Inulin Prebiotic Protects against Lethal Pseudomonas aeruginosa Acute Infection via γδ T Cell Activation.

Pseudomonas aeruginosa (P. aeruginosa) causes harmful lung infections, especially in immunocompromised patients. The immune system and Interleukin (IL)-17-producing γδ T cells (γδ T) are critical in controlling these infections in mice. The gut microbiota modulates host immunity in both cancer and infection contexts. Nutritional intervention is a powerful means of modulating both microbiota composition and functions, and subsequently the host's immune status. We have recently shown that inulin prebiotic supplementation triggers systemic γδ T activation in a cancer context. We hypothesized that prophylactic supplementation with inulin might protect mice from lethal P. aeruginosa acute lung infection in a γδ T-dependent manner. C57Bl/6 mice were supplemented with inulin for 15 days before the lethal P. aeruginosa lung infection, administered intranasally. We demonstrate that prophylactic inulin supplementation triggers a higher proportion of γδ T in the blood, accompanied by a higher infiltration of IL-17-producing γδ T within the lungs, and protects 33% of infected mice from death. This observation relies on γδ T, as in vivo γδ TcR blocking using a monoclonal antibody completely abrogates inulin-mediated protection. Overall, our data indicate that inulin supplementation triggers systemic γδ T activation, and could help resolve lung P. aeruginosa infections. Moreover, our data suggest that nutritional intervention might be a powerful way to prevent/reduce infection-related mortality, by reinforcing the microbiota-dependent immune system.

Inulin prebiotic reinforces host cancer immunosurveillance via ɣδ T cell activation.

The gut microbiota is now recognized as a key parameter affecting the host's anti-cancer immunosurveillance and ability to respond to immunotherapy. Therefore, optimal modulation for preventive and therapeutic purposes is very appealing. Diet is one of the most potent modulators of microbiota, and thus nutritional intervention could be exploited to improve host anti-cancer immunity. Here, we show that an inulin-enriched diet, a prebiotic known to promote immunostimulatory bacteria, triggers an enhanced Th1-polarized CD4+ and CD8+ αß T cell-mediated anti-tumor response and attenuates tumor growth in three preclinical tumor-bearing mouse models. We highlighted that the inulin-mediated anti-tumor effect relies on the activation of both intestinal and tumor-infiltrating ɣδ T cells that are indispensable for αß T cell activation and subsequent tumor growth control, in a microbiota-dependent manner. Overall, our data identified these cells as a critical immune subset, mandatory for inulin-mediated anti-tumor immunity in vivo, further supporting and rationalizing the use of such prebiotic approaches, as well as the development of immunotherapies targeting ɣδ T cells in cancer prevention and immunotherapy.

Bioengineering of Escherichia coli Nissle 1917 for Production and Excretion of Spermidine, a Key Metabolite in Human Health.

Microbiota-derived metabolites have biological importance for their host. Spermidine, a metabolite described for its protective effect in age-related diseases, is now studied for its role in the resolution of inflammation and gut homeostasis. Strategies to modulate its production in the gastrointestinal tract are of interest to increase host spermidine intakes. Here, we show that metabolic engineering can be used to increase spermidine production by the probiotic Escherichia coli Nissle 1917 (EcN), used in humans. First, we found that increasing the expression of genes involved in polyamine biosynthesis, namely the S-adenosylmethionine synthase speD and the spermidine synthase speE, resulted in an increase in spermidine produced and excreted by our engineered bacteria. The major drawback of this first attempt was the production of acetylated forms of spermidine. Next, we propose to solve this problem by increasing the expression of the spermidine exporter system MdtI/MdtJ. This second strategy had a major impact on the spermidine profile found in the culture supernatant. Our results demonstrate, for the first time, the feasibility of rationally engineering bacterial probiotic strains to increase their ability to deliver the microbiota-derived metabolite, spermidine. This work illustrates how metabolomic and synthetic biology can be used to design and improve engineered Live Biotherapeutic Products that have the potential to be used in personalized medicine.

Immune Checkpoint Inhibitor Rechallenge and Resumption: a Systematic Review.

PURPOSE OF THE REVIEW: The reintroduction of immune checkpoint inhibitors (ICIs) after disease progression (rechallenge) or immune-related adverse events (irAEs) recovering (resumption) raises questions in terms of efficacy and safety. RECENT FINDINGS: Here, we reviewed literature data about ICIs rechallenge/resumption in cancer patients along with their clinical characteristics to explore those factors associated with better outcomes. Heterogenous results were pointed out across rechallenge studies with an overall response rate between 0 and 54%, and a progression free survival ranged from 1.5 to 12.9 months and an overall survival between 6.5 and 23.8 months. Better outcomes have been recorded in patients with good ECOG PS, longer duration of initial ICI, discontinuation reason of initial ICI other than progression, and those who received ICI sequence other than the switch between anti-PD1 and anti-PDL1. Studies about ICI resumption highlighted that certain types of irAEs were more likely to relapse at retreatment. These results suggest that ICI rechallenge/resumption can be an interesting strategy for selected patients.

What We Know So Far about the Metabolite-Mediated Microbiota-Intestinal Immunity Dialogue and How to Hear the Sound of This Crosstalk.

Trillions of microorganisms, termed the "microbiota", reside in the mammalian gastrointestinal tract, and collectively participate in regulating the host phenotype. It is now clear that the gut microbiota, metabolites, and intestinal immune function are correlated, and that alterations of the complex and dynamic host-microbiota interactions can have deep consequences for host health. However, the mechanisms by which the immune system regulates the microbiota and by which the microbiota shapes host immunity are still not fully understood. This article discusses the contribution of metabolites in the crosstalk between gut microbiota and immune cells. The identification of key metabolites having a causal effect on immune responses and of the mechanisms involved can contribute to a deeper insight into host-microorganism relationships. This will allow a better understanding of the correlation between dysbiosis, microbial-based dysmetabolism, and pathogenesis, thus creating opportunities to develop microbiota-based therapeutics to improve human health. In particular, we systematically review the role of soluble and membrane-bound microbial metabolites in modulating host immunity in the gut, and of immune cells-derived metabolites affecting the microbiota, while discussing evidence of the bidirectional impact of this crosstalk. Furthermore, we discuss the potential strategies to hear the sound of such metabolite-mediated crosstalk.

Metabotypes of Pseudomonas aeruginosa Correlate with Antibiotic Resistance, Virulence and Clinical Outcome in Cystic Fibrosis Chronic Infections.

Pseudomonas aeruginosa (P.a) is one of the most critical antibiotic resistant bacteria in the world and is the most prevalent pathogen in cystic fibrosis (CF), causing chronic lung infections that are considered one of the major causes of mortality in CF patients. Although several studies have contributed to understanding P.a within-host adaptive evolution at a genomic level, it is still difficult to establish direct relationships between the observed mutations, expression of clinically relevant phenotypes, and clinical outcomes. Here, we performed a comparative untargeted LC/HRMS-based metabolomics analysis of sequential isolates from chronically infected CF patients to obtain a functional view of P.a adaptation. Metabolic profiles were integrated with expression of bacterial phenotypes and clinical measurements following multiscale analysis methods. Our results highlighted significant associations between P.a "metabotypes", expression of antibiotic resistance and virulence phenotypes, and frequency of clinical exacerbations, thus identifying promising biomarkers and therapeutic targets for difficult-to-treat P.a infections.