L-Selectin, α4β1, and α4β7 Integrins Participate in CD4+ T Cell Recruitment to Chronically Inflamed Small Intestine

Mucosal α4β7+ Lymphocytes and MAdCAM+ Venules Predict Response to Vedolizumab in Ulcerative Colitis

BACKGROUND

Therapeutic strategies for patients with ulcerative colitis (UC) are based on patient- and disease-related factors in combination with drug characteristics but fail to predict success in individual patients. A considerable proportion of UC patients do not respond to the biological vedolizumab. Therefore, pretreatment biomarkers for therapeutic efficacy are urgently needed. Mucosal markers related to the integrin-dependent T lymphocyte homing could be potent predictors.

METHODS

We prospectively included 21 biological- and steroid-naive UC patients with moderate-to-severe disease activity planned to escalate therapy to vedolizumab. At week 0, before initiating treatment, colonic biopsy specimens were obtained for immunophenotyping and immunohistochemistry. Clinical and endoscopic disease activity were determined at week 16 after 4 infusions of vedolizumab. In addition, we retrospectively included 5 UC patients who were first treated with anti-tumor necrosis factor α before receiving vedolizumab to compare with biological-naive patients.

RESULTS

Abundance of α4β7 on more than 8% of all CD3+ T lymphocytes in colonic biopsies at baseline was predictive for responsiveness to vedolizumab (sensitivity 100%, specificity 100%). The threshold for the proportion of MAdCAM-1+ and PNAd+ of all venules in the biopsies predictive for responsiveness to vedolizumab was ≥2.59% (sensitivity 89%, specificity 100%) and ≥2.41% (sensitivity 61%, specificity 50%), respectively. At week 16, a significant decrease of α4β7+CD3+T lymphocytes was demonstrated in responders (18% [12%-24%] to 8% [3%-9%]; P = .002), while no difference was seen in nonresponders (4% [3%-6%] to 3%; P = .59).

CONCLUSIONS

UC responders to vedolizumab have a higher percentage of α4β7+CD3+ T lymphocytes and a higher proportion of MAdCAM-1+ venules in colonic biopsies than nonresponders before initiating therapy. Both analyses could be promising predictive biomarkers for therapeutic response and may lead to more patient tailored treatment in the future.

Cytokine Profile in Predicting the Effectiveness of Advanced Therapy for Ulcerative Colitis: A Narrative Review

Cytokine-targeted therapies have shown efficacy in treating patients with ulcerative colitis (UC), but responses to these advanced therapies can vary. This variability may be due to differences in cytokine profiles among patients with UC. While the etiology of UC is not fully understood, abnormalities of the cytokine profiles are deeply involved in its pathophysiology. Therefore, an approach focused on the cytokine profile of individual patients with UC is ideal. Recent studies have demonstrated that molecular analysis of cytokine profiles in UC can predict response to each advanced therapy. This narrative review summarizes the molecules involved in the efficacy of various advanced therapies for UC. Understanding these associations may be helpful in selecting optimal therapeutic agents.

Immune cell trafficking: a novel perspective on the gut-skin axis

Immune cell trafficking, an essential mechanism for maintaining immunological homeostasis and mounting effective responses to infections, operates under a stringent regulatory framework. Recent advances have shed light on the perturbation of cell migration patterns, highlighting how such disturbances can propagate inflammatory diseases from their origin to distal organs. This review collates and discusses current evidence that demonstrates atypical communication between the gut and skin, which are conventionally viewed as distinct immunological spheres, in the milieu of inflammation. We focus on the aberrant, reciprocal translocation of immune cells along the gut-skin axis as a pivotal factor linking intestinal and dermatological inflammatory conditions. Recognizing that the translation of these findings into clinical practices is nascent, we suggest that therapeutic strategies aimed at modulating the axis may offer substantial benefits in mitigating the widespread impact of inflammatory diseases.

Human Intestinal Dendritic Cells Can Overcome Retinoic Acid Signaling to Generate Proinflammatory CD4 T Cells with Both Gut and Skin Homing Properties

Retinoic acid, produced by intestinal dendritic cells (DCs), promotes T cell trafficking to the intestinal mucosa by upregulating α4β7 integrin and inhibiting the generation of cutaneous leukocyte Ag (CLA) required for skin entry. In the present study, we report that activation of human naive CD4 T cells in an APC-free system generates cells expressing α4β7 alone; in contrast, activation by intestinal DCs that produce retinoic acid and induce high levels of α4β7 also results in CLA expression, generating CLA+α4β7+ "dual tropic" cells, with both gut and skin trafficking potential, that also express high levels of α4β1 integrin. DC generation of CLA+α4β7+ T cells is associated with upregulation of FUT7, a fucosyltransferase involved in CLA generation; requires cell contact; and is enhanced by IL-12/IL-23. The blood CD4+ T cell population contains CLA+α4β7+ cells, which are significantly enriched for cells capable of IFN-γ, IL-17, and TNF-α production compared with conventional CLA-α4β7+ cells. Dual tropic lymphocytes are increased in intestinal tissue from patients with Crohn's disease, and single-cell RNA-sequencing analysis identifies a transcriptionally distinct cluster of FUT7-expressing cells present only in inflamed tissue; expression of genes associated with cell proliferation suggests that these cells are undergoing local activation. The expression of multiple trafficking molecules by CLA+α4β7+ T cells can enable their recruitment by alternative pathways to both skin and gut; they may contribute to both intestinal and cutaneous manifestations of inflammatory bowel disease.

A Narrative Review of Cytokine Networks: Pathophysiological and Therapeutic Implications for Inflammatory Bowel Disease Pathogenesis

Inflammatory bowel disease (IBD) is a lifelong inflammatory immune mediated disorder, encompassing Crohn's disease (CD) and ulcerative colitis (UC); however, the cause and specific pathogenesis of IBD is yet incompletely understood. Multiple cytokines produced by different immune cell types results in complex functional networks that constitute a highly regulated messaging network of signaling pathways. Applying biological mechanisms underlying IBD at the single omic level, technologies and genetic engineering enable the quantification of the pattern of released cytokines and new insights into the cytokine landscape of IBD. We focus on the existing literature dealing with the biology of pro- or anti-inflammatory cytokines and interactions that facilitate cell-based modulation of the immune system for IBD inflammation. We summarize the main roles of substantial cytokines in IBD related to homeostatic tissue functions and the remodeling of cytokine networks in IBD, which may be specifically valuable for successful cytokine-targeted therapies via marketed products. Cytokines and their receptors are validated targets for multiple therapeutic areas, we review the current strategies for therapeutic intervention and developing cytokine-targeted therapies. New biologics have shown efficacy in the last few decades for the management of IBD; unfortunately, many patients are nonresponsive or develop therapy resistance over time, creating a need for novel therapeutics. Thus, the treatment options for IBD beyond the immune-modifying anti-TNF agents or combination therapies are expanding rapidly. Further studies are needed to fully understand the immune response, networks of cytokines, and the direct pathogenetic relevance regarding individually tailored, safe and efficient targeted-biotherapeutics.

Nanotargeted Delivery of Immune Therapeutics in Type 1 Diabetes

Immune therapeutics holds great promise in the treatment of type 1 diabetes (T1D). Nonetheless, their progress is hampered by limited efficacy, equipoise, or issues of safety. To address this, a novel and specific nanodelivery platform for T1D that targets high endothelial venules (HEVs) presented in the pancreatic lymph nodes (PLNs) and pancreas is developed. Data indicate that the pancreata of nonobese diabetic (NOD) mice and patients with T1D are unique in their expression of newly formed HEVs. Anti-CD3 mAb is encapsulated in poly(lactic-co-glycolic acid)-poly(ethylene glycol) nanoparticles (NPs), the surfaces of which are conjugated with MECA79 mAb that recognizes HEVs. Targeted delivery of these NPs improves accumulation of anti-CD3 mAb in both the PLNs and pancreata of NOD mice. Treatment of hyperglycemic NOD mice with MECA79-anti-CD3-NPs results in significant reversal of T1D compared to those that are untreated, treated with empty NPs, or provided free anti-CD3. This effect is associated with a significant reduction of T effector cell populations in the PLNs and a decreased production of pro-inflammatory cytokine in the mice treated with MECA79-anti-CD3-NPs. In summary, HEV-targeted therapeutics may be used as a means by which immune therapeutics can be delivered to PLNs and pancreata to suppress autoimmune diabetes effectively.

