Heat-shock protein 90 inhibition in autoimmunity to type VII collagen: evidence that nonmalignant plasma cells are not therapeutic targets

Heat shock protein 90 (Hsp90) inhibitor STA-9090 (Ganetespib) ameliorates inflammation in a mouse model of atopic dermatitis

Molecular chaperones belonging to the heat shock protein 90 (Hsp90) family are implicated in inflammatory processes and described as potential novel therapeutic targets in autoimmune/inflammatory skin diseases. While the pathological role of circulating Hsp90 has been recently proposed in patients with atopic dermatitis (AD), a chronic inflammatory skin disease characterized by intense itching and recurrent skin lesions, studies aimed at investigating the role of Hsp90 as a potential target of AD therapy have not yet been conducted. Here, the effects of the Hsp90 blocker STA-9090 (Ganetespib) applied systemically or topically were determined in an experimental mouse model of dinitrochlorobenzene (DNCB)-induced AD. Intraperitoneal administration of STA-9090 ameliorated clinical disease severity, histological epidermal thickness, and dermal leukocyte infiltration in AD mice which was associated with reducing the scratching behavior in DNCB-treated animals. Additionally, topically applied STA-9090 led to lowered disease activity in AD mice, reduced serum levels of IgE, and up-regulated filaggrin expression in lesional skin samples. Our observations suggest that Hsp90 may be a promising therapeutic target in atopic dermatitis and potentially other inflammatory or autoimmune dermatoses.

A life for autoimmune blistering diseases: in memoriam Detlef Zillikens

Detlef Zillikens, MD, director and chair of the Department of Dermatology at the University of Lübeck, Lübeck, Germany, died in September 2022, aged only 64. He dedicated his professional life to autoimmune blistering diseases (AIBDs) and built his department into one of the world's leading centers for these diseases. Herein, his professional life and the impact on the field of AIBDs and the research landscape at the University of Lübeck are addressed. With his warm, integrative, open-minded, ever-optimistic attitude, he was a highly reliable colleague, mentor, and friend to many in the field including each of the authors. Combined with his in-depth knowledge of dermatology, interest in many fields of life science, and hard work, Detlef Zillikens initiated the founding of two independent research institutes, the Lübeck Institute of Experimental Dermatology and the Institute and Comprehensive Center for Inflammation Medicine. He was also instrumental in establishing the Center for Research on Inflammation of the Skin, where in a new research building, over 140 scientists pursue research questions related to skin inflammation. By inviting numerous researchers and clinicians to his department and hosting two large international meetings, he brought the field of AIBDs much closer together and inspired multiple national and international research initiatives. His ideas will live on and grow in many of his colleagues and mentees.

Heat shock protein 90 inhibitor RGRN-305 potently attenuates skin inflammation

Introduction

Chronic inflammatory skin diseases may have a profound negative impact on the quality of life. Current treatment options may be inadequate, offering an unsatisfactory response or side effects. Therefore, ongoing efforts exist to identify novel effective and safe treatments. Heat shock protein (HSP) 90 is a chaperone that promotes the activity of a wide range of client proteins including key proinflammatory molecules involved in aberrant inflammation. Recently, a proof-of-concept clinical trial of 13 patients suggested that RGRN-305 (an HSP90 inhibitor) may be an oral treatment for psoriasis. However, HSP90 inhibition may be a novel therapeutic approach extending beyond psoriasis to include multiple immune-mediated inflammatory skin diseases.

Methods

This study aimed to investigate (i) the anti-inflammatory effects and mechanisms of HSP90 inhibition and (ii) the feasibility of topical RGRN-305 administration (new route of administration) in models of inflammation elicited by 12-O-tetradecanoylphorbol-13-acetate (TPA) in primary human keratinocytes and mice (irritative dermatitis murine model).

Results/Discussion

In primary human keratinocytes stimulated with TPA, a Nanostring® nCounter gene expression assay demonstrated that HSP90 inhibition with RGRN-305 suppressed many proinflammatory genes. Furthermore, when measured by quantitative real-time polymerase chain reaction (RT-qPCR), RGRN-305 significantly reduced the gene expression of TNF, IL1B, IL6 and CXCL8. We next demonstrated that topical RGRN-305 application significantly ameliorated TPA-induced skin inflammation in mice. The increase in ear thickness (a marker of inflammation) was significantly reduced (up to 89% inhibition). In accordance, RT-qPCR of the ear tissue demonstrated that RGRN-305 robustly reduced the gene expression of proinflammatory markers (Tnf, Il1b, Il6, Il17A and Defb4). Moreover, RNA sequencing revealed that RGRN-305 mitigated TPA-induced alterations in gene expression and suppressed genes implicated in inflammation. Lastly, we discovered that the anti-inflammatory effects were mediated, at least partly, by suppressing the activity of NF-κB, ERK1/2, p38 MAPK and c-Jun signaling pathways, which are consistent with previous findings in other experimental models beyond skin inflammation. In summary, HSP90 inhibition robustly suppressed TPA-induced inflammation by targeting key proinflammatory cytokines and signaling pathways. Our findings suggest that HSP90 inhibition may be a novel mechanism of action for treating immune-mediated skin disease beyond psoriasis, and it may be a topical treatment option.

Epidermolysis Bullosa Acquisita-Current and Emerging Treatments

Epidermolysis bullosa acquisita (EBA) is a rare chronic autoimmune subepidermal blistering disease of the skin and mucous membranes, usually beginning in adulthood. EBA is induced by autoantibodies to type VII collagen, a major component of anchoring fibrils in the dermal-epidermal junction (DEJ). The binding of autoantibodies to type-VII collagen subsequently leads to the detachment of the epidermis and the formation of mucocutaneous blisters. EBA has two major clinical subtypes: the mechanobullous and inflammatory variants. The classic mechanobullous variant presentation consists of skin fragility, bullae with minimal clinical or histological inflammation, erosions in acral distribution that heal with scarring, and milia formation. The inflammatory variant is challenging to differentiate from other autoimmune bullous diseases, most commonly bullous pemphigoid (BP) but also mucous membrane pemphigoid (MMP), Brunsting-Perry pemphigoid, and linear IgA dermatosis. Due to its recalcitrance conventional treatment of epidermolysis bullosa acquisita is shown to be demanding. Here we discuss novel therapeutic strategies that have emerged and which could potentially improve the quality of life in patients with EBA.

