bims-traimu Biomed News
on Trained immunity
Issue of 2022‒09‒18
six papers selected by
Yantong Wan
Southern Medical University

  1. PLoS Biol. 2022 Sep 12. 20(9): e3001765
      The antituberculosis vaccine Bacillus Calmette-Guérin (BCG) induces nonspecific protection against heterologous infections, at least partly through induction of innate immune memory (trained immunity). The amplitude of the response to BCG is variable, but the factors that influence this response are poorly understood. Metabolites, either released by cells or absorbed from the gut, are known to influence immune responses, but whether they impact BCG responses is not known. We vaccinated 325 healthy individuals with BCG, and collected blood before, 2 weeks and 3 months after vaccination, to assess the influence of circulating metabolites on the immune responses induced by BCG. Circulating metabolite concentrations after BCG vaccination were found to have a more pronounced impact on trained immunity responses, such as the increase in IL-1β and TNF-α production upon Staphylococcus aureus stimulation, than on specific adaptive immune memory, assessed as IFN-γ production in response to Mycobacterium tuberculosis. Circulating metabolites at baseline were able to predict trained immunity responses at 3 months after vaccination and enrichment analysis based on the metabolites positively associated with trained immunity revealed enrichment of the tricarboxylic acid (TCA) cycle and glutamine metabolism, both of which were previously found to be important for trained immunity. Several new metabolic pathways that influence trained immunity were identified, among which taurine metabolism associated with BCG-induced trained immunity, a finding validated in functional experiments. In conclusion, circulating metabolites are important factors influencing BCG-induced trained immunity in humans. Modulation of metabolic pathways may be a novel strategy to improve vaccine and trained immunity responses.
  2. Front Immunol. 2022 ;13 959656
      Bacillus Calmette-Guerin (BCG) has been used as a vaccine against tuberculosis since 1921 and remains the only currently approved vaccine for this infection. The recent discovery that BCG protects against initial infection, and not just against progression from latent to active disease, has significant implications for ongoing research into the immune mechanisms that are relevant to generate a solid host defense against Mycobacterium tuberculosis (Mtb). In this review, we first explore the different components of immunity that are augmented after BCG vaccination. Next, we summarize current efforts to improve the efficacy of BCG through the development of recombinant strains, heterologous prime-boost approaches and the deployment of non-traditional routes. These efforts have included the development of new recombinant BCG strains, and various strategies for expression of important antigens such as those deleted during the M. bovis attenuation process or antigens that are present only in Mtb. BCG is typically administered via the intradermal route, raising questions about whether this could account for its apparent failure to generate long-lasting immunological memory in the lungs and the inconsistent level of protection against pulmonary tuberculosis in adults. Recent years have seen a resurgence of interest in the mucosal and intravenous delivery routes as they have been shown to induce a better immune response both in the systemic and mucosal compartments. Finally, we discuss the potential benefits of the ability of BCG to confer trained immunity in a non-specific manner by broadly stimulating a host immunity resulting in a generalized survival benefit in neonates and the elderly, while potentially offering benefits for the control of new and emerging infectious diseases such as COVID-19. Given that BCG will likely continue to be widely used well into the future, it remains of critical importance to better understand the immune responses driven by it and how to leverage these for the design of improved vaccination strategies against tuberculosis.
    Keywords:  immunity; recombinant BCG; trained immunity; tuberculosis; vaccine
  3. BMC Immunol. 2022 Sep 14. 23(1): 43
      BACKGROUND: Autophagy is an important mechanism for promoting Mycobacterium clearance from macrophages. Pathogenic and non-pathogenic mycobacterium can activate the mTOR pathway while simultaneously inducing autophagy. M. tuberculosis and M. bovis BCG inhibit autophagy and favor intracellular bacteria survival.RESULTS: We observed that pre-infection of live or heat-killed BCG could prevent autophagy induced by pharmacological activators or M. smegmatis, a strong autophagy-inducing mycobacterium. BCG-derived lipids are responsible for autophagy inhibition. However, post-infection with BCG could not stop the autophagy initiated by M. smegmatis, which increases further autophagy induction and mycobacteria clearance. Coinfection with BCG and heat killed M. smegmatis enhanced antigen specific CD4+ T cell responses and reduced mycobacterial survival.
    CONCLUSION: These results suggest that autophagy-inducing M. smegmatis could be used to promote better innate and consequential adaptive immune responses, improving BCG vaccine efficacy.
    Keywords:  Autophagy; BCG; Innate immunity; Lipids; Mycobacterium smegmatis; Mycobacterium tuberculosis
  4. Vaccine. 2022 Sep 09. pii: S0264-410X(22)01087-8. [Epub ahead of print]
      BACKGROUND: Live vaccines potentially have non-specific effects that protect against other infections than those the vaccines are targeted against. The national vaccination program (NVP) in Finland was changed on September 1st, 2006: before BCG vaccine was given to all newborn babies and afterwards to babies in risk groups only. We used this natural experiment to study the non-specific effects of BCG in the frame of NVP using before-after design.METHODS: We compared the incidence of several outcomes obtained from Finnish health registers between children born between July 1st, 2004, and June 30th, 2006 (BCG-eligible) and an age- and season-matched reference cohort born between July 1st, 2007, and June 30th, 2009 (BCG-non-eligible) using Poisson regression. These cohorts were restricted to full-term children whose parents were born in Finland. Follow-up began at birth and lasted 3 months, which is the scheduled age for DTaP-IPV-Hib vaccination, and from 4 months until first birthday. The outcomes included all infections, pneumonia and injuries as a negative control outcome.
    RESULTS: The incidence rate ratio (IRR) of the BCG-eligible cohort (N = 93,658) compared to BCG-non-eligible cohort (N = 94,712) for hospital-diagnosed infections was 0.89 (95 %Cl 0.86-0.93) for the 3-month follow-up. The decrease was mainly caused by respiratory infections. In 4-12 months follow-up the BCG-eligible had slightly more infections than BCG-non-eligible children (IRR 1.03, 1.01-1.06).
    CONCLUSIONS: BCG vaccination was associated with a lower incidence of all hospital-diagnosed infections during the first three months of life. The difference cannot be attributed to lung tuberculosis, since only few paediatric cases occurred in Finland during 2000s. The disappearance of non-specific effect after administration of an inactivated vaccine is compatible with previous studies.
    Keywords:  BCG; Infections; Non-specific effect; Pneumonia
  5. BMB Rep. 2022 Sep 15. pii: 5681. [Epub ahead of print]
      Neutrophils, the most abundant innate immune cells, play essential roles in the innate immune system. As key innate immune cells, neutrophils detect intrusion of pathogens and initiate immune cascades with their functions; swarming (arresting), cytokine production, degranulation, phagocytosis, and projection of neutrophil extracellular trap. Because of their short lifespan and consumption during immune response, neutrophils need to be generated consistently, and generation of newborn neutrophils (granulopoiesis) should fulfill the environmental/systemic demands for training in cases of infection. Accumulating evidence suggests that neutrophils also play important roles in the regulation of adaptive immunity. Neutrophil-mediated immune responses end with apoptosis of the cells, and proper phagocytosis of the apoptotic body (efferocytosis) is crucial for initial and post resolution by producing tolerogenic innate/adaptive immune cells. However, inflammatory cues can impair these cascades, resulting in systemic immune activation; necrotic/pyroptotic neutrophil bodies can aggravate the excessive inflammation, increasing inflammatory macrophage and dendritic cell activation and subsequent TH1/TH17 responses contributing to the regulation of the pathogenesis of autoimmune disease. In this review, we briefly introduce recent studies of neutrophil function as players of immune response.