A systematic literature review informing the consensus statement on efficacy and safety of pharmacological treatment with interleukin-6 pathway inhibition with biological DMARDs in immune-mediated inflammatory diseases

Objectives

Informing an international task force updating the consensus statement on efficacy and safety of biological disease-modifying antirheumatic drugs (bDMARDs) selectively targeting interleukin-6 (IL-6) pathway in the context of immune-mediated inflammatory diseases.

Methods

A systematic literature research of all publications on IL-6 axis inhibition with bDMARDs published between January 2012 and December 2020 was performed using MEDLINE, EMBASE and Cochrane CENTRAL databases. Efficacy and safety outcomes were assessed in clinical trials including their long-term extensions and observational studies. Meeting abstracts from ACR, EULAR conferences and results on clinicaltrials.gov were taken into consideration.

Results

187 articles fulfilled the inclusion criteria. Evidence for positive effect of IL-6 inhibition was available in various inflammatory diseases such as rheumatoid arthritis, juvenile idiopathic arthritis, giant cell arteritis, Takayasu arteritis, adult-onset Still’s disease, cytokine release syndrome due to chimeric antigen receptor T cell therapy and systemic sclerosis-associated interstitial lung disease. Newcomers like satralizumab and anti-IL-6 ligand antibody siltuximab have expanded therapeutic approaches for Castleman’s disease and neuromyelitis optica, respectively. IL-6 inhibition did not provide therapeutic benefits in psoriatic arthritis, ankylosing spondylitis and certain connective tissue diseases. In COVID-19, tocilizumab (TCZ) has proven to be therapeutic in advanced disease. Safety outcomes did not differ from other bDMARDs, except higher risks of diverticulitis and lower gastrointestinal perforations. Inconsistent results were observed in several studies investigating the risk for infections when comparing TCZ to TNF-inhibitors.

Conclusion

IL-6 inhibition is effective for treatment of several inflammatory diseases with a safety profile that is widely comparable to other bDMARDs.

Natural Killer Cells Infiltration in the Joints Exacerbates Collagen-Induced Arthritis

Introduction

The role of natural killer (NK) cells in rheumatoid arthritis remains controversial. We aimed to assess the role of NK cells in the pathogenesis of rheumatoid arthritis.

Materials and Methods

The percentage of NK cells in the peripheral blood, spleen, lymph nodes and inflamed paws from collagen-induced arthritis mice were examined through the disease progression. Correlation between the proportion of NK cells and subsets with arthritis score, histopathological changes, and bone destruction were evaluated. Adoptive cell transfer was performed to determine the effect of NKp46⁺NK cells on arthritis development, and the role of receptor NKp46 was explored with NKp46 knockout mice.

Results

The percentage of NK cells in peripheral blood decreased at the late stage of the disease and negatively correlated with arthritis score. NK cells increased in the inflamed paws during arthritis development and were positively associated with arthritis score, histopathological change, and bone destruction. Adoptive transfer of NKp46⁺NK cells before disease onset resulted in increased NK cells infiltration in the joints, higher incidence of arthritis, more severe clinical symptoms, and more pronounced joint inflammation and bone damage. NKp46 deficiency had no significant influence on the incidence and severity of arthritis in collagen-induced arthritis mice.

Conclusions

NK cell infiltration in the joints positively correlates with arthritis progression, inflammation, and bone destruction. The pathogenic role of NK cells in rheumatoid arthritis may be independent of the receptor NKp46.

Mechanisms underlying DMARD inefficacy in difficult-to-treat rheumatoid arthritis: a narrative review with systematic literature search

Management of RA patients has significantly improved over the past decades. However, a substantial proportion of patients is difficult-to-treat (D2T), remaining symptomatic after failing biological and/or targeted synthetic DMARDs. Multiple factors can contribute to D2T RA, including treatment non-adherence, comorbidities and co-existing mimicking diseases (e.g. fibromyalgia). Additionally, currently available biological and/or targeted synthetic DMARDs may be truly ineffective (‘true’ refractory RA) and/or lead to unacceptable side effects. In this narrative review based on a systematic literature search, an overview of underlying (immune) mechanisms is presented. Potential scenarios are discussed including the influence of different levels of gene expression and clinical characteristics. Although the exact underlying mechanisms remain largely unknown, the heterogeneity between individual patients supports the assumption that D2T RA is a syndrome involving different pathogenic mechanisms.