Targeting heat shock proteins 90 and 70: A promising remedy for both autoimmune bullous diseases and COVID-19

Heat shock proteins (Hsps), including Hsp90 and Hsp70, are intra- and extracellular molecules implicated in cellular homeostasis and immune processes and are induced by cell stress such as inflammation and infection. Autoimmune bullous disorders (AIBDs) and COVID-19 represent potentially life-threatening inflammatory and infectious diseases, respectively. A significant portion of AIBDs remain refractory to currently available immunosuppressive therapies, which may represent a risk factor for COVID-19, and suffer from treatment side-effects. Despite advances in vaccination, there is still a need to develop new therapeutic approaches targeting SARS-CoV-2, especially considering vaccine hesitancy, logistical distribution challenges, and breakthrough infections. In this mini review, we briefly summarize the role of targeting Hsp90/70 as a promising double-edged sword in the therapy of AIBDs and COVID-19.

Heat shock proteins: Biological functions, pathological roles, and therapeutic opportunities

The heat shock proteins (HSPs) are ubiquitous and conserved protein families in both prokaryotic and eukaryotic organisms, and they maintain cellular proteostasis and protect cells from stresses. HSP protein families are classified based on their molecular weights, mainly including large HSPs, HSP90, HSP70, HSP60, HSP40, and small HSPs. They function as molecular chaperons in cells and work as an integrated network, participating in the folding of newly synthesized polypeptides, refolding metastable proteins, protein complex assembly, dissociating protein aggregate dissociation, and the degradation of misfolded proteins. In addition to their chaperone functions, they also play important roles in cell signaling transduction, cell cycle, and apoptosis regulation. Therefore, malfunction of HSPs is related with many diseases, including cancers, neurodegeneration, and other diseases. In this review, we describe the current understandings about the molecular mechanisms of the major HSP families including HSP90/HSP70/HSP60/HSP110 and small HSPs, how the HSPs keep the protein proteostasis and response to stresses, and we also discuss their roles in diseases and the recent exploration of HSP related therapy and diagnosis to modulate diseases. These research advances offer new prospects of HSPs as potential targets for therapeutic intervention.

Heat Shock Protein 90 (Hsp90) and Hsp70 as Potential Therapeutic Targets in Autoimmune Skin Diseases

Over a hundred different autoimmune diseases have been described to date, which can affect every organ in the body, including the largest one, the skin. In fact, up to one-fifth of the world's population suffers from chronic, noninfectious inflammatory skin diseases, the development of which is significantly influenced by an autoimmune response. One of the hallmarks of autoimmune diseases is the loss of immune tolerance, which leads to the formation of autoreactive lymphocytes or autoantibodies and, consequently, to chronic inflammation and tissue damage. The treatment of autoimmune skin diseases mainly focuses on immunosuppression (using, e.g., corticosteroids) but almost never leads to the development of permanent mechanisms of immune tolerance. In addition, current therapies and their long-term administration may cause serious adverse effects. Hence, safer and more effective therapies that bring sustained balance between pro- and anti-inflammatory responses are still desired. Both intra- and extracellular heat shock proteins (Hsps), specifically well-characterized inducible Hsp90 and Hsp70 chaperones, have been highlighted as therapeutic targets for autoimmune diseases. This review presents preclinical data on the involvement of Hsp90 and Hsp70 in modulating the immune response, specifically in the context of the treatment of selected autoimmune skin diseases with emphasis on autoimmune bullous skin diseases and psoriasis.

Heat shock protein 90 is a new potential target of anti-rejection therapy in allotransplantation

The critical roles of heat shock protein 90 (HSP90) in immune reactions associated with viral infection and autoimmune disease are well known. To date, however, its roles in the alloimmune response and the immunosuppressive effect of HSP90 inhibitors in allotransplantation have remained unknown. The purpose of this study was to examine the therapeutic efficacy of the HSP90 inhibitor 17-DMAG in allotransplantation models. C57BL/6 (H-2b) and BALB/c (H-2d) mice were used as donors for and recipients of skin and heart transplantation, respectively. Treatment with 17-DMAG (daily i.p.) or a vehicle was initiated 3 days before transplantation. Immunological outcomes were assessed by histopathological examinations, flow cytometric analysis, quantitative RT-PCR, ELISA, ELISPOT assay, and MLR. 17-DMAG treatment significantly prolonged the survival of both skin and heart allografts. In 17-DMAG-treated mice, donor-reactive splenocytes producing IFN-γ were significantly reduced along with the intragraft mRNA expression level and serum concentration of IFN-γ. Intragraft mRNA expression of cytokines and chemokines associated with both innate and adaptive immunity was suppressed in 17-DMAG-treated group. MLR showed suppression of the donor-specific proliferation of CD4 + T and CD19 + B cells in the spleens of 17-DMAG-treated mice. 17-DMAG treatment also reduced the number of activated NK cells. Furthermore, the treatment lowered the titers of donor-specific antibodies in the serum and prolonged a second skin allograft in mice sensitized by previous skin transplantation. HSP90 inhibition by 17-DMAG can affect various immune responses, including innate immunity, adaptive immunity, and humoral immunity, suggesting its therapeutic potential against acute rejection in allotransplantation.