Phase 2 study of natalizumab plus standard corticosteroid treatment for high-risk acute graft-versus-host disease

Graft-versus-host disease (GVHD) of the gastrointestinal (GI) tract is the main cause of nonrelapse mortality (NRM) after allogeneic hematopoietic cell transplantation. Ann Arbor (AA) scores derived from serum biomarkers at onset of GVHD quantify GI crypt damage; AA2/3 scores correlate with resistance to treatment and higher NRM. We conducted a multicenter, phase 2 study using natalizumab, a humanized monoclonal antibody that blocks T-cell trafficking to the GI tract through the α4 subunit of α4β7 integrin, combined with corticosteroids as primary treatment for patients with new onset AA2/3 GVHD. Seventy-five patients who were evaluable were enrolled and treated; 81% received natalizumab within 2 days of starting corticosteroids. Therapy was well tolerated with no treatment emergent adverse events in >10% of patients. Outcomes for patients treated with natalizumab plus corticosteroids were compared with 150 well-matched controls from the MAGIC database whose primary treatment was corticosteroids alone. There were no significant differences in overall or complete response between patients treated with natalizumab plus corticosteroids and those treated with corticosteroids alone (60% vs 58%; P = .67% and 48% vs 48%; P = 1.0, respectively) including relevant subgroups. There were also no significant differences in NRM or overall survival at 12 months in patients treated with natalizumab plus corticosteroids compared with controls treated with corticosteroids alone (38% vs 39%; P = .80% and 46% vs 54%; P = .48, respectively). In this multicenter biomarker-based phase 2 study, natalizumab combined with corticosteroids failed to improve outcome of patients with newly diagnosed high-risk GVHD. This trial was registered at www.clinicaltrials.gov as # NCT02133924.

Recruitment and Residence of Intestinal T Cells - Lessons for Therapy in Inflammatory Bowel Disease

Targeting leukocyte trafficking in the management of inflammatory bowel disease [IBD] has been a significant therapeutic advance over the past 15 years. However, as with other advanced therapies, phase III clinical trials report response to trafficking inhibitors in only a proportion of patients, with fewer achieving clinical remission or mucosal healing. Additionally, there have been significant side effects, most notably progressive multifocal leukoencephalopathy in association with the α4 inhibitor natalizumab. This article reviews the mechanisms underpinning T cell recruitment and residence, to provide a background from which the strength and limitations of agents that disrupt leukocyte trafficking can be further explored. The therapeutic impact of trafficking inhibitors is underpinned by the complexity and plasticity of the intestinal immune response. Pathways essential for gut homing in health may be bypassed in the inflamed gut, thus providing alternative routes of entry when conventional homing molecules are targeted. Furthermore, there is conservation of trafficking architecture between proinflammatory and regulatory T cells. The persistence of resident memory cells within the gut gives rise to local established pro-inflammatory populations, uninfluenced by inhibition of trafficking. Finally, trafficking inhibitors may give rise to effects beyond the intended response, such as the impact of vedolizumab on innate immunity, as well as on target side effects. With significant research efforts into predictive biomarkers already underway, it is ultimately hoped that a better understanding of trafficking and residence will help us predict which patients are most likely to respond to inhibition of leukocyte trafficking, and how best to combine therapies.

Enforced gut homing of murine regulatory T cells reduces early graft-versus-host disease severity

Damage to the gastrointestinal tract following allogeneic hematopoietic stem cell transplantation is a significant contributor to the severity and perpetuation of graft-versus-host disease. In preclinical models and clinical trials, we showed that infusing high numbers of regulatory T cells reduces graft-versus-host disease incidence. Despite no change in in vitro suppressive function, transfer of ex vivo expanded regulatory T cells transduced to overexpress G protein-coupled receptor 15 or C-C motif chemokine receptor 9, specific homing receptors for colon or small intestine, respectively, lessened graft-versus-host disease severity in mice. Increased regulatory T cell frequency and retention within the gastrointestinal tissues of mice that received gut homing T cells correlated with lower inflammation and gut damage early post-transplant, decreased graft-versus-host disease severity, and prolonged survival compared with those receiving control transduced regulatory T cells. These data provide evidence that enforced targeting of ex vivo expanded regulatory T cells to the gastrointestinal tract diminishes gut injury and is associated with decreased graft-versus-host disease severity.

Delivery of costimulatory blockade to lymph nodes promotes transplant acceptance in mice

The lymph node (LN) is the primary site of alloimmunity activation and regulation during transplantation. Here, we investigated how fibroblastic reticular cells (FRCs) facilitate the tolerance induced by anti-CD40L in a murine model of heart transplantation. We found that both the absence of LNs and FRC depletion abrogated the effect of anti-CD40L in prolonging murine heart allograft survival. Depletion of FRCs impaired homing of T cells across the high endothelial venules (HEVs) and promoted formation of alloreactive T cells in the LNs in heart-transplanted mice treated with anti-CD40L. Single-cell RNA sequencing of the LNs showed that anti-CD40L promotes a Madcam1+ FRC subset. FRCs also promoted the formation of regulatory T cells (Tregs) in vitro. Nanoparticles (NPs) containing anti-CD40L were selectively delivered to the LNs by coating them with MECA-79, which binds to peripheral node addressin (PNAd) glycoproteins expressed exclusively by HEVs. Treatment with these MECA-79-anti-CD40L-NPs markedly delayed the onset of heart allograft rejection and increased the presence of Tregs. Finally, combined MECA-79-anti-CD40L-NPs and rapamycin treatment resulted in markedly longer allograft survival than soluble anti-CD40L and rapamycin. These data demonstrate that FRCs are critical to facilitating costimulatory blockade. LN-targeted nanodelivery of anti-CD40L could effectively promote heart allograft acceptance.

Targeting neutrophils in inflammatory bowel disease: revisiting the role of adsorptive granulocyte and monocyte apheresis

INTRODUCTION

Inflammatory bowel disease (IBD) is a chronic immune-mediated disease of the gastrointestinal tract comprising Crohn's disease (CD) and ulcerative colitis (UC). While any part of the digestive tract can be affected in CD, mucosal inflammation in UC is limited to the colon. Differences and similarities between the two conditions are reflected by their pathophysiology.

AREAS COVERED

An overview of immunological aspects, pharmacological management, and biomarkers of IBD is provided. The role of adsorptive granulocyte and monocyte apheresis (GMA) is reviewed including its primary and secondary effects on the immune system, as well as clinical studies in IBD (mainly UC), and potential biomarkers for adsorptive GMA.

EXPERT OPINION

In UC, adsorptive GMA with Adacolumn (Adacolumn®, JIMRO Co., Ltd. Takasaki, Gunma, Japan) selectively depletes elevated myeloid lineage leukocytes and has a range of beneficial secondary immune effects. Adsorptive GMA is a safe and effective non-pharmacological treatment option for UC. Pilot studies have reported promising results for adsorptive GMA in combination with biological agents, although larger studies are required. Fecal calprotectin concentrations, neutrophil counts in histological samples and/or the neutrophil/lymphocyte ratio in peripheral blood may prove to be useful biomarkers for predicting GMA effectiveness in the future.