Toward Overcoming Treatment Failure in Rheumatoid Arthritis

Rheumatoid arthritis (RA) is an autoimmune disorder characterized by inflammation and bone erosion. The exact mechanism of RA is still unknown, but various immune cytokines, signaling pathways and effector cells are involved. Disease-modifying antirheumatic drugs (DMARDs) are commonly used in RA treatment and classified into different categories. Nevertheless, RA treatment is based on a "trial-and-error" approach, and a substantial proportion of patients show failed therapy for each DMARD. Over the past decades, great efforts have been made to overcome treatment failure, including identification of biomarkers, exploration of the reasons for loss of efficacy, development of sequential or combinational DMARDs strategies and approval of new DMARDs. Here, we summarize these efforts, which would provide valuable insights for accurate RA clinical medication. While gratifying, researchers realize that these efforts are still far from enough to recommend specific DMARDs for individual patients. Precision medicine is an emerging medical model that proposes a highly individualized and tailored approach for disease management. In this review, we also discuss the potential of precision medicine for overcoming RA treatment failure, with the introduction of various cutting-edge technologies and big data.

The role of NK cells in rheumatoid arthritis

OBJECTIVE

Natural killer (NK) cells are part of the innate immune system which not only provides a primary response to pathogenic conditions but can also play an important regulatory role in immune responses. Furthermore, these cells can influence immune responses by affecting other involved cells. Human NK cells can be classified as CD56^dim and CD56^bright; the former demonstrates mostly cytotoxic effects, while the latter comprises mostly tolerant or regulatory NK cells. These cells participate in the immunopathogenesis of rheumatoid arthritis (RA) and their role remains still unclear.

METHODS

We searched PubMed/MEDLINE and Scopus databases to review and analyze relevant literature on the impact of NK cells in the pathogenesis of RA.

RESULTS

Although the percentage of NK cells increases in peripheral blood of RA patients compared to healthy individuals, the cytotoxic function of these cells is impaired. It is demonstrated by reduced "perforin⁺ NK cells" and decreased per-cell lytic function. These cytotoxic NK cells may control the pathogenic bone absorptive function of osteoclasts by directly targeting these cells.

CONCLUSION

Collectively, the evidence collected in the current review emphasizes the possible protective role of CD56^dim NK cells in the pathogenesis of RA.

Neutrophil count reduction 1 month after initiating tocilizumab can predict clinical remission within 1 year in rheumatoid arthritis patients

Neutropenia is a common adverse event of tocilizumab (TCZ) in rheumatoid arthritis (RA) patients; however, the association between the decrease in neutrophil counts and the TCZ clinical efficacy remains inconclusive. This study aimed to examine whether TCZ-induced neutrophil decrease at 1 month predicts clinical remission within 1 year. We reviewed medical records of RA patients initiating TCZ between May 2011 and September 2019 in our hospital. The Clinical Disease Activity Index (CDAI) was evaluated at baseline (before initiating TCZ) and 1, 3, 6, and 12 months after administration. Clinical remission was defined when CDAI decreased ≤ 2.8. The ratio of neutrophil counts 1 month after initiating TCZ to those at baseline (neutrophil ratio) was also calculated. Among 255 TCZ-treated patients, 169 with valid CDAI and neutrophil counts were enrolled (with median age of 60 years and 79% females). Rheumatoid factor and anti-cyclic citrullinated peptide antibody were positive in 75% and 83%, respectively, and 56% of the patients had concomitant methotrexate (median dose: 8 mg/week). Multivariate logistic regression analysis suggested baseline CDAI (odds ratio (OR) 0.96, p = 0.045), concomitant PSL (OR 0.42, p = 0.030), and the neutrophil ratio (OR 0.19, p = 0.011) as predictors of CDAI remission. Neutrophil ratio ≤ 0.8 was associated with achieving remission (Fisher's exact test, p = 0.02) with no apparent increase of severe infection. More than 20% reduction of neutrophil count 1 month after initiating TCZ predicts clinical remission within 1 year at an early treatment phase.