Integrating 3D genomic and epigenomic data to enhance target gene discovery and drug repurposing in transcriptome-wide association studies

Transcriptome-wide association studies (TWAS) are popular approaches to test for association between imputed gene expression levels and traits of interest. Here, we propose an integrative method PUMICE (Prediction Using Models Informed by Chromatin conformations and Epigenomics) to integrate 3D genomic and epigenomic data with expression quantitative trait loci (eQTL) to more accurately predict gene expressions. PUMICE helps define and prioritize regions that harbor cis-regulatory variants, which outperforms competing methods. We further describe an extension to our method PUMICE +, which jointly combines TWAS results from single- and multi-tissue models. Across 79 traits, PUMICE + identifies 22% more independent novel genes and increases median chi-square statistics values at known loci by 35% compared to the second-best method, as well as achieves the narrowest credible interval size. Lastly, we perform computational drug repurposing and confirm that PUMICE + outperforms other TWAS methods.

Subunit-Specific Reactivity of Autoantibodies Against Laminin-332 Reveals Direct Inflammatory Mechanisms on Keratinocytes

Laminin-332 pemphigoid is a rare and severe autoimmune blistering disease, caused by IgG autoantibodies targeting laminin-332 in the dermal-epidermal basement zone. Laminin-332 pemphigoid is characterized by variable inflammatory infiltrate and the predominance of non-complement-fixing antibodies. Given these findings, we hypothesized that IgG autoantibodies to laminin-332 directly resulted in keratinocyte expression of inflammatory factors. We performed RNA-seq on primary human keratinocytes treated with IgG from patients with laminin-332 pemphigoid. Genes for numerous cytokines and chemokines were upregulated, including CSF2, CSF3, CXCL1, CXCL5, CXCL3, CXCL8, CXCL10, CXCL1, IL6, IL7, IL15, IL23, IL32, IL37, TGFB2 as well as metalloproteases. Considering the pro-inflammatory and proteolytic effect of autoantibodies from patients with laminin-332 pemphigoid identified in our initial experiment, we next questioned whether the reactivity against specific laminin subunits dictates the inflammatory and proteolytic keratinocyte response. Then, we treated keratinocytes with IgG from a separate cohort of patients with reactivity against individual subunits of laminin-332. We identified upregulation of IL-1α, IL-6, IL-8, CXCL1, MMP9, TSLP, and GM-CSF at the protein level, most notably in keratinocytes treated with IgG from laminin β3-reactive patients. We for the first time demonstrated a pro-inflammatory response, similar to that described in keratinocytes treated with IgG autoantibodies from patients with bullous pemphigoid, providing novel insight into the pathogenesis of laminin-332 pemphigoid and laminin-332 biology.

HSP90 inhibitor RGRN-305 for oral treatment of plaque type psoriasis: efficacy, safety and biomarker results in an open-label proof-of-concept study

BACKGROUND

HSP90 is a downstream regulator of tumor necrosis factor α (TNFα) and interleukin (IL)-17A signaling and may therefore serve as a novel target in the treatment of psoriasis.

OBJECTIVE

This phase 1b proof-of-concept study was undertaken to evaluate the safety and efficacy of a novel HSP90 inhibitor (RGRN-305) in the treatment of plaque psoriasis.

METHODS

An open-label, single-arm, dose-selection, single-center proof-of-concept study. Patients with plaque psoriasis were treated with 250 mg or 500 mg RGRN-305 daily for 12 weeks. Efficacy was evaluated clinically using Psoriasis Area and Severity Index (PASI), body surface area (BSA), and Physician Global Assessment (PGA) scores and by Dermatology Life Quality Index (DLQI). Skin biopsies collected at baseline and at 4, 8, and 12 weeks after treatment start were used for immunohistochemical staining and for gene expression analysis. Safety was monitored via laboratory tests, vital signs, ECG, and physical examinations.

RESULTS

Six of the eleven patients completing the study responded to RGRN-305 with a PASI improvement between 71% and 94%, whereas five patients were considered nonresponders with a PASI response < 50%. No severe adverse events were reported. Four of seven patients treated with 500 mg RGRN-305 daily experienced a mild to moderate exanthematous drug induced eruption due to study treatment. Two patients chose to discontinue the study due to this exanthematous eruption. RGRN-305 treatment resulted in pronounced inhibition of the IL-23, TNFα, and IL-17A signaling pathways and normalization of both histological changes and psoriatic lesion gene expression profiles in patients responding to treatment.

CONCLUSION

Treatment with RGRN-305 showed an acceptable safety, especially in the low-dose group, and was associated with clinically meaningful improvement in a subset of patients with plaque psoriasis, indicating that HSP90 may serve as a novel future target in psoriasis treatment.

Evidence for a role of extracellular heat shock protein 70 in epidermolysis bullosa acquisita

Heat shock protein 90 (Hsp90) and Hsp70 are chaperones implicated in different inflammatory disorders, given their property to impact innate and adaptive immune responses. Here, we determined the so far unknown role of extracellular Hsp70 in epidermolysis bullosa acquisita (EBA), an anti-type VII collagen autoantibody-mediated blistering dermatosis. The in vivo pathophysiological relevance of extracellular Hsp70 was demonstrated in an anti-type VII collagen antibody transfer-induced EBA mouse model in which elevated blood levels of this chaperone were recorded. We found that Hsp70-treated mice had a more intense clinical disease severity compared to controls that were paralleled by increased levels of cutaneous matrix metalloproteinase 9 and plasma hydrogen peroxide. The latter finding was confirmed in an independent reactive oxygen species release assay using EBA-specific immune complexes combined with recombinant Hsp70. Finally, cell culture experiments using human naive peripheral blood mononuclear cells (PBMC) revealed that extracellular Hsp70 stimulated the secretion of the T cell-derived pro-inflammatory cytokines IL-6 and IL-8. This work extends knowledge about the role of Hsps in autoimmune bullous diseases, suggesting that extracellular Hsp70 represents a pathophysiological factor and potential treatment target in EBA.

