Depleting plasmacytoid dendritic cells reduces local type I interferon responses and disease activity in patients with cutaneous lupus

An Integrative Mechanistic Model of Type 1 IFN-Mediated Inflammation in Systemic Lupus Erythematosus

Type I interferon (IFN1) pathway-targeting therapies represent a highly promising class of remedies for the treatment of systemic lupus erythematosus. However, the overall clinical benefit of these compounds is afflicted by marked variability. In this study, we developed a quantitative systems pharmacology model of type I IFN-mediated inflammation and applied it for an indirect comparison of anifrolumab, sifalimumab, daxdilimab, and litifilimab pharmacodynamic response, represented in the model by the change in IFN1 gene signature (IFNGS). The model consists of 20 ordinary differential equations and 68 parameters, among which four systemic parameters (including one random effect) were estimated using patient-level data from Phase IIb anifrolumab clinical trial. Within-target and within-pathway validation was performed using study-level pharmacokinetics, IFNα, and/or IFNGS data from five anifrolumab, four sifalimumab, one daxdilimab, and one litifilimab trials. The model successfully captured overall trends in IFNGS at clinically relevant doses of these compounds and discriminated IFNGS response between patients with low (< 2.75) and high (≥ 2.75) baseline IFNGS. Overprediction of treatment benefit was observed for the low range of anifrolumab doses (100-150 mg every 4 weeks). In contrast, IFNGS response under 150 mg of daxdilimab was underpredicted, despite the accurate description of plasmacytoid dendritic cells and IFNα biomarkers. Results of the global sensitivity analysis revealed baseline IFNGS, IFNα, and IFNα fraction as key factors affecting treatment benefit the most. In terms of maximum IFNGS reduction, anifrolumab showed superior potential compared to sifalimumab, daxdilimab, and litifilimab (ΔIFNGS~25%), which was further enhanced in patients with high baseline IFNGS or IFNα (ΔIFNGS~50%-60%).

Altered X-chromosome inactivation of the TLR7/8 locus and heterogeneity of pDCs in systemic sclerosis

Systemic sclerosis (SSc) is an autoimmune disease that has a strong female predominance. Both the X-linked TLR7 and TLR8 can induce type I IFN (IFN-I) by plasmacytoid DCs (pDCs), which can promote fibrosis. We identified five subclusters of pDCs, including ISGhigh clusters that were over-represented in SSc patients. We observed that both TLR7 and TLR8 genes escape from X chromosome inactivation (XCI) at higher frequency in pDCs of SSc patients, which was associated with changes in TLR7 protein profile. Combined DNA/RNA FISH analysis revealed that the TLR7/8 locus is preferentially located outside of the inactive X (Xi) territory when TLR7 is expressed, suggesting that higher-order loop formation is linked to TLR7/8 expression from the Xi. Furthermore, the expression levels of XIST and the transcriptional repressor SPEN were reduced in SSc pDCs. Hence, our data revealed the heterogeneity of pDCs in SSc and suggested that altered XCI at the TLR7/8 locus may contribute to the chronic IFN-I activity of pDCs in female SSc patients.

Mechanosensing regulates pDC activation in the skin through NRF2 activation

Plasmacytoid DCs (pDCs) infiltrate the skin, chronically produce type I interferon (IFN-I), and promote skin lesions and fibrosis in autoimmune patients. However, what controls their activation in the skin is unknown. Here, we report that increased stiffness inhibits the production of IFN-I by pDCs. Mechanistically, mechanosensing activates stress pathways including NRF2, which induces the pentose phosphate pathway and reduces pyruvate levels, a product necessary for pDC responses. Modulating NRF2 activity in vivo controlled the pDC response, leading to resolution or chronic induction of IFN-I in the skin. In systemic sclerosis (SSc) patients, although NRF2 was induced in skin-infiltrating pDCs, as compared with blood pDCs, the IFN response was maintained. We observed that CXCL4, a profibrotic chemokine elevated in fibrotic skin, was able to overcome stiffness-mediated IFN-I inhibition, allowing chronic IFN-I responses by pDCs in the skin. Hence, these data identify a novel regulatory mechanism exerted by the skin microenvironment and identify points of dysregulation of this mechanism in patients with skin inflammation and fibrosis.

A focused report on IFN-1 targeted therapies for lupus erythematosus

INTRODUCTION

Patients with Systemic Lupus Erythematosus (SLE) experience varied manifestations and unpredictable flares, complicating treatment and drug development. Despite these challenges, anifrolumab, voclosporin, and belimumab were approved by FDA. These treatments complement, but don't replace, traditional therapies like NSAIDs, corticosteroids, antimalarials, and immunosuppressives. Therefore, there remains an unmet need for more effective medications targeting excessive proinflammatory cytokines in SLE patients.

AREAS COVERED

This review summarizes the clinical trial outcomes of four upcoming medications targeting cytokine activity: Litifilimab showed a 7-point reduction in CLASI-A in its phase II trial. Daxdilimab was unsuccessful in its phase II trial. Anifrolumab reduced SLE activity in both phase II and III trials. Deucravacitinib decreased disease activity by multiple measures in its phase II trial.

EXPERT OPINION

High levels of IFN-I (type 1 interferon) are present in most SLE patients, making this pathway an attractive target for drug development. Litifilimab downregulates IFN-I by targeting BDCA2, while dexadilimab targets ILT7 to recruit effector cells, reducing IFN-I production by killing PDCs. Anifrolumab binds to the IFN-I receptor, blocking the activity of all IFN-Is, and deucravacitinib reduces IFN-I by inhibiting TYK2, thereby interfering with downstream signaling. Therapies that target IFN-I represents a promising class of medications for SLE patients.

IRF5 Controls Plasma Cell Generation and Antibody Production via Distinct Mechanisms Depending on the Antigenic Trigger

Elevated levels of serum autoantibodies are a hallmark of systemic lupus erythematosus (SLE) and are produced by plasma cells in response to a variety of antigenic triggers. In SLE, the triggers are complex and may include both T cell-dependent/-independent and TLR-dependent/-independent mechanisms of immune activation, which ultimately contributes to the significant immune dysregulation seen in patients at the level of cytokine production and cellular activation (B cells, T cells, dendritic cells, neutrophils and macrophages). Interferon regulatory factor 5 (IRF5) has been identified as an autoimmune susceptibility gene and polymorphisms in IRF5 associate with altered expression and hyper-activation in distinct SLE immune cell subsets. To gain further insight into the mechanisms that drive IRF5-mediated SLE immune activation, we characterised wild-type (WT) and Irf5 -/- Balb/c mice in response to immunisation. WT and Irf5 -/- Balb/c mice were immunised to activate various signalling pathways in vivo followed by systemic immunophenotyping and detection of antibody production by multi-colour flow cytometry and ELISPOT. We identified two pathways, TLR9-dependent and T cell-dependent that resulted in IRF5 cell type-specific function. Immunisation with either CpG-B + Alum or NP-KLH + Alum but not with R848 + Alum, NP-LPS + Alum or NP-Ficoll+Alum resulted in decreased plasma cell generation and reduced antibody production in Irf5 -/- mice. Notably, the mechanism(s) leading to this downstream phenotype was distinct. In CpG-B + Alum immunised mice, we found reduced activation of plasmacytoid dendritic cells, resulting in reduced IFNα and IL6 production in Irf5 -/- mice. Conversely, mice immunised with NP-KLH + Alum had reduced numbers of T follicular helper cells and germinal centre B cells with reduced expression of Bcl6 in Irf5 -/- mice. Moreover, T follicular helper cells from Irf5 -/- mice were functionally defective. Even though the downstream phenotype of reduced antibody production in Irf5 -/- mice was conserved between T cell-dependent and TLR9-dependent immunisation, the mechanisms leading to this phenotype were antigen- and cell type-specific.