Emerging translational strategies and challenges for enhancing regulatory T cell therapy for graft-versus-host disease

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is a curative therapy for many types of cancer. Genetic disparities between donor and host can result in immune-mediated attack of host tissues, known as graft versus host disease (GVHD), a major cause of morbidity and mortality following HSCT. Regulatory CD4+ T cells (Tregs) are a rare cell type crucial for immune system homeostasis, limiting the activation and differentiation of effector T cells (Teff) that are self-reactive or stimulated by foreign antigen exposure. Adoptive cell therapy (ACT) with Treg has demonstrated, first in murine models and now in patients, that prophylactic Treg infusion can also suppress GVHD. While clinical trials have demonstrated Treg reduce severe GVHD occurrence, several impediments remain, including Treg variability and practical need for individualized Treg production for each patient. Additionally, there are challenges in the use of in vitro expansion techniques and in achieving in vivo Treg persistence in context of both immune suppressive drugs and in lymphoreplete patients being treated for GVHD. This review will focus on 3 main translational approaches taken to improve the efficacy of tTreg ACT in GVHD prophylaxis and development of treatment options, following HSCT: genetic modification, manipulating TCR and cytokine signaling, and Treg production protocols. In vitro expansion for Treg ACT presents a multitude of approaches for gene modification to improve efficacy, including: antigen specificity, tissue targeting, deletion of negative regulators/exhaustion markers, resistance to immunosuppressive drugs common in GVHD treatment. Such expansion is particularly important in patients without significant lymphopenia that can drive Treg expansion, enabling a favorable Treg:Teff ratio in vivo. Several potential therapeutics have also been identified that enhance tTreg stability or persistence/expansion following ACT that target specific pathways, including: DNA/histone methylation status, TCR/co-stimulation signaling, and IL-2/STAT5 signaling. Finally, this review will discuss improvements in Treg production related to tissue source, Treg subsets, therapeutic approaches to increase Treg suppression and stability during tTreg expansion, and potential for storing large numbers of Treg from a single production run to be used as an off-the-shelf infusion product capable of treating multiple recipients.

Harnessing murine models of Crohn's disease ileitis to advance concepts of pathophysiology and treatment

Crohn's disease (CD) and ulcerative colitis (UC) are both characterized by chronic inflammation and severe dysfunction of the gastrointestinal tract. These two forms of inflammatory bowel disease (IBD) represent distinct clinical disorders with diverse driving mechanisms; however, this divergence is not reflected in currently approved therapeutics that commonly target general proinflammatory pathways. A compelling need therefore remains to understand factors that differentiate the topology and the distinct clinical manifestations of CD versus UC, in order to develop more effective and specialized therapies. Animal models provide valuable platforms for studying IBD heterogeneity and deciphering disease-specific mechanisms. Both the established and the newly developed ileitis mouse models are characterized by various disease initiating mechanisms and diverse phenotypic outcomes that reflect the complexity of human CD-ileitis. Microbial dysbiosis, destruction of epithelial barrier integrity, immune cell deregulation, as well as the recently described genome instability and stromal cell activation have all been proposed as the triggering factors for the development of ileitis-associated pathology. In this review, we aim to critically evaluate the mechanistic underpinnings of murine models of CD-ileitis, discuss their phenotypic similarities to human disease, and envisage their further exploitation for the development of novel targeted and personalized therapeutics.

Navigating complex peptide structures using macrocycle conformational maps

Identification of turn motifs that are stabilized by intramolecular hydrogen bonds can be useful in describing the conformation of peptide systems. However, this approach is somewhat insufficient for cyclic peptides because peptide regions that are not positioned within a hydrogen bond can be left with no description. Furthermore, non-regular secondary structures and other rarely-observed conformations can be left without detailed evaluation. Herein, we describe “higher-order” ϕ/ψ plots termed macrocycle conformational maps (MCMs) as a tool for evaluating and comparing the conformations of a series of structurally related macrocyclic peptides.

Identification of turn motifs that are stabilized by hydrogen bonds can be useful in describing the conformation of peptides. Herein, we describe “higher-order” ϕ/ψ plots termed macrocycle conformational maps (MCMs) as a tool to evaluate and compare the conformations of related macrocycles.

Exploring the Early Phase of Crohn's Disease

The development of Crohn's disease (CD) is characterized by a breakdown of homeostatic immune-bacterial communication, which takes place at the intestinal mucosa when environmental triggers impact genetically predisposed individuals. Converging lines of evidence support the hypothesis that this pathogenetic model develops through sequential, although inter-related, steps that indicate failure of mucosal defense mechanisms at various stages. In this context, immunologic phenomena that mediate the initial appearance of inflammatory lesions across the intestinal tissue may differ substantially from those that mediate and perpetuate chronic inflammatory responses. A compromise in the integrity of the epithelial barrier is among the earliest events and leads to accelerated influx of intraluminal antigens and intact microorganisms within the immunologically rich lamina propria. Inadequate clearance of invading microorganisms also may occur as a result of defects in innate immunity, preventing the timely and complete resolution of acute inflammatory responses. The final step is the development of persistent adaptive responses, which also differ between early and late Crohn's disease. Current progress in our ability to delineate single-cell transcriptomics and proteomics has allowed the discovery of cellular and molecular mechanisms that participate in each sequential step of CD development. This not only will advance our understanding of CD pathogenesis, but also facilitate the design of targeted therapeutic approaches.

Target-Based Small Molecule Drug Discovery Towards Novel Therapeutics for Inflammatory Bowel Diseases

Inflammatory bowel disease (IBD), including ulcerative colitis (UC) and Crohn's disease (CD), is a class of severe and chronic diseases of the gastrointestinal (GI) tract with recurrent symptoms and significant morbidity. Long-term persistence of chronic inflammation in IBD is a major contributing factor to neoplastic transformation and the development of colitis-associated colorectal cancer. Conversely, persistence of transmural inflammation in CD is associated with formation of fibrosing strictures, resulting in substantial morbidity. The recent introduction of biological response modifiers as IBD therapies, such as antibodies neutralizing tumor necrosis factor (TNF)-α, have replaced nonselective anti-inflammatory corticosteroids in disease management. However, a large proportion (~40%) of patients with the treatment of anti-TNF-α antibodies are discontinued or withdrawn from therapy because of (1) primary nonresponse, (2) secondary loss of response, (3) opportunistic infection, or (4) onset of cancer. Therefore, the development of novel and effective therapeutics targeting specific signaling pathways in the pathogenesis of IBD is urgently needed. In this comprehensive review, we summarize the recent advances in drug discovery of new small molecules in preclinical or clinical development for treating IBD that target biologically relevant pathways in mucosal inflammation. These include intracellular enzymes (Janus kinases, receptor interacting protein, phosphodiesterase 4, IκB kinase), integrins, G protein-coupled receptors (S1P, CCR9, CXCR4, CB2) and inflammasome mediators (NLRP3), etc. We will also discuss emerging evidence of a distinct mechanism of action, bromodomain-containing protein 4, an epigenetic regulator of pathways involved in the activation, communication, and trafficking of immune cells. We highlight their chemotypes, mode of actions, structure-activity relationships, characterizations, and their in vitro/in vivo activities and therapeutic potential. The perspectives on the relevant challenges, new opportunities, and future directions in this field are also discussed.

Regulation and Role of αE Integrin and Gut Homing Integrins in Migration and Retention of Intestinal Lymphocytes during Inflammatory Bowel Disease

Adhesion molecules are upregulated in inflamed intestinal mucosa in IBD patients.

Baseline β7 expression does not impact αE induction or gene expression in T cells.

Phospho-SMAD3 is increased in inflamed mucosa in IBD.

Targeting interactions between α4β7 integrin and endothelial adhesion molecule MAdCAM-1 to inhibit lymphocyte migration to the gastrointestinal tract is an effective therapy in inflammatory bowel disease (IBD). Following lymphocyte entry into the mucosa, a subset of these cells expresses αEβ7 integrin, which is expressed on proinflammatory lymphocytes, to increase cell retention. The factors governing lymphocyte migration into the intestinal mucosa and αE integrin expression in healthy subjects and IBD patients remain incompletely understood. We evaluated changes in factors involved in lymphocyte migration and differentiation within tissues. Both ileal and colonic tissue from active IBD patients showed upregulation of ICAM-1, VCAM-1, and MAdCAM-1 at the gene and protein levels compared with healthy subjects and/or inactive IBD patients. β1 and β7 integrin expression on circulating lymphocytes was similar across groups. TGF-β1 treatment induced expression of αE on both β7⁺ and β7⁻ T cells, suggesting that cells entering the mucosa independently of MAdCAM-1/α4β7 can become αEβ7⁺. ITGAE gene polymorphisms did not alter protein induction following TGF-β1 stimulation. Increased phospho-SMAD3, which is directly downstream of TGF-β, and increased TGF-β–responsive gene expression were observed in the colonic mucosa of IBD patients. Finally, in vitro stimulation experiments showed that baseline β7 expression had little effect on cytokine, chemokine, transcription factor, and effector molecule gene expression in αE⁺ and αE⁻ T cells. These findings suggest cell migration to the gut mucosa may be altered in IBD and α4β7⁻, and α4β7⁺ T cells may upregulate αEβ7 in response to TGF-β once within the gut mucosa.

