Summary Pro-carcinogenic bacteria have the potential to initiate and/or promote colon cancer, in part via immune mechanisms that are incompletely understood. Using ApcMin mice colonized with the human pathobiont enterotoxigenic Bacteroides fragilis (ETBF) as a model of microbial-induced colon tumorigenesis, we show that the Bacteroides fragilis toxin (BFT) triggers a pro-carcinogenic multi-step inflammatory cascade requiring IL-17R, NF-κB, and Stat3 signaling in colonic epithelial cells (CECs). Although necessary, Stat3 activation in CECs is not sufficient to trigger ETBF colon tumorigenesis. Notably, IL-17-dependent NF-κB activation in CECs induces a proximal to distal mucosal gradient of C-X-C chemokines, including CXCL1 that mediates the recruitment of CXCR2-expressing polymorphonuclear immature myeloid cells with parallel onset of ETBF-mediated distal colon tumorigenesis. Thus, BFT induces a procarcinogenic signaling relay from the CEC to a mucosal Th17 response that results in NFκB activation selectively in distal colon CECs, that collectively triggers myeloid cell-dependent distal colon tumorigenesis.

Enterotoxigenic Bacteroides fragilis (ETBF), a human commensal and candidate pathogen in colorectal cancer (CRC), is a potent initiator of IL-17-dependent colon tumorigenesis in MinApc+/-mice. We examined the role of IL-17 and ETBF on the differentiation of myeloid cells into myeloid-derived suppressor cells (MDSC) and tumor-associated macrophages (TAM), which are known to promote tumorigenesis. The myeloid compartment associated with ETBF-induced colon tumorigenesis in Min mice was defined using flow cytometry and gene expression profiling. Cell sorted immature myeloid cells were functionally assayed for inhibition of T cell proliferation and iNOS expression in order to delineate MDSC populations. A comparison of ETBF infection to that of other oncogenic bacteria (Fusobacterium nucleatum or pks+ E. coli) revealed a specific, ETBF-associated colonic immune infiltrate. ETBF-triggered colon tumorigenesis is associated with an IL-17-driven myeloid signature characterized by subversion of steady-state myelopoiesis in favor of the generation of protumoral monocytic (MO)-MDSCs. Combined action of the Bacteroides fragilis enterotoxin BFT and IL-17 on colonic epithelial cells promoted the differentiation of MO-MDSCs, which selectively upregulated Arg1 and Nos2, produced NO and suppressed T cell proliferation. Evidence of a pathogenic inflammatory signature in humans colonized with ETBF may allow for the identification of populations at risk for developing colon cancer.

SummaryPro-carcinogenic bacteria have the potential to initiate and/or promote colon cancer, in part via immune mechanisms that are incompletely understood. Using Apc Min mice colonized with the human pathobiont enterotoxigenic Bacteroides fragilis (ETBF) as a model of microbial-induced colon tumorigenesis, we show that the Bacteroides fragilis toxin (BFT) triggers a pro-carcinogenic multi-step inflammatory cascade requiring IL-17R, NF-κB, and Stat3 signaling in colonic epithelial cells (CECs). Although necessary, Stat3 activation in CECs is not sufficient to trigger ETBF colon tumorigenesis. Notably, IL-17-dependent NF-κB activation in CECs induces a proximal to distal mucosal gradient of C-X-C chemokines, including CXCL1 that mediates the recruitment of CXCR2-expressing polymorphonuclear immature myeloid cells with parallel onset of ETBF-mediated distal colon tumorigenesis. Thus, BFT induces a procarcinogenic signaling relay from the CEC to a mucosal Th17 response that results in NFκB activation selectively in distal colon CECs, that collectively triggers myeloid cell-dependent distal colon tumorigenesis.

In XIAP deficiency, ileitis is driven by TNFR1- and TNFR2-dependent targeting of TLR5-expressing Paneth and dendritic cells.

Since their recent discovery, T helper 17 (Th17) cells have been frequently detected in the tumor microenvironment of many malignancies, but their clinical implications remain largely unknown. Interleukin-17 (IL-17) detection is commonly related with poor outcomes in colorectal cancers, yet its presence is associated with antitumor responses in ovarian carcinomas. Numerous experimental models illustrate the divergent roles of Th17 cells in tumor immunity, which appears to be mainly dependent on the tumor context (type, location, and stage of cancer). It is recognized that IL-17 is produced by a variety of cell types and that Th17 cells are endowed with a unique functional plasticity. Therefore, when trying to elucidate potential immune biomarkers and immunotargets, it is extremely important to make a clear dissociation between strategies targeting Th17 versus its hallmark cytokine, IL-17. In this review, we will summarize the data regarding the detection of IL-17 and Th17 in human cancers, consider the experimental evidence on their respective roles in antitumor activity, and discuss the potential of IL-17 as an immune target for therapeutic interventions.