Immunization with desmoglein 3 induces non-pathogenic autoantibodies in mice

Background

Pemphigus vulgaris (PV) is a rare autoimmune blistering disease characterized by the development of autoantibodies targeting desmoglein (Dsg) 3, but also against Dsg1 in mucocutaneous disease. Given that existing PV animal models only recapitulate aspects of the disease, we aimed to establish a more comprehensive disease model based on the immunization of mice with PV autoantigen(s).

Methods

The following immunization strategies were tested: (i) C57Bl/6J, B6.SJL-H2s C3c/1CyJ, DBA2/J, or SJL/J mice were immunized with recombinant murine Dsg3 (mDsg3), (ii) DBA2/J and SJL/J mice were immunized with mDsg3 and additionally injected a single non-blister inducing dose of exfoliative toxin A (ETA), and (iii) DBA2/J and SJL/J mice were immunized with human Dsg (hDsg) 1 and 3.

Results

Despite the induction of autoantibodies in each immunization protocol, the mice did not develop a clinical phenotype. Tissue-bound autoantibodies were not detected in the skin or mucosa. Circulating autoantibodies did not bind to the native antigen in indirect immunofluorescence microscopy using monkey esophagus as a substrate.

Conclusion

Immunization with PV autoantigens induced non-pathogenic Dsg1/3 antibodies, but did not cause skin/mucous membrane disease in mice. These findings, confirmed by failure of binding of the induced autoantibodies to their target in the skin, suggest that the autoantibodies which were formed were unable to bind to the conformational epitope present in vivo.

Circulating heat shock protein 90 (Hsp90) and autoantibodies to Hsp90 are increased in patients with atopic dermatitis

Atopic dermatitis (AD) is one of the most common chronic inflammatory dermatoses characterized by persistent itching and recurrent eczematous lesions. While the primary events and key drivers of AD are topics of ongoing debate, cutaneous inflammation due to inappropriate IgE (auto)antibody-related immune reactions is frequently considered. Highly conserved and immunogenic heat shock protein 90 (Hsp90), a key intra- and extracellular chaperone, can activate the immune response driving the generation of circulating anti-Hsp90 autoantibodies that are found to be elevated in several autoimmune disorders. Here, for the first time, we observed that serum levels of Hsp90 and anti-Hsp90 IgE autoantibodies are significantly elevated (p < 0.0001) in AD patients (n = 29) when compared to age- and gender-matched healthy controls (n = 70). We revealed a positive correlation (0.378, p = 0.042) between serum levels of Hsp90 and the severity of AD assessed by Scoring Atopic Dermatitis (SCORAD). In addition, seropositivity for anti-Hsp90 IgE has been found in 48.27% of AD patients and in 2.85% of healthy controls. Although further studies on a larger group of patients are needed to confirm presented data, our results suggest that extracellular Hsp90 and autoantibodies to Hsp90 deserve attention in the study of the mechanisms that promote the development and/or maintenance of atopic dermatitis.

The Pathophysiological Role of Heat Shock Response in Autoimmunity: A Literature Review

Within the last two decades, there has been increasing evidence that heat-shock proteins can have a differential influence on the immune system. They can either provoke or ameliorate immune responses. This review focuses on outlining the stimulatory as well as the inhibitory effects of heat-shock proteins 27, 40, 70, 65, 60, and 90 in experimental and clinical autoimmune settings.

Inhibition of Hsp90 Counteracts the Established Experimental Dermal Fibrosis Induced by Bleomycin

Our previous study demonstrated that heat shock protein 90 (Hsp90) is overexpressed in the involved skin of patients with systemic sclerosis (SSc) and in experimental dermal fibrosis. Pharmacological inhibition of Hsp90 prevented the stimulatory effects of transforming growth factor-beta on collagen synthesis and the development of dermal fibrosis in three preclinical models of SSc. In the next step of the preclinical analysis, herein, we aimed to evaluate the efficacy of an Hsp90 inhibitor, 17-dimethylaminoethylamino-17-demethoxygeldanamycin (17-DMAG), in the treatment of established experimental dermal fibrosis induced by bleomycin. Treatment with 17-DMAG demonstrated potent antifibrotic and anti-inflammatory properties: it decreased dermal thickening, collagen content, myofibroblast count, expression of transforming growth factor beta receptors, and pSmad3-positive cell counts, as well as leukocyte infiltration and systemic levels of crucial cytokines/chemokines involved in the pathogenesis of SSc, compared to vehicle-treated mice. 17-DMAG effectively prevented further progression and may induce regression of established bleomycin-induced dermal fibrosis to an extent comparable to nintedanib. These findings provide further evidence of the vital role of Hsp90 in the pathophysiology of SSc and characterize it as a potential target for the treatment of fibrosis with translational implications due to the availability of several Hsp90 inhibitors in clinical trials for other indications.

Updates on diagnosis and management of autoimmune blistering diseases

Over the last several decades, advances in the understanding of the pathogenesis of autoimmune blistering diseases has resulted in significant improvements in diagnosis and management. These improvements include new diagnostic assays and therapies targeted at specific disease mediators. Furthermore, the abundance of new therapies in clinic trials for autoimmune blistering diseases will translate to an enhanced therapeutic armamentarium for clinicians. The aim of this article is to review new developments in the understanding of autoimmune blistering diseases and to summarize advancements in their diagnosis and management.

