Therapeutic induction of antigen-specific immune tolerance

The development of therapeutic approaches for the induction of robust, long-lasting and antigen-specific immune tolerance remains an important unmet clinical need for the management of autoimmunity, allergy, organ transplantation and gene therapy. Recent breakthroughs in our understanding of immune tolerance mechanisms have opened new research avenues and therapeutic opportunities in this area. Here, we review mechanisms of immune tolerance and novel methods for its therapeutic induction.

Diverse macrophage populations contribute to distinct manifestations of human cutaneous graft-versus-host disease

BACKGROUND

Graft-versus-host disease (GvHD) is a major life-threatening complication of allogeneic haematopoietic stem cell transplantation (HSCT), limiting the broad application of HSCT for haematological malignancies. Cutaneous GvHD is described as a post-transplant inflammatory reaction by skin-infiltrating donor T cells and remaining recipient tissue-resident memory T cells. Despite the major influence of lymphocytes on GvHD pathogenesis, the complex role of mononuclear phagocytes (MNPs) in tissues affected by GvHD is increasingly appreciated.

OBJECTIVES

To characterize the identity, origin and functions of MNPs in patients with acute cutaneous GvHD.

METHODS

Using single-cell RNA sequencing and multiplex tissue immunofluorescence, we identified an increased abundance of MNPs in skin and blood from 36 patients with acute cutaneous GvHD. In cases of sex-mismatched transplantation, we used expression of X-linked genes to detect rapid tissue adaptation of newly recruited donor MNPs resulting in similar transcriptional states of host- and donor-derived macrophages within GvHD skin lesions.

RESULTS

We showed that cutaneous GvHD lesions harbour expanded CD163+ tissue-resident macrophage populations with anti-inflammatory and tissue-remodelling properties including interleukin-10 cytokine production. Cell-cell interaction analyses revealed putative signalling to strengthen regulatory T-cell responses. Notably, macrophage polarization in chronic cutaneous GvHD types was proinflammatory and drastically differed from acute GvHD, supporting the notion of distinct cellular players in different clinical GvHD subtypes.

CONCLUSIONS

Overall, our data reveal a surprisingly dynamic role of MNPs after HSCT. Specific and time-resolved targeting to repolarize this cell subset may present a promising therapeutic strategy in combatting GvHD skin inflammation.

Genomic profiling and associated B cell lineages delineate the efficacy of neoadjuvant anti-PD-1-based therapy in oesophageal squamous cell carcinoma

BACKGROUND

Neoadjuvant chemoimmunotherapy has offered novel therapeutic options for patients with locally advanced oesophageal squamous cell carcinoma (ESCC). Depicting the landscape of genomic and immune profiles is critical in predicting therapeutic responses.

METHODS

We integrated whole-exome sequencing, single-cell RNA sequencing, and immunofluorescence data of ESCC samples from 24 patients who received neoadjuvant treatment with PD-1 inhibitors plus paclitaxel and platinum-based chemotherapy to identify correlations with therapeutic responses.

FINDINGS

An elevation of small insertions and deletions was observed in responders. DNA mismatch repair (MMR) pathway alternations were highly frequent in patients with optimal responses and correlated with tumour infiltrating lymphocytes (TILs). Among the TILs in ESCC, dichotomous developing trajectories of B cells were identified, with one lineage differentiating towards LMO2+ germinal centre B cells and another lineage differentiating towards CD55+ memory B cells. While LMO2+ germinal centre B cells were enriched in responding tumours, CD55+ memory B cells were found to correlate with inferior responses to combination therapy, exhibiting immune-regulating features and impeding the cytotoxicity of CD8+ T cells. The comprehensive evaluation of transcriptomic B cell lineage features was validated to predict responses to immunotherapy in patients with cancer.

INTERPRETATION

This comprehensive evaluation of tumour MMR pathway alternations and intra-tumoural B cell features will help to improve the selection and management of patients with ESCC to receive neoadjuvant chemoimmunotherapy.

FUNDING

National Science Foundation of China (82373371, 82330053), Eastern Scholar Program at Shanghai Institutions of Higher Learning, National Science and Technology Major Project of China (2023YFA1800204, 2020YFC2008402), and Science and Technology Commission of Shanghai Municipality (22ZR1410700, 20ZR1410800).

