2024

B cell tolerance and autoimmunity: Lessons from repertoires

Jacques Deguine and Ramnik Xavier review the current knowledge on B cell repertoire analyses, focusing on their implications for autoimmunity. These studies demonstrate that a failure of tolerance occurs at multiple independent checkpoints in different autoimmune contexts, particularly during B cell maturation, plasmablast differentiation, and within germinal centers. These failures are marked by distinct repertoire features that may be used to identify disease- or patient-specific therapeutic approaches.  

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Discovery of disease-adapted bacterial lineages in inflammatory bowel diseases

IBD is associated with reduced species diversity of gut bacteria, but figuring out which strains are involved, and how, has proven challenging. A new study led by Christopher Smillie analyzed fecal metagenomes and identified hundreds of ancient strains enriched in IBD patients. These strains have adapted over millions of years to survive in the difficult environment imposed by inflammation, outcompeting healthy strains during bouts of heightened inflammation. Moreover, health-associated strains were predictive of an inflammation biomarker, indicating their possible protective role and potential as a diagnostic tool.

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CSIBD investigator Andrew Chan awarded Cancer Grand Challenges grant for early-onset cancer research

Andrew Chan is co-leading the global team known as PROSPECT, which received a grant of up to $25 million over five years from Cancer Grand Challenges, to study early-onset colorectal cancer. Co-founded by Cancer Research UK and the National Cancer Institute, Cancer Grand Challenges supports a community of multidisciplinary teams to unite, think differently, and tackle some of cancer’s toughest challenges. PROSPECT aims to understand the pathways, risk factors, and molecules involved in the development of early-onset colorectal cancer. The team’s vision is to understand and ultimately reverse the network of causal factors that disrupts normal biological processes to promote this disease. 

Identification of highly selective SIK1/2 inhibitors that modulate innate immune activation and suppress intestinal inflammation

Insights from human disease genetics provide opportunities to devise mechanistic strategies for the development of new therapeutics. IL-10 and several pathway regulators, including salt inducible kinases (SIKs), have been implicated in genetic susceptibility to IBD. Ramnik Xavier and Dan Graham collaborated on a structure-based design strategy for developing potent, highly selective SIK inhibitors to dampen intestinal inflammation. The investigators identified SIK1/2 inhibitors that suppress pro-inflammatory while inducing anti-inflammatory cytokine responses in human myeloid cells. Further, oral dosing of these inhibitors ameliorated disease in a murine model of colitis. These findings define an approach to generate highly selective SIK1/2 inhibitors and demonstrate their ability to suppress pathological inflammation in vivo.

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Linking microbial genes to plasma and stool metabolites uncovers host-microbial interactions underlying ulcerative colitis disease course

Understanding how the microbiome contributes to inflammatory diseases requires the identification of microbial effector molecules. Ramnik Xavier and Lee Denson at the Cincinnati Children’s Hospital Medical Center integrated paired metagenomics and metabolomics from the PROTECT pediatric UC cohort with culturomics to identify host-microbial interactions across disease severity. Microbial changes uncovered in severe disease included an increase in bacteria, such as Veillonella parvula, that typically colonize the oral cavity. Metabolite changes in severe disease included dipeptides and bile acids in stool and polyamines in plasma. The investigators linked V. parvula to production of immunomodulatory tryptophan metabolites in culture and demonstrated that this bacteria can metabolize immunosuppressive thiopurine drugs. These findings establish an approach to link microbes to metabolite changes in disease pathology and have important implications for efficacy of therapeutic treatment.

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Register for the upcoming Keystone Symposium on Innate Immunity Across the Molecular, Cellular, Tissue, and Therapeutic!
April 9-12, 2024
Banff, Canada

Organized by Kate Jeffrey, Ramnik Xavier and Xu Zhou, this conference will provide multidisciplinary perspectives on new horizons and the unexpected in innate immunity. The program will highlight innovative techniques and novel read outs of innate immunity at the molecular, cellular and tissue level to place importance of innate immunity in human health. We will also take a deep dive into clinical aspects of disease and contemporary drug discovery approaches to harness for innate immune modulation. This meeting will be a unique forum for researchers from diverse and traditionally non-overlapping fields (immunology, metabolism, artificial intelligence, drug discovery, structural biology), to build fresh ideas and collaborations for the next chapter of innate immune discovery and translation. The conference will be held jointly with the Keystone Symposium on Systems and Engineering Immunology: Advancing Immunological Insights in Health and Disease, to enable cross-disciplinary insights and collaborations towards utilization of systems immunology tools to advance our understanding of innate immunity in health and disease.

Deadlines for abstracts and discounted registration are approaching. See event details here.