The Immunomodulatory and Anti-Inflammatory Effect of Curcumin on Immune Cell Populations, Cytokines, and In Vivo Models of Rheumatoid Arthritis

Rheumatoid arthritis (RA) is a widespread chronic autoimmune disorder affecting the joints, causing irreversible cartilage, synovium, and bone degradation. During the course of the disease, many immune and joint cells are activated, causing inflammation. Immune cells including macrophages, lymphocytes, neutrophils, mast cells, natural killer cells, innate lymphoid cells, as well as synovial tissue cells, like fibroblast-like synoviocytes, chondrocytes, and osteoclasts secrete different proinflammatory factors, including many cytokines, angiogenesis-stimulating molecules and others. Recent studies reveal that curcumin, a natural dietary anti-inflammatory compound, can modulate the response of the cells engaging in RA course. This review comprises detailed data about the pathogenesis and inflammation process in rheumatoid arthritis and demonstrates scientific investigations about the molecular interactions between curcumin and immune cells responsible for rheumatoid arthritis development to discuss this herbal drug’s immunoregulatory role in RA treatment.

Predicting treatment response to IL6R blockers in rheumatoid arthritis

Patients with severe, active RA who have not responded to conventional therapy may receive biological disease modifying anti-rheumatic drugs (bDMARDs). However, 40% of cases do not achieve complete disease control, resulting in a negative impact on patient quality of life and representing a waste of healthcare resources. Ongoing research seeks to establish biomarkers, which can be used to predict treatment response to biologics in RA to enable more targeted approaches to treatment. However, much of the work has focused on one class of biologic drug, the TNF inhibitors (TNFi). Here, we will review the current state of research to identify biomarkers predictive of response to the class of bDMARDs targeting the IL6R. While success has been limited thus far, serum drug and low ICAM1 levels have shown promise, with associations reported in independent studies. The challenges faced by researchers and lessons learned from studies of TNFi will be discussed.

Impaired natural killer cell counts and cytolytic activity in patients with severe COVID-19

The global pandemic of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)-driven coronavirus disease 2019 (COVID-19) has caused unprecedented human death and has seriously threatened the global economy. Early data suggest a surge in proinflammatory cytokines in patients with severe COVID-19, which has been associated with poor outcomes. We recently postulated that the inflammatory response in patients with severe COVID-19 disease is not inhibited by natural killer (NK) cells, resulting in a "cytokine storm." Here, we assessed the NK-cell functional activity and the associated cytokines and soluble mediators in hospitalized COVID-19 patients. Significantly impaired NK-cell counts and cytolytic activity were observed in COVID-19 patients when compared with healthy controls. Also, cytokines like interleukin 12 (IL12), IL15, and IL21 that are important for NK-cell activity were not detected systematically. Serum concentrations of soluble CD25 (sCD25)/soluble IL2 receptor α (sIL2-Rα) were significantly elevated and were inversely correlated with the percentage of NK cells. Impaired NK-cell cytolytic activity together with other laboratory trends including elevated sCD25 were consistent with a hyperinflammatory state in keeping with macrophage-activation syndrome. Our findings suggest that impaired counts and cytolytic activity of NK cells are important characteristics of severe COVID-19 and can potentially facilitate strategies for immunomodulatory therapies.

Dawn of Monitoring Regulatory T Cells in (Pre-)clinical Studies: Their Relevance Is Slowly Recognised

Regulatory T cells (Tregs) have a prominent role in the control of immune homeostasis. Pharmacological impact on their activity or balance with effector T cells could contribute to (impaired) clinical responses or adverse events. Monitoring treatment-related effects on T cell subsets may therefore be part of (pre-)clinical studies for medicinal products. However, the extent of immune monitoring performed in studies for marketing authorisation and the degree of correspondence with data available in the public domain is not known. We evaluated the presence of T cell immunomonitoring in 46 registration dossiers of monoclonal antibodies indicated for immune-related disorders and published scientific papers. We found that the depth of Treg analysis in registration dossiers was rather small. Nevertheless, data on treatment-related Treg effects are available in public academia-driven studies (post-registration) and suggest that Tregs may act as a biomarker for clinical responses. However, public data are fragmented and obtained with heterogeneity of experimental approaches from a diversity of species and tissues. To reveal the potential added value of T cell (and particular Treg) evaluation in (pre-)clinical studies, more cell-specific data should be acquired, at least for medicinal products with an immunomodulatory mechanism. Therefore, extensive analysis of T cell subset contribution to clinical responses and the relevance of treatment-induced changes in their levels is needed. Preferably, industry and academia should work together to obtain these data in a standardised manner and to enrich our knowledge about T cell activity in disease pathogenesis and therapies. This will ultimately elucidate the necessity of T cell subset monitoring in the therapeutic benefit-risk assessment.