Role of Adhesion G Protein-Coupled Receptors in Immune Dysfunction and Disorder

Disorders of the immune system, including immunodeficiency, immuno-malignancy, and (auto)inflammatory, autoimmune, and allergic diseases, have a great impact on a host’s health. Cellular communication mediated through cell surface receptors, among different cell types and between cell and microenvironment, plays a critical role in immune responses. Selective members of the adhesion G protein-coupled receptor (aGPCR) family are expressed differentially in diverse immune cell types and have been implicated recently in unique immune dysfunctions and disorders in part due to their dual cell adhesion and signaling roles. Here, we discuss the molecular and functional characteristics of distinctive immune aGPCRs and their physiopathological roles in the immune system.

Erratum: Type 1 regulatory T cell-mediated tolerance in health and disease

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Type 1 regulatory T cell-mediated tolerance in health and disease

Type 1 regulatory T (Tr1) cells, in addition to other regulatory cells, contribute to immunological tolerance to prevent autoimmunity and excessive inflammation. Tr1 cells arise in the periphery upon antigen stimulation in the presence of tolerogenic antigen presenting cells and secrete large amounts of the immunosuppressive cytokine IL-10. The protective role of Tr1 cells in autoimmune diseases and inflammatory bowel disease has been well established, and this led to the exploration of this population as a potential cell therapy. On the other hand, the role of Tr1 cells in infectious disease is not well characterized, thus raising concern that these tolerogenic cells may cause general immune suppression which would prevent pathogen clearance. In this review, we summarize current literature surrounding Tr1-mediated tolerance and its role in health and disease settings including autoimmunity, inflammatory bowel disease, and infectious diseases.

[DNAM-1 regulates the proliferation and function of T regulatory type 1 cells via the IL-2/STAT5 pathway]

OBJECTIVE

To explore the role of DNAM-1 in the activation, proliferation and function of type Ⅰ regulatory T cells (Tr1 cells).

METHODS

Anti-CD3/CD28 antibodies were used to stimulate mouse T cells derived from the spleen of wild-type (WT) mice, and the expression level of DNAM-1 in resting and activated Tr1 cells was evaluated with flow cytometry. Na?ve CD4⁺ T cells isolated by magnetic cell sorting from the spleens of WT mice and DNAM-1 knockout (KO) mice were cultured in Tr1 polarizing conditions for 3 days, after which CD25 and CD69 expressions were measured using flow cytometry. The induced Tr1 cells were labelled with CFSE and cultured in the presence of anti-CD/CD28 antibodies for 3 days, and their proliferative activity was analyzed. The expressions of IL-10 and p-STAT5 in DNAM-1-deficient Tr1 cells were detected before and after IL-2 stimulation.

RESULTS

The expression level of DNAM-1 was significantly upregulated in CD4⁺ T cells and Tr1 cells after stimulation with anti-CD3/CD28 antibodies (P < 0.05). DNAM-1 knockout did not cause significant changes in the number or proportion of Tr1 cells, but but significantly increased the expression levels of the activation markers CD69 and CD25 (P < 0.05). Compared with WT Tr1 cells, DNAM-1-deficient Tr1 cells exhibited reduced proliferative activity in vitro (P < 0.05) with downregulated IL-10 production (P < 0.05) and decreased expressions of Il-10 and Gzmb mRNA (P < 0.05). In DNAM-1-deficient Tr1 cells, IL-2 stimulation significantly reduced IL-10 secretion level and the expression of p-STAT5 as compared with WT Tr1 cells.

CONCLUSION

DNAM-1 participate in the activation and proliferation of Tr1 cells and affect the biological functions of Tr1 cells through the IL-2/STAT5 pathway.

Adhesion G protein-coupled receptor gluing action guides tissue development and disease

Phylogenetic analysis of human G protein-coupled receptors (GPCRs) divides these transmembrane signaling proteins into five groups: glutamate, rhodopsin, adhesion, frizzled, and secretin families, commonly abbreviated as the GRAFS classification system. The adhesion GPCR (aGPCR) sub-family comprises 33 different receptors in humans. Majority of the aGPCRs are orphan receptors with unknown ligands, structures, and tissue expression profiles. They have a long N-terminal extracellular domain (ECD) with several adhesion sites similar to integrin receptors. Many aGPCRs undergo autoproteolysis at the GPCR proteolysis site (GPS), enclosed within the larger GPCR autoproteolysis inducing (GAIN) domain. Recent breakthroughs in aGPCR research have created new paradigms for understanding their roles in organogenesis. They play crucial roles in multiple aspects of organ development through cell signaling, intercellular adhesion, and cell-matrix associations. They are involved in essential physiological processes like regulation of cell polarity, mitotic spindle orientation, cell adhesion, and migration. Multiple aGPCRs have been associated with the development of the brain, musculoskeletal system, kidneys, cardiovascular system, hormone secretion, and regulation of immune functions. Since aGPCRs have crucial roles in tissue patterning and organogenesis, mutations in these receptors are often associated with diseases with loss of tissue integrity. Thus, aGPCRs include a group of enigmatic receptors with untapped potential for elucidating novel signaling pathways leading to drug discovery. We summarized the current knowledge on how aGPCRs play critical roles in organ development and discussed how aGPCR mutations/genetic variants cause diseases.