Innovations in Cutaneous Lupus

Cutaneous lupus erythematosus (CLE) is an autoimmune-mediated skin disease under the family of lupus erythematosus. Systemic immunosuppressants and topical treatments have been used to manage CLE; however, these treatments tend to be moderately efficacious and leave patients with unmet therapeutic needs. There is a need for medications that target pruritus, scarring, dyspigmentation, and other symptoms of chronic CLE that contribute to decreased quality of life. The introduction of new biologics and other systemic medications has expanded dermatologists' and rheumatologists' ability to manage CLE. This article discusses new pharmaceuticals and guidelines providing an updated overview of the clinical management of CLE.

Innovation in Alopecia Areata

Advances in understanding of AA have led to the first approved therapies for this disease, and in the past two years, there have been three medicines approved for the treatment of severe alopecia areata. There are numerous clinical trials of novel therapeutics underway across the spectrum of AA.

Dual-Action Psoriasis Therapy: Antiproliferative and Immunomodulatory Effects via Self-Locking Microneedles

Psoriasis is a chronic, immune-mediated disorder characterized by immune regulation disorders and abnormal keratinocyte proliferation. Deucravacitinib (Deu), a selective oral Tyrosine Kinase 2 (TYK2) inhibitor, shows promise in treating psoriasis but may cause systemic side effects and fail to address persistent localized thickened lesions. Herein, a self-locking microneedle (MN) patch with a polyvinyl alcohol (PVA) inner ring loaded with Deu is developed, designed to penetrate the transdermal barriers and dissolve rapidly, downregulating the IL-23/IL-17 pathway and serve as the first line of defense against the spread of skin-originated inflammation. Additionally, Calcipotriol (Cal), a vitamin D derivative, is incorporated into a methacrylated hyaluronic acid (HAMA) backing layer and outer ring that mimics occlusive administration, maintaining localized skin surface retention for prolonged anti-proliferative therapy. The Deu@Cal MN demonstrates satisfactory adhesiveness due to swelling-mediated mechanical interlocking via the outer ring, ensuring targeted drug release at lesion site. Besides its effectiveness in alleviating both skin inflammation and proliferation, it inhibits the differentiation of Th17 cells in the spleen, suggesting potential to reduce systemic inflammation. These findings offer a new therapeutic approach for treating psoriasis and other autoimmune and inflammatory conditions.

Severity Scores for Cutaneous Lupus Erythematosus

Despite the significant disease burden of cutaneous lupus erythematosus (CLE), there have been no United States Food and Drug Administration-approved therapies for 65 years. To facilitate advancement of therapies, severity scores are needed to evaluate QOL, how patients feel, activity of disease, and organ-specific damage to assess response to therapies and disease progression. In this paper, we delineate the development process of provider- and patient-reported severity scores for CLE. Cutaneous Lupus Disease Area and Severity Index (CLASI), a provider-reported measure that distinguishes between activity and damage, has undergone rigorous validation and reliability testing for over 20 years. Its performance has been tested in clinical trials as a primary or secondary endpoint and tool to stratify patients. As an objective disease measure that captures a provider's perspective of disease activity and damage, the CLASI inherently does not assess disease impact on patients' QOL. Cutaneous Lupus Erythematosus Quality of Life (CLEQoL), a patient-reported measure, captures features elucidated through focus groups, including symptoms, emotions, functioning, body image, and photosensitivity. It has undergone psychometric property testing to ensure reliability and validity. Together, CLASI and CLEQoL are simple and reliable CLE-specific severity scores capturing disease activity, damage, and QOL from provider and patient perspectives.

Immunopathogenesis of systemic lupus erythematosus: An update

Systemic lupus erythematosus (SLE) is a chronic systemic autoimmune disease characterized by dysregulated immune responses leading to widespread inflammation and damage in various organs. Environmental factors such as infections, hormonal influences and exposure to ultraviolet light can trigger the disease in genetically predisposed individuals. Genome-wide association studies have identified over 100 susceptibility loci linked to immune regulation, interferon (IFN) signaling and antigen presentation in SLE. In addition, rare cases of monogenic lupus have been instrumental in understanding critical underlying disease mechanisms. Several immunological abnormalities contribute to the loss of self-tolerance and the perpetuation of autoimmune responses in SLE. In particular, defective clearance of apoptotic cells due to defective phagocytosis and complement activation leads to accumulation of self-antigens. Dysregulated innate immune responses activate the adaptive immune system, amplifying the inflammatory response with an important role for type I IFNs. Abnormalities in B cell development and activation lead to the production of autoreactive antibodies, forming immune complexes that cause tissue damage. Similarly, disturbances in T-cell compartments, altered regulatory T-cell functions and altered cytokine production, particularly IFN-α, contribute to tissue damage. Understanding of the immunopathogenesis of SLE is evolving rapidly, with ongoing research identifying new molecular pathways and potential therapeutic targets. Future classifications of SLE are likely to be based on underlying biological pathways rather than clinical and serological signs alone. This review aims to provide a detailed update on the most recent findings regarding the immunopathogenesis of SLE, focusing on the variability of biological pathways and the implications for future therapeutic strategies, in particular chimeric antigen receptor T (CAR T) cells.

The role of plasmacytoid dendritic cells (pDCs) in immunity during viral infections and beyond

Type I and III interferons (IFNs) are essential for antiviral immunity and act through two different but complimentary pathways. First, IFNs activate intracellular antimicrobial programs by triggering the upregulation of a broad repertoire of viral restriction factors. Second, IFNs activate innate and adaptive immunity. Dysregulation of IFN production can lead to severe immune system dysfunction. It is thus crucial to identify and characterize the cellular sources of IFNs, their effects, and their regulation to promote their beneficial effects and limit their detrimental effects, which can depend on the nature of the infected or diseased tissues, as we will discuss. Plasmacytoid dendritic cells (pDCs) can produce large amounts of all IFN subtypes during viral infection. pDCs are resistant to infection by many different viruses, thus inhibiting the immune evasion mechanisms of viruses that target IFN production or their downstream responses. Therefore, pDCs are considered essential for the control of viral infections and the establishment of protective immunity. A thorough bibliographical survey showed that, in most viral infections, despite being major IFN producers, pDCs are actually dispensable for host resistance, which is achieved by multiple IFN sources depending on the tissue. Moreover, primary innate and adaptive antiviral immune responses are only transiently affected in the absence of pDCs. More surprisingly, pDCs and their IFNs can be detrimental in some viral infections or autoimmune diseases. This makes the conservation of pDCs during vertebrate evolution an enigma and thus raises outstanding questions about their role not only in viral infections but also in other diseases and under physiological conditions.

An update on clinical trials for cutaneous lupus erythematosus

Cutaneous lupus erythematosus (CLE) comprises dermatologic manifestations that may occur independently or with systemic lupus erythematosus (SLE). Despite advancements in refining CLE classification, establishing precise subtype criteria remains challenging due to overlapping presentations and difficulty in distinguishing morphology. Current treatments encompass preventive measures, topical therapies, and systemic approaches. Hydroxychloroquine and glucocorticoids are the sole US Food and Drug Administration (FDA)-approved medications for CLE, with numerous off-label treatments available. However, these treatments are often not covered by insurance, imposing a significant financial burden on patients. The exclusion of most CLE patients, particularly those without concurrent SLE, from trials designed for SLE has resulted in a lack of targeted treatments for CLE. To develop effective CLE treatments, validated outcome measures for tracking patient responsiveness are essential. The Cutaneous Lupus Erythematosus Disease Area and Severity Index is widely utilized for its reliability, validity, and ability to differentiate between skin activity and damage. In contrast, the FDA mandates the use of the Investigator's Global Assessment, a five-point Likert scale related to lesion characteristics, for skin-related therapeutic trials. It requires the disease to resolve or almost completely resolve to demonstrate improvement, which can be difficult when there is residual erythema or incomplete clearance that is meaningfully improved from a patient perspective. Various classes of skin lupus medications target diverse pathways, allowing tailored treatment based on the patient's lupus inflammatory profile, resulting in improved outcomes. Promising targeted therapeutic drugs include anifrolumab (anti-type 1 interferon), deucravacitinib (allosteric tyrosine kinase 2 inhibitor), litifilimab (plasmacytoid dendritic cell-directed therapy), iberdomide (cereblon-targeting ligand), and belimumab (B-cell directed therapy). Despite the significant impact of CLE on quality of life, therapeutic options remain inadequate. While promising treatments for cutaneous lupus are emerging, it is crucial to underscore the urgency for skin-focused treatment outcomes and the implementation of validated measures to assess therapeutic effectiveness in clinical trials.