Understanding the Molecular Drivers of Disease Heterogeneity in Crohn's Disease Using Multi-omic Data Integration and Network Analysis

Crohn's disease (CD), a form of inflammatory bowel disease (IBD), is characterized by heterogeneity along multiple clinical axes, which in turn impacts disease progression and treatment modalities. Using advanced data integration approaches and systems biology tools, we studied the contribution of CD susceptibility variants and gene expression in distinct peripheral immune cell subsets (CD14+ monocytes and CD4+ T cells) to relevant clinical traits. Our analyses revealed that most clinical traits capturing CD heterogeneity could be associated with CD14+ and CD4+ gene expression rather than disease susceptibility variants. By disentangling the sources of variation, we identified molecular features that could potentially be driving the heterogeneity of various clinical traits of CD patients. Further downstream analyses identified contextual hub proteins such as genes encoding barrier functions, antimicrobial peptides, chemokines, and their receptors, which are either targeted by drugs used in CD or other inflammatory diseases or are relevant to the biological functions implicated in disease pathology. These hubs could be used as cell type-specific targets to treat specific subtypes of CD patients in a more individualized approach based on the underlying biology driving their disease subtypes. Our study highlights the importance of data integration and systems approaches to investigate complex and heterogeneous diseases such as IBD.

Targeting Immune Cell Trafficking - Insights From Research Models and Implications for Future IBD Therapy

Inflammatory bowel diseases (IBDs), including Crohn's disease (CD) and ulcerative colitis (UC) are multifactorial diseases with still unknown aetiology and an increasing prevalence and incidence worldwide. Despite plentiful therapeutic options for IBDs, the lack or loss of response in certain patients demands the development of further treatments to tackle this unmet medical need. In recent years, the success of the anti-α4β7 antibody vedolizumab highlighted the potential of targeting the homing of immune cells, which is now an important pillar of IBD therapy. Due to its complexity, leukocyte trafficking and the involved molecules offer a largely untapped resource for a plethora of potential therapeutic interventions. In this review, we aim to summarise current and future directions of specifically interfering with immune cell trafficking. We will comment on concepts of homing, retention and recirculation and particularly focus on the role of tissue-derived chemokines. Moreover, we will give an overview of the mode of action of drugs currently in use or still in the pipeline, highlighting their mechanisms and potential to reduce disease burden.

Integrin-Ligand Interactions in Inflammation, Cancer, and Metabolic Disease: Insights Into the Multifaceted Roles of an Emerging Ligand Irisin

Integrins are transmembrane proteins that mediate cellular adhesion and migration to neighboring cells or the extracellular matrix, which is essential for cells to undertake diverse physiological and pathological pathways. For integrin activation and ligand binding, bidirectional signaling across the cell membrane is needed. Integrins aberrantly activated under pathologic conditions facilitate cellular infiltration into tissues, thereby causing inflammatory or tumorigenic progressions. Thus, integrins have emerged to the forefront as promising targets for developing therapeutics to treat autoimmune and cancer diseases. In contrast, it remains a fact that integrin-ligand interactions are beneficial for improving the health status of different tissues. Among these ligands, irisin, a myokine produced mainly by skeletal muscles in an exercise-dependent manner, has been shown to bind to integrin αVβ5, alleviating symptoms under unfavorable conditions. These findings may provide insights into some of the underlying mechanisms by which exercise improves quality of life. This review will discuss the current understanding of integrin-ligand interactions in both health and disease. Likewise, we not only explain how diverse ligands play different roles in mediating cellular functions under both conditions via their interactions with integrins, but also specifically highlight the potential roles of the emerging ligand irisin in inflammation, cancer, and metabolic disease.

Sphingosine-1-Phosphate Lyase Inhibition Alters the S1P Gradient and Ameliorates Crohn's-Like Ileitis by Suppressing Thymocyte Maturation

BACKGROUND

Lymphocytes recirculate from tissues to blood following the sphingosine-1-phosphate (S1P) gradient (low in tissues, high in blood), maintained by synthetic and degradative enzymes, among which the S1P lyase (SPL) irreversibly degrades S1P. The role of SPL in the intestine, both during homeostasis and IBD, is poorly understood. We hypothesized that modulation of tissue S1P levels might be advantageous over S1P receptor (S1PR) agonists (eg, fingolimod, ozanimod, etrasimod), as without S1PR engagement there might be less likelihood of potential off-target effects.

METHODS

First we examined SPL mRNA transcripts and SPL localization in tissues by quantitative reverse transcription polymerase chain reaction and immunohistochemistry. The in vivo effects of the SPL inhibitors 4-deoxypyridoxine hydrochloride (30 mg/L) and 2-acetyl-4 (tetrahydroxybutyl)imidazole (50 mg/L) were assessed through their oral administration to adult TNF∆ARE mice, which spontaneously develop Crohn's-like chronic ileitis. The effect of SPL inhibition on circulating and tissue lymphocytes, transcriptional regulation of proinflammatory cytokines, and on the histological severity of ileitis was additionally examined. Tissue S1P levels were determined by liquid chromatography-mass spectrometry. Mechanistically, the potential effects of high S1P tissue levels on intestinal leukocyte apoptosis were assessed via terminal deoxynucleotidyl transferase dUTP nick end-labeling assay and annexin 5 staining. Finally, we examined the ability of T cells to home to the intestine, along with the effects of SPL inhibition on cellular subsets within immune compartments via flow and mass cytometry.

RESULTS

S1P lyase was ubiquitously expressed. In the gut, immunohistochemistry predominantly localized it to small intestinal epithelia, although the lamina propria leukocyte fraction had higher mRNA transcripts. Inhibition of SPL markedly increased local intestinal S1P levels, induced peripheral lymphopenia, downregulated proinflammatory cytokines, and attenuated chronic ileitis in mice. SPL inhibition reduced T and myeloid cells in secondary lymphoid tissues and the intestine and decreased naïve T-cell recruitment. The anti-inflammatory activity of SPL inhibition was not mediated by leukocyte apoptosis, nor by interference with the homing of lymphocytes to the intestine, and was independent of its peripheral lymphopenic effect. However, SPL inhibition promoted thymic atrophy and depleted late immature T cells (CD4+CD8+ double positive), with accumulation of mature CD4+CD8- and CD4-CD8+ single-positive cells.

CONCLUSIONS

Inhibition of the S1P lyase alters the S1P gradient and attenuates chronic ileitis via central immunosuppression. SPL inhibition could represent a potential way to tame an overactive immune response during IBD and other T-cell-mediated chronic inflammatory diseases.

IL-12 and Mucosal CD14+ Monocyte-Like Cells Induce IL-8 in Colonic Memory CD4+ T Cells of Patients With Ulcerative Colitis but not Crohn's Disease

BACKGROUND AND AIMS

CD14+ mononuclear phagocytes [MNPs] and T cells infiltrate colon in ulcerative colitis [UC]. Here we investigated how CD14+ MNPs and the cytokines they produce shape the colonic effector T cell profile.

METHODS

Colonic or mesenteric lymph node [mLNs] CD4+ T cells isolated from UC or Crohn's disease [CD] patients were stimulated with cytokines or autologous CD14+ MNPs. Cytokine expression was assessed by intracytoplasmic staining and multiplex ELISA. Unsupervised phenotypic multicolour analysis of colonic CD14+ MNPs was performed using the FlowSOM algorithm.

RESULTS

Among CD14+CD64+HLA-DR+SIRPα + MNPs, only the pro-inflammatory cytokine-producing CD163- subpopulation accumulated in inflamed UC colon and promoted mucosal IL-1β-dependent Th17, Th17/Th1, Th17/Th22 but not Th1 responses. Unsupervised phenotypic analysis of CD14+CD64+ MNPs segregated CD163- monocyte-like cells and CD163+ macrophages. Unexpectedly, IL-12, IL-1β and CD163-, but not CD163+, cells induced IL-8 expression in colonic CD4+ T cells, which co-expressed IFN-γ and/or IL-17 in UC and not CD. The CD163- monocyte-like cells increased the frequency of IL-8+IL-17+/-IFN-γ +/- T cells through IL-1β and IL-12. Finally, colonic IL-8+ T cells co-expressing GM-CSF, TNF-α and IL-6 were detected ex vivo and, promoted by IL-12 in the mucosa and mLNs in UC only.

