Myeloid HIF-1α regulates pulmonary inflammation during experimental Mycobacterium tuberculosis infection.

The transcription factor hypoxia-inducible factor-1 alpha (HIF-1α) is a key regulator of the response and function of myeloid cells in hypoxic and inflammatory microenvironments. To define the role of HIF-1α in tuberculosis, the progression of aerosol Mycobacterium tuberculosis infection was analysed in mice deficient in HIF-1α in the myeloid lineage (mHIF-1α-/- ). We show that myeloid HIF-1α is not required for the containment of the infection, as both wild-type (WT) and mHIF-1α-/- mice mounted normal Th1 responses and maintained control of bacterial growth throughout infection. However, during chronic infection mHIF-1α-/- mice developed extensive lymphocytic inflammatory involvement of the interstitial lung tissue and died earlier than WT mice. These data support the hypothesis that HIF-1α activity coordinates the response of myeloid cells during M. tuberculosis infection to prevent excessive leucocyte recruitment and immunopathological consequences to the host.

Immune-evasion Strategies of Mycobacteria and Their Implications for the Protective Immune Response.

Mycobacteria are intracellular pathogens that have macrophages as their main host cells. However, macrophages are also the primary line of defense against invading microorganisms. To survive in the intracellular compartment, virulent mycobacteria have developed several strategies to modulate the activation and the effector functions of macrophages. Despite this, antigen-specific T cells develop during infection. While T cell responses are critical for protection they can also contribute to the success of mycobacteria as human pathogens, as immunopathology associated with these responses facilitates transmission. Here, we provide a brief overview of different immune-evasion strategies of mycobacteria and their impact on the protective immune response. This understanding will further our knowledge in host-pathogen interactions and may provide critical insights for the development of novel host-specific therapies.

IL-10 Overexpression After BCG Vaccination Does Not Impair Control of Mycobacterium tuberculosis Infection.

Control of tuberculosis depends on the rapid expression of protective CD4+ T-cell responses in the Mycobacterium tuberculosis (Mtb)-infected lungs. We have recently shown that the immunomodulatory cytokine IL-10 acts intrinsically in CD4+ T cells and impairs their parenchymal migratory capacity, thereby preventing control of Mtb infection. Herein, we show that IL-10 overexpression does not impact the protection conferred by the established memory CD4+ T-cell response, as BCG-vaccinated mice overexpressing IL-10 only during Mtb infection display an accelerated, BCG-induced, Ag85b-specific CD4+ T-cell response and control Mtb infection. However, IL-10 inhibits the migration of recently activated ESAT-6-specific CD4+ T cells into the lung parenchyma and impairs the development of ectopic lymphoid structures associated with reduced expression of the chemokine receptors CXCR5 and CCR7. Together, our data support a role for BCG vaccination in preventing the immunosuppressive effects of IL-10 in the fast progression of Mtb infection and may provide valuable insights on the mechanisms contributing to the variable efficacy of BCG vaccination.

Early IL-10 promotes vasculature-associated CD4+ T cells unable to control Mycobacterium tuberculosis infection.

Cytokine-producing CD4+ T cells play a crucial role in the control of Mycobacterium tuberculosis infection; however, there is a delayed appearance of effector T cells in the lungs following aerosol infection. The immunomodulatory cytokine IL-10 antagonizes control of M. tuberculosis infection through mechanisms associated with reduced CD4+ T cell responses. Here, we show that IL-10 overexpression only before the onset of the T cell response impaired control of M. tuberculosis growth; during chronic infection, IL-10 overexpression reduced the CD4+ T cell response without affecting the outcome of infection. IL-10 overexpression early during infection did not, we found, significantly impair the kinetics of CD4+ T cell priming and effector differentiation. However, CD4+ T cells primed and differentiated in an IL-10-enriched environment displayed reduced expression of CXCR3 and, because they did not migrate into the lung parenchyma, their ability to control infection was limited. Importantly, these CD4+ T cells maintained their vasculature phenotype and were unable to control infection, even after adoptive transfer into low IL-10 settings. Together our data support a model wherein, during M. tuberculosis infection, IL-10 acts intrinsically on T cells, impairing their parenchymal migratory capacity and ability to engage with infected phagocytic cells, thereby impeding control of infection.

Changes in the Immune Phenotype and Gene Expression Profile Driven by a Novel Tuberculosis Nanovaccine: Short and Long-Term Post-immunization.