Ontogeny and Function of Plasmacytoid Dendritic Cells

Plasmacytoid dendritic cells (pDCs) represent a unique cell type within the innate immune system. Their defining property is the recognition of pathogen-derived nucleic acids through endosomal Toll-like receptors and the ensuing production of type I interferon and other soluble mediators, which orchestrate innate and adaptive responses. We review several aspects of pDC biology that have recently come to the fore. We discuss emerging questions regarding the lineage affiliation and origin of pDCs and argue that these cells constitute an integral part of the dendritic cell lineage. We emphasize the specific function of pDCs as innate sentinels of virus infection, particularly their recognition of and distinct response to virus-infected cells. This essential evolutionary role of pDCs has been particularly important for the control of coronaviruses, as demonstrated by the recent COVID-19 pandemic. Finally, we highlight the key contribution of pDCs to systemic lupus erythematosus, in which therapeutic targeting of pDCs is currently underway.

Systemic lupus erythematosus therapeutic strategy: From immunotherapy to gut microbiota modulation

Systemic lupus erythematosus (SLE) is characterized by a systemic dysfunction of the innate and adaptive immune systems, leading to an attack on healthy tissues of the body. During the development of SLE, pathogenic features, such as the formation of autoantibodies to self-nuclear antigens, caused tissue damage including necrosis and fibrosis, with an increased expression of type Ⅰ interferon (IFN) regulated genes. Treatment of lupus with immunosuppressants and glucocorticoids, which are used as the standard therapy, is not effective enough and causes side effects. As an alternative, more effective immunotherapies have been developed, including monoclonal and bispecific antibodies that target B cells, T cells, co-stimulatory molecules, cytokines or their receptors, and signaling molecules. Encouraging results have been observed in clinical trials with some of these therapies. Furthermore, a chimeric antigen receptor T cells (CAR-T) therapy has emerged as the most effective, safe, and promising treatment option for SLE, as demonstrated by successful pilot studies. Additionally, emerging evidence suggests that gut microbiota dysbiosis may play a significant role in the severity of SLE, and the use of methods to normalize the gut microbiota, particularly fecal microbiota transplantation (FMT), opens up new opportunities for effective treatment of SLE.

Uncoupling interferons and the interferon signature explains clinical and transcriptional subsets in SLE

Systemic lupus erythematosus (SLE) displays a hallmark interferon (IFN) signature. Yet, clinical trials targeting type I IFN (IFN-I) have shown variable efficacy, and blocking IFN-II failed to treat SLE. Here, we show that IFN type levels in SLE vary significantly across clinical and transcriptional endotypes. Whereas skin involvement correlated with IFN-I alone, systemic features like nephritis associated with co-elevation of IFN-I, IFN-II, and IFN-III, indicating additive IFN effects in severe SLE. Notably, while high IFN-II/-III levels without IFN-I had a limited effect on disease activity, IFN-II was linked to IFN-I-independent transcriptional profiles (e.g., OXPHOS and CD8+GZMH+ cells), and IFN-III enhanced IFN-induced gene expression when co-elevated with IFN-I. Moreover, dysregulated IFNs do not explain the IFN signature in 64% of patients or clinical manifestations including cytopenia, serositis, and anti-phospholipid syndrome, implying IFN-independent endotypes in SLE. This study sheds light on mechanisms underlying SLE heterogeneity and the variable response to IFN-targeted therapies in clinical trials.

Neutrophil-plasmacytoid dendritic cell interaction leads to production of type I IFN in response to Mycobacterium tuberculosis

Mycobacterium tuberculosis (Mtb) can cause a latent infection that sometimes progresses to clinically active tuberculosis (TB). Type I interferons (IFN-I) have been implicated in initiating the progression from latency to active TB, in part because IFN-I stimulated genes are the earliest genes to be upregulated in patients as they advance to active TB. Plasmacytoid dendritic cells (pDCs) are major producers of IFN-I during viral infections and in response to autoimmune-induced neutrophil extracellular traps. pDCs have also been suggested to be the major producers of IFN-I during Mtb infection of mice and nonhuman primates, but direct evidence has been lacking. Here, we found that Mtb did not stimulate isolated human pDCs to produce IFN-I, but human neutrophils infected with Mtb-activated co-cultured pDCs to do so. Mtb-infected neutrophils produced neutrophil extracellular traps, whose exposed DNA is a well-known mechanism to activate pDCs to secrete IFN-I. We conclude that pDCs contribute to the IFN-I response during Mtb infection by interacting with infected neutrophils which may then promote Mtb pathogenesis.

Type 1 interferons: A target for immune-mediated inflammatory diseases (IMIDs)

The improved understanding of the molecular basis of innate immunity have led to the identification of type I interferons (IFNs), particularly IFN-α, as central mediators in the pathogenesis of several Immune-mediated inflammatory diseases (IMIDs) such as systemic lupus erythematosus (SLE), systemic sclerosis, inflammatory myositis and Sjögren's syndrome. Here, we review the main data regarding the opportunity to target type I IFNs for the treatment of IMIDs. Type I IFNs and their downstream pathways can be targeted pharmacologically in several manners. One approach is to use monoclonal antibodies against IFNs or the IFN-receptors (IFNARs, such as with anifrolumab). The downstream signaling pathways of type I IFNs also contain several targets of interest in IMIDs, such as JAK1 and Tyk2. Of these, anifrolumab is licensed and JAK1/Tyk2 inhibitors are in phase III trials in SLE. Targeting IFN-Is for the treatment of SLE is already a reality and in the near future may prove useful in other IMIDs. IFN assays will find a role in routine clinical practice for the care of IMIDs as further validation work is completed and a greater range of targeted therapies becomes available.

HERC6 regulates STING activity in a sex-biased manner through modulation of LATS2/VGLL3 Hippo signaling

Interferon (IFN) activity exhibits a gender bias in human skin, skewed toward females. We show that HERC6, an IFN-induced E3 ubiquitin ligase, is induced in human keratinocytes through the epidermal type I IFN; IFN-κ. HERC6 knockdown in human keratinocytes results in enhanced induction of interferon-stimulated genes (ISGs) upon treatment with a double-stranded (ds) DNA STING activator cGAMP but not in response to the RNA-sensing TLR3 agonist. Keratinocytes lacking HERC6 exhibit sustained STING-TBK1 signaling following cGAMP stimulation through modulation of LATS2 and TBK1 activity, unmasking more robust ISG responses in female keratinocytes. This enhanced female-biased immune response with loss of HERC6 depends on VGLL3, a regulator of type I IFN signature. These data identify HERC6 as a previously unrecognized negative regulator of ISG expression specific to dsDNA sensing and establish it as a regulator of female-biased immune responses through modulation of STING signaling.