From bench to bedside: evolving therapeutic targets in autoimmune blistering disease

Autoimmune blistering diseases comprise a group of heterogenous conditions characterized by the loss of tolerance and subsequent development of autoantibodies targeting epidermal and subepidermal adhesion proteins. Blisters and erosions form on the skin and mucous membranes leading to significant morbidity and mortality. Traditional therapies rely on systemic immunosuppression. Advancements in our understanding of the pathophysiology of pemphigus and pemphigoid have led to the development of molecules which target specific pathways involved in induction and perpetuation of disease. In this review, we outline the novel therapeutic strategies including B-cell depletion, T-regulatory cell repletion, cell signalling inhibitors and small molecular inhibitors, inhibitory monoclonal antibodies, as well as complement inhibition. We additionally review their current level of clinical evidence. We lastly review therapeutics targets gleaned from the experimental epidermolysis bullosa acquisita mouse model. These emerging treatments offer an exciting progression from basic science discoveries that have the potential to transform the treatment paradigm in autoimmune blistering diseases.

Skin Barrier and Autoimmunity-Mechanisms and Novel Therapeutic Approaches for Autoimmune Blistering Diseases of the Skin

One of the most important functions of the skin besides regulating internal body temperature includes formation of the barrier between the organism and the external environment, hence protecting against pathogen invasion, chemical and physical assaults and unregulated loss of water and solutes. Disruption of the protective barrier is observed clinically in blisters and erosions of the skin that form in autoimmune blistering diseases where the body produces autoantibodies against structural proteins of the epidermis or the epidermal-dermal junction. Although there is no cure for autoimmune skin blistering diseases, immune suppressive therapies currently available offer opportunities for disease management. In cases where no treatment is sought, these disorders can lead to life threatening complications and current research efforts have focused on developing therapies that target autoantibodies which contribute to disease symptoms. This review will outline the involvement of the skin barrier in main skin-specific autoimmune blistering diseases by describing the mechanisms underpinning skin autoimmunity and review current progress in development of novel therapeutic approaches targeting the underlying causes of autoimmune skin blistering diseases.

Epidermolysis Bullosa Acquisita: The 2019 Update

Epidermolysis bullosa acquisita (EBA) is an orphan autoimmune disease. Patients with EBA suffer from chronic inflammation as well as blistering and scarring of the skin and mucous membranes. Current treatment options rely on non-specific immunosuppression, which in many cases, does not lead to a remission of treatment. Hence, novel treatment options are urgently needed for the care of EBA patients. During the past decade, decisive clinical observations, and frequent use of pre-clinical model systems have tremendously increased our understanding of EBA pathogenesis. Herein, we review all of the aspects of EBA, starting with a detailed description of epidemiology, clinical presentation, diagnosis, and current treatment options. Of note, pattern analysis via direct immunofluorescence microscopy of a perilesional skin lesion and novel serological test systems have significantly facilitated diagnosis of the disease. Next, a state-of the art review of the current understanding of EBA pathogenesis, emerging treatments and future perspectives is provided. Based on pre-clinical model systems, cytokines and kinases are among the most promising therapeutic targets, whereas high doses of IgG (IVIG) and the anti-CD20 antibody rituximab are among the most promising "established" EBA therapeutics. We also aim to raise awareness of EBA, as well as initiate basic and clinical research in this field, to further improve the already improved but still unsatisfactory conditions for those diagnosed with this condition.

HSP90 inhibition enhances cancer immunotherapy by upregulating interferon response genes

T-cell-based immunotherapies are promising treatments for cancer patients. Although durable responses can be achieved in some patients, many patients fail to respond to these therapies, underscoring the need for improvement with combination therapies. From a screen of 850 bioactive compounds, we identify HSP90 inhibitors as candidates for combination with immunotherapy. We show that inhibition of HSP90 with ganetespib enhances T-cell-mediated killing of patient-derived human melanoma cells by their autologous T cells in vitro and potentiates responses to anti-CTLA4 and anti-PD1 therapy in vivo. Mechanistic studies reveal that HSP90 inhibition results in upregulation of interferon response genes, which are essential for the enhanced killing of ganetespib treated melanoma cells by T cells. Taken together, these findings provide evidence that HSP90 inhibition can potentiate T-cell-mediated anti-tumor immune responses, and rationale to explore the combination of immunotherapy and HSP90 inhibitors.

Many patients fail to respond to T cell based immunotherapies. Here, the authors, through a high-throughput screening, identify HSP90 inhibitors as a class of preferred drugs for treatment combination with immunotherapy.

Hsp90 inhibition ameliorates CD4+ T cell-mediated acute Graft versus Host disease in mice

Introduction

For many patients with leukemia only allogeneic bone marrow transplantion provides a chance of cure. Co‐transplanted mature donor T cells mediate the desired Graft versus Tumor (GvT) effect required to destroy residual leukemic cells. The donor T cells very often, however, also attack healthy tissue of the patient inducing acute Graft versus Host Disease (aGvHD)—a potentially life‐threatening complication.

Methods

Therefore, we used the well established C57BL/6 into BALB/c mouse aGvHD model to evaluate whether pharmacological inhibition of heat shock protein 90 (Hsp90) would protect the mice from aGvHD.

Results

Treatment of the BALB/c recipient mice from day 0 to +2 after allogeneic CD4⁺ T cell transplantation with the Hsp90 inhibitor 17‐(dimethylaminoethylamino)‐17‐demethoxygeldanamycin (DMAG) partially protected the mice from aGvHD. DMAG treatment was, however, insufficient to prolong overall survival of leukemia‐bearing mice after transplantation of allogeneic CD4⁺ and CD8⁺ T cells. Ex vivo analyses and in vitro experiments revealed that DMAG primarily inhibits conventional CD4⁺ T cells with a relative resistance of CD4⁺ regulatory and CD8⁺ T cells toward Hsp90 inhibition.

Conclusions

Our data, thus, suggest that Hsp90 inhibition might constitute a novel approach to reduce aGvHD in patients without abrogating the desired GvT effect.