ChREBP is activated by reductive stress and mediates GCKR-associated metabolic traits

A single glucokinase regulator (GCKR) allele has been linked to over 100 human traits and diseases. Alan Mullen, Vamsi Mootha, Russell Goodman, and colleagues examined the mechanism underlying these associations and found that multiple metabolic traits associated with GCKR are influenced by hepatic reductive stress. The investigators detailed a new mechanism by which reductive stress activates the ChREBP transcription factor and demonstrated that reductive stress induces GCKR-associated traits such as increased hepatic fat and circulating triglycerides. Moreover, a transcriptional signature of hepatic reductive stress was upregulated in fatty liver disease and downregulated after bariatric surgery in humans. These findings suggest a role for a GCKR-reductive stress-ChREBP axis in multiple human metabolic disorders.

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2023

The Gene Lay Institute of Immunology and Inflammation

Brigham and Women’s Hospital announced that a momentous $100 million gift from BioLegend founder and CEO Gene Lay, MS, DVM has established The Gene Lay Institute of Immunology and Inflammation. This gift opens a promising new chapter of better understanding the roles that immunology and inflammation play in disease. Vijay Kuchroo, DVM, PhD will serve as director of this new institute along with vice directors Arlene Sharpe, MD, PhD and Ramnik Xavier, MD, PhD.

Learn more about the institute here.

Gut microbial metabolism of 5-ASA diminishes its clinical efficacy in inflammatory bowel disease

To identify the microbes and enzymes responsible for inactivating the IBD drug 5-aminosalicylic acid (5-ASA), Curtis Huttenhower and colleagues developed a workflow combining metagenomic, metatranscriptomic, and metabolomic data from 132 controls and IBD patients. The investigators associated 12 previously uncharacterized microbial acetyltransferases belonging to two superfamilies (thiolases and acyl-CoA N-acyltransferases) with 5-ASA inactivation and confirmed that representatives from both families are able to acetylate 5-ASA in vitro. Further analysis revealed that three of these microbial thiolases and one acyl-CoA N-acyltransferase are associated with an increased risk of treatment failure among 5-ASA users. Overall, these data address a longstanding challenge in IBD management, outline a method for the discovery of previously uncharacterized gut microbial activities, and advance the potential of microbiome-based personalized medicine.

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Germline determinants of esophageal adenocarcinoma

Barret’s esophagus (BE) is a strong risk factor for esophageal adenocarcinoma (EAC), but clinical risk factors are insufficient to account for progression from BE to EAC. Omer Yilmaz collaborated on a study that examined monoallelic, pathogenic germline mutations in cancer-predisposing genes in 640 patients with EAC to account for this risk. Pathogenic germline mutations were found in 9% of progressors, with ATM and CHEK2 being the two most frequently mutated genes, compared to 2.7% of non-progressors. This study suggests that the mutations identified, along with environmental factors, facilitate progression of BE to EAC.

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Chronic metabolic stress drives developmental programs and loss of tissue functions in non-transformed liver that mirror tumor states and stratify survival

Alex Shalek, Wolfram Goessling, Omer Yilmaz, Georg Lauer, and colleagues demonstrated how chronic stress drives adaptations that balance cell survival and homeostatic functions. The researchers applied longitudinal single-cell multiomics to a mouse model of chronic metabolic stress and dissected temporal adaptation trajectories in hepatocytes. They further developed computational methods to identify cell-extrinsic and cell-intrinsic drivers of hepatocyte adaptation, and experimentally validated their findings. Collectively, this work defined cellular features of liver adaptation to chronic stress as well as their links to long-term disease outcomes and cancer hallmarks.

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Alterations in the gut microbiome implicate key taxa and metabolic pathways across inflammatory arthritis phenotypes

Several subtypes of musculoskeletal diseases share genetic backgrounds with IBD, and the microbial perturbations observed in these conditions overlap with IBD microbiome phenotypes. To better understand the involvement of the gut microbiome, Curtis Huttenhower and colleagues profiled stool metagenomes from 221 patients with rheumatoid arthritis, ankylosing spondylitis, or psoriatic arthritis plus 219 controls. The findings indicated that distal inflammatory conditions result in similar alterations to gut microbial composition as do local conditions, such as IBD, albeit with lower magnitude. Concurrent with taxonomic shifts, several differentially encoded pathways were identified in the inflammatory arthritis gut microbiome, including iron sequestration and vitamin B salvage and biosynthesis. This work expands understandings of gut microbiome perturbation in response to systemic inflammation.

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Challenges and opportunities in sharing microbiome data and analyses

Curtis Huttenhower and colleagues addressed gaps in the identification and use of resources for data sharing and reproducibility that have emerged as microbiome data, metadata, and analytical workflows increase in volume and complexity. The authors outlined current challenges, best practices, and opportunities for progress in data sharing in microbiome research.