Immune-Mediated Necrotizing Myopathy (IMNM): A Story of Antibodies

Immune-mediated necrotizing myopathy (IMNM) is a rare and severe disease that corresponds to a specific entity of idiopathic inflammatory myopathy. Patients with IMNM suffer from proximal muscle weakness, and present high levels of creatine kinase and necrotic myofibers. Anti-Signal Recognition Particle (SRP) and anti-3-hydroxy-3-methylglutaryl-coenzyme A reductase autoantibodies (HMGCR) have recently been identified in two thirds of patients with IMNM and are used as a hallmark of the disease. In this review, we provide a detailed description of these antibodies and the tests used to detect them in the serum of patients. Based on in vitro studies and mouse models of IMNM, we discuss the role of autoantibodies in the pathogenesis of the disease. Finally, in the light of the latest knowledge, we conclude with a review of recent therapeutic approaches in IMNM.

Topical drug delivery strategies for enhancing drug effectiveness by skin barriers, drug delivery systems and individualized dosing

Topical drug delivery is widely used in various diseases because of the advantages of not passing through the gastrointestinal tract, avoiding gastrointestinal irritation and hepatic first-pass effect, and reaching the lesion directly to reduce unnecessary adverse reactions. The skin helps the organism to defend itself against a huge majority of external aggressions and is one of the most important lines of defense of the body. However, the skin's strong barrier ability is also a huge obstacle to the effectiveness of topical medications. Allowing the bioactive, composition in a drug to pass through the stratum corneum barrier as needed to reach the target site is the most essential need for the bioactive, composition to exert its therapeutic effect. The state of the skin barrier, the choice of delivery system for the bioactive, composition, and individualized disease detection and dosing planning influence the effectiveness of topical medications. Nowadays, enhancing transdermal absorption of topically applied drugs is the hottest research area. However, enhancing transdermal absorption of drugs is not the first choice to improve the effectiveness of all drugs. Excessive transdermal absorption enhances topical drug accumulation at non-target sites and the occurrence of adverse reactions. This paper introduces topical drug delivery strategies to improve drug effectiveness from three perspectives: skin barrier, drug delivery system and individualized drug delivery, describes the current status and shortcomings of topical drug research, and provides new directions and ideas for topical drug research.

Biomarkers for systemic lupus erythematosus - a focus on organ damage

INTRODUCTION

Systemic lupus erythematosus (SLE) is complex autoimmune disease with heterogenous manifestations, unpredictable disease course and response to treatment. One of the critical needs in SLE management is the identification of reliable biomarkers that can aid in early diagnosis, accurate monitoring of disease activity, and assessment of treatment response.

AREAS COVERED

In the current review, we focus on the commonly affected organs (skin, kidney, and nervous system) in SLE to summarize the emerging biomarkers that show promise in disease diagnosis, monitoring and treatment response assessment. The subtitles within each organ domain were determined based on the most relevant and promising biomarkers for that specific organ damage.

EXPERT OPINION

Biomarkers have the potential to significantly benefit the management of SLE by aiding in diagnosis, disease activity monitoring, prognosis, and treatment response assessment. However, despite decades of research, none has been validated and implemented for routine clinical use. Novel biomarkers could lead to the development of precision medicine for SLE, guide personalized treatment, and improve patient outcomes. Challenges in biomarker research in SLE include defining clear and clinically relevant questions, accounting for the heterogeneity of SLE, and confirming initial findings in larger, multi-center, multi-ethnic, independent cohorts that reflect real-world clinical scenarios.

The development of litifilimab (BIIB 059) for cutaneous and systemic lupus erythematosus

This review describes the litifilimab (BIIB 059) development program to date for systemic lupus erythematosus (SLE) and cutaneous lupus erythematosus (CLE). Plasmacytoid dendritic cells (pDCs), major producers of type I interferons (IFN-I), play a key role in SLE pathogenesis. Litifilimab, a humanized monoclonal antibody, binds to BDCA2, a protein uniquely expressed on pDCs. The consequence of BDCA2 ligation is the inhibition of IFN-I as well as IFN-III, cytokine and chemokine production. Phase I and II LILAC trial parts A and B achieved primary end points in SLE and CLE patients, confirming the importance of pDCs and IFN-I in SLE and CLE. Litifilimab is currently being evaluated in phase III trials in both SLE and CLE.

Helios as a Potential Biomarker in Systemic Lupus Erythematosus and New Therapies Based on Immunosuppressive Cells

The Helios protein (encoded by the IKZF2 gene) is a member of the Ikaros transcription family and it has recently been proposed as a promising biomarker for systemic lupus erythematosus (SLE) disease progression in both mouse models and patients. Helios is beginning to be studied extensively for its influence on the T regulatory (Treg) compartment, both CD4+ Tregs and KIR+/Ly49+ CD8+ Tregs, with alterations to the number and function of these cells correlated to the autoimmune phenomenon. This review analyzes the most recent research on Helios expression in relation to the main immune cell populations and its role in SLE immune homeostasis, specifically focusing on the interaction between T cells and tolerogenic dendritic cells (tolDCs). This information could be potentially useful in the design of new therapies, with a particular focus on transfer therapies using immunosuppressive cells. Finally, we will discuss the possibility of using nanotechnology for magnetic targeting to overcome some of the obstacles related to these therapeutic approaches.

Emerging immunotherapeutic strategies for cutaneous lupus erythematosus: an overview of recent phase 2 and 3 clinical trials

INTRODUCTION

Cutaneous lupus erythematosus (CLE) is an autoimmune disease that is clinically heterogenous and may occur with or without the presence of systemic lupus erythematosus (SLE). While existing on a spectrum, CLE and SLE present differences in their underlying pathogenesis and therapeutic responses. No new therapies have been approved in recent decades by the U.S. Food and Drug Administration for CLE, although frequently refractory to conventional therapies. There is an unmet need to develop effective drugs for CLE as it significantly impacts patients' quality of life and may leave irreversible disfiguring damage.

AREAS COVERED

This review provides an update on the latest phase 2 and 3 clinical trials performed in CLE or SLE using skin-specific outcome measures. Emergent therapies are presented alongside their mechanism of action as recent translational studies have permitted identification of critical targets among immune cells and/or pathways involved in CLE.

EXPERT OPINION

While the recent literature has few trials for CLE, drugs targeting type I interferon, its downstream signaling and plasmacytoid dendritic cells have shown promising results. Further research is required to develop long-awaited effective therapies, and this review highlights the importance of implementing trials dedicated to CLE to fill the current gap in CLE therapeutics.

Endosomal trafficking inhibitor EGA can control TLR7-mediated IFNα expression by human plasmacytoid dendritic cells

Plasmacytoid dendritic cells (pDC) are the major producer of type 1 IFN in response to TLR7 agonists. Aberrant TLR7 activation and type 1 IFN expression by pDCs are linked to the pathogenesis of certain types of autoimmune diseases, including systemic lupus erythematosus (SLE). This study investigated the underlying mechanisms for TLR7-mediated cytokine expression by pDCs using a late endosome trafficking inhibitor, EGA (4-bromobenzaldehyde N-(2,6-dimethylphenyl) semicarbazone). We found that EGA treatment decreased IFNα expression by pDCs stimulated with imiquimod (R837), single-stranded RNA40, and influenza virus. EGA also decreased TNFα expression and secretion by R837-stimulated pDCs. Mechanistically, EGA treatment decreased phosphorylation of IKKα/β, STAT1, and p38, and prolonged degradation of IκBα. Furthermore, EGA treatment decreased the colocalization of 3F, a substituted adenine TLR7 agonist, with LAMP1+ compartments in pDCs. EGA was also capable of diminishing IFNα expression by SLE pDCs treated with R837 or live PR8/A/34 influenza viruses. Therefore, we concluded that trafficking of TLR7 agonists to LAMP1+ compartments is important for IFNα expression by pDCs. Data from this study support additional examinations of the potential benefits of EGA in treating type 1 IFN-associated inflammatory diseases in the future.