CONCLUSIONS

Our findings established a link between monocyte-like CD163- MNPs, IL-12, IL-1β and the detection of colonic memory IL-8-producing CD4+ T cells, which might all contribute to the pathogenesis of UC.

β7 Integrin Inhibition Can Increase Intestinal Inflammation by Impairing Homing of CD25hiFoxP3+ Regulatory T Cells

BACKGROUND & AIMS

Integrin α4β7 mediates lymphocyte trafficking to the gut and gut-associated lymphoid tissues, a process critical for recruitment of effector lymphocytes from the circulation to the gut mucosa in inflammatory bowel disease (IBD) and murine models of intestinal inflammation. Antibody blockade of β7 integrins generally is efficacious in IBD; however, some patients fail to respond, and a few patients can experience exacerbations. This study examined the effects of loss of β7 integrin function in murine models of IBD.

METHODS

In a mouse IBD model caused by lack of interleukin 10, a cytokine important in CD25hiFoxP3+ regulatory T cell (Treg) function, genetic deletion of β7 integrin or antibody blockade of α4β7-mucosal addressin cell adhesion molecule-1 interaction paradoxically exacerbated colitis.

RESULTS

Loss of β7 impaired the capacity of Tregs homing to the gut and therefore suppress intestinal inflammation in an adoptive T-cell transfer model; however, the intrinsic suppressive function of β7-deficient Tregs remained intact, indicating that the β7 deficiency selectively impacts gut homing. Deletion of β7 integrin did not worsen colitis in an acute dextran sodium sulfate model in which Treg number and function were normal.

CONCLUSIONS

In Integrin subunit beta (Itgb)7-/-Il10-/- mice, loss of β7-dependent Treg homing to gut-associated lymphoid tissues combined with loss of intrinsic Treg function exacerbated intestinal inflammation. These results suggest that IBD patients with reduced CD25hiFoxP3+ Treg numbers or function or lack of interleukin 10 could be at risk for failure of α4β7 blocking therapy.

Comparison of the integrin α4β7 expression pattern of memory T cell subsets in HIV infection and ulcerative colitis

Anti-α4β7 therapy with vedolizumab (VDZ) has been suggested as possible immune intervention in HIV. Relatively little is known about the α4β7-integrin (α4β7) expression of different T-cell subsets in different anatomical compartments of healthy individuals, patients with HIV or inflammatory bowel disease (IBD). Surface expression of α4β7 as well as the frequency of activation, homing and exhaustion markers of T cells were assessed by multicolour flow cytometry in healthy volunteers (n = 15) compared to HIV infected patients (n = 52) or patients diagnosed with ulcerative colitis (UC) (n = 14), 6 of whom treated with vedolizumab. In addition, lymph nodal cells (n = 6), gut-derived cells of healthy volunteers (n = 5) and patients with UC (n = 6) were analysed. Additionally, we studied longitudinal PBMC samples of an HIV patient who was treated with vedolizumab for concomitant UC. Overall, only minor variations of the frequency of α4β7 on total CD4⁺ T cells were detectable regardless of the disease status or (VDZ) treatment status in peripheral blood and the studied tissues. Peripheral α4β7⁺ CD4⁺ T cells of healthy individuals and patients with UC showed a higher activation status and were more frequently CCR5⁺ than their α4β7^- counterparts. Also, the frequency of α4β7⁺ cells was significantly lower in peripheral blood CD4⁺ effector memory T cells of HIV-infected compared to healthy individuals and this reduced frequency did not recover in HIV patients on ART. Conversely, the frequency of peripheral blood naïve α4β7⁺ CD4⁺ T cells was significantly reduced under VDZ treatment. The results of the current study will contribute to the understanding of the dynamics of α4β7 expression pattern on T cells in HIV and UC and will be useful for future studies investigating VDZ as possible HIV cure strategy.

MAdCAM-1-Mediated Intestinal Lymphocyte Homing Is Critical for the Development of Active Experimental Autoimmune Encephalomyelitis

Lymphocyte homing into the intestine is mediated by binding of leukocytes to mucosal addressin cell adhesion molecule 1 (MAdCAM-1), expressed on endothelial cells. Currently, the immune system of the gut is considered a major modulator not only of inflammatory bowel disease, but also of extra-intestinal autoimmune disorders, including multiple sclerosis (MS). Despite intense research in this field, the exact role of the intestine in the pathogenesis of (neuro-)inflammatory disease conditions remains to be clarified. This prompted us to investigate the role of MAdCAM-1 in immunological processes in the intestine during T cell-mediated autoimmunity of the central nervous system (CNS). Using the experimental autoimmune encephalomyelitis model of MS, we show that MAdCAM-1-deficient (MAdCAM-1-KO) mice are less susceptible to actively MOG₃₅₋₅₅-induced disease. Protection from disease was accompanied by decreased numbers of immune cells in the lamina propria and Peyer's patches as well as reduced immune cell infiltration into the spinal cord. MOG₃₅₋₅₅-recall responses were intact in other secondary lymphoid organs of MAdCAM-1-KO mice. The composition of specific bacterial groups within the microbiome did not differ between MAdCAM-1-KO mice and controls, while MAdCAM-1-deficiency severely impaired migration of MOG₃₅₋₅₅-activated lymphocytes to the gut. Our data indicate a critical role of MAdCAM-1 in the development of CNS inflammation by regulating lymphocyte homing to the intestine, and may suggest a role for the intestinal tract in educating lymphocytes to become encephalitogenic.

The Notch signaling pathway promotes basophil responses during helminth-induced type 2 inflammation

Basophils promote type 2 inflammation that mediates worm clearance during murine infection with the gastrointestinal helminth parasite Trichuris muris. Webb et al. show for the first time that basophil–intrinsic Notch signaling is required for basophil gene expression and a functional program that support helminth expulsion.

Type 2 inflammation drives the clearance of gastrointestinal helminth parasites, which infect over two billion people worldwide. Basophils are innate immune cells that support host-protective type 2 inflammation during murine infection with the helminth Trichuris muris. However, the mechanisms required for basophil function and gene expression regulation in this context remain unclear. We show that during T. muris infection, basophils localized to the intestine and up-regulated Notch receptor expression, rendering them sensitive to Notch signals that rapidly regulate gene expression programs. In vitro, Notch inhibition limited basophil cytokine production in response to cytokine stimulation. Basophil-intrinsic Notch signaling was required for T. muris–elicited changes in genome-wide basophil transcriptional programs. Mice lacking basophil-intrinsic functional Notch signaling had impaired worm clearance, decreased intestinal type 2 inflammation, altered basophil localization in the intestine, and decreased CD4⁺ T helper 2 cell responses following infection. These findings demonstrate that Notch is required for basophil gene expression and effector function associated with helminth expulsion during type 2 inflammation.

Cell Trafficking Interference in Inflammatory Bowel Disease: Therapeutic Interventions Based on Basic Pathogenesis Concepts

After 20 years of successful targeting of pro-inflammatory cytokines for the treatment of IBD, an alternative therapeutic strategy has emerged, based on several decades of advances in understanding the pathogenesis of IBD. The targeting of molecules involved in leukocyte traffic has recently become a safe and effective alternative. With 2 currently approved drugs (ie, natalizumab, vedolizumab) and several others in phase 3 trials (eg, etrolizumab, ozanimod, anti-MAdCAM-1), the blockade of trafficking molecules has firmly emerged as a new therapeutic era for IBD. We discuss the targets that have been explored in clinical trials: chemokines and its receptors (eg, IP10, CCR9), integrins (eg, natalizumab, AJM300, vedolizumab, and etrolizumab), and its endothelial ligands (MAdCAM-1, ICAM-1). We also discuss a distinct strategy that interferes with lymphocyte recirculation by blocking lymphocyte egress from lymph nodes (small molecule sphingosine-phosphate receptor [S1PR] agonists: fingolimod, ozanimod, etrasimod, amiselimod). Strategies on the horizon include additional small molecules, allosteric inhibitors that specifically bind to the active integrin form and nanovectors that allow for the use of RNA interference in the quest to modulate pro-inflammatory leukocyte trafficking in IBD.

