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Recent studies demonstrate that gut microbiota regulate tumor response to immune checkpoint blockade. Still, the mechanisms by which microbiota control tumor response to immunotherapy remain unclear. We colonized germ-free mice with cultured human-derived microbiota prior to tumor inoculation. While no human donor microbiota altered tumor growth, two distinct gut microbiota inhibited tumor response to anti-PD-L1. Colonization with non-responder microbiota led to reduced tumor immune cell infiltration and modified antigen presenting cell phenotype. RNA sequencing of tumor-infiltrating CD8+ T cells revealed enrichment for stem cell-like genes in non-responders and reduced effector-like expression conferring cytotoxic potential. Antibiotic depletion and microbiota transplant restored anti-PD-L1 response in non-responders, with expansion of effector cells and cytotoxicity. Concomitant blockade of TNFα similarly improved response to anti-PD-L1 and increased cytotoxicity. These results demonstrate inhibitory roles for the microbiota in checkpoint blockade and reveal the potential for microbiota transplant and TNF blockade to overcome microbiota-mediated resistance.

Fecal IgA production depends on colonization by a gut microbiota. However, the bacterial strains that drive gut IgA production remain largely unknown. By accessing the IgA-inducing capacity of a diverse set of human gut microbial strains, we identified Bacteroides ovatus as the species that best induced gut IgA production. However, this induction varied biomodally across different B. ovatus strains. The high IgA-inducing B. ovatus strains preferentially elicited more IgA production in the large intestine through both T-cell-dependent and T-cell-independent B cell-activation pathways. Remarkably, a low-IgA phenotype in mice could be robustly and consistently converted into a high-IgA phenotype by transplanting a multiplex cocktail of high IgA-inducing B. ovatus strains but not individual ones. Thus, microbial strain specificity is essential for the optimal induction of high-IgA responses in the gut. Our results highlight the critical importance of microbial strains in driving phenotype variation in the mucosal immune system and provide a strategy to robustly modify a gut immune phenotype, including IgA production.

Summary Fecal IgA production depends on colonization by a gut microbiota. However, the bacterial strains that drive gut IgA production remain largely unknown. Here, we assessed the IgA-inducing capacity of a diverse set of human gut microbial strains by monocolonizing mice with each strain. We identified Bacteroides ovatus as the species that best induced gut IgA production. However, this induction varied bimodally across different B. ovatus strains. The high IgA-inducing B. ovatus strains preferentially elicited more IgA production in the large intestine through the T cell-dependent B cell-activation pathway. Remarkably, a low-IgA phenotype in mice could be robustly and consistently converted into a high-IgA phenotype by transplanting a multiplex cocktail of high IgA-inducing B. ovatus strains but not individual ones. Our results highlight the critical importance of microbial strains in driving phenotype variation in the mucosal immune system and provide a strategy to robustly modify a gut immune phenotype, including IgA production.

International audience; Background: It has been demonstrated in many chronic conditions, including inflammatory bowel disease (IBD), that better patient knowledge about pathology and treatment improves the course and management of disease. The aim of this study was to develop an updated self-questionnaire to assess patients' level of knowledge of IBD. Methods: The IBD-INFO included 3 parts: an original part (Q1) and 2 parts from the translation of the preexisting questionnaires Crohn's and Colitis Knowledge score (CCKNOW) (Q2) and Crohn's and Colitis Pregnancy Knowledge score (CCPKNOW) (Q3). The reliability and discriminatory ability of the questionnaire were validated in 3 groups of non-IBD volunteers with various theoretical knowledge levels. The final questionnaire (64 validated questions) was then tested on 364 in- and out- IBD patients from 4 French university hospitals. The score for each part of the questionnaire was calculated, and factors associated with low scores were identified by univariate and multivariate logistic regression analyses. Results: The scores obtained by the 3 non-IBD volunteer groups differed significantly (P \textless 0.0001), and the IBD-INFO questionnaire showed excellent internal reliability and consistency (α = 0.98). The median total score obtained by the IBD patients was 27/64 (range, 0-59), and scores for Q1, Q2, and Q3 were, respectively, 10/23 (range, 0-21), 11/24 (range, 0-23), and 4/17 (range, 0-16). In multivariate analysis, lack of a university degree, not being a member of a patient association, not receiving anti-tumor necrosis factor alpha (anti-TNFα) treatment, duration of IBD