Human leukocyte immunoglobulin-like receptors in health and disease

Human leukocyte immunoglobulin (Ig)-like receptors (LILR) are a family of 11 innate immunomodulatory receptors, primarily expressed on lymphoid and myeloid cells. LILRs are either activating (LILRA) or inhibitory (LILRB) depending on their associated signalling domains (D). With the exception of the soluble LILRA3, LILRAs mediate immune activation, while LILRB1-5 primarily inhibit immune responses and mediate tolerance. Abnormal expression and function of LILRs is associated with a range of pathologies, including immune insufficiency (infection and malignancy) and overt immune responses (autoimmunity and alloresponses), suggesting LILRs may be excellent candidates for targeted immunotherapies. This review will discuss the biology and clinical relevance of this extensive family of immune receptors and will summarise the recent developments in targeting LILRs in disease settings, such as cancer, with an update on the clinical trials investigating the therapeutic targeting of these receptors.

Ubc9 regulates the expression of MHC II in dendritic cells to enhance DSS-induced colitis by mediating RBPJ SUMOylation

SUMOylation is an evolutionary conserved regulatory mechanism, in which Ubc9 is the only E2 conjugating enzyme. Previous studies demonstrated that SUMOylation is involved in multiple biological processes, but its role in dendritic cells (DCs) remains to be fully addressed. Herein in this report, we found that DCs deficient in Ubc9 protected mice from dextran sulfate sodium (DSS)-induced colitis, as evidenced by the ameliorated weight loss, colon length, and disrupted colon structure. Mechanistically, Ubc9 mediated SUMOylation of RBPJ, by which it stabilized RBPJ from ubiquitin-mediated degradation to enhance its transcriptional activity, while Ciita, a critical transcription factor, is a direct target downstream of RBPJ, which forms an enhanceosome complex to transcribe the expression of MHC II genes. Therefore, loss of Ubc9 abolished RBPJ SUMOylation, which was coupled with reduced Ciita transcription, thereby attenuating the expression of MHC class II genes. As a consequence of defective MHC II expression, Ubc9-/- DCs were featured by the impaired capability to process antigen and to prime effector CD4+ T cells, thereby protecting mice from DSS-induced colitis. Together, our results shed novel insight into the understanding of SUMOylation in the regulation of DC functions in pathological conditions.

CAR-T cells and CAR-Tregs targeting conventional type-1 dendritic cell suppress experimental autoimmune encephalomyelitis

Conventional type 1 dendritic cells (DC1) contribute to the development of pathogenic T helper type 1 (Th1) cells in part via the production of the proinflammatory cytokine interleukin-12. Thus, depletion of DC1 has the potential to dampen autoimmune responses. Here, we developed X-C motif chemokine receptor 1 (XCR1)-specific chimeric antigen receptor (CAR)-T cells and CAR-Tregs that specifically targeted DC1. XCR1 CAR-T cells were successfully generated as CD4+ and CD8+ T cells, expressed XCR1 CAR efficiently, and induced XCR1-dependent activation, cytokine production and proliferation. XCR1 CAR-T cells selectively depleted DC1 when transferred into RAG2-/- mice with a compensatory increase in conventional type 2 DC (DC2) and plasmacytoid DC (pDC). XCR1 CAR-T cell-mediated depletion of DC1 modestly suppressed the onset of Th1-driven experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis. Diphtheria toxin-mediated DC1 depletion in XCR1-diphtheria toxin receptor mice also suppressed EAE, suggesting that DC1 depletion was responsible for EAE suppression. XCR1 CAR-Tregs were successfully generated and suppressed effector T cells in the presence of XCR1+ cells. Therapeutic treatment with XCR1 CAR-Tregs suppressed Th1-driven EAE. Therefore, we conclude that depletion of DC1 with XCR1 CAR-T cells or immune suppression with XCR1 CAR-Tregs can modestly suppress Th1-driven EAE.

Phospholipase D4 as a signature of toll-like receptor 7 or 9 signaling is expressed on blastic T-bet + B cells in systemic lupus erythematosus

BACKGROUND

In systemic lupus erythematosus (SLE), autoreactive B cells are thought to develop by-passing immune checkpoints and contribute to its pathogenesis. Toll-like receptor (TLR) 7 and 9 signaling have been implicated in their development and differentiation. Although some B cell subpopulations such as T-bet + double negative 2 (DN2) cells have been identified as autoreactive in the past few years, because the upregulated surface markers of those cells are not exclusive to them, it is still challenging to specifically target autoreactive B cells in SLE patients.

METHODS

Our preliminary expression analysis revealed that phospholipase D4 (PLD4) is exclusively expressed in plasmacytoid dendritic cells (pDCs) and B cells in peripheral blood mononuclear cells (PBMCs) samples. Monoclonal antibodies against human PLD4 were generated, and flow cytometry analyses were conducted for PBMCs from 23 healthy donors (HDs) and 40 patients with SLE. In vitro cell culture was also performed to study the conditions that induce PLD4 in B cells from HDs. Finally, recombinant antibodies were synthesized from subpopulations of PLD4 + B cells from a patient with SLE, and their antinuclear activity was measured through enzyme-linked immunosorbent assay.

RESULTS

pDCs from both groups showed comparable frequency of surface PLD4 expression. PLD4 + B cells accounted for only a few percent of HD B cells, whereas they were significantly expanded in patients with SLE (2.1% ± 0.4% vs. 10.8% ± 1.2%, P < 0.005). A subpopulation within PLD4 + B cells whose cell size was comparable to CD38 + CD43 + plasmablasts was defined as "PLD4 + blasts," and their frequencies were significantly correlated with those of plasmablasts (P < 0.005). PLD4 + blasts phenotypically overlapped with double negative 2 (DN2) cells, and, in line with this, their frequencies were significantly correlated with several clinical markers of SLE. In vitro assay using healthy PBMCs demonstrated that TLR7 or TLR9 stimulation was sufficient to induce PLD4 on the surface of the B cells. Finally, two out of three recombinant antibodies synthesized from PLD4 + blasts showed antinuclear activity.

CONCLUSION

PLD4 + B cells, especially "blastic" ones, are likely autoreactive B cells undergoing TLR stimulation. Therefore, PLD4 is a promising target marker in SLE treatment.

Type I Interferons in Autoimmunity: Implications in Clinical Phenotypes and Treatment Response

Type I interferon (IFN-I) is thought to play a role in many systemic autoimmune diseases. IFN-I pathway activation is associated with pathogenic features, including the presence of autoantibodies and clinical phenotypes such as more severe disease with increased disease activity and damage. We will review the role and potential drivers of IFN-I dysregulation in 5 prototypic autoimmune diseases: systemic lupus erythematosus, dermatomyositis, rheumatoid arthritis, primary Sjögren syndrome, and systemic sclerosis. We will also discuss current therapeutic strategies that directly or indirectly target the IFN-I system.

Uncoupling interferons and the interferon signature explain clinical and transcriptional subsets in SLE

Interferons (IFN) are thought to be key players in systemic lupus erythematosus (SLE). The unique and interactive roles of the different IFN families in SLE pathogenesis, however, remain poorly understood. Using reporter cells engineered to precisely quantify IFN-I, IFN-II and IFN-III activity levels in serum/plasma, we found that while IFNs play essential role in SLE pathogenesis and disease activity, they are only significant in specific subsets of patients. Interestingly, whereas IFN-I is the main IFN that governs disease activity in SLE, clinical subsets are defined by the co-elevation of IFN-II and IFN-III. Thus, increased IFN-I alone was only associated with cutaneous lupus. In contrast, systemic features, such as nephritis, were linked to co-elevation of IFN-I plus IFN-II and IFN-III, implying a synergistic effect of IFNs in severe SLE. Intriguingly, while increased IFN-I levels were strongly associated with IFN-induced gene expression (93.5%), in up to 64% of cases, the IFN signature was not associated with IFN-I. Importantly, neither IFN-II nor IFN-III explained IFN-induced gene expression in patients with normal IFN-I levels, and not every feature in SLE was associated with elevated IFNs, suggesting IFN-independent subsets in SLE. Together, the data suggest that, unlike the IFN signature, direct quantification of bioactive IFNs can identify pathogenic and clinically relevant SLE subsets amenable for precise anti-IFN therapies. Since IFN-I is only elevated in a subset of SLE patients expressing the IFN signature, this study explains the heterogeneous response in clinical trials targeting IFN-I, where patients were selected based on IFN-induced gene expression rather than IFN-I levels.