Chemo- and mechanosensing by dendritic cells facilitate antigen surveillance in the spleen

Spleen dendritic cells (DC) are critical for initiation of adaptive immune responses against blood-borne invaders. Key to DC function is their positioning at sites of pathogen entry, and their abilities to selectively capture foreign antigens and promptly engage T cells. Focusing on conventional DC2 (cDC2), we discuss the contribution of chemoattractant receptors (EBI2 or GPR183, S1PR1, and CCR7) and integrins to cDC2 positioning and function. We give particular attention to a newly identified role in cDC2 for adhesion G-protein coupled receptor E5 (Adgre5 or CD97) and its ligand CD55, detailing how this mechanosensing system contributes to splenic cDC2 positioning and homeostasis. Additional roles of CD97 in the immune system are reviewed. The ability of cDC2 to be activated by circulating missing self-CD47 cells and to integrate multiple red blood cell (RBC)-derived inputs is discussed. Finally, we describe the process of activated cDC2 migration to engage and prime helper T cells. Throughout the review, we consider the insights into cDC function in the spleen that have emerged from imaging studies.

Monocyte biology conserved across species: Functional insights from cattle

Similar to human monocytes, bovine monocytes can be split into CD14^highCD16^- classical, CD14^highCD16^high intermediate and CD14^-/dimCD16^high nonclassical monocytes (cM, intM, and ncM, respectively). Here, we present an in-depth analysis of their steady-state bulk- and single-cell transcriptomes, highlighting both pronounced functional specializations and transcriptomic relatedness. Bulk gene transcription indicates pro-inflammatory and antibacterial roles of cM, while ncM and intM appear to be specialized in regulatory/anti-inflammatory functions and tissue repair, as well as antiviral responses and T-cell immunomodulation. Notably, intM stood out by high expression of several genes associated with antigen presentation. Anti-inflammatory and antiviral functions of ncM are further supported by dominant oxidative phosphorylation and selective strong responses to TLR7/8 ligands, respectively. Moreover, single-cell RNA-seq revealed previously unappreciated heterogeneity within cM and proposes intM as a transient differentiation intermediate between cM and ncM.

Exosomes secreted by palmitic acid-treated hepatocytes promote LX-2 cell activation by transferring miRNA-107

Activation of hepatic stellate cells (HSCs) is a key inducer of liver fibrogenesis in nonalcoholic fatty liver disease (NAFLD). Exosomes play an important role between hepatocytes and HSCs. This study aims to explore the role of exosomes derived from palmitic acid (PA)-treated hepatocytes in regulating HSCs (LX-2 cell) proliferation and activation and the underlying mechanisms. Exosomes were isolated from PA-treated human normal hepatocytes and incubated with LX-2 cells. Cell Counting Kit-8 (CCK-8) was performed to determine LX-2 cell proliferation, and the expression of fibrosis markers α-smooth muscle actin (α-SMA) and collagen type 1 α1 (CoL1A1) were examined to evaluateLX-2 cell activation. PA induced hepatocytes to release more exosomes enriched in miR-107. Mechanically, on the one hand, exosomes from PA-treated hepatocytes shuttled miR-107 to LX-2 cells, where miR-107 activated Wnt signaling by targeting DKK1 and thereby induced LX-2 cell activation; on the other hand, PA-treated hepatocytes derived exosomes also delivered miR-107 to CD4 + T lymphocytes, where miR-107 elevated IL-9 expression by targeting Foxp1, which bound to the IL-9 promoter in CD4 + T cells and suppressed Th9 cell differentiation and reduced IL-9 expression, and thus promoted LX-2 cell activation by activating Raf/MEK/ERK signaling pathway.