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The landscape of immune dysregulation in Crohn’s disease revealed through single-cell transcriptomic profiling in the ileum and colon

Ramnik Xavier charted the cellular landscape of the terminal ileum and colon at single-cell resolution in patients with Crohn’s disease (CD), revealing location- and cell type-specific alterations during active inflammation. The study additionally validated three regulators of fibroblast collagen induction that may represent novel targets for the management of fibrotic complications.

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Remodeling of colon plasma cell repertoire within ulcerative colitis patients

To address the elusive role of plasma cells in ulcerative colitis (UC) pathogenesis, Ramnik Xavier profiled B cells from the colons of UC patients with active inflammation, UC patients in remission, and healthy individuals. Active inflammation disrupted the B cell landscape throughout the colon, causing transcriptional changes, clonal expansion, and immunoglobulin isotype skewing.

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Centenarians have a diverse gut virome with the potential to modulate metabolism and promote healthy lifespan

Individuals who reach 100 or more years of age (known as centenarians) are less susceptible to illnesses associated with aging, such as chronic inflammation and infectious diseases. Ramnik Xavier revealed that the viral component of the centenarian gut microbiome is more diverse than other age groups. The study also revealed metabolic pathways enriched in centenarian viromes that may promote healthy lifespan.

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Association of distinct microbial signatures with premalignant colorectal adenomas

Daniel Chung studied the gut microbiome in relation to premalignant colorectal adenomas, finding that the two major adenoma subtypes were associated with distinct microbioal profiles that also correlated with diet and medication. This study illustrated that the gut microbiome can serve as an integrator of environmental exposures that are a major risk factor for developing colorectal cancer.

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Lectin-Seq: A method to profile lectin-microbe interactions in native communities

Human lectins are key components of innate immunity, but their specificity for microbial species is not well understood. To address this, Laura Kiessling developed a method to profile lectin–microbe interactions in native communities, called Lectin-seq, and applied it to the human microbiome using mannose-binding lectin and interlectin-1. Microbial interactions with these two lectins differed in composition and diversity, revealing striking differences in microbial recognition by human lectins.

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HLA-II immunopeptidome profiling and deep learning reveal features of antigenicity to inform antigen discovery

Class II human leukocyte antigen (HLA-II) is remarkably polymorphic, allowing for presentation of diverse antigens to T cells but also forming the basis for genetic associations with a range of immunopathologies. Daniel Graham developed Context Aware Predictor of T cell Antigens (CAPTAn) to predict antigens based on HLA-II binding properties and structural features and discovered novel T cell epitopes from human gut microbes and SARS-CoV-2.

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Leveraging polygenic enrichments of gene features to predict genes underlying complex traits and diseases

Hilary Finucane introduced a new tool, polygenic priority score (PoPS), that learns trait-relevant gene features, such as cell-type-specific expression, to prioritize genes identified by genome-wide association studies. When combined with orthogonal methods, PoPS prioritized over 10,000 unique gene-trait pairs across 113 complex traits and diseases with high precision, finding not only well-established relationships but nominating new genes at unresolved loci.

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CXCL10 chemokine regulates heterogeneity of the CD8+ T cell response and viral set point during chronic infection

Andrew Luster identified an important role of the CXCL10-CXCR3 chemokine signaling axis in control of T cell heterogeneity during chronic infection. Chronic CXCL10 signaling reduced survival of stem-like cells and favored differentiation of T cells, resulting in impaired persistence of T cells over time.

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CXCR6 positions cytotoxic T cells to receive critical survival signals in the tumor microenvironment

Cytotoxic T lymphocyte (CTL) responses against tumors are maintained by stem-like memory cells that self-renew but also give rise to effector-like cells that gradually lose their anti-tumor activity and lead to tumor tolerance. Thorsten Mempel demonstrated that the chemokine receptor CXCR6 positions effector-like CTLs to receive survival signals in the tumor microenvironment to maximize their anti-tumor activity before progressing to irreversible dysfunction.  

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2022

The gut virome autonomously influences intestinal homeostasis and IBD phenotypes

A new study from Kate Jeffrey and colleagues compared the enteric virome from patients with IBD and control subjects, utilizing biopsies from the Prospective Registry in IBD Study at MGH (PRISM) cohort. The authors demonstrated that IBD viromes elicit and exacerbate inflammation while non-IBD viromes are anti-inflammatory and, furthermore, capable of suppressing inflammation driven by IBD-associated viruses. Protective effects of the virome were dependent on the host virus receptor MDA5. Together, these findings show that perturbations to the enteric virome or viral sensing pathways contribute to IBD and expand the therapeutic potential of the gut microbiome.

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2021

Multi-omic markers of IBD treatment

By Broad Communications

Response to treatment for inflammatory bowel disease (IBD) is difficult to predict because of the complex intestinal microbiome and lack of predictive biomarkers. Visiting scientist Jonathan Wei Jie Lee, group leader Damian Plichta, core institute member Ramnik Xavier of the Infectious Disease and Microbiome Program and colleagues profiled stool and blood samples from patients with IBD before treatment and then tracked treatment response. They used modeling and machine learning to identify metagenomic, metabolomic and proteomic markers that could predict which patients would achieve remission. Biomarkers varied by therapy class, with microbial diversity in the gut being a strong indicator of anti-cytokine therapy success. These response markers could lead to better IBD treatment selection.
 
