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Gastrointestinal infections caused by enteric yersiniae can become persistent and complicated by relapsing enteritis and severe autoimmune disorders. To establish a persistent infection, the bacteria have to cope with hostile surroundings when they transmigrate through the intestinal epithelium and colonize underlying gut-associated lymphatic tissues. How the bacteria gain a foothold in the face of host immune responses is poorly understood. Here, we show that the CNFY toxin, which enhances translocation of the antiphagocytic Yop effectors, induces inflammatory responses. This results in extensive tissue destruction, alteration of the intestinal microbiota and bacterial clearance. Suppression of CNFY function, however, increases interferon-γ-mediated responses, comprising non-inflammatory antimicrobial activities and tolerogenesis. This process is accompanied by a preterm reprogramming of the pathogen's transcriptional response towards persistence, which gives the bacteria a fitness edge against host responses and facilitates establishment of a commensal-type life style., Author summary A complex cascade of events is triggered by the mammalian host upon a bacterial infection to prevent pathogen-induced damage. Many pathogens are successfully eliminated by the host immune system. However, some bacterial pathogens, including enteric yersiniae, evolved strategies to efficiently evade immune surveillance. This enables the pathogen to colonize specific sites in the host in which they can persist for years. These persistent infections are often asymptomatic for long time periods, but can undergo reactivation and cause clinical symptoms. In order to understand how enteric bacteria can persist in gut-associated host niches, we investigated changes of bacterial and host responses from an acute to a persistent infection. We found that persistency of Y. pseudotuberculosis in the cecum is characterized by suppression of pathogen-induced inflammation and tissue destruction, and an induction of interferon-γ promoted tolerogenic responses. We further show that the removal of a single bacterial virulence factor, the CNFY toxin, can trigger this process and drives the bacteria into persistency.

Summary Inflammatory bowel disease comprises a group of heterogeneous diseases characterized by chronic and relapsing mucosal inflammation. Alterations in microbiota composition have been proposed to contribute to disease development, but no uniform signatures have yet been identified. Here, we compare the ability of a diverse set of microbial communities to exacerbate intestinal inflammation after chemical damage to the intestinal barrier. Strikingly, genetically identical wild-type mice differing only in their microbiota composition varied strongly in their colitis susceptibility. Transfer of distinct colitogenic communities in gene-deficient mice revealed that they triggered disease via opposing pathways either independent or dependent on adaptive immunity, specifically requiring antigen-specific CD4+ T cells. Our data provide evidence for the concept that microbial communities may alter disease susceptibility via different immune pathways despite eventually resulting in similar host pathology. This suggests a potential benefit for personalizing IBD therapies according to patient-specific microbiota signatures., Graphical Abstract, Highlights • Gut microbiota composition modulates colitis severity in immunocompetent hosts • Colitogenic microbiota drive colitis via innate or adaptive immunity • Distinct microbiota members induce pathogenic CD4+ T cells to drive colitis, Alterations in the microbiota contribute to the development of intestinal inflammation. Roy et al. demonstrate that distinct intestinal microbial communities cause colitis via opposing effector mechanisms independent or dependent on adaptive immunity. Their findings suggest that personalized immunomodulatory treatment according to distinct microbial signatures may be beneficial for IBD patients.

Inflammasomes play a central role in regulating intestinal barrier function and immunity during steady state and disease. Because the discoveries of a passenger mutation and a colitogenic microbiota in the widely used caspase-1-deficient mouse strain have cast doubt on previously identified direct functions of caspase-1, we reassessed the role of caspase-1 in the intestine. To this end, we generated Casp1(-/-) and Casp11(-/-) mice and rederived them into an enhanced barrier facility to standardize the microbiota. We found that caspase-11 does not influence caspase-1-dependent processing of IL-18 in homeostasis and during DSS colitis. Deficiency of caspase-1, but not caspase-11, ameliorated the severity of DSS colitis independent of microbiota composition. Ablation of caspase-1 in intestinal epithelial cells was sufficient to protect mice against DSS colitis. Moreover, Casp1(-/-) mice developed fewer inflammation-induced intestinal tumors than control mice. These data show that canonical inflammasome activation controls caspase-1 activity, contributing to exacerbation of chemical-induced colitis.

