Environmental effects on protection against Mycobacterium tuberculosis after immunization with Ad85A

Airway delivery of both a BCG prime and adenoviral boost drives CD4 and CD8 T cells into the lung tissue parenchyma

Heterologous BCG prime-boost regimens represent a promising strategy for an urgently required improved tuberculosis vaccine. Identifying the mechanisms which underpin the enhanced protection induced by such strategies is one key aim which would significantly accelerate rational vaccine development. Experimentally, airway vaccination induces greater efficacy than parenteral delivery; in both conventional vaccination and heterologous boosting of parenteral BCG immunisation. However, the effect of delivering both the component prime and boost immunisations via the airway is not well known. Here we investigate delivery of both the BCG prime and adenovirus boost vaccination via the airway in a murine model, and demonstrate this approach may be able to improve the protective outcome over parenteral prime/airway boost. Intravascular staining of T cells in the lung revealed that the airway prime regimen induced more antigen-specific multifunctional CD4 and CD8 T cells to the lung parenchyma prior to challenge and indicated the route of both prime and boost to be critical to the location of induced resident T cells in the lung. Further, in the absence of a defined phenotype of vaccine-induced protection to tuberculosis; the magnitude and phenotype of vaccine-specific T cells in the parenchyma of the lung may provide insights into potential correlates of immunity.

Variable BCG efficacy in rhesus populations: Pulmonary BCG provides protection where standard intra-dermal vaccination fails

M.bovis BCG vaccination against tuberculosis (TB) notoriously displays variable protective efficacy in different human populations. In non-human primate studies using rhesus macaques, despite efforts to standardise the model, we have also observed variable efficacy of BCG upon subsequent experimental M. tuberculosis challenge. In the present head-to-head study, we establish that the protective efficacy of standard parenteral BCG immunisation varies among different rhesus cohorts. This provides different dynamic ranges for evaluation of investigational vaccines, opportunities for identifying possible correlates of protective immunity and for determining why parenteral BCG immunisation sometimes fails. We also show that pulmonary mucosal BCG vaccination confers reduced local pathology and improves haematological and immunological parameters post-infection in animals that are not responsive to induction of protection by standard intra-dermal BCG. These results have important implications for pulmonary TB vaccination strategies in the future.

Commonly administered bacille Calmette-Guerin strains induce comparable immune response

Bacille Calmette-Guerin (BCG) is currently the only available vaccine against tuberculosis (TB), but its protective efficacy in adults is highly variable. This study aimed to compare the immune response induced by two widely used BCG strains: BCG China strain (derivative of BCG Danish strain) in DU2-III group and BCG Pasteur in DU2 -IV group. Healthy BALB/c mice were immunized with BCG China strain or BCG Pasteur strain. Specific IgG, IgG1, and IgG2a antibodies titers, the proliferation of splenocytes, the percentages of splenocyte subsets and the concentrations of induced IFN-γ and IL-4 at 6(th), 8(th), 10(th), and 12(th) weeks after the immunization were detected. We found that BCG Pasteur strain induced higher specific IgG and IgG1 titers, higher proliferation of splenocytes, higher percentages of CD4(+) or CD8(+) T cells, and higher concentration of secreted IFN-γ than BCG China strain. However, there were no significant differences in IgG2a titer and IL-4 concentration between both strains. In conclusion, our study shows that immune responses to BCG vaccine differ by strain, which may account for variable outcomes of BCG immunization.