Recent studies demonstrate that inflammatory signals regulate hematopoietic stem cells (HSCs). Granulocyte-colony stimulating factor (G-CSF) is often induced with infection and plays a key role in the stress granulopoiesis response. However, its effects on HSCs are less clear. Herein, we show that treatment with G-CSF induces expansion and increased quiescence of phenotypic HSCs, but causes a marked, cell-autonomous HSC repopulating defect associated with induction of toll-like receptor (TLR) expression and signaling. The G-CSF-mediated expansion of HSCs is reduced in mice lacking TLR2, TLR4 or the TLR signaling adaptor MyD88. Induction of HSC quiescence is abrogated in mice lacking MyD88 or in mice treated with antibiotics to suppress intestinal flora. Finally, loss of TLR4 or germ free conditions mitigates the G-CSF-mediated HSC repopulating defect. These data suggest that low level TLR agonist production by commensal flora contributes to the regulation of HSC function and that G-CSF negatively regulates HSCs, in part, by enhancing TLR signaling.

Haematopoietic stem cells (HSCs) primarily reside in the bone marrow where signals generated by stromal cells regulate their self-renewal, proliferation and trafficking. Endosteal osteoblasts and perivascular stromal cells including endothelial cells, CXCL12-abundant reticular cells, leptin-receptor-positive stromal cells, and nestin-green fluorescent protein (GFP)-positive mesenchymal progenitors have all been implicated in HSC maintenance. However, it is unclear whether specific haematopoietic progenitor cell (HPC) subsets reside in distinct niches defined by the surrounding stromal cells and the regulatory molecules they produce. CXCL12 (chemokine (C-X-C motif) ligand 12) regulates both HSCs and lymphoid progenitors and is expressed by all of these stromal cell populations. Here we selectively deleted Cxcl12 from candidate niche stromal cell populations and characterized the effect on HPCs. Deletion of Cxcl12 from mineralizing osteoblasts has no effect on HSCs or lymphoid progenitors. Deletion of Cxcl12 from osterix-expressing stromal cells, which include CXCL12-abundant reticular cells and osteoblasts, results in constitutive HPC mobilization and a loss of B-lymphoid progenitors, but HSC function is normal. Cxcl12 deletion from endothelial cells results in a modest loss of long-term repopulating activity. Strikingly, deletion of Cxcl12 from nestin-negative mesenchymal progenitors using Prx1-cre (Prx1 also known as Prrx1) is associated with a marked loss of HSCs, long-term repopulating activity, HSC quiescence and common lymphoid progenitors. These data suggest that osterix-expressing stromal cells comprise a distinct niche that supports B-lymphoid progenitors and retains HPCs in the bone marrow, and that expression of CXCL12 from stromal cells in the perivascular region, including endothelial cells and mesenchymal progenitors, supports HSCs.

Abstract 510 Hematopoietic stem cells (HSCs) reside in a specialized microenvironment in the bone marrow that provides key signals required for HSC maintenance. Neither the stromal cell population(s) that comprise this stem cell niche nor their HSC-regulatory signals are well defined. In particular, there is controversy about the relative importance of the endosteal niche, which is comprised of osteoblasts and their progenitors, and the perivascular niche, which is comprised of endothelial cells, CXCL12-abundant reticular (CAR) cells, and mesenchymal stem and progenitor cells (including Nestin-GFP+ cells). CXCL12 is a key component of the stem cell niche that regulates HSC trafficking and function. CXCL12 is constitutively expressed by several stromal cell populations, including endothelial cells, osteoblasts, and perivascular stromal cells. Here we generated a floxed allele of Cxcl12 to conditionally delete Cxcl12 from candidate niche cells in the bone marrow and assess the effect on HSCs. Deletion of Cxcl12 in endothelial cells and mature osteoblasts was mediated by the Tie2-Cre recombinase (Cre) and osteocalcin (Oc)-Cre transgenes, respectively. To target Cxcl12 deletion in CAR cells and osteoprogenitors, we used the osterix (Osx)-Cre transgene. Finally, to target multipotent mesenchymal progenitors, we used the Prx1-Cre transgene. Prx1 is a transcription factor expressed early during limb bud mesoderm development, and Prx1-Cre targets all cells derived from limb bud mesoderm. We first performed lineage mapping studies using transgenic mice carrying a knock-in of the green fluorescent protein (GFP) gene into the Cxcl12 locus. As reported previously, the highest CXCL12 expression was observed in CAR cells, which is a heterogeneous perivascular stromal cell population that contains osteoprogenitors. Lineage mapping with Osx- and Prx1-Cre show that both transgenes mediate efficient and equivalent recombination in nearly all mature osteoblasts, osteoblast progenitors, and CAR cells. Prx1-Cre, but not Osx-Cre, also targets a novel subset of PDGFRα+ Sca+ mesenchymal progenitors. We show that deletion of Cxcl12 from mature osteoblasts has no effect on HSC number or function. Deletion of Cxcl12 from Osx-Cre-targeted stromal cells, which includes osteoprogenitors and CAR cells, results in constitutive mobilization of hematopoietic progenitors; however, HSC number and function are normal. Cxcl12 deletion in endothelial cells results in a modest loss of long-term repopulating activity. Strikingly, deletion of Cxcl12 in mesenchymal progenitors is associated with a marked loss of HSCs and HSC quiescence. In addition to endothelial cells, we thus identify a novel Prx1-Cre targeted subset of mesenchymal progenitors that appears to be necessary to support HSCs. These data show that expression of CXCL12 from stromal cells in the perivascular region is required for HSC maintenance. Disclosures: No relevant conflicts of interest to declare.