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The Global Microbiome Conservancy

Improving our understanding of how the microbiome interacts with its human host has been hindered in part by the limited number of bacterial isolates available to test mechanistic hypotheses. Furthermore, microbiome research has centered largely on industrialized European and North American communities, providing little information about the microbiomes of non-industrialized populations that are often more diverse. To address these obstacles, CSIBD researchers are leading an important initiative: the Global Microbiome Conservancy (GMbC) aims to build extensive archives of human gut isolates from communities around the world. The GMbC isolate collection comprises approximately 10,000 gut bacteria and their genomes from under-represented populations. This collection was used to demonstrate that gut bacteria continuously acquire new capabilities based on the lifestyle of the human host.

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2020

Highlight: Pathway Paradigms Revealed from the Genetics of Inflammatory Bowel Disease

By Katie E. Golden, MD

In a recently published paper in Nature, CSIBD faculty provide a comprehensive review of the scientific advances that have brought us to our current understanding of inflammatory bowel disease (IBD) pathophysiology, and how this has provided valuable insights into the metabolic pathways that contribute to microbiome-related disorders on a larger scale. Their in-depth survey illustrates how the evolution of genetics-based research has built a valuable framework to explore the clinical implications of the molecular pathways that contribute to IBD development and progression.

Our understanding of inflammatory bowel disease (IBD) has dramatically evolved over the last decade as a result of advanced genetic, immunology, and microbiome research. We have moved away from a traditional model that categorizes the disease into two subtypes (Ulcerative Colitis and Crohn’s Disease), to understand IBD as a heterogeneous condition with varied phenotypes resulting from a complex interaction between genetic and environmental factors. Investigating the underlying pathophysiology of an inherently complex condition has demanded the development of innovative research technology, particularly in functional genetics, which in turn has resulted in broader applications to human health and disease.

In a recently published paper, authors Graham and Xavier provide an eloquent and comprehensive review of the scientific advances that have brought us to our current understanding of IBD pathophysiology, and how this has provided valuable insights into the metabolic pathways that contribute to microbiome-related disorders on a larger scale. Their in-depth survey of the most relevant IBD discoveries inspires an appreciation of how the evolution of genetics-based research has successfully built a valuable framework for the biomedical research community to explore the clinical implications of the molecular pathways that contribute to disease development and progression.

The inherent complexity of IBD has long been apparent from the observed phenotypic variation, unpredictable treatment response from patient to patient, and even the extra-intestinal systemic manifestations of the disease. Identifying causal genes and their variants within risk loci was only the first step; scientists had to understand how genetic variants translated to causal disease mechanisms to make a clinical impact. This pressure inspired the development of exome sequencing, CRISPR technology, and single-cell genomics to capture in vivo data demonstrating how intestinal microbiota affect transcriptional activity. This expansion of functional genomics yielded a blueprint of IBD pathology as a complicated interplay between gut mucosal immunity and aberrant antimicrobial responses.

The elaboration of cellular and molecular pathways that lead to IBD pathogenesis has created opportunities for therapeutic intervention, as well as biomarker development to predict and monitor disease severity and treatment response. This includes the identified roles of epithelial barrier function, mucosal immunity and stem cell response, microbe-sensing pathways, and cytokine networks that have important implications for both intestinal homeostasis as well as systemic inflammatory responses. In reviewing these discoveries, Graham and Xavier move us beyond the oversimplification of IBD as a genetic disease that is triggered by environmental conditions, to help us understand how it arises from a complicated relationship between host genetics, a dynamic microbiome that influences host metabolism, and resultant dysregulation of mucosal epithelium and immunity.

Read the review.
Celebrate International Women's Day by Sharing Pioneering Work from CSIBD Investigator Kate Jeffrey

Courtesy of the Kenneth Rainin Foundation

With her lab at Harvard Medical School and Massachusetts General Hospital, immunologist Dr. Kate Jeffrey has embarked on a new frontier to research the human virome. It holds promise for treatment breakthroughs for Inflammatory Bowel Disease.

Watch the video to learn about her breakthrough moment.

The Kenneth Rainin Foundation and the CSIBD are proud to celebrate International Women’s Day on March 8 and honor the achievements of women like Dr. Jeffrey around the world.

A Requirement for Argonaute 4 in Mammalian Antiviral Defense

Mammals have four RNA interference (RNAi) and micro RNA (miRNA) effector proteins: Argonautes 1–4, AGO1–AGO4 for short. A recent study in Cell Reports by Adiliaghdam et al. sought to determine their individual functions during viral infections, revealing that cells deficient in AGO4 are more susceptible to viral infection than those deficient in AGO1 or AGO3. Moreover, AGO4-deficient mice infected with influenza displayed a significantly higher viral burden and titers in vivo. Together, the authors establish a unique and essential role for AGO4 in mammalian antiviral defense. 