HLA-C: An Accomplice in Rheumatic Diseases

Human leukocyte antigen c (HLA-C) is a polymorphic membrane protein encoded by the HLA-C gene in the class I major histocompatibility complex. HLA-C plays an essential role in protection against cancer and viruses but has also been implicated in allograft rejection, preeclampsia, and autoimmune disease. This review summarizes reports and proposed mechanisms for the accessory role of HLA-C in rheumatic diseases. Historically, contributions of HLA-C to rheumatic diseases were eclipsed by the stronger association with HLA-DRB1 alleles containing the "shared epitope" with rheumatoid arthritis. Larger genetic association studies and more powerful analytical approaches have revealed independent associations of HLA-C with rheumatic disease-associated phenotypes, including development of anticitrullinated peptide antibodies. HLA-C functions by presenting antigens to T cells and by binding activatory and inhibitory receptors on natural killer (NK) cells, but the exact mechanisms by which the HLA-C locus contributes to autoimmunity are largely undefined. Studies have suggested that HLA-C and NK cell receptor polymorphisms may predict responsiveness to pharmacotherapy. Understanding the mechanisms of the role of HLA-C in rheumatic disease could uncover therapeutic targets or guide precision pharmacologic treatments.

Using the Immunophenotype to Predict Response to Biologic Drugs in Rheumatoid Arthritis

Tumour necrosis factor (TNF)-α is a key mediator of inflammation in rheumatoid arthritis, and its discovery led to the development of highly successful anti-TNF therapy. Subsequently, other biologic drugs targeting immune pathways, namely interleukin-6 blockade, B cell depletion, and T cell co-stimulation blockade, have been developed. Not all patients respond to a biologic drug, leading to a knowledge gap between biologic therapies available and the confident prediction of response. So far, genetic studies have failed to uncover clinically informative biomarkers to predict response. Given that the targets of biologics are immune pathways, immunological study has become all the more pertinent. Furthermore, advances in single-cell technology have enabled the characterization of many leucocyte subsets. Studying the blood immunophenotype may therefore, define biomarker profiles relevant to each individual patient's disease and treatment outcome. This review summarises our current understanding of how immune biomarkers might be able to predict treatment response to biologic drugs.

T cells, natural killer cells, and γδT cells in a large patient cohort with rheumatoid arthritis: influence of age and anti-rheumatic therapy

Objective: The aim of this cohort study was to evaluate the distribution of natural killer (NK) cells and T-cell subsets, including γδT cells, in the peripheral blood of patients with rheumatoid arthritis (RA) in a large real-life patient cohort, taking into account the patients' demographics, disease characteristics, and anti-rheumatic therapy.Method: The study recruited 508 RA patients between November 2013 and August 2015. Lymphocyte differentiation using eight-colour flow cytometry (fluorescence-activated cell sorting) of the peripheral blood was performed for all patients. Clinical data, including age, gender, disease duration, serostatus, disease activity, antibody status, immunosuppressive therapy including use of different biological disease-modifying anti-rheumatic drugs (bDMARDs) and conventional synthetic DMARDs, were retrospectively assessed using electronic patient files. Multivariate regression analysis was performed to assess the effect of these variables on T-cell, NK-cell, and γδT-cell counts.Results: The median patient age was 61.0 years and 74.1% were female. The median disease duration of RA was 12.0 years. Median Disease Activity Score based on 28-joint count was 2.8 and 56.3% were treated with bDMARDs. There were no differences in immunosuppressive therapy between different age groups. While rituximab, abatacept, and tocilizumab had no influence on lymphocyte subdifferentiation, tumour necrosis factor (TNF) inhibitors and age significantly influenced the numbers of T cells, T-helper cells, T-NK cells, NK cells, and γδT cells.Conclusion: Age and TNF-inhibition therapy influence lymphocyte subdifferentiation in patients with RA. It may be prudent to use age- and therapy-adjusted standard values for lymphocyte subsets during clinical trials and treatment of RA.