Clinical features and diagnosis of epidermolysis bullosa acquisita

INTRODUCTION

Epidermolysis bullosa acquisita (EBA) is a rare autoimmune blistering disease of skin and mucous membranes. EBA is caused by autoantibodies against type VII collagen, which is a major component of anchoring fibrils, attaching epidermis to dermis. Binding of autoantibodies to type VII collagen leads to skin fragility and, finally, blister formation. The clinical picture of EBA is polymorphic, with several distinct phenotypes being described. Despite recent progress in understanding the pathophysiology of EBA, its diagnosis is still challenging. Areas covered: This review provides an update on the clinical manifestations and diagnostic methods of EBA. We searched PubMed using the terms 'epidermolysis bullosa acquisita' covering articles in English between 1 January 2005 and 31 May 2016. Relevant older publications were retrieved form cited literature. Expert commentary: While the clinical picture is highly variable, diagnosis relies on direct immunofluorescence (IF) microscopy of a perilesional skin biopsy. Linear deposits of IgG, IgA and/or C3 along the dermal-epidermal junction with an u-serrated pattern are diagnostic for EBA alike the detection of serum autoantibodies against type VII collagen. Several test systems for the serological diagnosis of EBA have recently become widely available. In some patients, sophisticated diagnostic approaches only available in specialized centers are required.

Anti-Hsp90 therapy in autoimmune and inflammatory diseases: a review of preclinical studies

Heat shock protein 90 (Hsp90), a 90-kDa molecular chaperone, is responsible for biological activities of key signaling molecules (clients) such as protein kinases, ubiquitin ligases, steroid receptors, cell cycle regulators, and transcription factors regulating various cellular processes, including growth, survival, differentiation, and apoptosis. Because Hsp90 is also involved in stabilization of oncogenic 'client' proteins, its specific chaperone activity blockers are currently being tested as anticancer agents in advanced clinical trials. Recent in vitro and in vivo studies have shown that Hsp90 is also involved in activation of innate and adaptive cells of the immune system. For these reasons, pharmacological inhibition of Hsp90 has been evaluated in murine models of autoimmune and inflammatory diseases. This mini-review summarizes current knowledge of the effects of Hsp90 inhibitors on autoimmune and inflammatory diseases' features and is based solely on preclinical studies.

Immune mechanism-targeted treatment of experimental epidermolysis bullosa acquisita

Epidermolysis bullosa acquisita (EBA) is an autoimmune bullous dermatosis characterized by chronic mucocutaneous blistering caused by autoantibodies directed against type VII collagen. EBA causes a high morbidity and is difficult to treat. Model systems have significantly broadened our understanding of EBA pathogenesis, leading to the identification of numerous therapeutic targets. Of these, so far, a few have been evaluated for their therapeutic potential in preclinical models. In mice, EBA can be induced by transfer of anti-type VII collagen antibodies or by immunization with the protein. The latter model, immunization-induced EBA, is ideal to test drugs for their therapeutic efficacy. Here, mice with already established disease can be treated for prolonged periods. Albeit time consuming, results from immunization-induced EBA will pave the way for clinical application in patients. As the key pathogenic principle, that is, autoantibody-induced, leukocyte-mediated tissue injury and inflammation, is shared by other diseases, these findings may have translational applications beyond EBA.

Evidence for a role of autoantibodies to heat shock protein 60, 70, and 90 in patients with dermatitis herpetiformis

Heat shock proteins (Hsp) are highly conserved immunomodulatory molecules upregulated when cells are exposed to stressful stimuli, such as inflammation. Their involvement in various autoimmune diseases, including autoimmune bullous diseases and celiac disease, has been increasingly recognized. To further study the role of Hsp in autoimmune bullous diseases, we have investigated for the first time the humoral autoimmune response to Hsp40, Hsp60, Hsp70, and Hsp90 in patients with dermatitis herpetiformis (DH; n = 26), bullous pemphigoid (BP; n = 23), and pemphigus vulgaris (PV; n = 16), the first representing a cutaneous manifestation of celiac disease. While in patients with active BP and PV, serum levels of autoantibodies against these Hsp did not differ from the corresponding age- and gender-matched healthy controls (n = 9-14); circulating autoantibodies against Hsp60, Hsp70, and Hsp90 were found to be increased at the active disease stage of DH. Further analysis of this latter patient subgroup showed that these anti-Hsp autoantibodies decreased in parallel with serum autoantibodies against epidermal and tissue transglutaminase during remission of skin lesions following a gluten-free diet, revealing significantly positive correlations. Although further studies on larger groups of patients will be needed to confirm the present data, our results support the notion that autoantibodies against Hsp60, Hsp70, and Hsp90 deserve attention in the study of the mechanisms that promote the development and maintenance of DH and possibly also the underlying celiac disease as well as potential novel disease biomarkers.

Hsp90 blockade modulates bullous pemphigoid IgG-induced IL-8 production by keratinocytes

Bullous pemphigoid (BP) is the most common subepidermal autoimmune blistering skin disease characterized by autoantibodies against the hemidesmosomal proteins BP180 and BP230. The cell stress chaperone heat shock protein 90 (Hsp90) has been implicated in inflammatory responses, and recent evidence suggests that it represents a novel treatment target in autoimmune bullous diseases. The aim of the study was to investigate the contribution of Hsp90 to the proinflammatory cytokine production in keratinocytes induced by autoantibodies to BP180 from BP patient serum. HaCaT cells were treated with purified human BP or normal IgG in the absence or presence of the Hsp90 blocker 17-DMAG and effects on viability, interleukin 6 (IL-6) and IL-8 (cytokines critical for BP pathology), NFκB (their major transcription factor), and Hsp70 (marker of effective Hsp90 inhibition and potent negative regulator of inflammatory responses) were investigated. We found that BP IgG stimulated IL-6 and IL-8 release from HaCaT cells and that non-toxic doses of 17-DMAG inhibited this IL-8, but not IL-6 secretion in a dose- and time-dependent fashion. Inhibition of this IL-8 production was also observed at the transcriptional level. In addition, 17-DMAG treatment blunted BP IgG-mediated upregulation of NFκB activity and was associated with Hsp70 induction. This study provides important insights that Hsp90 is involved as crucial regulator in anti-BP180 IgG-induced production of keratinocyte-derived IL-8. By adding to the knowledge of the multimodal anti-inflammatory effects of Hsp90 blockade, our data further support the introduction of Hsp90 inhibitors into the clinical setting for treatment of autoimmune diseases, especially for BP.