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RICOPILI: Rapid Imputation for COnsortias PIpeLIne

Challenges in analyzing genome-wide association studies (GWAS) arise in the rapid processing of large-scale, multi-cohort GWAS. To address these, Lam et al. introduced RICOPILI, an open-sourced pipeline that integrates quality control, imputation and association analysis. RICOPILI features technical and genomic quality control in case-control and trio cohorts, genome-wide phasing and imputation, association analysis, meta-analysis, polygenic risk scoring, and replication analysis. Its framework allows scalable processing of GWAS data and is computationally efficient with portability to a wide range of high-performance computing environments. The design, implementation, and comparisons with other GWAS pipelines were published in Bioinformatics.

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Global IBD care in the 21st century

The changing global landscape of inflammatory bowel diseases (IBD) will impact their future burden on care. In a review published in Clinical Gastroenterology and Hepatology, Ananthakrishnan et al. highlight recent trends in epidemiological patterns of IBD, explore modifiable environmental exposures that may reduce incidence of IBD, and discuss the evolving healthcare burden of IBD – offering an outline of key research and clinical steps toward sustainable global IBD care.

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Sulfur-metabolizing gut bacteria linked to colorectal cancer risk in men

Colorectal cancer (CRC) is the third most frequently occurring and third most lethal form of cancer in the US. As a genetic predisposition is unclear in most new cases, lifestyle changes are considered a top priority for disease prevention. Nguyen et al. investigate the impact of diet, specifically on the composition and function of the gut microbiome, on CRC risk in a cohort of men enrolled in the prospective Health Professionals Follow-up Study. The results, published in Gastroenterology, associated a dietary pattern (high in processed meats and low-calorie drink and low in vegetables and legumes) with sulfur-metabolizing bacteria, which have been implicated in CRC development and are known to produce genotoxic metabolites. The authors were further able to demonstrate that the presence of these bacteria was coupled to their metabolic activities. Overall, this study provides a rationale for dietary modification as a means of modulating the gut microbiome to mediate disease risk.

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Summary: Growth Effects of N-acylethanolamines on Gut Bacteria Reflect Altered Bacterial Abundances in Inflammatory Bowel Disease

By Katie E. Golden, MD

In a recently published study that takes a closer look at the role of the metabolome in the progression of inflammatory bowel disease (IBD), researchers identify a specific lipid metabolite that is abnormally abundant in IBD patients. Their subsequent investigations reveal how this metabolite stimulates the growth of species that are well established to be overrepresented in IBD patients. Remarkably, when they treated healthy stool samples with these specific lipids, they observed taxonomic shifts in bacterial populations that mirrored microbiome composition in IBD.

As our understanding of the pathophysiologic picture of inflammatory bowel disease (IBD) is evolving, current research is illustrating an increasingly complex relationship between gut microorganisms and the host’s immune system that drives disease. While the earliest microbiome research focused on the microbial taxonomic changes in IBD, scientists are now recognizing that the gut metabolome is of equal importance. Small molecules, derived from the environment as well as host and bacterial cellular processes, are proving to be an integral component of the dynamic microbiome that is so intimately linked to intestinal homeostasis and dysbiosis.

In a recent study published in Nature Microbiology, Fornelos et al. identify specific metabolites that play a role in the pathophysiology of IBD. The authors first identified lipid metabolites (N-acylethanolamines, or NAEs) that are differentially abundant in IBD, and then analyzed how they affect the growth of intestinal bacteria. They found that NAEs stimulated the growth of species that are well established to be aberrantly abundant in IBD patients, and furthermore restricted the growth of species that are depleted in disease. To analyze these findings under further scientific rigor, they treated healthy stool samples ex vivo with NAEs and analyzed bacterial populations changes. In comparison to controls, the investigators observed taxonomic shifts in bacterial populations that mirrored microbiome composition in IBD. More specifically, metagenomic analysis revealed two bacterial shifts that are well-established changes characteristically seen in IBD: enhanced growth of Enterobacteriaceae, as well as proliferation of Proteobacteria at the expense of Bacteroides species.

Their results implicated enhanced NAE production as an important contributor to the pathologic bacterial growth that underlies IBD. In the final phase of their investigation, they used metatranscriptomic analysis to analyze exactly how NAEs alter bacterial cellular processes. They found that the bacterial respiratory chain played a critical role in the metabolism of the metabolites, which in turn induced upregulated cellular metabolism of facultative aerobes (Enterobacteriaceae), and a subsequent pro-inflammatory feedback loop that further increased NAE production. Their work not only advances our understanding of the metabolome’s role in disease, but also successfully identifies the potential for NAEs as both a therapeutic target and a biomarker of disease severity in IBD patients.