Decreased A20 expression on circulating CD56bright NK cells contributes to a worse disease status in patients with ankylosing spondylitis

A20, a pivotal anti-inflammatory protein, preserves immune homeostasis and regulates prolonged inflammation. A previous study has shown that A20 expression levels are down-regulated in peripheral blood mononuclear cells (PBMCs) from patients with ankylosing spondylitis (AS). However, the precise role of A20 in reducing autoimmune disorders needs to be further elucidated. In this study, A20 expression was found to be preferentially reduced on circulating CD56^bright natural killer (NK) cells in patients with AS, and its level was negatively correlated with that of proinflammatory cytokines. Further investigation demonstrated that A20 reduces interferon (IFN)-γ and tumour necrosis factor (TNF)-α production in CD56^bright NK cells after stimulation with monokines or phorbol myristate acetate (PMA)/ionomycin(P/I). Furthermore, CD56^bright NK cells isolated from AS patients promote TNF-α secretion by autologous monocytes, and increasing the A20 expression level partially attenuates this process. More importantly, decreased A20 expression on circulating CD56^bright NK cells is associated with worse disease status in patients with AS. Our findings reveal that A20 participates in the pathogenesis of AS by negatively regulating CD56^bright NK cells and that its reduced expression contributes to a worsened disease status in patients with AS.

Characterization and Changes of Lymphocyte Subsets in Baricitinib-Treated Patients With Rheumatoid Arthritis: An Integrated Analysis

OBJECTIVE

Baricitinib is an orally administered inhibitor of JAK1 and JAK2 that has been shown to be effective in treating rheumatoid arthritis (RA). This study was undertaken to analyze changes in lymphocyte cell subsets during baricitinib treatment and to correlate these changes with clinical outcomes.

METHODS

An integrated analysis was conducted by pooling data from 3 completed phase III trials comparing placebo with baricitinib treatment (RA-BEAM, RA-BUILD, and RA-BEACON) and 1 ongoing long-term extension study (RA-BEYOND) in patients with active RA (n = 2,186).

RESULTS

Baricitinib treatment was associated with an early transient increase in total lymphocyte count at week 4, which returned to baseline by week 12. Transient changes within normal reference ranges in T cells and subsets were observed with baricitinib treatment, up to week 104. B cells and relevant subpopulations increased after 4 weeks of baricitinib treatment, with no further increases noted through 104 weeks of treatment. Natural killer (NK) cells temporarily increased after 4 weeks of baricitinib treatment, before decreasing below baseline levels and then stabilizing over time. With baricitinib treatment, few correlations were observed between changes in lymphocyte subsets and clinical end points, and most correlations were also observed within the placebo group. A modest potential association between low NK cell numbers and treatment-emergent infections was observed in the baricitinib 4 mg/day treatment group, but not for serious infections or herpes zoster.

CONCLUSION

Overall, these findings demonstrate that changes in lymphocyte subsets were largely within normal reference ranges across the baricitinib phase III RA clinical program and were not associated with increased risk of serious infections.

IL-6: a cytokine at the crossroads of autoimmunity

IL-6 is implicated in the development and progression of autoimmune diseases in part by influencing CD4 T cell lineage and regulation. Elevated IL-6 levels drive inflammation in a wide range of autoimmune diseases, some of which are also characterized by enhanced T cell responses to IL-6. Notably, the impact of IL-6 on inflammation is contextual in nature and dependent on the cell type, cytokine milieu and tissue. Targeting the IL-6/IL-6R axis in humans has been shown to successfully ameliorate a subset of autoimmune conditions. In this review, we discuss recent studies investigating how IL-6 regulates the CD4 T cell response in the context of autoimmune disease and highlight how blocking different aspects of the IL-6 pathway is advantageous in the treatment of disease.

Genotypes, phenotypes and treatment with immunomodulators in the rheumatic diseases

The autoimmune rheumatological diseases rheumatoid arthritis (RA), spondyloarthritis (SpA) and systemic lupus erythematosus (SLE) are treated with conventional immunosuppressive agents and with modern biological immunomodulators. The latter group of medications have brought about a major change in our ability to control RA and SpA, with more modest results for SLE. The biologicals are very specific in their mechanisms of action, targeting one specific cytokine or one particular cellular marker. Because of this, their efficacy can readily be linked to a single immunomodulatory mechanism. This observation has fuelled hopes that the efficacy of these agents can be predicted at the individual level based on the patient's genetic predisposition, immunological profile or disease phenotype. Whilst the biologic therapies have improved the prospects for patients with these diseases very significantly, the hope that they could be targeted to the patient in an individualized manner has not completely born fruit. In this review, I will argue that we are witnessing important progress in this field, and that justified hope exists for true advances in precision medicine in the autoimmune diseases in the coming years.