Vedolizumab is associated with changes in innate rather than adaptive immunity in patients with inflammatory bowel disease

OBJECTIVE

Vedolizumab, a monoclonal antibody directed against the integrin heterodimer α4β7, is approved for the treatment of Crohn's disease and ulcerative colitis. The efficacy of vedolizumab has been suggested to result from inhibition of intestinal T cell trafficking although human data to support this conclusion are scarce. We therefore performed a comprehensive analysis of vedolizumab-induced alterations in mucosal and systemic immunity in patients with inflammatory bowel disease (IBD), using anti-inflammatory therapy with the TNFα antibody infliximab as control.

DESIGN

Immunophenotyping, immunohistochemistry, T cell receptor profiling and RNA sequencing were performed using blood and colonic biopsies from patients with IBD before and during treatment with vedolizumab (n=18) or, as control, the anti-TNFα antibody infliximab (n=20). Leucocyte trafficking in vivo was assessed using single photon emission computed tomography and endomicroscopy.

RESULTS

Vedolizumab was not associated with alterations in the abundance or phenotype of lamina propria T cells and did not affect the mucosal T cell repertoire or leucocyte trafficking in vivo. Surprisingly, however, α4β7 antibody treatment was associated with substantial effects on innate immunity including changes in macrophage populations and pronounced alterations in the expression of molecules involved in microbial sensing, chemoattraction and regulation of the innate effector response. These effects were specific to vedolizumab, not observed in response to the TNFα antibody infliximab, and associated with inhibition of intestinal inflammation.

CONCLUSION

Our findings suggest that modulation of innate immunity contributes to the therapeutic efficacy of vedolizumab in IBD.

TRIAL REGISTRATION NUMBER

NCT02694588.

Gut-Selective Integrin-Targeted Therapies for Inflammatory Bowel Disease

Integrins are cell surface receptors with bidirectional signalling capabilities that can bind to adhesion molecules in order to mediate homing of leukocytes to peripheral tissues. Gut-selective leukocyte homing is facilitated by interactions between α4β7 and its ligand, mucosal addressin cellular adhesion molecule-1 [MAdCAM-1], while retention of lymphocytes in mucosal tissues is mediated by αEβ7 binding to its ligand E-cadherin. Therapies targeting gut-selective trafficking have shown efficacy in inflammatory bowel disease [IBD], confirming the importance of leukocyte trafficking in disease pathobiology. This review will provide an overview of integrin structure, function and signalling, and highlight the role that these molecules play in leukocyte homing and retention. Anti-integrin therapeutics, including gut-selective antibodies against the β7 integrin subunit [etrolizumab] and the α4β7 integrin heterodimer [vedolizumab and abrilumab], and the non-gut selective anti-α4 integrin [natalizumab], will be discussed, as well as novel targeting approaches using small molecules.

An in vitro system of autologous lymphocytes culture that allows the study of homeostatic proliferation mechanisms in human naive CD4 T-cells

The size of peripheral T-cell pool is kept constant throughout life. However, a decline in lymphocyte numbers is a feature of several human disorders, in which fast and slow homeostatic proliferation play a crucial role. Several in vitro and in vivo models have been developed to study such processes. Nevertheless, self- and commensal- antigens, well-known triggers of homeostatic proliferation, have not been examined in these models. We have designed an in vitro culture of human T-cells exposed to rIL7 and autologous antigen-presenting cells (aAPC) that allows the simultaneous characterization of the different types of homeostatic proliferation. Using our model, we first confirmed that both rIL7 and aAPC are survival signals ultimately leading to homeostatic proliferation. In addition, we explored the modulation of different anti-apoptotic, proliferative, activation and homing markers during fast and slow homeostatic proliferation. Finally, different subsets of Treg were generated during homeostatic proliferation in our model. In summary, our in vitro system is able to simultaneously reproduce both types of homeostatic proliferation of human naive CD4 T-cells, and allows the characterization of these processes. Our in vitro system is a useful tool to explore specific features of human homeostatic proliferation in different human lymphopenia-related disorders and could be used as a cell therapy approach.

Blockade of αEβ7 integrin suppresses accumulation of CD8+ and Th9 lymphocytes from patients with IBD in the inflamed gut in vivo

OBJECTIVE

Therapeutically targeting lymphocyte adhesion is of increasing relevance in IBD. Yet, central aspects of the action of antiadhesion compounds are incompletely understood. We investigated the role of αEβ7 and α4β7 integrins and their blockade by vedolizumab and etrolizumab for trafficking of IBD T lymphocytes in an in vivo model of homing to and retention in the inflamed gut.

DESIGN

We explored integrin expression in patients with IBD by flow cytometry and immunohistochemistry, while regulation of integrins was studied in T cell cultures. The functional relevance of integrins was assessed by adhesion assays and a recently established humanised mouse model in dextran sodium sulfate-treated immunodeficient mice.

RESULTS

High expression of αEβ7 was noted on CD8⁺ and CD4⁺ Th9 cells, while α4β7 was expressed on CD8⁺, Th2 and Th17 cells. T cell receptor stimulation and transforming growth factor β were key inducers of αEβ7 on human T cells, while butyric acid suppressed αEβ7. In comparison to α4β7 blockade via vedolizumab, blockade of β7 via etrolizumab surrogate antibody superiorly reduced colonic numbers of CD8⁺ and Th9 cells in vivo after 3 hours, while no difference was noted after 0.5 hours. AEβ7 expression was higher on CD8⁺ T cells from patients with IBD under vedolizumab therapy.

CONCLUSIONS

AEβ7 is of key relevance for gut trafficking of IBD CD8⁺ T cells and CD4⁺ Th9 cells in vivo and mainly retention might account for this effect. These findings indicate that blockade of αEβ7 in addition to α4β7 may be particularly effective in intestinal disorders with expansion of CD8⁺ and Th9 cells such as IBD.

Systemic Chemokine Levels with "Gut-Specific" Vedolizumab in Patients with Inflammatory Bowel Disease-A Pilot Study

Vedolizumab, a gut-specific biological treatment for inflammatory bowel disease (IBD), is an antibody that binds to the α₄β₇ integrin and blocks T-cell migration into intestinal mucosa. We aimed to investigate chemokine levels in serum of IBD-patients treated with vedolizumab. In this pilot study, we included 11 IBD patients (8 Crohn’s disease, 3 ulcerative colitis) previously non-respondent to anti-tumor necrosis factor (TNF)-agents. Patients received vedolizumab at week 0, 2 and 6 and were evaluated for clinical efficacy at week 10. Clinical characteristics and routine laboratory parameters were obtained and patients were classified as responders or non-responders. Expression of 21 chemokines in serum was measured using Proximity Extension Assay and related to clinical outcome. At week 10, 6 out of 11 patients had clinically responded. Overall expression of CCL13 increased after treatment. In non-responders, expression of CCL13 and CXCL8 increased after treatment, and CCL20 and CXCL1 expressions were higher compared to responders. In responders, CCL28 decreased after treatment. C-reactive protein (CRP) correlated negatively with 6 chemokines before therapy, but not after therapy. Systemic CCL13 expression increases in IBD-patients after vedolizumab therapy and several chemokine levels differ between responders and non-responders. An increased CCL13-level when starting vedolizumab treatment, might indicate potential prognostic value of measuring chemokine levels when starting therapy with vedolizumab. This study provides new information on modulation of systemic chemokine levels after vedolizumab treatment.

Clinical Response to Vedolizumab in Ulcerative Colitis Patients Is Associated with Changes in Integrin Expression Profiles

Background

Despite large clinical success, deeper insights into the immunological effects of vedolizumab therapy for inflammatory bowel diseases are scarce. In particular, the reasons for differential clinical response in individual patients, the precise impact on the equilibrium of integrin-expressing T cell subsets, and possible associations between these issues are not clear.

Methods

Blood samples from patients receiving clinical vedolizumab therapy were sequentially collected and analyzed for expression of integrins and chemokine receptors on T cells. Moreover, clinical and laboratory data from the patients were collected, and changes between homing marker expression and clinical parameters were analyzed for possible correlations.

Results

While no significant correlation of changes in integrin expression and changes in outcome parameters were identified in Crohn’s disease (CD), increasing α4β7 levels in ulcerative colitis (UC) seemed to be associated with favorable clinical development, whereas increasing α4β1 and αEβ7 correlated with negative changes in outcome parameters. Changes in α4β1 integrin expression after 6 weeks were significantly different in responders and non-responders to vedolizumab therapy as assessed after 16 weeks with a cutoff of +4.2% yielding 100% sensitivity and 100% specificity in receiver-operator-characteristic analysis.