Effects of intravenous immunoglobulins on mice with experimental epidermolysis bullosa acquisita

Although well-designed prospective trials are generally lacking, intravenous immunoglobulins (IVIG) seem an effective adjuvant treatment for autoimmune bullous skin diseases. Here, efficacy of IVIG monotherapy was compared with corticosteroid treatment in mice with immunization-induced experimental epidermolysis bullosa acquisita (EBA), an autoimmune bullous skin disease characterized by autoantibodies against type VII collagen. We found that IVIG significantly ameliorated clinical disease severity and skin neutrophil infiltration compared with vehicle-treated mice, whereas methylprednisolone showed comparatively less pronounced effects. Efficacy of IVIG was accompanied by reduced levels of autoantibodies, a shift toward noncomplement-fixing autoantibodies, and lower complement deposition at the dermal-epidermal junction. In addition, peripheral Gr-1-positive cells of IVIG-treated animals showed reduced expression of the activating Fcγ receptor IV, which we recently described as a major mediator of tissue injury in experimental EBA. These data show that treatment with IVIG is superior to systemic corticosteroids in experimental EBA and that the effects of IVIG are pleiotropic involving modulation of both the adaptive and innate immune response, although the detailed mode of action of IVIG in this model remains in need of further elucidation.

Plasma cells in immunopathology: concepts and therapeutic strategies

Plasma cells are terminally differentiated B cells that secrete antibodies, important for immune protection, but also contribute to any allergic and autoimmune disease. There is increasing evidence that plasma cell populations exhibit a considerable degree of heterogeneity with respect to their immunophenotype, migration behavior, lifetime, and susceptibility to immunosuppressive drugs. Pathogenic long-lived plasma cells are refractory to existing therapies. In contrast, short-lived plasma cells can be depleted by steroids and cytostatic drugs. Therefore, long-lived plasma cells are responsible for therapy-resistant autoantibodies and resemble a challenge for the therapy of antibody-mediated autoimmune diseases. Both lifetime and therapy resistance of plasma cells are supported by factors produced within their microenviromental niches. Current results suggest that plasma cell differentiation and survival factors such as IL-6 also signal via mammalian miRNAs within the plasma cell to modulate downstream transcription factors. Recent evidence also suggests that plasma cells and/or their immediate precursors (plasmablasts) can produce important cytokines and act as antigen-presenting cells, exhibiting so far underestimated roles in immune regulation and bone homeostasis. Here, we provide an overview on plasma cell biology and discuss exciting, experimental, and potential therapeutic approaches to eliminate pathogenic plasma cells.

Inhibitory effects of heat shock protein 90 blockade on proinflammatory human Th1 and Th17 cell subpopulations

Background

Heat shock protein 90 (Hsp90), a chaperone that regulates activity of many client proteins responsible for cellular growth, differentiation, and apoptosis, has been proposed as an important clinical and preclinical therapeutic target in a number of malignancies and autoimmune diseases, respectively. In this study, we evaluated the effects of pharmacological Hsp90 inhibition on human proinflammatory T cell responses.

Findings

Using anti-CD3 antibody-stimulated human peripheral blood mononuclear cell cultures, we observed that Hsp90 inhibition by non-toxic concentrations of the geldanamycin derivative 17-DMAG significantly blocked T cell proliferation, reduced IFN-γ and IL-17 expression on CD4⁺ T lymphocytes, and arrested secretion of proinflammatory IFN-γ, TNF-α, and IL-17, cytokines characteristic of Th1 and Th17 cells, respectively. These effects were associated with inhibition of NF-kB activity, upregulation of Hsp70 protein expression, and disruption of T cell-specific nonreceptor tyrosine kinase Lck activation.

Conclusions

Our results further support the potential use of Hsp90 inhibitors in patients with autoimmune diseases where uncontrolled Th1 or Th17 activation frequently occurs.

Aberrant expression and secretion of heat shock protein 90 in patients with bullous pemphigoid

The cell stress chaperone heat shock protein 90 (Hsp90) has been implicated in inflammatory responses and its inhibition has proven successful in different mouse models of autoimmune diseases, including epidermolysis bullosa acquisita. Here, we investigated expression levels and secretory responses of Hsp90 in patients with bullous pemphigoid (BP), the most common subepidermal autoimmune blistering skin disease. In comparison to healthy controls, the following observations were made: (i) Hsp90 was highly expressed in the skin of BP patients, whereas its serum levels were decreased and inversely associated with IgG autoantibody levels against the NC16A immunodominant region of the BP180 autoantigen, (ii) in contrast, neither aberrant levels of circulating Hsp90 nor any correlation of this protein with serum autoantibodies was found in a control cohort of autoimmune bullous disease patients with pemphigus vulgaris, (iii) Hsp90 was highly expressed in and restrictedly released from peripheral blood mononuclear cells of BP patients, and (iv) Hsp90 was potently induced in and restrictedly secreted from human keratinocyte (HaCaT) cells by BP serum and isolated anti-BP180 NC16A IgG autoantibodies, respectively. Our results reveal an upregulated Hsp90 expression at the site of inflammation and an autoantibody-mediated dysregulation of the intracellular and extracellular distribution of this chaperone in BP patients. These findings suggest that Hsp90 may play a pathophysiological role and represent a novel potential treatment target in BP.