Lymphocytes as Biomarkers of Therapeutic Response in Rheumatic Autoimmune Diseases, Is It a Realistic Goal?

Many therapies are available for patients with rheumatoid arthritis (RA) while biological therapies have limited effects in patients with systemic lupus erythematosus (SLE) and primary Sjögren's syndrome (pSS). In both cases, biomarkers predicting drug response would be very useful to guide clinicians in their choice. We performed a systematic review to evaluate the value of lymphocyte phenotyping as a marker of therapeutic response. Of the 1063 articles retrieved, 39 fulfilled inclusion criteria and were included in the present review (25 for RA, 10 for SLE, and 4 for pSS). Lymphocyte phenotyping was described as a biomarker of therapeutic response in many studies, but most results could not be confirmed by independent teams using multivariate analysis. The most consistent result might be the association between rituximab response and the levels of memory B cells before therapy, although some studies were controversial. Thus, lymphocyte phenotyping cannot yet be proposed as a biomarker of response in rheumatic autoimmune diseases. The lack of reproducibility between studies may be explained by technical issues influencing lymphocyte phenotyping so standardization procedures should be developed for future studies. The patients' characteristics vary between studies, and large population studies, including a wide range of patients' characteristics and biomarkers, are required to provide predictive models for clinical outcomes. The use of new flow cytometry techniques such as single-cell mass cytometry technology might also help finder reliable biomarkers in the future.

Leveraging blood and tissue CD4+ T cell heterogeneity at the single cell level to identify mechanisms of disease in rheumatoid arthritis

CD4+ T cells have been long known to play an important role in the pathogenesis of rheumatoid arthritis (RA), but the specific cell populations and states that drive the disease have been challenging to identify with low dimensional single cell data and bulk assays. The advent of high dimensional single cell technologies-like single cell RNA-seq or mass cytometry-has offered promise to defining key populations, but brings new methodological and statistical challenges. Recent single cell profiling studies have revealed a broad diversity of cell types among CD4+ T cells, identifying novel populations that are expanded or altered in RA. Here, we will review recent findings on CD4+ T cell heterogeneity and RA that have come from single cell profiling studies and discuss the best practices for conducting these studies.

Prediction of Response to Targeted Treatment in Rheumatoid Arthritis

Rheumatoid arthritis is an autoimmune syndrome presenting with chronic inflammation of the joints. Patients with the same diagnosis can present with different phenotypes. In some patients severe joint inflammation and early joint destruction are observed, whereas a milder phenotype can be seen in others. Conversely, patients with the same signs and symptoms may exhibit different immunological and molecular abnormalities. Since the introduction of early treatment in clinical practice, the treat to target principle, and new medicines such as biologic disease-modifying antirheumatic drugs, clinical remission can be achieved early in the disease course, albeit not in all patients. The clinical response and efficacy of biologic disease-modifying antirheumatic drugs vary among different individuals. Therefore, there is a need to develop a more personalized approach toward treatment to achieve rapid remission in every patient to prevent disability and restore and maintain quality of life, without unnecessary adverse effects, in a cost-effective manner. The latest data from explorative studies of predictive markers of response are discussed here, together with a preliminary treatment algorithm based on currently available knowledge.

The role of interleukin-6 signalling and its therapeutic blockage in skewing the T cell balance in rheumatoid arthritis

Therapeutic blockage of cytokine signalling in autoimmune diseases has improved our understanding of the role of these cytokines in triggering, shaping and perpetuating autoimmune responses. In rheumatoid arthritis (RA), immunopathology is driven by a predominance of arthritogenic T helper cells secreting interferon-γ [T helper type 1 (Th1)] and interleukin (IL)-17 (Th17) over regulatory T cells (T_reg ). The pleiotropic cytokine IL-6 is crucial to the differentiation of Th17 cells and the balance between pathogenic Th17 and protective T_reg . Targeting the IL-6 receptor (IL-6R) by humanized antibodies improves signs and symptoms of RA, and has provided new insights into the mechanisms of inflammation and immune regulation. Here we review current evidence on the role of IL-6 in the pathogenesis of RA and the molecular consequences of IL-6R blockage in disease, with special focus on the Th17/T_reg balance and plasticity.