Discussion

Our data show that clinical response to vedolizumab therapy in UC but not in CD is associated with specific changes in integrin expression profiles opening novel avenues for mechanistic research and possibly prediction of response to therapy.

T-lymphocyte homing: an underappreciated yet critical hurdle for successful cancer immunotherapy

Advances in cancer immunotherapy have offered new hope for patients with metastatic disease. This unfolding success story has been exemplified by a growing arsenal of novel immunotherapeutics, including blocking antibodies targeting immune checkpoint pathways, cancer vaccines, and adoptive cell therapy (ACT). Nonetheless, clinical benefit remains highly variable and patient-specific, in part, because all immunotherapeutic regimens vitally hinge on the capacity of endogenous and/or adoptively transferred T-effector (T_eff) cells, including chimeric antigen receptor (CAR) T cells, to home efficiently into tumor target tissue. Thus, defects intrinsic to the multi-step T-cell homing cascade have become an obvious, though significantly underappreciated contributor to immunotherapy resistance. Conspicuous have been low intralesional frequencies of tumor-infiltrating T-lymphocytes (TILs) below clinically beneficial threshold levels, and peripheral rather than deep lesional TIL infiltration. Therefore, a T_eff cell 'homing deficit' may arguably represent a dominant factor responsible for ineffective immunotherapeutic outcomes, as tumors resistant to immune-targeted killing thrive in such permissive, immune-vacuous microenvironments. Fortunately, emerging data is shedding light into the diverse mechanisms of immune escape by which tumors restrict T_eff cell trafficking and lesional penetrance. In this review, we scrutinize evolving knowledge on the molecular determinants of T_eff cell navigation into tumors. By integrating recently described, though sporadic information of pivotal adhesive and chemokine homing signatures within the tumor microenvironment with better established paradigms of T-cell trafficking under homeostatic or infectious disease scenarios, we seek to refine currently incomplete models of T_eff cell entry into tumor tissue. We further summarize how cancers thwart homing to escape immune-mediated destruction and raise awareness of the potential impact of immune checkpoint blockers on T_eff cell homing. Finally, we speculate on innovative therapeutic opportunities for augmenting T_eff cell homing capabilities to improve immunotherapy-based tumor eradication in cancer patients, with special focus on malignant melanoma.

The α4β1 Homing Pathway Is Essential for Ileal Homing of Crohn's Disease Effector T Cells In Vivo

BACKGROUND

The precise mechanisms controlling homing of T effector (Teff) cells to the inflamed gut in Crohn's disease (CD) are still unclear, and clinical outcome data from patients with inflammatory bowel disease treated with the anti-α4β7 integrin antibody vedolizumab suggest differences between ulcerative colitis and CD.

METHODS

Expression of homing molecules was studied with flow cytometry and immunohistochemistry. Their functional role was investigated in in vitro adhesion assays and in a humanized mouse model of T cell homing to the inflamed gut in vivo.

RESULTS

Despite in vitro blockade of CD Teff adhesion to mucosal vascular addressin cell adhesion molecule-1 (MadCAM-1) and in contrast to previous observations in ulcerative colitis, anti-α4β7 treatment did not result in reduced Teff cell homing to the colon in vivo. However, the integrin α4β1 was expressed in higher levels on Teffs from patients with CD compared with controls, while its expression in the peripheral blood declined, and its expression in the intestine increased during the course of clinical vedolizumab treatment. Consistently, adhesion of CD Teffs to vascular cell adhesion molecule-1 (VCAM-1) was blocked by inhibition of α4 and α4β1 in vitro. Moreover, in vivo homing of CD Teffs to the ileum was reduced by inhibition of α4 and α4β1 integrins, but not α4β7 integrins.

CONCLUSIONS

Our findings suggest that Teff cell homing to the ileum through the axis α4β1-VCAM-1 is an essential and nonredundant pathway in CD in vivo, possibly affecting efficacy of clinical treatment with antiadhesion compounds.

Colitis ImmunoPET: Defining Target Cell Populations and Optimizing Pharmacokinetics

BACKGROUND

Positron emission tomography combined with a specific probe presents the ability to noninvasively assess inflammatory bowel disease. We previously reported increased intestinal uptake of a Cu-labeled anti-β7 integrin antibody (clone FIB504.64) in colitic mice. Here, we evaluated an anti-α4β7 integrin antibody (clone DATK32), and the F(ab')2 and Fab fragments of the anti-β7 antibody, which should have faster blood clearance than the intact antibody, as imaging probes for the detection of colitis in a mouse model.

METHODS

The immunoproteins were labeled with Cu, injected into mice with dextran sodium sulphate-induced colitis. Positron emission tomography data were collected between 1 and 48 hours postinjection.

RESULTS

Focal uptake of the anti-β7 fragments was observed in the gut as early as 1 hour postinjection, and they cleared more rapidly from normal tissues than the whole antibody. For example, the blood concentrations at 24 hours postinjection were 23.3 ± 3.0% ID/g for Cu-labeled DATK32, 12.9 ± 2.1% ID/g for FIB504.64, 4.1 ± 0.4% ID/g for FIB504.64-F(ab')2, and 0.62 ± 0.2% ID/g for FIB504.64-Fab (P < 0.0001, analysis of variance). The ratio of uptake of DATK32 between the colitis and control groups in the large intestine (1.38) was lower than for the FIB504.64 fragments (3.15 for F(ab')2, 1.84 for Fab) or intact FIB504.64 (1.78).

CONCLUSIONS

The lower intestinal uptake ratio of the Cu-labeled anti-α4β7 antibody (DATK32) compared with the anti-β7 immunoproteins suggests that targeting all β7-expressing lymphocytes, not just those expressing α4β7, is a more promising route to the development of an inflammatory bowel disease imaging agent. The FIB504.64-F(ab')2 fragment demonstrated the greatest differential between colitis and control groups, and is therefore the most promising lead molecule for the development of an inflammatory bowel disease-specific imaging agent.

Leukocyte Trafficking to the Small Intestine and Colon

Leukocyte trafficking to the small and large intestines is tightly controlled to maintain intestinal immune homeostasis, mediate immune responses, and regulate inflammation. A wide array of chemoattractants, chemoattractant receptors, and adhesion molecules expressed by leukocytes, mucosal endothelium, epithelium, and stromal cells controls leukocyte recruitment and microenvironmental localization in intestine and in the gut-associated lymphoid tissues (GALTs). Naive lymphocytes traffic to the gut-draining mesenteric lymph nodes where they undergo antigen-induced activation and priming; these processes determine their memory/effector phenotypes and imprint them with the capacity to migrate via the lymph and blood to the intestines. Mechanisms of T-cell recruitment to GALT and of T cells and plasmablasts to the small intestine are well described. Recent advances include the discovery of an unexpected role for lectin CD22 as a B-cell homing receptor GALT, and identification of the orphan G-protein-coupled receptor 15 (GPR15) as a T-cell chemoattractant/trafficking receptor for the colon. GPR15 decorates distinct subsets of T cells in mice and humans, a difference in species that could affect translation of the results of mouse colitis models to humans. Clinical studies with antibodies to integrin α4β7 and its vascular ligand mucosal vascular addressin cell adhesion molecule 1 are proving the value of lymphocyte trafficking mechanisms as therapeutic targets for inflammatory bowel diseases. In contrast to lymphocytes, cells of the innate immune system express adhesion and chemoattractant receptors that allow them to migrate directly to effector tissue sites during inflammation. We review the mechanisms for innate and adaptive leukocyte localization to the intestinal tract and GALT, and discuss their relevance to human intestinal homeostasis and inflammation.