Deciphering protection mechanisms against Mycobacterium tuberculosis (Mtb) remains a critical challenge for the development of new vaccines and therapies. We analyze the phenotypic and transcriptomic profile in lung of a novel tuberculosis (TB) nanoparticle-based boosting mucosal vaccine Nano-FP1, which combined to BCG priming conferred enhanced protection in mice challenged with low-dose Mtb. We analyzed the vaccine profile and efficacy at short (2 weeks), medium (7 weeks) and long term (11 weeks) post-vaccination, and compared it to ineffective Nano-FP2 vaccine. We observed several changes in the mouse lung environment by both nanovaccines, which are lost shortly after boosting. Additional boosting at long-term (14 weeks) recovered partially cell populations and transcriptomic profile, but not enough to enhance protection to infection. An increase in both total and resident memory CD4 and CD8 T cells, but no pro-inflammatory cytokine levels, were correlated with better protection. A unique gene expression pattern with differentially expressed genes revealed potential pathways associated to the immune defense against Mtb. Our findings provide an insight into the critical immune responses that need to be considered when assessing the effectiveness of a novel TB vaccine.

Metabolic Host Response to Intracellular Infections.

The interaction between intracellular bacterial pathogens with the host immune response can result in multiple outcomes that range from asymptomatic clearance to the establishment of infection. At its core, these interactions result in multiple metabolic adaptations of both the pathogen and its host cell. There is growing evidence that the host metabolic response plays a key role in the development of immune responses against the invading pathogen. However, successful intracellular pathogens have developed multiple mechanisms to circumvent the host response to thrive in the intracellular compartment. Here, we provide a brief overview on the crucial role of fundamental metabolic host responses in the generation of protective immunity to intracellular bacterial pathogens and discuss some of the mechanisms used by these pathogens to exploit the host metabolic response to their own advantage. This understanding will further our knowledge in host-pathogen interactions and may provide new insights for the development of novel therapies.

A Nonribosomal Peptide Synthase Gene Driving Virulence in Mycobacterium tuberculosis.

Nonribosomal peptide synthases produce short peptides in a manner that is distinct from classical mRNA-dependent ribosome-mediated translation. The Mycobacterium tuberculosis genome harbors a nonribosomal peptide synthase gene, nrp, which is part of a gene cluster proposed to be involved in the biosynthesis of isonitrile lipopeptides. Orthologous clusters are found in other slow-growing pathogenic mycobacteria and actinomycetes. To probe the role of the nrp gene in infection, we generated an nrp deletion mutant in M. tuberculosis H37Rv and tested its virulence in immunocompetent (C57BL/6) mice. The nrp mutant strain displayed lower initial growth rates in the lungs and a defective dissemination to the spleens of infected mice. Mice infected with the mutant strain also survived for twice as long as those infected with wild-type M. tuberculosis and, remarkably, showed subdued pathology, despite similar bacterial loads at later stages of infection. The differences in the course of infection between wild-type and nrp mutant strains were accompanied by distinct dynamics of the immune response. Most strikingly, the nrp mutant was highly attenuated in immunodeficient (SCID-, recombination activating 2 [RAG2]-, and gamma interferon [IFN-γ]-deficient) mice, suggesting that macrophages control the nrp mutant more efficiently than they control the wild-type strain. However, in the presence of IFN-γ, both strains were equally controlled. We propose that the nrp gene and its associated cluster are drivers of virulence during the early stages of infection.IMPORTANCE Over 10 million people developed tuberculosis (TB) in 2016, and over 1.8 million individuals succumbed to the disease. These numbers make TB the ninth leading cause of death worldwide and the leading cause from a single infectious agent. Therefore, finding novel therapeutic targets in Mycobacterium tuberculosis, the pathogen that causes most cases of human TB, is critical. In this study, we reveal a novel virulence factor in M. tuberculosis, the nrp gene. The lack of nrp highly attenuates the course of M. tuberculosis infection in the mouse model, which is particularly relevant in immune-deficient hosts. This is very relevant as TB is particularly incident in immune-suppressed individuals, such as HIV patients.

Development of Inhalable Superparamagnetic Iron Oxide Nanoparticles (SPIONs) in Microparticulate System for Antituberculosis Drug Delivery.

Tuberculosis (TB) is an infectious disease which affects millions of people worldwide. Inhalable polymeric dry powders are promising alternatives as anti-TB drug carriers to the alveoli milieu and infected macrophages, with potential to significantly improve the therapeutics efficiency. Here, the development of a magnetically responsive microparticulate system for pulmonary delivery of an anti-TB drug candidate (P3) is reported. Microparticles (MPs) are developed based on a cast method using calcium carbonate sacrificial templates and incorporate superparamagnetic iron oxide nanoparticles to concentrate MPs in alveoli and enable drug on demand release upon actuation of an external alternate magnetic field (AMF). The MPs are shown to be suitable for P3 delivery to the lower airways and for alveolar macrophage phagocytosis. The developed MPs reveal unique and promising features to be used as an inhalable dry powder allowing the AMF control over dosage and frequency of drug delivery anticipating improved TB treatments.