Endothelial cell (EC) dysfunction is a key feature of multiple organ injury, the primary cause of fatality seen in critically ill patients. Although the development of EC dysfunction in the heart and lung is well studied in sepsis, it remains unclear in the liver. Herein, we report that liver sinusoidal ECs (LSECs; defined as CD146(+)CD45(-)) exhibit increased intercellular adhesion molecule-1 (CD54) and Fas in response to sepsis induced by cecal ligation and puncture (CLP). By using magnetically enriched LSEC (CD146(+)) populations, we show evidence of marked apoptosis, with a twofold decline in viable LSECs in CLP animals compared with sham controls. These changes and increased serum alanine aminotransferase levels were all mitigated in septic Fas(-/-) and Fas ligand(-/-) animals. Although we previously reported increased numbers of Fas ligand expressing CD8(+) T lymphocytes in the septic liver, CD8(+) T-cell deficiency did not reverse the onset of LSEC apoptosis/damage. However, Kupffer cell depletion with clodronate liposomes resulted in greater apoptosis and Fas expression after CLP and a decrease in glycoprotein 130 expression on LSECs, suggesting that STAT3 activation may protect these cells from injury. Our results document a critical role for death receptor-mediated LSEC injury and show the first evidence that Kupffer cells are essential to the viability of LSECs, which appears to be mediated through glycoprotein 130 expression in sepsis.

Recent studies demonstrate that inflammatory signals regulate hematopoietic stem cells (HSCs). Granulocyte-colony stimulating factor (G-CSF) is often induced with infection and plays a key role in the stress granulopoiesis response. However, its effects on HSCs are unclear. Herein, we show that treatment with G-CSF induces expansion and increased quiescence of phenotypic HSCs, but causes a marked, cell-autonomous HSC repopulating defect. RNA profiling and flow cytometry studies of HSCs from G-CSF treated mice show that multiple toll- like receptors (TLRs) are upregulated in HSCs upon G-CSF treatment, and gene set enrichment analysis shows enhancement of TLR signaling in G-CSF-treated HSCs. G-CSF-induced expansion of phenotypic HSCs is reduced in mice lacking the TLR signaling adaptors MyD88 or Trif, and the induction of quiescence is abrogated in mice lacking these adaptors. Furthermore, loss of TLR4 mitigates the G-CSF-mediated HSC repopulating defect. Interestingly, baseline HSC function is also dependent on TLR signaling. We show that HSC long-term repopulating activity is enhanced in Tlr4-/- and MyD88-/- mice, but not Trif-/- mice. One potential source of TLR ligands affecting HSC function in the bone marrow is the gut microbiota. Indeed, we show that in mice treated with antibiotics to suppress intestinal flora, G-CSF induced HSC quiescence and hematopoietic progenitor mobilization are attenuated. Moreover, in germ free mice, HSC long-term repopulating activity is enhanced. Collectively these data suggest that low level TLR agonist production by commensal flora contributes to the regulation of HSC function and that G-CSF negatively regulates HSCs, in part, by enhancing TLR signaling. Our finding of enhanced TLR signaling upon G-CSF treatment, and the mitigation of G-CSF’s effects in mice deficient for TLR signaling or commensal organisms, suggest that TLR antagonists and/or agonists may ultimately be used clinically to enhance engraftment following bone marrow transplantation or applied toward the treatment of patients with bone marrow failure. Disclosures: No relevant conflicts of interest to declare.