The Yin and Yang of Type 1 Regulatory T Cells: From Discovery to Clinical Application

Regulatory T cells are essential players of peripheral tolerance and suppression of inflammatory immune responses. Type 1 regulatory T (Tr1) cells are FoxP3^- regulatory T cells induced in the periphery under tolerogenic conditions. Tr1 cells are identified as LAG3⁺CD49b⁺ mature CD4⁺ T cells that promote peripheral tolerance through secretion of IL-10 and TGF-β in addition to exerting perforin- and granzyme B-mediated cytotoxicity against myeloid cells. After the initial challenges of isolation were overcome by surface marker identification, ex vivo expansion of antigen-specific Tr1 cells in the presence of tolerogenic dendritic cells (DCs) and IL-10 paved the way for their use in clinical trials. With one Tr1-enriched cell therapy product already in a Phase I clinical trial in the context of allogeneic hematopoietic stem cell transplantation (allo-HSCT), Tr1 cell therapy demonstrates promising results so far in terms of efficacy and safety. In the current review, we identify developments in phenotypic and molecular characterization of Tr1 cells and discuss the potential of engineered Tr1-like cells for clinical applications of Tr1 cell therapies. More than 3 decades after their initial discovery, Tr1 cell therapy is now being used to prevent graft versus host disease (GvHD) in allo-HSCT and will be an alternative to immunosuppression to promote graft tolerance in solid organ transplantation in the near future.

Tr1 Cells as a Key Regulator for Maintaining Immune Homeostasis in Transplantation

The immune system is composed of effectors and regulators. Type 1 regulatory T (Tr1) cells are classified as a distinct subset of T cells, and they secret high levels of IL-10 but lack the expression of the forkhead box P3 (Foxp3). Tr1 cells act as key regulators in the immune network, and play a central role in maintaining immune homeostasis. The regulatory capacity of Tr1 cells depends on many mechanisms, including secretion of suppressive cytokines, cell-cell contacts, cytotoxicity and metabolic regulation. A breakdown of Tr1-cell-mediated tolerance is closely linked with the pathogenesis of various diseases. Based on this observation, Tr1-cell therapy has emerged as a successful treatment option for a number of human diseases. In this review, we describe an overview of Tr1 cell identification, functions and related molecular mechanisms. We also discuss the current protocols to induce/expand Tr1 cells in vitro for clinical application, and summarize the recent progress of Tr1 cells in transplantation.

Genomic biomarkers in chronic beryllium disease and sarcoidosis

Background Previous gene expression studies have identified genes IFNγ, TNFα, RNase 3, CXCL9, and CD55 as potential biomarkers for sarcoidosis and/or chronic beryllium disease (CBD). We hypothesized that differential expression of these genes could function as diagnostic biomarkers for sarcoidosis and CBD, and prognostic biomarkers for sarcoidosis. Study Design/Methods We performed RT-qPCR on whole blood samples from CBD (n = 132), beryllium sensitized (BeS) (n = 109), and sarcoidosis (n = 99) cases and non-diseased controls (n = 97) to determine differential expression of target genes. We then performed logistic regression modeling and generated ROC curves to determine which genes could most accurately differentiate: 1) CBD versus sarcoidosis 2) CBD versus BeS 3) sarcoidosis versus controls 4) non-progressive versus progressive sarcoidosis. Results CD55 and TNFα were significantly upregulated, while CXCL9 was significantly downregulated in CBD compared to sarcoidosis (p < 0.05). The ROC curve from the logistic regression model demonstrated high discriminatory ability of the combination of CD55, TNFα, and CXCL9 to distinguish between CBD and sarcoidosis with an AUC of 0.98. CD55 and TNFα were significantly downregulated in sarcoidosis compared to controls (p < 0.05). The ROC curve from the model showed a reasonable discriminatory ability of CD55 and TNFα to distinguish between sarcoidosis and controls with an AUC of 0.86. There was no combination of genes that could accurately differentiate between CBD and BeS or sarcoidosis phenotypes. Interpretation CD55, TNFα and CXCL9 expression levels can accurately differentiate between CBD and sarcoidosis, while CD55 and TNFα expression levels can accurately differentiate sarcoidosis and controls.

The expression of membrane-bound complement regulatory proteins CD46, CD55 and CD59 in oral lichen planus

OBJECTIVE

To investigate the expression levels of membrane-anchored complement regulatory proteins (mCRPs), CD46, CD55 and CD59 in oral lichen planus (OLP), and evaluate the activation status of complement.