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2019

Summary: Cryo-electron Microscopy Structures of Human Oligosaccharyltransferase Complexes OST-A and OST-B

By Katie E. Golden, MD

In a recent paper published in Science, investigators expand on prior CSIBD research to define the chemical structure of two important glycosylation enzymes. By combining advanced cryo-electron microscopy with traditional western blot analysis, scientists identify the subtle structural differences in two related human oligosaccharyltransferase complexes that accounts for their unique cellular functions.

Back in 2016, CSIBD researchers proposed a mechanism by which a gene-dense locus on chromosome 11, TMEM258, plays an important role in the pathogenesis of inflammatory bowel disease. They illustrated how it is a component of the oligosaccharyltransferase (OST) complex that is required for protein glycosylation, and without it, mice models demonstrated severe colonic inflammation.

In a more recent paper published in Science, researchers use cryo-electron microscopy to define the chemical structure of two human OST complexes that play an important role in secretory protein modification. This is not only an exciting discovery that builds on the work by Graham et al. in 2016, but is also an important example of advanced basic science research that unmasks physiologic mechanisms with potential clinical relevance.

To break it down, when proteins are translated from genetic material in the cell, those proteins need to be modified before they are functional. A process called N-glycosylation is one of the most common ways that proteins are modified, and is catalyzed by OST complexes located in the endoplasmic reticulum (a specialized membrane found inside mammalian cells that aids in protein synthesis). Humans have two distinct OST complexes: OST-A and OST-B. Despite similar molecular structures, these complexes have distinct functions in the glycosylation process. In this most recent paper by Ramírez et al., the authors discovered the specific catalytic subunits (STT3A and STT3B) that account for the unique substrate affinities of each complex. OST-A associates with the translocon and binds unfolded proteins to process the N-glycosylation sites needed for protein modification. OST-B, contrastingly, does not associate with the translocon but has a stronger affinity for glycosylation sites and is thus able to bind and process proteins that are partially folded and modified.

While the above is an oversimplification of a complicated process, this paper decisively identifies the subtle but specific structural changes that translate to unique enzymatic function. Given the ubiquitous nature of these cellular processes, Ramírez and his team have laid important groundwork for the design of N-glycosylation inhibitors, which could ultimately be used to augment specific disease processes in the clinical setting.

Read the study by Graham et al.

Read the study by Ramírez et al.

Migratory DCs activate TGF-β to precondition naïve T cell fate

The function of epithelial resident memory T (eTRM) cells is key to protect against previously encountered pathogens, but how eTRM cells are formed remained unclear. Mani et al. address this question in a study published in Science using a mouse model of skin vaccination. The authors show that during homeostasis, resting naïve CD8+ T cells in the lymph nodes are epigenetically primed to become eTRM cells through the activation of cytokine transforming growth factor β (TGF-β) by migratory dendritic cells. These results present a contrasting view of the preimmune T cell repertoire, in which naïve T cell fate potential is preconditioned and not less uniform than expected.

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BIO-ML: not your entomologist’s library

To facilitate mechanistic research aimed at understanding how the gut microbiome interacts with its human host, the CSIBD, Center for Microbiome Informatics and Therapeutics, and Broad Institute established the Broad Institute-OpenBiome Microbiome Library (BIO-ML). This phylogenetically diverse collection of gut bugs — described by Poyet et al. in Nature Medicine — contains thousands of bacterial isolates from healthy donors with corresponding longitudinal multi’omic data. As the microbiome field moves from characterization of structure and composition toward functional studies during health and disease, BIO-ML provides an unparalleled resource of clinically-relevant human gut strains, including hundreds implicated in inflammatory bowel diseases, for hypothesis-driven studies and microbiome-based therapeutic advancements.

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Assessing the impact of biologic therapy initiation on fatigue in IBD patients

A new study by Borren et al. published in the Journal of Crohn’s and Colitis examined the effects of biologic therapies used to treat inflammatory bowel diseases (IBD) on the persistent fatigue often experienced by patients. The study followed 326 IBD patients initiating either anti-TNF, vedolizumab, or ustekinumab over a one-year period. At therapy initiation, 198 patients (61%) reported significant fatigue, which was associated with female sex, depressive symptoms, active disease, and disturbed sleep. After 14, 30, and 54 weeks, 86 (70%), 55 (63%), and 44 (61%) of these patients remained fatigued. Clinical remission at each of these time points was associated with lower likelihood of fatigue; however, a significant proportion of patients continued to experience persistent fatigue after a year of biologic therapy.