Structural requirements of mono- and multivalent L-selectin blocking aptamers for enhanced receptor inhibition in vitro and in vivo

L-selectin mediates extravasation of leukocytes from blood into the surrounding tissue during inflammation and is therefore a therapeutical target in certain overwhelming immune reactions. In this study, we characterized an L-selectin specific blocking DNA aptamer with respect to nucleotide composition and target binding. Introduction of deletions and nucleotide exchanges resulted in an optimized DNA sequence but preservation of the IC50 in the low nanomolar range. The inhibitory potential was significantly increased when the aptamer was displayed as a di- and trimer connected via appropriate linker length. Similar to monoclonal antibodies, trimer yielded picomolar IC50 values in a competitive binding assay. In comparison to the monovalent aptamer, the trivalent assembly reduced PBMC interactions to L-selectin ligands 90-fold under shear and exerted superior inhibition of PBMC rolling in vivo. In conclusion, our work demonstrates the feasibility of optimizing aptamer sequences and shows that multivalent ligand presentation enables superior adhesion receptor targeting.

FROM THE CLINICAL EDITOR

During inflammation, leukocytes extravasate from blood vessels under chemotaxic signals. The presence of L-selectin on endothelium acts as a mediator for the extravasation process. In this study, the authors investigated an L-selectin specific blocking DNA aptamer in various forms, as inhibitors to leukocyte binding and extravasation. This new approach confirmed the potential use of aptamers in clinical setting.

[Targeting and role of α4β7 integrin in the pathophysiology of IBD and HIV infection]

Integrins are a large family of heterodimeric cell adhesion molecules that are key regulators in multiple biological functions. They orchestrate cell-cell and cell-extracellular matrix (ECM) adhesive interactions from embryonic development to mature tissue function, and are thus involved in cell migration, proliferation, differentiation, and survival. As such, they are also involved in human diseases, such as thrombotic diseases, inflammation, cancer, fibrosis and infectious diseases. Integrins are exciting pharmacological targets because they are exposed on the cell surface. Indeed, several compounds have been developed that block integrins function, and five have been approved as therapeutic drugs for use in clinic. This review will detail the role of α4β7, an integrin of particular relevance for mucosal diseases such as IBD (inflammatory bowel disease) and also, as reported more recently, HIV infection.

Dysregulated intrahepatic CD4+ T-cell activation drives liver inflammation in ileitis-prone SAMP1/YitFc mice

BACKGROUND AND AIMS

Liver inflammation is a common extraintestinal manifestation of inflammatory bowel disease (IBD); however, whether liver involvement is a consequence of a primary intestinal defect or results from alternative pathogenic processes remains unclear. Therefore, we sought to determine the potential pathogenic mechanism(s) of concomitant liver inflammation in an established murine model of IBD.

METHODS

Liver inflammation and immune cell subsets were characterized in ileitis-prone SAMP1/YitFc (SAMP) and AKR/J (AKR) control mice, lymphocyte-depleted SAMP (SAMPxRag-1^-/-), and immunodeficient SCID recipient mice receiving SAMP or AKR donor CD4⁺ T-cells. Proliferation and suppressive capacity of CD4⁺ T-effector (Teff) and T-regulatory (Treg) cells from gut-associated lymphoid tissue (GALT) and livers of SAMP and AKR mice were measured.

RESULTS

Surprisingly, prominent inflammation was detected in 4-wk-old SAMP livers, prior to histologic evidence of ileitis, while both disease phenotypes were absent in age-matched AKRs. SAMP liver disease was characterized by abundant infiltration of lymphocytes, required for hepatic inflammation to occur, a Th1-skewed environment, and phenotypically-activated CD4⁺ T-cells. SAMP intrahepatic CD4⁺ T-cells also had the ability to induce liver and ileal inflammation when adoptively transferred into SCID recipients, whereas GALT-derived CD4⁺ T-cells produced milder ileitis, but not liver inflammation. Interestingly, SAMP intrahepatic CD4⁺ Teff cells showed increased proliferation compared to both SAMP GALT- and AKR liver-derived CD4⁺ Teff cells, while SAMP intrahepatic Tregs were decreased among CD4⁺ T-cells and impaired in in vitro suppressive function compared to AKR.

CONCLUSIONS

Activated intrahepatic CD4⁺ T-cells induce liver inflammation and contribute to experimental ileitis via locally-impaired hepatic immunosuppressive function.

On naivety of T cells in inflammatory bowel disease: a review

: Little is known about different phases of T-cell maturation in gut mucosa. Based on current knowledge about the migratory pathways of naive and memory T cells, it is believed that access to peripheral, nonlymphoid tissues is restricted to memory T cells. Surprisingly, there is increasing evidence of high numbers of naive T cells in the chronically inflamed gut tissue of patients with inflammatory bowel disease. This could partially be explained by new formation of ectopic lymphoid organs. Ongoing recruitment of naive T cells at inflammatory sites might play a role in the immunopathogenesis of inflammatory bowel disease.

Leukocyte integrins: role in leukocyte recruitment and as therapeutic targets in inflammatory disease

Infection or sterile inflammation triggers site-specific attraction of leukocytes. Leukocyte recruitment is a process comprising several steps orchestrated by adhesion molecules, chemokines, cytokines and endogenous regulatory molecules. Distinct adhesive interactions between endothelial cells and leukocytes and signaling mechanisms contribute to the temporal and spatial fine-tuning of the leukocyte adhesion cascade. Central players in the leukocyte adhesion cascade include the leukocyte adhesion receptors of the β2-integrin family, such as the αLβ2 and αMβ2 integrins, or of the β1-integrin family, such as the α4β1-integrin. Given the central involvement of leukocyte recruitment in different inflammatory and autoimmune diseases, the leukocyte adhesion cascade in general, and leukocyte integrins in particular, represent key therapeutic targets. In this context, the present review focuses on the role of leukocyte integrins in the leukocyte adhesion cascade. Experimental evidence that has implicated leukocyte integrins as targets in animal models of inflammatory disorders, such as experimental autoimmune encephalomyelitis, psoriasis, inflammatory bone loss and inflammatory bowel disease as well as preclinical and clinical therapeutic applications of antibodies that target leukocyte integrins in various inflammatory disorders are presented. Finally, we review recent findings on endogenous inhibitors that modify leukocyte integrin function, which could emerge as promising therapeutic targets.

T cell-associated α4β7 but not α4β1 integrin is required for the induction and perpetuation of chronic colitis

Anti-adhesion therapies that target α(4) integrins (e.g., natalizumab) are thought to work by blocking T-cell recruitment to the intestinal tissues in patients with Crohn's disease (CD); however, little direct evidence is available to confirm this contention. We wished to evaluate the importance of T cell-associated α(4) integrins in a chronic colitis model in mice and to determine the effect of natalizumab treatment on intestinal tissue T-cell accumulation in human CD. Adoptive transfer of T cells lacking α(4) (α(4)(-/-)) but not β(1) integrin into immunodeficient mice produced significantly attenuated disease. This was correlated with reduced numbers of colon CD4 T cells compared with the control mice; however, tissue distribution of T helper type 1 (Th1) and T helper type 17 (Th17) cells and regulatory T cells (Tregs) was not affected by the lack of α(4). Furthermore, α(4)(-/-) T cells demonstrated defective homing to the chronically inflamed small intestines and colons. Finally, patients treated with natalizumab showed significant reduction in mucosal CD4 T cells and no skewing in the foxp3(+) Treg or T-bet(+)Th1 fractions thereof. These results demonstrate a direct role for T cell-associated α(4)β(7) but not α(4)β(1) integrins during initiation and perpetuation of chronic colitis. Moreover, our data demonstrated that natalizumab treatment reduced mucosal CD4 T-cell accumulation in CD patients.

The role of glycosylation in IBD

A number of genetic and immunological studies give impetus for investigating the role of glycosylation in IBD. Experimental mouse models have helped to delineate the role of glycosylation in intestinal mucins and to explore the putative pathogenic role of glycosylation in colitis. These experiments have been extended to human studies investigating the glycosylation patterns of intestinal mucins as well as levels of glycans of serum glycoproteins and expression of glycan receptors. These early human studies have generated interesting hypotheses regarding the pathogenic role of glycans in IBD, but have generally been restricted to fairly small underpowered studies. Decreased glycosylation has been observed in the intestinal mucus of patients with IBD, suggesting that a defective inner mucus layer might lead to increased bacterial contact with the epithelium, potentially triggering inflammation. In sera, decreased galactosylation of IgG has been suggested as a diagnostic marker for IBD. Advances in glycoprofiling technology make it technically feasible and affordable to perform high-throughput glycan pattern analyses and to build on previous work investigating a much wider range of glycan parameters in large numbers of patients.