CSL362 potently and specifically depletes pDCs invitro and ablates SLE-immune complex-induced IFN responses

Systemic lupus erythematosus (SLE) is an autoimmune disease with significant morbidity and mortality. Type I interferon (IFN) drives SLE pathology and plasmacytoid dendritic cells (pDCs) are potent producers of IFN; however, the specific effects of pDC depletion have not been demonstrated. We show CD123 was highly expressed on pDCs and the anti-CD123 antibody CSL362 potently depleted pDCs in vitro. CSL362 pre-treatment abrogated the induction of IFNα and IFN-induced gene transcription following stimulation with SLE patient-derived serum or immune complexes. RNA transcripts induced in pDCs by ex vivo stimulation with TLR ligands were reflected in gene expression profiles of SLE blood, and correlated with disease severity. TLR ligand-induced protein production by SLE patient peripheral mononuclear cells was abrogated by CSL362 pre-treatment including proteins over expressed in SLE patient serum. These findings implicate pDCs as key drivers in the cellular activation and production of soluble factors seen in SLE.

Cutaneous Lupus Erythematosus: An Update on Pathogenesis and Future Therapeutic Directions

Lupus erythematosus comprises a spectrum of autoimmune diseases that may affect various organs (systemic lupus erythematosus [SLE]) or the skin only (cutaneous lupus erythematosus [CLE]). Typical combinations of clinical, histological and serological findings define clinical subtypes of CLE, yet there is high interindividual variation. Skin lesions arise in the course of triggers such as ultraviolet (UV) light exposure, smoking or drugs; keratinocytes, cytotoxic T cells and plasmacytoid dendritic cells (pDCs) establish a self-perpetuating interplay between the innate and adaptive immune system that is pivotal for the pathogenesis of CLE. Therefore, treatment relies on avoidance of triggers and UV protection, topical therapies (glucocorticosteroids, calcineurin inhibitors) and rather unspecific immunosuppressive or immunomodulatory drugs. Yet, the advent of licensed targeted therapies for SLE might also open new perspectives in the management of CLE. The heterogeneity of CLE might be attributable to individual variables and we speculate that the prevailing inflammatory signature defined by either T cells, B cells, pDCs, a strong lesional type I interferon (IFN) response, or combinations of the above might be suitable to predict therapeutic response to targeted treatment. Therefore, pretherapeutic histological assessment of the inflammatory infiltrate could stratify patients with refractory CLE for T-cell-directed therapies (e.g. dapirolizumab pegol), B-cell-directed therapies (e.g. belimumab), pDC-directed therapies (e.g. litifilimab) or IFN-directed therapies (e.g. anifrolumab). Moreover, Janus kinase (JAK) and spleen tyrosine kinase (SYK) inhibitors might broaden the therapeutic armamentarium in the near future. A close interdisciplinary exchange with rheumatologists and nephrologists is mandatory for optimal treatment of lupus patients to define the best therapeutic strategy.

Viral recognition and the antiviral interferon response

Interferons (IFNs) are antiviral cytokines that play a key role in the innate immune response to viral infections. In response to viral stimuli, cells produce and release interferons, which then act on neighboring cells to induce the transcription of hundreds of genes. Many of these gene products either combat the viral infection directly, e.g., by interfering with viral replication, or help shape the following immune response. Here, we review how viral recognition leads to the production of different types of IFNs and how this production differs in spatial and temporal manners. We then continue to describe how these IFNs play different roles in the ensuing immune response depending on when and where they are produced or act during an infection.

Signaling pathways involved in the biological functions of dendritic cells and their implications for disease treatment

The ability of dendritic cells (DCs) to initiate and regulate adaptive immune responses is fundamental for maintaining immune homeostasis upon exposure to self or foreign antigens. The immune regulatory function of DCs is strictly controlled by their distribution as well as by cytokines, chemokines, and transcriptional programming. These factors work in conjunction to determine whether DCs exert an immunosuppressive or immune-activating function. Therefore, understanding the molecular signals involved in DC-dependent immunoregulation is crucial in providing insight into the generation of organismal immunity and revealing potential clinical applications of DCs. Considering the many breakthroughs in DC research in recent years, in this review we focused on three basic lines of research directly related to the biological functions of DCs and summarized new immunotherapeutic strategies involving DCs. First, we reviewed recent findings on DC subsets and identified lineage-restricted transcription factors that guide the development of different DC subsets. Second, we discussed the recognition and processing of antigens by DCs through pattern recognition receptors, endogenous/exogenous pathways, and the presentation of antigens through peptide/major histocompatibility complexes. Third, we reviewed how interactions between DCs and T cells coordinate immune homeostasis in vivo via multiple pathways. Finally, we summarized the application of DC-based immunotherapy for autoimmune diseases and tumors and highlighted potential research prospects for immunotherapy that targets DCs. This review provides a useful resource to better understand the immunomodulatory signals involved in different subsets of DCs and the manipulation of these immune signals can facilitate DC-based immunotherapy.

New biologics and targeted therapies in systemic lupus: From new molecular targets to new indications. A systematic review

INTRODUCTION

Despite available therapies, persistently active and corticosteroid-dependent Systemic Lupus Erythematosus (SLE) represent a significant therapeutic challenge. The purpose of this systematic review was to provide an updated view of targeted therapies currently in clinical development in SLE, with a special focus on the most promising ones.

METHODS

We performed a systematic review of targeted therapies in clinical development in SLE in clinicaltrials.gov (search date: 28th of August 2022). Targeted therapies (defined as drugs specifically designed to block certain molecules, receptors, or pathways involved in the development of SLE) were extracted. For each investigational drug, we considered only the study at the most advanced stage of clinical development.

RESULTS

The systematic review yielded a total of 92 targeted therapies (58 biological DMARDs [bDMARDs] and 34 targeted synthetic [ts]DMARDs) assessed in a total of 203 clinical trials. The candidate drugs reached phase I (n=20), Ia/IIb (n=6), phase II (n=51), phase II/III (n=1), phase III (n=13) and phase IV (n=1). These trials were reported as recruiting (n=31), active but not recruiting (n=8), not yet recruiting (n=4), enrolling by invitation (n=2), completed (n=31), prematurely terminated (n=12) and withdrawn in 1 (status unknown in 3). The main investigational drugs for SLE target inflammatory cytokines, chemokines or their receptors (n=19), intracellular signaling pathways (n=18), B cells (n=14) or plasma cells (n=7),T/B cells co-stimulation molecules (n=10), complement molecules (n=5),T lymphocytes (n=2), plasmacytoid dendritic cells (n=2), as well as various other immune targets (n=15).

CONCLUSION

The pipeline of investigational drugs in SLE is highly diversified and will hopefully enable more optimal Treat-To-Target with the goal of disease modification. Companion biomarkers will be needed to better characterized SLE heterogeneity and optimize treatment selection at the individual-patient level.

Disruption of endosomal trafficking with EGA alters TLR9 cytokine response in human plasmacytoid dendritic cells

Plasmacytoid dendritic cells (pDCs) exhibit bifurcated cytokine responses to TLR9 agonists, an IRF7-mediated type 1 IFN response or a pro-inflammatory cytokine response via the activation of NF-κB. This bifurcated response has been hypothesized to result from either distinct signaling endosomes or endo-lysosomal trafficking delay of TLR9 agonists allowing for autocrine signaling to affect outcomes. Utilizing the late endosome trafficking inhibitor, EGA, we assessed the bifurcated cytokine responses of pDCs to TLR9 stimulation. EGA treatment of pDCs diminished both IFNα and pro-inflammatory cytokine expression induced by CpG DNAs (D- and K-type), CpG-DNAs complexed with DOTAP, and genomic DNAs complexed with LL37. Mechanistically, EGA suppressed phosphorylation of IKKα/β, STAT1, Akt, and p38, and decreased colocalization of CpG oligodeoxynucleotides with LAMP⁺ endo-lysosomes. EGA also diminished type 1 IFN expression by pDCs from systemic lupus erythematosus patients. Therefore, our findings help understand mechanisms for the bifurcated cytokine responses by pDCs and support future examination of the potential benefit of EGA in treating type 1 IFN-associated inflammatory diseases in the future.

