expressed during pulmonary infection in vivo, are immunogenic, induce strong T cell responses in long-term latently M. tuberculosis-infected individuals, and may therefore represent attractive Ags for new TB vaccines.

Cross-species immunity following immunization with a circumsporozoite protein-based vaccine for malaria.

Malaria continues to be a major public health concern, and there are concerted efforts to eliminate it. The quest for a vaccine remains a top priority, and vaccines based on the circumsporozoite protein (CSP) are among the lead candidates, with the RTS,S vaccine currently undergoing phase 3 testing in Africa. Previous studies have reported anti-CSP antibody-mediated enhancement of in vitro invasion of homologous sporozoites. This effect has been shown to be concentration dependent; high-level antibodies are inhibitory, whereas low-level antibodies lead to enhancement of invasion. Nondominant shared epitopes may lead to the generation of low titers of cross-reactive antibodies that may prove to be detrimental. We report cross-species recognition of Plasmodium falciparum and Plasmodium berghei sporozoites by anti-Plasmodium vivax CSP serum samples. In addition, we report that vaccination of mice with VMP001, a P. vivax CSP vaccine candidate, reduces, not enhances, P. berghei infection in mice.

Dominant role of the sst1 locus in pathogenesis of necrotizing lung granulomas during chronic tuberculosis infection and reactivation in genetically resistant hosts.

Significant host heterogeneity in susceptibility to tuberculosis exists both between and within mammalian species. Using a mouse model of infection with virulent Mycobacterium tuberculosis (Mtb), we identified the genetic locus sst1 that controls the progression of pulmonary tuberculosis in immunocompetent hosts. In this study, we demonstrate that within the complex, multigenic architecture of tuberculosis susceptibility, sst1 functions to control necrosis within tuberculosis lesions in the lungs; this lung-specific sst1 effect is independent of both the route of infection and genetic background of the host. Moreover, sst1-dependent necrosis was observed at low bacterial loads in the lungs during reactivation of the disease after termination of anti-tuberculosis drug therapy. We demonstrate that in sst1-susceptible hosts, nonlinked host resistance loci control both lung inflammation and production of inflammatory mediators by Mtb-infected macrophages. Although interactions of the sst1-susceptible allele with genetic modifiers determine the type of the pulmonary disease progression, other resistance loci do not abolish lung necrosis, which is, therefore, the core sst1-dependent phenotype. Sst1-susceptible mice from tuberculosis-resistant and -susceptible genetic backgrounds reproduce a clinical spectrum of pulmonary tuberculosis and may be used to more accurately predict the efficacy of anti-tuberculosis interventions in genetically heterogeneous human populations.

H2 complex controls CD4/CD8 ratio, recurrent responsiveness to repeated stimulations, and resistance to activation-induced apoptosis during T cell response to mycobacterial antigens.

Genetic variation in the major histocompatibility complex (MHC) influences susceptibility and immune responses to Mycobacterium tuberculosis in mice and humans, but connections among the severity of tuberculosis (TB), dynamic changes in T cell responses to mycobacteria, and MHC genetic polymorphisms are poorly characterized. The overall effect of the MHC genes on TB susceptibility and cellular responses to mycobacteria is moderate; thus, such studies provide reliable results only if congenic mouse strains bearing a variety of H2 haplotypes on an identical genetic background are analyzed. Using a panel of H2-congenic strains on the B10 background, we demonstrate that T cells from mice of three different strains, which are resistant to TB infection, readily respond by proliferation to repeated stimulations with mycobacterial sonicate, whereas T cells from three susceptible mouse strains die after the second stimulation with antigen. This difference is specific, as T cells from TB-susceptible and -resistant mouse strains do not differ in response to irrelevant antigens. The CD4/CD8 ratio in immune lymph nodes correlates strongly and inversely with TB susceptibility, being significantly lower in resistant mice as a result of an increased content of CD8+ cells. These differences between the two sets of mouse strains correlate with an elevated level of activation-induced T cell apoptosis in TB-susceptible mice and a higher proportion of activated CD44+ CD62 ligand- T cells in TB-resistant mice. These results may shed some light on the nature of the cellular basis of MHC-linked differences in susceptibility to TB.

Progression of pulmonary tuberculosis and efficiency of bacillus Calmette-Guérin vaccination are genetically controlled via a common sst1-mediated mechanism of innate immunity.

Using a mouse model for genetic analysis of host resistance to virulent Mycobacterium tuberculosis, we have identified a genetic locus sst1 on mouse chromosome 1, which controls progression of pulmonary tuberculosis. In vitro, this locus had an effect on macrophage-mediated control of two intracellular bacterial pathogens, M. tuberculosis and Listeria monocytogenes. In this report, we investigated a specific function of the sst1 locus in antituberculosis immunity in vivo, especially its role in control of pulmonary tuberculosis. We found that the sst1 locus affected neither activation of Th1 cytokine-producing T lymphocytes, nor their migration to the lungs, but rather controlled an inducible NO synthase-independent mechanism of innate immunity. Although the sst1(S) macrophages responded to stimulation with IFN-gamma in vitro, their responsiveness to activation by T cells was impaired. Boosting T cell-mediated immunity by live attenuated vaccine Mycobacterium bovis bacillus Calmette-Guérin or the adoptive transfer of mycobacteria-activated CD4(+) T lymphocytes had positive systemic effect, but failed to improve control of tuberculosis infection specifically in the lungs of the sst1(S) animals. Thus, in the mouse model of tuberculosis, a common genetic mechanism of innate immunity mediated control of tuberculosis progression in the lungs and the efficiency of antituberculosis vaccine. Our data suggest that in immunocompetent humans the development of pulmonary tuberculosis and the failure of the existing vaccine to protect against it, in some cases, may be explained by a similar defect in a conserved inducible NO synthase-independent mechanism of innate immunity, either inherited or acquired.