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Recent studies highlight immunoregulatory functions of type I interferons (IFN-I) during the pathogenesis of graft-versus-host disease (GVHD) after allogeneic hematopoietic stem cell transplantation (allo-HSCT). We demonstrated that selective activation of IFN-I pathways including RIG-I/MAVS and cGAS/STING prior to allo-HSCT conditioning therapy can ameliorate the course of GVHD. However, direct effects of IFN-Is on immune cells remain ill characterized. We applied RIG-I agonists (3pRNA) to stimulate IFN-I production in murine models of conditioning therapy with total body irradiation (TBI) and GVHD. Using IFN-I receptor-deficient donor T cells and hematopoietic cells, we found that endogenous and RIG-I-induced IFN-Is do not reduce GVHD by acting on these cell types. However, 3pRNA applied before conditioning therapy reduced the ability of CD11c+ recipient cells to stimulate proliferation and interferon gamma expression of allogeneic T cells. Consistently, RIG-I activation before TBI reduced the proliferation of transplanted allogeneic T-cells. The reduced allogenicity of CD11c+ recipient cells was dependent on IFN-I signaling. Notably, this immunosuppressive function of DCs was restricted to a scenario where tissue damage occurs. Our findings uncover a context (damage by TBI) and IFN-I dependent modulation of T cells by DCs and extend the understanding about the cellular targets of IFN-I during allo-HSCT and GVHD.

The intestinal microbiome directly effects outcomes in patients undergoing allogeneic stem cell transplantation (ASCT) (Peled et al., N Engl J Med, 2020). Recent developments in microbiome research allow us to look beyond bacterial communities at the composition of the intestinal mycobiome and virome. However, only few studies have addressed these fungal (Zhang et al., Nat Commun, 2021; Legoff et al., Nat Med, 2017) and viral communities (Van Der Velden et al., Biol Blood Marrow Transplant, 2013) in the ASCT setting. Loss of bacterial diversity and domination of single taxa was linked to increased incidence of graft-versus-host-disease (aGvHD) and mortality. However, the functional consequences of intestinal dysbiosis remain poorly understood. Recently, microbial-derived metabolites such as short-chain fatty acids (SCFAs), indoles and secondary bile acids (BA) have been proposed to explain how microbiota exert effects on epithelial and immune responses and shown to protect from GVHD in animal models. To assemble a complete picture of the phylogenetic and metabolic changes which occur as patients undergo ASCT we designed a multiomics approach and identified patterns in bacteriome, mycobiome, virome and metabolome dynamics in relation to clinical factors and GvHD. 353 stool samples from 80 patients undergoing ASCT were obtained at two different transplantation centers (Munich and Regensburg) at defined timepoints before and after transplantation. Changes in metabolite composition were evaluated via mass spectrometry using a targeted metabolomic profiling approach, accompanied by bacterial 16S rDNA-, fungal 18S-ITS- and deep virome sequencing. Results were linked among each other and with clinical metadata such as GvHD, response to steroids, antimicrobial therapy and mortality. Longitudinal profiling of ASCT patients revealed a significant loss of bacterial, fungal and viral diversity following ASCT. At both centers, the effect was most pronounced in the early post-transplant period. Patients that developed GI-GVHD had the lowest diversity scores (Panel 1). GVHD patient samples were dominated by Enteroccocus and Candida, and loss of Caudovirales species, indicative of deep dysbiosis effecting all intestinal communities. ASCT had a strong impact on microbiome function and their ability to produce metabolites. We assayed each sample for production of metabolites with reported protective effects: SCFAs (acetate, butyrate and propionate), indoles (indole-3-carboxylaldehyde, ICA) and BAs (deoxycholic and lithocholic acid). When admitted to the transplantation unit (timepoint "conditioning") most patients had rich metabolite expression profiles. In the early post-transplant period, metabolite levels became progressively more depleted. GVHD patients displayed a nearly complete loss of metabolites (Panel 2a). Importantly, levels of the metabolite ICA at early timepoints could predict the occurrence of GVHD, leading us to consider prophylactic administration in future studies. We performed beta diversity analysis to identify clinical factors that had the highest impact on microbial communities. As expected, we noted that administration of broad-spectrum antibiotics had a profound impact of bacteria, fungi and viruses; but also had a significant negative effect on metabolites levels. Lastly, we report on a case of successful treatment of severe GI-GVHD with fecal microbiota transplant. Response to treatment was characterized by the recipient adopting the FMT donor's rich metabolite expression profile (Panel 2b) . To our knowledge, this is the first multicenter study that combines bacteriome, mycobiome, virome and metabolome analyses a longitudinal fashion in matched patient cohorts. Our results are consistent with previous findings that there are major alterations in gut microbiome and metabolite composition after ASCT. We expand upon those findings by characterizing the time course of phylogenetic alterations and their functional consequences. Those alterations play an important role in GvHD pathogenesis and might serve as potential biomarkers to identify patients at high risk for developing lethal GvHD early on. Our results highlight two strategies for targeted microbiome-based interventions: (1) preventing loss of microbial communities by restrictive use of antibiotics and (2) prophylactic administration of metabolite cocktails. Figure 1 Figure 1. Disclosures No relevant conflicts of interest to declare.