// Dino Kocijancic 1, * , Sebastian Felgner 1, 2, * , Tim Schauer 1 , Michael Frahm 1 , Ulrike Heise 3 , Kurt Zimmermann 4 , Marc Erhardt 2 and Siegfried Weiss 1, 5 1 Molecular Immunology, Helmholtz Center for Infection Research, Braunschweig, Germany 2 Infection Biology of Salmonella, Helmholtz Center for Infection Research, Braunschweig, Germany 3 Mouse-Pathology Service Unit, Helmholtz Center for Infection Research, Braunschweig, Germany 4 Symbio Gruppe GmbH & Co KG, Herborn, Germany 5 Institute of Immunology, Medical School Hannover, Hannover, Germany * These authors have contributed equally to this work Correspondence to: Dino Kocijancic, email: dino.kocijancic@helmholtz-hzi.de Keywords: Intra-tumoral injection, Salmonella, E. coli, bacteria mediated tumor therapy, murine tumor model Received: October 29, 2016 Accepted: May 05, 2017 Published: June 07, 2017 ABSTRACT Cancer is a devastating disease and a large socio-economic burden. Novel therapeutic solutions are on the rise, although a cure remains elusive. Application of microorganisms represents an ancient therapeutic strategy, lately revoked and refined via simultaneous attenuation and amelioration of pathogenic properties. Salmonella Typhimurium has prevailed in preclinical development. Yet, using virulent strains for systemic treatment might cause severe side effects. In the present study, we highlight a modified strain based on Salmonella Typhimurium UK-1 expressing hexa-acylated Lipid A. We corroborate improved anti-tumor properties of this strain and investigate to which extent an intra-tumoral (i.t.) route of infection could help improve safety and retain advantages of systemic intravenous (i.v.) application. Our results show that i.t. infection exhibits therapeutic efficacy against CT26 and F1.A11 tumors similar to a systemic route of inoculation. Moreover, i.t. application allows extensive dose titration without compromising tumor colonization. Adverse colonization of healthy organs was generally reduced via i.t. infection and accompanied by less body weight loss of the murine host. Despite local application, adjuvanticity remained, and a CT26-specific CD8 + T cell response was effectively stimulated. Most interestingly, also secondary tumors could be targeted with this strategy, thereby extending the unique tumor targeting ability of Salmonella . The i.t. route of inoculation may reap the benefits of systemic infection and aid in safety assurance while directing potency of an oncolytic vector to where it is most needed, namely the primary tumor.

Foxp3-expressing regulatory T cells (Tregs) are essential regulators of immune homeostasis and, thus, are prime targets for therapeutic interventions of diseases such as cancer and autoimmunity. c-REL and IκBNS are important regulators of Foxp3 induction in Treg precursors upon γ-chain cytokine stimulation. In c-REL/IκBNS double-deficient mice, Treg numbers were dramatically reduced, indicating that together, c-REL and IκBNS are pivotal for Treg development. However, despite the highly reduced Treg compartment, double-deficient mice did not develop autoimmunity even when aged to more than 1 y, suggesting that c-REL and IκBNS are required for T cell effector function as well. Analyzing Treg development in more detail, we identified a CD122+ subset within the CD25−Foxp3− precursor population, which gave rise to classical CD25+Foxp3− Treg precursors. Importantly, c-REL, but not IκBNS, controlled the generation of classical CD25+Foxp3− precursors via direct binding to the Cd25 locus. Thus, we propose that CD4+GITR+CD122+CD25−Foxp3− cells represent a Treg pre-precursor population, whose transition into Treg precursors is mediated via c-REL.

To date, virulent bacteria remain the basis of most bacteria mediated cancer therapies. For clinical application attenuation is required. However, this might result in a drastically lowered therapeutic capacity. Herein we argue that the E. coli probiotic Symbioflor-2, with a history of safe application may constitute a viable tumor therapeutic candidate. We demonstrate that Symbioflor-2 displays a highly specific tumor targeting ability as determined in murine CT26 and RenCa tumor models. The excellent specificity was ascribed to reduced levels of adverse colonization. A high safety standard was demonstrated in WT and Rag1-/- mice. Thus, Symbioflor-2 may represent an ideal tumor targeting delivery system for therapeutic molecules. Moreover, Symbioflor-2 was capable of inducing CT26 tumor clearance as result of an adjuvant effect on tumor specific CD8+ T cells analogous to the Salmonella variant SL7207. However, lower therapeutic efficacy against RenCa tumors suggested a generally reduced therapeutic potency for probiotics. Interestingly, concurrent depletion of Gr-1+ or Ly6G+ cells installed therapeutic efficacy equal to SL7207, thus highlighting the role of innate effector cells in restraining the anti-tumor effects of Symbioflor-2. Collectively, our findings argue for a strategy of safe strain application and a more sustainable use of bacteria as a delivery system for therapeutic molecules.