The role and therapeutic targeting of IL-6 in rheumatoid arthritis

INTRODUCTION

Rheumatoid arthritis (RA) is an autoimmune chronic disease with joint and systemic inflammation and it has been found that interleukin-6 (IL-6) plays a key role in RA. Indeed, various clinical studies have proved that the first-in-class IL-6 inhibitor, tocilizumab, a humanized anti-IL-6 receptor monoclonal antibody, showed outstanding efficacy in RA. Areas covered: We review here the role of IL-6 in the inflammatory conditions and how IL-6 contributes to pathogenesis of RA, what induces IL-6 and how IL-6 expression is regulated. Furthermore, clinical studies of tocilizumab for RA are summarized, Expert commentary: We review and discuss the prospects for future applications of IL-6 targeting therapy and new therapeutic strategies targeting IL-6. Finally, we discuss relevant issues with regard to the clinical management of IL-6 blockade in RA.

Understanding the Regulatory Roles of Natural Killer T Cells in Rheumatoid Arthritis: T Helper Cell Differentiation Dependent or Independent?

Rheumatoid arthritis (RA) is the most common chronic systemic autoimmune disease. This disease is thought to be caused by pathogenic T cells. Th1, Th2, Th17 and Treg cells have been implicated in the pathogenesis of RA. These Th cells differentiate from CD4+ T cells primarily due to the effects of cytokines. Natural killer T (NKT) cells are a distinct subset of lymphocytes that can rapidly secrete massive amount of cytokines, including IL-2, IL-4, IL-12 and IFN-γ. Numerous studies showed that NKT cells can influence the differentiation of CD4+ T cells via cytokines in vitro. These findings suggest that NKT cells play an important role in RA by polarizing Th1, Th2, Th17 and Treg cells. In view of the complexity of RA, we discussed whether NKT cells really influence the development of RA through regulating the differentiation of Th cells.

The Proportion of Regulatory T Cells in Patients with Rheumatoid Arthritis: A Meta-Analysis

Background

Regulatory T cells (Tregs) have important functions in peripheral immune tolerance. Dysfunction of Tregs is considered to be a pivotal cause of autoimmune diseases, including rheumatoid arthritis (RA). However, previous reports describing the proportion of Tregs among CD4⁺ T cells in RA patients were controversial because a range of markers are used to identify Tregs with little consensus. To clarify the status of Tregs in RA, we investigated the proportion of Tregs with focusing on the definitions of them.

Methods

We identified the studies reporting the proportion of Tregs in RA patients using PubMed and Google Scholar. We performed a systematic review of them and a meta-analysis to evaluate the proportion of Tregs (FOXP3-positive and/or CD25-positive) among CD4⁺ T cells in peripheral blood (PB) and synovial fluid (SF) of RA patients and control subjects.

Results

A total 31 studies were selected. The proportion of Tregs defined by all definitions among CD4⁺ T cells in PB was not significantly different between RA patients and control subjects (-0.65, [-1.30, 0.01]). Then we performed sub-analyses based on individual definitions. The proportion of Tregs defined by either CD25 or FOXP3 alone did not differ between RA patients and control subjects. The proportion of Tregs defined by both FOXP3 and CD25 was lower in RA patients than that in control subjects (-2.42 [-3.49, -1.34]). The proportion of Tregs defined by both FOXP3 and CD25 was higher in SF than that in PB among RA patients (3.27 [0.40, 6.14]).

Conclusion

The status of Tregs varied according to the definition system. The proportion of Tregs defined by stricter and functionally validated methods decreased in PB and increased in SF among RA patients. If the proportion of Tregs differs in RA, accurate and functionally relevant definitions of Tregs are necessary to elucidate their status in RA.