Cutaneous Involvement in Systemic Lupus Erythematosus: A Review for the Rheumatologist

The majority of patients with systemic lupus erythematosus (SLE) have cutaneous manifestations at some point in their disease course. The skin findings in SLE are classified as SLE-specific or SLE-nonspecific based on histopathologic findings. SLE-specific skin diseases include chronic cutaneous lupus erythematosus (CLE), subacute CLE, and acute CLE. There are subsets of skin lesions within each group and the likelihood of associated SLE varies among them. SLE-nonspecific lesions are more common in patients with SLE and tend to coincide with active systemic disease. SLE-nonspecific lesions may be seen as a feature of another disease process, including other connective tissue diseases. It is important for the rheumatologist to be familiar with the spectrum of cutaneous diseases in SLE to help prognosticate the likelihood of systemic disease and to ensure patients receive timely dermatologic care with the goal of controlling disease activity to prevent damage.

Association between increased peripheral blood CD86-positive plasmacytoid dendritic cells and immune-related adverse events in patients with non-small cell lung cancer

The occurrence of immune-related adverse events (irAEs) after immune checkpoint inhibitors (ICIs) is unpredictable. Profiles of peripheral blood mononuclear cells (PBMCs) represent the host immune system and have the potential to predict irAEs. We analyzed PBMC subsets using multicolor flow cytometry before and at weeks 2 and 8 after the start of ICIs in patients with non-small cell lung cancer. Sixteen eligible patients were evaluated. The irAEs occurred in 6 patients (37.5%): diarrhea in 2, diarrhea and a rash in 1, pituitary dysfunction in 1, cholangitis in 1, and pneumonitis in 1. Patients experiencing irAEs had higher levels of CD86⁺plasmacytoid dendritic cells (pDCs) at the baseline and weeks 2 and 8 after the ICIs than those not experiencing irAEs (p = 0.005, 0.038, and 0.050, respectively). In patients experiencing irAEs, the levels of CD86⁺pDCs significantly decreased at weeks 2 and 8 compared to the baseline (p = 0 .034 and 0.025, respectively) but did not change in those not experiencing irAEs. The levels of other PBMC subsets were not significantly associated with irAEs. Higher levels of natural killer (NK) cells were significantly associated with an overall objective response (p = 0.024). In conclusion, higher levels of CD86⁺pDCs at the baseline and a reduction in those levels 2 and 8 weeks after ICIs were associated with the occurrence of irAEs. Higher levels of NK cells were associated with an objective response to ICIs. Evaluation of PBMCs may help to predict the efficacy and safety of ICIs.

Advances in lupus therapeutics: Achieving sustained control of the type I interferon pathway

Achieving sustained control of disease activity in patients with systemic lupus erythematosus has been impeded by the complexity of its immunopathogenesis as well its clinical heterogeneity. In spite of these challenges, gains in understanding disease mechanisms have identified immune targets that are currently under study in trials of candidate therapeutics. Defining the type I interferon (IFN-I) pathway and autoantibodies specific for nucleic acid binding proteins as core pathogenic mediators allows an analysis of approaches that could control production of those mediators and improve patient outcomes. This review describes therapeutic targets and agents that could achieve control of the IFN-I pathway. Toll-like receptor 7, involved in IFN-I production and differentiation of B cells, and long-lived plasma cells, the producers of autoantibodies specific for RNA-binding proteins, components of the immune complex drivers of IFN-I, are particularly attractive therapeutic targets.

The relation of the frequency and functional molecules expression on plasmacytoid dendritic cells to postpartum hepatitis in women with HBeAg-positive chronic hepatitis B virus infection

OBJECTIVE

To explore the correlation between postpartum hepatitis and changes of plasmacytoid dendritic cells' (pDC) function and frequency in hepatitis B e antigen (HBeAg)-positive pregnant women with chronic hepatitis B virus (HBV) infection.

METHODS

Pregnant women with chronic HBV infection receiving antiviral treatment (treated group) or not receiving antiviral treatment (untreated group) were enrolled and demographic information was collected before delivery. Clinical biochemical, virological serology, pDC frequency and functional molecular expression were tested before delivery and at 6, 12, 24 weeks after delivery.

RESULTS

90 eligible pregnant women were enrolled, 36 in the untreated group and 54 in the treated group. 36 patients developed postpartum hepatitis, including 17 (17/36, 47.2%) in the untreated group and 19 (19/54, 35.2%) in the treated group (χ2 = 1.304 p=0.253), and 22 cases of hepatitis occurred at 6 weeks postpartum, 12 at 12 weeks postpartum, and 2 at 24 weeks postpartum. The alanine transaminase (ALT) levels at any time postpartum were significantly higher than that of the antepartum, especially at 6 weeks and 12 weeks postpartum. However, the frequencies of pDCs, CD83+ pDCs and CD86+ pDCs antepartum had no significant difference from any time postpartum. The frequencies of CD83+ pDCs, CD86+ pDCs in the treated group antepartum were significantly higher than those in the untreated group [12.70 (9.46, 15.08) vs. 10.20 (7.96, 11.85), p=0.007; 22.05 (19.28, 33.03) vs. 18.05 (14.33, 22.95), p=0.011], and the same at 12 weeks postpartum [12.80 (10.50, 15.50) vs. 9.38 (7.73, 12.60), p=0.017; 22.50 (16.80, 31.20) vs. 16.50 (12.65, 20.80), p=0.001]. The frequency of CD86+ pDCs in the treated group was significantly higher than that in the untreated group at 24 weeks postpartum [22.10 (16.70, 30.00) vs. 17.10 (13.70, 20.05), p=0.006].

CONCLUSIONS

Postpartum hepatitis in HBV infected women mainly occurs at 6-12 weeks postpartum. Antiviral treatment during pregnancy can significantly increase the frequencies of CD83+ pDCs and CD86+ pDCs in pregnant women with chronic HBV infection.

Chronic activation of pDCs in autoimmunity is linked to dysregulated ER stress and metabolic responses

Plasmacytoid dendritic cells (pDCs) chronically produce type I interferon (IFN-I) in autoimmune diseases, including systemic sclerosis (SSc) and systemic lupus erythematosus (SLE). We report that the IRE1α-XBP1 branch of the unfolded protein response (UPR) inhibits IFN-α production by TLR7- or TLR9-activated pDCs. In SSc patients, UPR gene expression was reduced in pDCs, which inversely correlated with IFN-I-stimulated gene expression. CXCL4, a chemokine highly secreted in SSc patients, downregulated IRE1α-XBP1-controlled genes and promoted IFN-α production by pDCs. Mechanistically, IRE1α-XBP1 activation rewired glycolysis to serine biosynthesis by inducing phosphoglycerate dehydrogenase (PHGDH) expression. This process reduced pyruvate access to the tricarboxylic acid (TCA) cycle and blunted mitochondrial ATP generation, which are essential for pDC IFN-I responses. Notably, PHGDH expression was reduced in pDCs from patients with SSc and SLE, and pharmacological blockade of TCA cycle reactions inhibited IFN-I responses in pDCs from these patients. Hence, modulating the IRE1α-XBP1-PHGDH axis may represent a hitherto unexplored strategy for alleviating chronic pDC activation in autoimmune disorders.