DESIGN

Thirty-seven cases of OLP patients (20 non-erosive OLP and 17 erosive OLP) and twenty healthy controls were recruited in this study. The proteins and mRNA expression levels of CD46, CD55 and CD59 in OLP tissues were detected by western blotting and RT-qPCR respectively, and the expression levels of complement C3 and sC5b-9 in OLP patients' saliva were detected by ELISA to evaluate the activation status of complement. In addition, mucosa tissues of another 3 non-erosive OLP patients and another 3 healthy controls were collected, and the epithelial layer of two groups were separated to culture primary keratinocytes in vitro. Immunofluorescence was used to further detect the expression of mCRPs at the cellular level.

RESULTS

The levels of CD46, CD55 and CD59 in OLP tissues and cells were significantly decreased compared with those of the healthy control group, and the level of complement C3 in the patients' saliva was significantly decreased, while the level of sC5b-9 was increased.

CONCLUSIONS

These results suggest that the reduced expression of mCRPs keeps the complement system in a continuously active state, which may be the reason of the persistent local immune inflammatory state in OLP. This study aimed to provide new insights for the etiology and therapy of OLP.

The microRNA miR-133b functions to slow Duchenne muscular dystrophy pathogenesis

KEY POINTS

Impairment of muscle biogenesis contributes to the progression of Duchenne muscular dystrophy (DMD). As a muscle enriched microRNA that has been implicated in muscle biogenesis, the role of miR-133b in DMD remains unknown. To assess miR-133b function in DMD-affected skeletal muscles, we genetically ablated miR-133b in the mdx mouse model of DMD. We show that deletion of miR-133b exacerbates the dystrophic phenotype of DMD-afflicted skeletal muscle by dysregulating muscle stem cells involved in muscle biogenesis, in addition to affecting signalling pathways related to inflammation and fibrosis. Our results provide evidence that miR-133b may underlie DMD pathology by affecting the proliferation and differentiation of muscle stem cells.

ABSTRACT

Duchenne muscular dystrophy (DMD) is characterized by progressive skeletal muscle degeneration. No treatments are currently available to prevent the disease. While the muscle enriched microRNA miR-133b has been implicated in muscle biogenesis, its role in DMD remains unknown. To assess miR-133b function in DMD-affected skeletal muscles, we genetically ablated miR-133b in the mdx mouse model of DMD. In the absence of miR-133b, the tibialis anterior muscle of P30 mdx mice is smaller in size and exhibits a thickened interstitial space containing more mononucleated cells. Additional analysis revealed that miR-133b deletion influences muscle fibre regeneration, satellite cell proliferation and differentiation, and induces widespread transcriptomic changes in mdx muscle. These include known miR-133b targets as well as genes involved in cell proliferation and fibrosis. Altogether, our data demonstrate that skeletal muscles utilize miR-133b to mitigate the deleterious effects of DMD.

CD226: An Emerging Role in Immunologic Diseases

CD226, a member of the immunoglobulin superfamily, is a functional protein initially expressed on natural killer and T cells. In recent years, the function of CD226 has been increasingly realized and researched. Accumulating evidence shows that CD226 is closely related to the occurrence of autoimmune diseases, infectious diseases, and tumors. Because of the CD226’s increasing importance, the author herein discusses the structure, mechanism of action, and role of CD226 in various pathophysiological environments, allowing for further understanding of the function of CD226 and providing the basis for further research in related diseases.

Early-onset inflammatory bowel disease as a model disease to identify key regulators of immune homeostasis mechanisms

Rare, monogenetic diseases present unique models to dissect gene functions and biological pathways, concomitantly enhancing our understanding of the etiology of complex (and often more common) traits. Although inflammatory bowel disease (IBD) is a generally prototypic complex disease, it can also manifest in an early-onset, monogenic fashion, often following Mendelian modes of inheritance. Recent advances in genomic technologies have spurred the identification of genetic defects underlying rare, very early-onset IBD (VEO-IBD) as a disease subgroup driven by strong genetic influence, pinpointing key players in the delicate homeostasis of the immune system in the gut and illustrating the intimate relationships between bowel inflammation, systemic immune dysregulation, and primary immunodeficiency with increased susceptibility to infections. As for other human diseases, it is likely that adult-onset diseases may represent complex diseases integrating the effects of host genetic susceptibility and environmental triggers. Comparison of adult-onset IBD and VEO-IBD thus provides beautiful models to investigate the relationship between monogenic and multifactorial/polygenic diseases. This review discusses the present and novel findings regarding monogenic IBD as well as key questions and future directions of IBD research.