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Ulcerative colitis rewires the human gut

The human gut represents a circuit – a network of interconnected components, in this case various types of cells, that performs a function. Disruptions in the circuit cause malfunctions, or diseases such as the chronic inflammatory condition ulcerative colitis (UC). Mapping the gut as a circuit holds diagnostics and therapeutic value; comparisons between healthy and disease states expose pathological disturbances and potential therapeutic entry points. In a study published in Cell, Smillie et al. generated such maps by analyzing single cells from the colons of healthy individuals and UC patients. The authors classified new cell types, associating them with disease and resistance to treatment, and pinpointed populations in which susceptibility genes function. This work provides new insights into complex interactions underlying UC that will lead to a better understanding of gut health and inflammation.

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Human Microbiome Project profiles Inflammatory Bowel Disease activity

Inflammatory bowel diseases (IBD) are characterized by chronic inflammation of the digestive tract, often involving periods of remission and relapse. Genetics, environment, and the gut microbiome – the community of microorganisms inhabiting the human intestines – contribute to these complex diseases and are the subjects of extensive research. As part of the Integrative Human Microbiome Project that aims to determine how microbiomes influence human health and disease, Lloyd-Price et al. collected data from 132 individuals for one year to survey alterations within IBD patients and their microbiomes during states of remission and relapse. The most comprehensive description of dynamic perturbations in IBD to date, this study identifies factors central to disease activity and paves the way for future research and clinical advances.

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Gut Sphingolipids send signals about health and disease

Sphingolipids, a signaling molecule and structural component of both bacterial and mammalian cell membranes, play a central role in regulating inflammation, immunity, growth, and cell survival. To date, the specific roles of bacterial sphingolipids in regulating innate immunity or metabolism in the mammalian gut have been largely unknown. Reporting in Cell Host & Microbe, Eric Brown, Ramnik Xavier, Hera Vlamakis, Clary Clish and colleagues describe sphingolipid metabolite alterations in stool as a defining signature in inflammatory bowel disease in humans and further demonstrate in mice that bacterial sphingolipid production plays a significant role in the host’s gut health and disease.

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2018

Eavesdropping on gut gossip

The gut's intestinal stem cells (ISCs) "talk" to other cell types to help maintain a robust and healthy cellular community. In this week's Cell, Moshe Biton, Adam Haber, Noga Rogel, Aviv Regev, Ramnik Xavier, and colleagues dive into one such conversation, between ISCs and T helper (Th) cells. They found that some ISCs express MCH II (a surface complex that activates Th cells), while Th cells produce cytokines (chemical messages) that influence ISCs’ behavior. The crosstalk may help maintain the right balance of immune activity in the gut, as well as a hardy stem cell pool. Read more in a Broad news story.

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Like taking microbes from a baby

In search of microbial triggers for type 1 diabetes (T1D), a team led by Tommi Vatanen, Curtis Huttenhower, and Ramnik Xavier analyzed nearly 11,000 metagenomes in stool samples from children at risk for T1D, collected monthly starting at three months of age. Known as The Environmental Determinants of Diabetes in the Young (TEDDY) study, it produced the most shotgun metagenomic microbiome profiles published for a single target population to date. Appearing in Nature, the work finds that the microbiome gains adult-like functions as early as one year of age, and suggests that short-chain fatty acids may protect against early-onset T1D.

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Summary: Antigen Discovery and Specification of Immunodominance Hierarchies for MHCII-restricted Epitopes

by Katie E. Golden, MD

For well over a decade, the world of immunology has been gaining traction as a core focus to better understand, and cure, many human diseases. The science and medical community alike have gained appreciation for the role of immunological processes in infectious diseases, autoimmune diseases, and cancer. As the prevalence of these conditions increases, there has never a more critical time for researchers to better understand the immune system and its potential for therapeutics.

Behind the development of new and exciting immunotherapy and pharmaceutical interventions is rigorous, basic science research that forms the foundation upon which we can develop these advanced treatments. We still have a lot to learn about how the human immune system functions, how it can both keep us healthy or lead to disease, and how we can best study these mechanisms. In the newly published paper by Graham et al. in Nature Medicine, immunologists and researchers take on the difficult task of identifying the key components of immunologic processes.

In their investigation, the authors developed a way to identify the T cell epitopes that play a dominant role in antigenicity. More specifically, they outline a unique approach to identifying and predicting the specific molecules that initiate clinically significant immune responses. They focused on epitopes associated with major histocompatibility complex II (MHCII), which are the key proteins that bind the T cell to activate immune mechanisms implicated in both health and disease. Using a broad, unbiased survey of proteins, they developed a model that predicts dominant MHCII epitopes on a genome-wide scale.

This essentially provides researchers with the tool to take a collection of bacterial species, for example from the human gut microbiome, and create a map of the immunodominant epitopes. This is an important step in identifying the antigenic pathways that lead to development and propagation of disease (such as in inflammatory bowel disease, in keeping with the microbiome example). When they put their model to the test, it accurately predicted novel T cell epitopes from both pathogenic and commensal bacteria.