An update on the management of refractory cutaneous lupus erythematosus

Management of cutaneous lupus erythematosus (CLE) involves a combination of preventive measures, topical and systemic drugs, fairly similar for the different subtypes. Although guidelines exist, to date, no specific drugs have been specifically licensed for CLE. Antimalarials remain the first-line systemic treatment, but many patients do not respond, making refractory lupus a challenge for clinicians. The choice of alternative medication should be based on effectiveness, safety and cost. Most of the available drugs for CLE have been adapted from systemic lupus erythematosus (SLE) treatment but the existing literature is limited to small studies and evidence often lacks. As knowledge of pathogenesis of both CLE and SLE is improving, promising new therapies are emerging. In this review, we discuss the available medications, focusing on the novelties under development for CLE.

Sensing of SARS-CoV-2 by pDCs and their subsequent production of IFN-I contribute to macrophage-induced cytokine storm during COVID-19

Lung-infiltrating macrophages create a marked inflammatory milieu in a subset of patients with COVID-19 by producing a cytokine storm, which correlates with increased lethality. However, these macrophages are largely not infected by SARS-CoV-2, so the mechanism underlying their activation in the lung is unclear. Type I interferons (IFN-I) contribute to protecting the host against SARS-CoV-2 but may also have some deleterious effect, and the source of IFN-I in the lungs of infected patients is not well defined. Plasmacytoid dendritic cells (pDCs), a key cell type involved in antiviral responses, can produce IFN-I in response to SARS-CoV-2. We observed the infiltration of pDCs in the lungs of SARS-CoV-2-infected patients, which correlated with strong IFN-I signaling in lung macrophages. In patients with severe COVID-19, lung macrophages expressed a robust inflammatory signature, which correlated with persistent IFN-I signaling at the single-cell level. Hence, we observed the uncoupling in the kinetics of the infiltration of pDCs in the lungs and the associated IFN-I signature, with the cytokine storm in macrophages. We observed that pDCs were the dominant IFN-α-producing cells in response to the virus in the blood, whereas macrophages produced IFN-α only when in physical contact with infected epithelial cells. We also showed that IFN-α produced by pDCs, after the sensing of SARS-CoV-2 by TLR7, mediated changes in macrophages at both transcriptional and epigenetic levels, which favored their hyperactivation by environmental stimuli. Together, these data indicate that the priming of macrophages can result from the response by pDCs to SARS-CoV-2, leading to macrophage activation in patients with severe COVID-19.

Emerging Therapies in Cutaneous Lupus Erythematosus

Cutaneous lupus erythematosus (CLE) is an autoimmune disease that can occur with or without underlying systemic lupus erythematosus (SLE) and often has a profoundly negative impact on patient quality of life. There is substantial need for new and more effective therapies to treat CLE. CLE has a multifactorial pathogenesis that involves several key immune cells and pathways, including abnormalities in innate (e.g., type 1 interferon pathways) and adaptive immune responses (e.g., B and T cell autoreactivity), presenting multiple opportunities for more targeted therapies that do not require immunosuppression. Here we review several emerging therapies and their efficacy in CLE. Anifrolumab and belimumab have both been approved for the treatment of SLE in recent years, and clinical trial evidence suggests some forms of CLE may improve with these agents. Therapies currently in development that are being evaluated with CLE-specific outcome measures include BIIB059 and VIB7734, which target plasmacytoid dendritic cells (pDCs), and iberdomide, a cereblon modulator. These novel therapies all have previously demonstrated clinical benefit in some forms of CLE. Other therapies which target molecules believed to play a role in CLE pathogenesis, such as Janus kinases (JAKs), spleen tyrosine kinase (SYK), interferon γ (IFNγ), IL-12, and IL-23, have been evaluated in lupus clinical trials with skin-specific outcomes but failed to meet their primary endpoints.

Chemokines form nanoparticles with DNA and can superinduce TLR-driven immune inflammation

Chemokines control the migratory patterns and positioning of immune cells to organize immune responses to pathogens. However, many chemokines have been associated with systemic autoimmune diseases that have chronic IFN signatures. We report that a series of chemokines, including CXCL4, CXCL10, CXCL12, and CCL5, can superinduce type I IFN (IFN-I) by TLR9-activated plasmacytoid DCs (pDCs), independently of their respective known chemokine receptors. Mechanistically, we show that chemokines such as CXCL4 mediate transcriptional and epigenetic changes in pDCs, mostly targeted to the IFN-I pathways. We describe that chemokines physically interact with DNA to form nanoparticles that promote clathrin-mediated cellular uptake and delivery of DNA in the early endosomes of pDCs. Using two separate mouse models of skin inflammation, we observed the presence of CXCL4 associated with DNA in vivo. These data reveal a noncanonical role for chemokines to serve as nucleic acid delivery vectors to modulate TLR signaling, with implications for the chronic presence of IFN-I by pDCs in autoimmune diseases.

Current Concepts on Pathogenic Mechanisms and Histopathology in Cutaneous Lupus Erythematosus

Cutaneous lupus erythematosus (CLE) is an interferon (IFN)-driven autoimmune disease that may be limited to the skin or can be associated with systemic lupus erythematosus (SLE). CLE occurs in several morphologic subtypes ranging from isolated, disc-shaped plaques to disseminated skin lesions. The typical histopathologic pattern of skin lesions is named interface dermatitis and characterized by a lymphocytic infiltrate and necroptotic keratinocytes at the dermo-epidermal junction. Other histopathologic patterns primarily involve the dermis or subcutis, depending on the subtype. One critical mechanism in CLE is the chronic reactivation of innate and adaptive immune pathways. An important step in this process is the recognition of endogenous nucleic acids released from dying cells by various pattern recognition receptors (PRRs), including Toll-like receptors (TLRs) and other cytosolic receptors. Crucial cells in CLE pathogenesis comprise plasmacytoid dendritic cells (pDCs) as major producers of type I IFN, T cells exerting cytotoxic effects, and B cells, previously believed to contribute via secretion of autoantibodies. However, B cells are increasingly considered to have additional functions, supported by studies finding them to occur in highest numbers in chronic discoid lupus erythematosus (CDLE), a subtype in which autoantibodies are often absent. More precise knowledge of how CLE subtypes differ pathophysiologically may allow a tailored pharmacotherapy in the future, taking into account the specific molecular signature in relation to the morphologic subtype.

Unmet Medical Needs in Chronic, Non-communicable Inflammatory Skin Diseases

An estimated 20-25% of the population is affected by chronic, non-communicable inflammatory skin diseases. Chronic skin inflammation has many causes. Among the most frequent chronic inflammatory skin diseases are atopic dermatitis, psoriasis, urticaria, lichen planus, and hidradenitis suppurativa, driven by a complex interplay of genetics and environmental factors. Autoimmunity is another important cause of chronic skin inflammation. The autoimmune response may be mainly T cell driven, such as in alopecia areata or vitiligo, or B cell driven in chronic spontaneous urticaria, pemphigus and pemphigoid diseases. Rare causes of chronic skin inflammation are autoinflammatory diseases, or rheumatic diseases, such as cutaneous lupus erythematosus or dermatomyositis. Whilst we have seen a significant improvement in diagnosis and treatment, several challenges remain. Especially for rarer causes of chronic skin inflammation, early diagnosis is often missed because of low awareness and lack of diagnostics. Systemic immunosuppression is the treatment of choice for almost all of these diseases. Adverse events due to immunosuppression, insufficient therapeutic responses and relapses remain a challenge. For atopic dermatitis and psoriasis, a broad spectrum of innovative treatments has been developed. However, treatment responses cannot be predicted so far. Hence, development of (bio)markers allowing selection of specific medications for individual patients is needed. Given the encouraging developments during the past years, we envision that many of these challenges in the diagnosis and treatment of chronic inflammatory skin diseases will be thoroughly addressed in the future.