What rheumatologists need to know about innate lymphocytes

Many rheumatic diseases are characterized by having an autoimmune background. Determining the mechanisms underlying autoimmunity is, therefore, important to further understand these diseases and to inform future lines of research aimed at developing new treatments and cures. As fast responders, innate lymphocytes have protective or pathogenic roles in the initiation as well as the maintenance of immune responses in general, and they contribute to tissue homeostasis, among other functions. Innate lymphocytes also seem to be involved in autoimmunity in particular. Since 2010, accumulating evidence clearly shows that different populations of innate lymphocytes have roles in responding to antigen-specific autoantibody and autoreactive T cells, thereby amplifying or attenuating disease processes. Cytotoxicity is a cardinal feature of many innate lymphocytes and can contribute to inflammatory tissue damage. Finally, innate lymphocytes can respond to biologic therapies for autoimmune diseases. Consequently, like TNF and other effector molecules, certain innate lymphocyte subsets might be appropriate therapeutic targets to ameliorate various autoimmune diseases. In this Review, we summarize the main characteristics and functions of innate lymphocyte subsets, and describe their roles in autoimmune disease. We also discuss how biologic therapies influence innate lymphocyte function and consider the potential for these cell subsets to act as future therapeutic targets.

Human CD56bright NK Cells: An Update

Human NK cells can be subdivided into various subsets based on the relative expression of CD16 and CD56. In particular, CD56(bright)CD16(-/dim) NK cells are the focus of interest. They are considered efficient cytokine producers endowed with immunoregulatory properties, but they can also become cytotoxic upon appropriate activation. These cells were shown to play a role in different disease states, such as cancer, autoimmunity, neuroinflammation, and infection. Although their phenotype and functional properties are well known and have been extensively studied, their lineage relationship with other NK cell subsets is not fully defined, nor is their precise hematopoietic origin. In this article, we summarize recent studies about CD56(bright) NK cells in health and disease and briefly discuss the current controversies surrounding them.

Immunogenicity of tocilizumab in patients with rheumatoid arthritis

OBJECTIVE

The immunogenicity of tocilizumab (TCZ) has been poorly studied. We assessed the immunogenicity of TCZ and serum TCZ trough levels in rheumatoid arthritis (RA) patients and the preexisting TCZ-specific CD4+ T cell repertoire in healthy controls.

METHODS

Anti-drug antibodies (ADAs) to TCZ and serum TCZ trough levels in RA patients were assessed at different times by ELISA. Frequencies of naive anti-TCZ CD4+ precursors were studied in healthy controls.

RESULTS

In total, 91 samples from 40 RA patients were analyzed: 21 patients within the first 6 months after treatment initiation and 19 during follow-up after a mean TCZ treatment duration of 21±13 months. None of the 91 samples showed persistent ADAs to TCZ. Only 3 RA patients showed transient and low titers of anti-TCZ ADAs. Serum TCZ trough levels were associated with neither patient characteristics (gender, body mass index) nor disease activity and were identical for patients with and without co-treatment with methotrexate. Three of 9 healthy donors showed preexisting TZC-specific CD4+ T cells at a low level.

CONCLUSION

Serum TCZ trough levels were not affected by patient characteristics. The occurrence of ADAs to TCZ was a rare event. Because healthy donors show the same frequency of naive TCZ-specific and infliximab-specific CD4+ T cell precursors, the low prevalence of ADAs to TCZ might result from interleukin-6 blockade.

Peptide motif analysis predicts alphaviruses as triggers for rheumatoid arthritis

Rheumatoid arthritis (RA) develops in response to both genetic and environmental factors. The strongest genetic determinant is HLA-DR, where polymorphisms within the P4 and P6 binding pockets confer elevated risk. However, low disease concordance across monozygotic twin pairs underscores the importance of an environmental factor, probably infectious. The goal of this investigation was to predict the microorganism most likely to interact with HLA-DR to trigger RA under the molecular mimicry hypothesis. A set of 185 structural proteins from viruses or intracellular bacteria was scanned for regions of sequence homology with a collagen peptide that binds preferentially to DR4; candidates were then evaluated against a motif required for T cell cross-reactivity. The plausibility of the predicted agent was evaluated by comparison of microbial prevalence patterns to epidemiological characteristics of RA. Peptides from alphavirus capsid proteins provided the closest fit. Variations in the P6 position suggest that the HLA binding preference may vary by species, with Ross River virus, Chikungunya virus, and Mayaro virus peptides binding preferentially to DR4, and peptides from Sindbis/Ockelbo virus showing stronger affinity to DR1. The predicted HLA preference is supported by epidemiological studies of post-infection chronic arthralgia. Parallels between the cytokine profiles of RA and chronic alphavirus infection are discussed.