Amidst a thirst for promising new immunotherapies to treat chronic and terminal disease, this paper is a powerful reminder of the role, and necessity, for developing new ways to study core immunologic mechanisms and pathways.

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Peptide presentation prognosticator produced

We don't fully understand the immune system's rules for determining whether a peptide from a bacterium and other source will 1) be presented to T cells, and 2) spark an immune response. To help bring new clarity, Dan Graham, Chengwei Luo, Ramnik Xavier, and colleagues profiled the "peptidome" of potential antigens bound to MHC class II (a protein complex that presents peptides to T cells) in mice. They used their data to build and train BOTA, a machine learning algorithm that predicts antigenic peptides based on bacterial whole genome data. Read more in a Broad news story.

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Summary: Compositional and Temporal Changes in the Gut Microbiome of Pediatric Ulcerative Colitis Patients Are Linked to Disease Course

By Katie E. Golden, MD

The incidence of inflammatory bowel disease (IBD) is quickly rising, though despite the prevalence of disease, treatment options for patients are limited. Our current approach to treatment consists of pharmacologic immunosuppression, which is often only partially effective, or surgical removal of diseased portions of the intestine. These interventions often come with significant comorbidities for the patient, and are poorly tailored to their individual disease phenotypes as we still struggle to understand the pathophysiology of IBD.

The current research and future of IBD treatment is focused on understanding the interplay between the gut microbiome and the development and progression of disease. Research has consistently demonstrated how the microbiomes of IBD patients are less diverse compared to healthy control, and lack populations of protective, healthy bacteria. We have yet to understand, however, exactly how this dysbiosis of intestinal bacteria contributes to disease progression, and subsequently how it can be harnessed for treatment.

A new study, published in Cell Host & Microbe by Schirmer et al., brings us one step closer to the future of a more tailored, elegant approach to IBD therapeutics. Investigators looked at pediatric patients diagnosed with ulcerative colitis (UC), a form of IBD, to understand the correlation between disease severity and microbiome characteristics, and how this changes over time with treatment. More specifically, researchers followed a population of newly diagnosed, treatment-naive children, treated with one of two immunosuppression regimens (corticosteroids or 5-ASA), and monitored changes in fecal microbial populations and disease progression. They collected stool samples and tissue biopsies before, during, and after treatment over the course of a year.

During their investigation, researchers uncovered several important associations between microbiome characteristics, disease severity, and response to treatment. In the pre-treatment population, they found that disease severity correlated with increased populations of oral cavity bacteria (that do not typically colonize the intestine) and depleted populations of protective, commensal bacteria (such as Ruminococcaceae and Lachnospiraceae species).

Several of these disease-associated microbiome characteristics, furthermore, were predictive of refractory disease and seen in patients who ultimately required colectomy for treatment. In patients who did respond to medical therapy, the investigators observed similar changes in microbiome characteristics over time in both treatment arms, challenging prior research that suggested treatment response was highly individualized. These findings provided an important step forward in predicting individual prognosis and response to treatment based on pre-treatment microbiome characteristics.

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CSIBD Investigators receive 2018 BMA Medical Book Award

Ramnik Xavier, Director of CSIBD, and Ashwin Ananthakrishnan, Technical Director of the Clinical Core, together with Daniel Podolsky at UT Southwestern received a Highly Commended certificate in the Internal Medicine category for their book, Inflammatory Bowel Diseases: A Clinician's Guide.

The annual BMA Medical Book Awards recognize outstanding contributions to medical literature, promoting excellence in medical publishing and demonstrating its importance to medical education and training. Prizes are awarded in 20 categories, and an overall BMA Medical Book of the Year Award is selected from the category winners.

2017

Researchers produce the first draft cell atlas of the small intestine

Courtesy of Broad Communications

By surveying gene expression in over 53,000 cells from the small intestine, researchers have created a rich reference for understanding the biology of inflammatory bowel disease and food allergies, among other conditions. Read more in a Broad news story.

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Oral bacteria in the gut associated with inflammatory bowel disease

Bacteria living in the mouth are ingested with saliva, but normally do not persist in healthy intestine. In several disease states—inflammatory bowel disease (IBD), HIV infection, liver cirrhosis, colon cancer—orally-derived bacteria are found living in patients’ guts, leading researchers to hypothesize that oral bacteria colonizing the gut contribute to disease.

Collaborating with researchers in Japan, Dr. Ramnik Xavier and his laboratory at MGH recently published a study in Science demonstrating that certain strains of antibiotic-resistant oral bacteria colonize the gut and drive inflammation in genetically susceptible hosts. These bacteria were significantly more abundant in the guts of IBD and Crohn’s disease patients than of healthy individuals.

These findings highlight the disease potential of bacterial strains in susceptible hosts and the need to better understand the relationships between human hosts, their genomes, and resident bacterial communities.

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