SV-BR-1-GM, a Clinically Effective GM-CSF-Secreting Breast Cancer Cell Line, Expresses an Immune Signature and Directly Activates CD4+ T Lymphocytes

Targeted cancer immunotherapy with irradiated, granulocyte–macrophage colony-stimulating factor (GM-CSF)-secreting, allogeneic cancer cell lines has been an effective approach to reduce tumor burden in several patients. It is generally assumed that to be effective, these cell lines need to express immunogenic antigens coexpressed in patient tumor cells, and antigen-presenting cells need to take up such antigens then present them to patient T cells. We have previously reported that, in a phase I pilot study (ClinicalTrials.gov NCT00095862), a subject with stage IV breast cancer experienced substantial regression of breast, lung, and brain lesions following inoculation with clinical formulations of SV-BR-1-GM, a GM-CSF-secreting breast tumor cell line. To identify diagnostic features permitting the prospective identification of patients likely to benefit from SV-BR-1-GM, we conducted a molecular analysis of the SV-BR-1-GM cell line and of patient-derived blood, as well as a tumor specimen. Compared to normal human breast cells, SV-BR-1-GM cells overexpress genes encoding tumor-associated antigens (TAAs) such as PRAME, a cancer/testis antigen. Curiously, despite its presumptive breast epithelial origin, the cell line expresses major histocompatibility complex (MHC) class II genes (HLA-DRA, HLA-DRB3, HLA-DMA, HLA-DMB), in addition to several other factors known to play immunostimulatory roles. These factors include MHC class I components (B2M, HLA-A, HLA-B), ADA (encoding adenosine deaminase), ADGRE5 (CD97), CD58 (LFA3), CD74 (encoding invariant chain and CLIP), CD83, CXCL8 (IL8), CXCL16, HLA-F, IL6, IL18, and KITLG. Moreover, both SV-BR-1-GM cells and the responding study subject carried an HLA-DRB3*02:02 allele, raising the question of whether SV-BR-1-GM cells can directly present endogenous antigens to T cells, thereby inducing a tumor-directed immune response. In support of this, SV-BR-1-GM cells (which also carry the HLA-DRB3*01:01 allele) treated with yellow fever virus (YFV) envelope (Env) 43–59 peptides reactivated YFV-DRB3*01:01-specific CD4⁺ T cells. Thus, the partial HLA allele match between SV-BR-1-GM and the clinical responder might have enabled patient T lymphocytes to directly recognize SV-BR-1-GM TAAs as presented on SV-BR-1-GM MHCs. Taken together, our findings are consistent with a potentially unique mechanism of action by which SV-BR-1-GM cells can act as APCs for previously primed CD4⁺ T cells.

The cell surface phenotype of human dendritic cells

Dendritic cells (DC) are bone marrow derived leucocytes that are part of the mononuclear phagocytic system. These are surveillance cells found in all tissues and, as specialised antigen presenting cells, direct immune responses. Membrane molecules on the DC surface form a landscape that defines them as leucocytes and part of the mononuclear phagocytic system, interacts with their environment and directs interactions with other cells. This review describes the DC surface landscape, reflects on the different molecules confirmed to be on their surface and how they provide the basis for manipulation and translation of the potent functions of these cells into new diagnostics and immune therapies for the clinic.

Complement as a regulator of adaptive immunity

The complement system is an ancient and evolutionarily conserved effector system comprising in mammals over 50 circulating and membrane bound proteins. Complement has long been described as belonging to the innate immune system; however, a number of recent studies have demonstrated its key role in the modulation of the adaptive immune response. This review does not set out to be an exhaustive list of the numerous interactions of the many complement components with adaptive immunity; rather, we will focus more precisely on the role of some complement molecules in the regulation of antigen presenting cells, as well as on their direct effect on the activation of the core adaptive immune cells, B and T lymphocytes. Recent reports on the local production and activation of complement proteins also suggest a major role in the control of effector responses. The crucial role of complement in adaptive immunity is further highlighted by several examples of dysregulation of these pathways in human diseases.

Dissecting the mechanisms involved in anti-human T-lymphocyte immunoglobulin (ATG)-induced tolerance in the setting of allogeneic stem cell transplantation - potential implications for graft versus host disease