Regulatory T-Cells at the Interface between Human Host and Pathogens in Infectious Diseases and Vaccination

Regulatory T-cells (Tregs) act at the interface of host and pathogen interactions in human infectious diseases. Tregs are induced by a wide range of pathogens, but distinct effects of Tregs have been demonstrated for different pathogens and in different stages of infection. Moreover, Tregs that are induced by a specific pathogen may non-specifically suppress immunity against other microbes and parasites. Thus, Treg effects need to be assessed not only in homologous but also in heterologous infections and vaccinations. Though Tregs protect the human host against excessive inflammation, they probably also increase the risk of pathogen persistence and chronic disease, and the possibility of disease reactivation later in life. Mycobacterium leprae and Mycobacterium tuberculosis, causing leprosy and tuberculosis, respectively, are among the most ancient microbes known to mankind, and are master manipulators of the immune system toward tolerance and pathogen persistence. The majority of mycobacterial infections occur in settings co-endemic for viral, parasitic, and (other) bacterial coinfections. In this paper, we discuss recent insights in the activation and activity of Tregs in human infectious diseases, with emphasis on early, late, and non-specific effects in disease, coinfections, and vaccination. We highlight mycobacterial infections as important models of modulation of host responses and vaccine-induced immunity by Tregs.

Helicobacter hepaticus infection in BALB/c mice abolishes subunit-vaccine-induced protection against M. tuberculosis

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Neonatal Hh infection of mice upregulates colonic IL10 message.

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Neonatal Hh infection reduces lung immune responses after immunisation with Ad85A.

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Protection against Mtb challenge induced by Ad85A is abolished in Hh infected mice.

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IL10R blockade reverses the effects of Hh infection on Ad85A induced protection.

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Addition of Hh to the microbiota abolishes protection induced by a subunit vaccine.

BCG, the only licensed vaccine against tuberculosis (TB), provides geographically variable protection, an effect ascribed to exposure to environmental mycobacteria (EM). Here we show that altering the intestinal microbiota of mice by early-life infection with the commensal bacterium Helicobacter hepaticus (Hh) increases their susceptibility to challenge with Mycobacterium tuberculosis (Mtb). Furthermore Hh-infected mice immunised parenterally with the recombinant subunit vaccine, human adenovirus type 5 expressing the immunodominant antigen 85A of Mtb (Ad85A), display a reduced lung immune response and protection against Mtb challenge is also reduced. Expression of interleukin 10 (IL10) messenger RNA is increased in the colon of Hh infected mice. Treatment of Hh-infected Ad85A-immunised mice with anti-IL10 receptor antibody, following challenge with Mtb, restores the protective effect of the vaccine. These data show for the first time that alteration of the intestinal microbiota by addition of a single commensal organism can profoundly influence protection induced by a TB subunit vaccine via an IL10-dependent mechanism, a result with implications for the deployment of such vaccines in the field.

The hidden 'mycobacteriome' of the human healthy oral cavity and upper respiratory tract

The incidence of opportunistic non-tuberculous mycobacteria (NTM) infections has increased considerably in the past decades causing an array of infections, including respiratory and soft-tissue infections. NTM are ubiquitous and can be found in numerous environments, including households and water plants. However, NTM have not been reported to be associated with the healthy human oral microbiome. Since the oral cavity and upper respiratory track are the main ports of entry of microorganisms into the human body, elucidating NTM diversity and prevalence will assist in the assessment of the potential risks of infection elicited by these opportunistic pathogens. Here, we report the identification of a ‘non-tuberculous mycobacteriome’ in healthy individuals. We employed a modified DNA extraction procedure in conjunction with mycobacterial-specific primers to screen niches in the oral cavity (buccal mucosa and dental plaque) and upper respiratory tract (nostrils and oropharynx) of 10 healthy subjects. A total of 50 prevalent operational taxonomic units sequenced on MiSeq (Illumina) using 16S rRNA V3–V4 region were detected across all screened niches, showing the presence of diverse NTM communities. NTM DNA was detected in the nostrils of all 10 subjects, in buccal mucosa of 8 subjects, in the oropharynx of 7 subjects, and in the dental plaques of 5 subjects. Results from quantitative PCR showed each individual harbored 10³–10⁴ predicted NTM per each screened niche. The modification of standard DNA isolation methods to increase sensitivity toward mycobacterial species represents an important step to advance the knowledge of the oral as well as the overall human microbiome. These findings clearly reveal for the first time that healthy individuals harbor a ‘non-tuberculous mycobacteriome’ in their oral cavity and upper respiratory tract and may have important implications in our understanding of infections caused by NTM.