Polyclonal anti-human thymocyte globulins (ATG) have been recently shown to significantly reduce the incidence of graft versus host disease (GVHD) post allogeneic stem cell transplantation (HSCT) from both sibling and unrelated donors. Induction of regulatory T cells has been suggested as one of the possible mechanisms. The aim of current study was to further characterize the T cell populations induced by ATG treatment and to delineate the mechanisms involved in ATG-induced tolerance. Phenotypic characterization revealed a significant increase in the expression of FoxP3, GITR, CD95, PD-1 and ICOS as well as the complement inhibitory molecules CD55, CD58 and CD59 on CD4+CD25+ T cells upon ATG treatment. Addition of ATG-treated cells to autologous and allogeneic peripheral blood mononuclear cells (PBMCs) stimulated with anti-CD3/anti-CD28 antibodies resulted in significant inhibition of proliferation. Moreover, T-cell activation and IFNγ secretion were reduced in the presence of ATG-induced Treg cells. The CD4+CD25+CD127-low Treg fraction sorted from ATG-treated culture demonstrated greater suppressive potency than negative fraction. Conditioned medium produced by ATG-treated but not IgG-treated cells contained TGFβ and suppressed T cell proliferation and activation in a TGFβ receptor-dependent manner. TGFβ receptor kinase inhibitor SB431542 interfered with the suppressive activity of ATG-primed cells, enabling partial rescue of proliferation and IFNγ secretion. Moreover, SB431542 prevented Treg phenotype induction upon ATG treatment. Altogether, our data reveal the role of TGFβ signaling in ATG-mediated immunosuppression and further support the use of ATG, a potent inducer of regulatory T cells, for prevention of GVHD post HSCT and potentially other therapeutic applications.

Hypoxia-Inducible Factor-1α Regulates CD55 in Airway Epithelium

Airway epithelial CD55 down-regulation occurs in several hypoxia-associated pulmonary diseases, but the mechanism is unknown. Using in vivo and in vitro assays of pharmacologic inhibition and gene silencing, the current study investigated the role of hypoxia-inducible factor (HIF)-1α in regulating airway epithelial CD55 expression. Hypoxia down-regulated CD55 expression on small-airway epithelial cells in vitro, and in murine lungs in vivo; the latter was associated with local complement activation. Treatment with pharmacologic inhibition or silencing of HIF-1α during hypoxia-recovered CD55 expression in small-airway epithelial cells. HIF-1α overexpression or blockade, in vitro or in vivo, down-regulated CD55 expression. Collectively, these data show a key role for HIF-1α in regulating the expression of CD55 on airway epithelium.

A prebiotic galactooligosaccharide mixture reduces severity of hyperpnoea-induced bronchoconstriction and markers of airway inflammation

Gut microbes have a substantial influence on systemic immune function and allergic sensitisation. Manipulation of the gut microbiome through prebiotics may provide a potential strategy to influence the immunopathology of asthma. This study investigated the effects of prebiotic Bimuno-galactooligosaccharide (B-GOS) supplementation on hyperpnoea-induced bronchoconstriction (HIB), a surrogate for exercise-induced bronchoconstriction, and airway inflammation. A total of ten adults with asthma and HIB and eight controls without asthma were randomised to receive 5·5 g/d of either B-GOS or placebo for 3 weeks separated by a 2-week washout period. The peak fall in forced expiratory volume in 1 s (FEV1) following eucapnic voluntary hyperpnoea (EVH) defined HIB severity. Markers of airway inflammation were measured at baseline and after EVH. Pulmonary function remained unchanged in the control group. In the HIB group, the peak post-EVH fall in FEV1 at day 0 (-880 (sd 480) ml) was unchanged after placebo, but was attenuated by 40 % (-940 (sd 460) v. -570 (sd 310) ml, P=0·004) after B-GOS. In the HIB group, B-GOS reduced baseline chemokine CC ligand 17 (399 (sd 140) v. 323 (sd 144) pg/ml, P=0·005) and TNF-α (2·68 (sd 0·98) v. 2·18 (sd 0·59) pg/ml, P=0·040) and abolished the EVH-induced 29 % increase in TNF-α. Baseline C-reactive protein was reduced following B-GOS in HIB (2·46 (sd 1·14) v. 1·44 (sd 0·41) mg/l, P=0·015) and control (2·16 (sd 1·02) v. 1·47 (sd 0·33) mg/l, P=0·050) groups. Chemokine CC ligand 11 and fraction of exhaled nitric oxide remained unchanged. B-GOS supplementation attenuated airway hyper-responsiveness with concomitant reductions in markers of airway inflammation associated with HIB.

Tr1-Like T Cells - An Enigmatic Regulatory T Cell Lineage

The immune system evolved to respond to foreign invaders and prevent autoimmunity to self-antigens. Several types of regulatory T cells facilitate the latter process. These include a subset of Foxp3⁻ CD4⁺ T cells able to secrete IL-10 in an antigen-specific manner, type 1 regulatory (Tr1) T cells. Although their suppressive function has been confirmed both in vitro and in vivo, their phenotype remains poorly defined. It has been suggested that the surface markers LAG-3 and CD49b are biomarkers for murine and human Tr1 cells. Here, we discuss these findings in the context of our data regarding the expression pattern of inhibitory receptors (IRs) CD49b, TIM-3, PD-1, TIGIT, LAG-3, and ICOS on Tr1-like human T cells generated in vitro from CD4⁺ memory T cells stimulated with αCD3 and αCD28 antibodies. We found that there were no differences in IR expression between IL-10⁺ and IL-10⁻ T cells. However, CD4⁺IL-10⁺ T cells isolated ex vivo, following a short stimulation and cytokine secretion assay, contained significantly higher proportions of TIM-3⁺ and PD-1⁺ cells. They also expressed significantly higher TIGIT mRNA and showed a trend toward increased TIM-3 mRNA levels. These data led us to conclude that large pools of IRs may be stored intracellularly; hence, they may not represent ideal candidates as cell surface biomarkers for Tr1-like T cells.

Type 1 regulatory T cells: a new mechanism of peripheral immune tolerance

The lack of immune response to an antigen, a process known as immune tolerance, is essential for the preservation of immune homeostasis. To date, two mechanisms that drive immune tolerance have been described extensively: central tolerance and peripheral tolerance. Under the new nomenclature, thymus-derived regulatory T (tT(reg)) cells are the major mediators of central immune tolerance, whereas peripherally derived regulatory T (pT(reg)) cells function to regulate peripheral immune tolerance. A third type of T(reg) cells, termed iT(reg), represents only the in vitro-induced T(reg) cells(1). Depending on whether the cells stably express Foxp3, pT(reg), and iT(reg) cells may be divided into two subsets: the classical CD4(+)Foxp3(+) T(reg) cells and the CD4(+)Foxp3(-) type 1 regulatory T (Tr1) cells(2). This review focuses on the discovery, associated biomarkers, regulatory functions, methods of induction, association with disease, and clinical trials of Tr1 cells.

Expression and prognostic value of CD97 and its ligand CD55 in pancreatic cancer

CD97 is a member of the epidermal growth factor-seven transmembrane family. It affects tumor aggressiveness by binding its cellular ligand CD55 and exhibits adhesive properties. Previous studies have shown that CD97 and CD55 are involved in the dedifferentiation, migration, invasiveness and metastasis of tumors. However, little is known regarding the roles of CD97 and CD55 in pancreatic cancer. In this study, immunohistochemistry was used to analyze CD97 and CD55 protein expression in samples obtained from 37 pancreatic cancer patients. CD97 and CD55 were absent or only weakly expressed in the normal pancreatic tissues but strongly expressed in pancreatic cancer tissues (P<0.05), particularly in tissues with lymph node involvement, metastasis or vascular invasion (P<0.05). Notably, CD97 and CD55 were expressed consistently in pancreatic cancer tissues (r²=0.5422; P<0.05). In addition, CD97 and CD55 expression levels were found to significantly correlate with tumor aggressiveness (P<0.01). Multivariate analyses revealed that CD97 and CD55 expression levels were closely associated with prognosis (P<0.05). Taken together, these results indicated that CD97 and its ligand CD55 are upregulated in pancreatic cancers and are closely associated with lymph node involvement, metastasis and vascular invasion. Thus, analysis of both CD97 and CD55 expression may present potential prognostic value for pancreatic cancer.

The role of decay accelerating factor in environmentally induced and idiopathic systemic autoimmune disease

Decay accelerating factor (DAF) plays a complex role in the immune system through complement-dependent and -independent regulation of innate and adaptive immunity. Over the past five years there has been accumulating evidence for a significant role of DAF in negatively regulating adaptive T-cell responses and autoimmunity in both humans and experimental models. This review discusses the relationship between DAF and the complement system and highlights major advances in our understanding of the biology of DAF in human disease, particularly systemic lupus erythematosus. The role of DAF in regulation of idiopathic and environmentally induced systemic autoimmunity is discussed including studies showing that reduction or absence of DAF is associated with autoimmunity. In contrast, DAF-mediated T cell activation leads to cytokine expression consistent with T regulatory cells. This is supported by studies showing that interaction between DAF and its molecular partner, CD97, modifies expression of autoimmunity promoting cytokines. These observations are used to develop a hypothetical model to explain how DAF expression may impact T cell differentiation via interaction with CD97 leading to T regulatory cells, increased production of IL-10, and immune tolerance.