Clinical presentation, pathogenesis, diagnosis, and treatment of epidermolysis bullosa acquisita

Epidermolysis bullosa acquisita (EBA) is a chronic mucocutaneous autoimmune skin blistering disease. The pathogenic relevance of autoantibodies targeting type VII collagen (COL7) has been well-documented. Therefore, EBA is a prototypical autoimmune disease with a well-characterized pathogenic relevance of autoantibody binding to the target antigen. EBA is a rare disease with an incidence of 0.2 new cases per million and per year. The current treatment of EBA relies on general immunosuppressive therapy, which does not lead to remission in all cases. Therefore, there is a high, so far unmet medical need for the development of novel therapeutic options. During the last 10 years, several novel in vitro and in vivo models of EBA have been established. These models demonstrated a critical role of the genetic background, T cells, and cytokines for mediating the loss of tolerance towards COL7. Neutrophils, complement activation, Fc gamma receptor engagement, cytokines, several molecules involved in cell signaling, release of reactive oxygen species, and matrix metalloproteinases are crucial for autoantibody-induced tissue injury in EBA. Based on this growing understanding of the diseases' pathogenesis, several potential novel therapeutic targets have emerged. In this review, the clinical presentation, pathogenesis, diagnosis, and current treatment options for EBA are discussed in detail.

Metabolite analysis distinguishes between mice with epidermolysis bullosa acquisita and healthy mice

Background

Epidermolysis bullosa acquisita (EBA) is a rare skin blistering disease with a prevalence of 0.2/ million people. EBA is characterized by autoantibodies against type VII collagen. Type VII collagen builds anchoring fibrils that are essential for the dermal-epidermal junction. The pathogenic relevance of antibodies against type VII collagen subdomains has been demonstrated both in vitro and in vivo. Despite the multitude of clinical and immunological data, no information on metabolic changes exists.

Methods

We used an animal model of EBA to obtain insights into metabolomic changes during EBA. Sera from mice with immunization-induced EBA and control mice were obtained and metabolites were isolated by filtration. Proton nuclear magnetic resonance (NMR) spectra were recorded and analyzed by principal component analysis (PCA), partial least squares discrimination analysis (PLS-DA) and random forest.

Results

The metabolic pattern of immunized mice and control mice could be clearly distinguished with PCA and PLS-DA. Metabolites that contribute to the discrimination could be identified via random forest. The observed changes in the metabolic pattern of EBA sera, i.e. increased levels of amino acid, point toward an increased energy demand in EBA.

Conclusions

Knowledge about metabolic changes due to EBA could help in future to assess the disease status during treatment. Confirming the metabolic changes in patients needs probably large cohorts.

Epidermolysis bullosa acquisita

Epidermolysis bullosa acquisita (EBA) is a chronic autoimmune subepidermal bullous disease with clinical features similar to the genetic form of dystrophic epidermolysis bullosa. EBA is characterized by the presence of autoantibodies against type VII collagen which is a major component of the anchoring fibrils at the dermal-epidermal junction. EBA can be divided into two main clinical types; mechanobullous and inflammatory EBA. Mechanobullous EBA, referred to as classic EBA, presents with skin fragility, blisters and dystrophic changes on trauma-prone areas. Inflammatory EBA resembles other autoimmune subepidermal bullous diseases. Compelling evidence from mouse models supports a pathogenic role of autoantibodies against type VII collagen in EBA. Treatment of EBA is often unsatisfactory. The most widely used systemic treatment is corticosteroids. Colchicine and dapsone have been reported to be good treatment modalities when combined with corticosteroids. Some intractable cases of EBA have successfully been treated with intravenous immunoglobulin or rituximab.

Evidence for pathogenicity of autoreactive T cells in autoimmune bullous diseases shown by animal disease models

Autoimmune bullous diseases (AIBDs) are characterized by blisters and erosions on the skin and/or mucous membranes, which are caused by autoantibodies directed to structural proteins of the epidermis and the epidermal basement membrane zone. This Viewpoint Essay discusses the contribution by autoreactive T cells to the pathogenesis of bullous pemphigoid, pemphigus and epidermolysis bullosa acquisita, with an emphasis on studies using active animal mouse models for these diseases. Previous studies have demonstrated that cytokines produced by autoreactive T cells, the interaction between antigen-specific T cells and B cells and the function of regulatory T cells are likely related to the pathogenesis of AIBDs. In interpreting the experimental results, the limitations of those animal models should be considered. Further understanding of the pathogenicity of autoreactive CD4(+) T cells may lead to disease-specific treatments.

Pathogenesis of epidermolysis bullosa acquisita, an autoimmune subepidermal bullous disease

Autoimmune bullous diseases (ABDs) are organ-specific autoimmune diseases, in which blisters on the skin and mucous membranes develop through binding of pathogenic autoantibodies to target antigens. There are two major ABD groups: the pemphigus group, showing autoantibodies to desmosomal components; and the subepidermal ABD group, showing autoantibodies to hemidesmosomal components in the epidermal basement membrane zone. Recent immunological, biochemical and molecular biological studies revealed many new autoantigens, including desmocollins, various plakin family proteins and integrins. A revised ABD classification includes new disease entities such as paraneoplastic pemphigus, IgA pemphigus and anti-laminin γ1 pemphigoid. In addition to systemic corticosteroids and various immunosuppressive agents, various adjuvant therapies for ABDs have developed. Among them, intravenous immunoglobulin (IVIG) is a promising therapy, although the therapeutic mechanisms are still unknown. Various disease models for ABDs have developed, particularly for pemphigus vulgaris, bullous pemphigoid and epidermolysis bullosa acquisita (EBA), and these have provided insights into the pathogenesis of various ADBs that suggest possible new treatment strategies. However, the fundamental mechanisms in disruption of immune-tolerance are still unknown. EBA shows autoimmunity to type VII collagen, the major component of anchoring fibrils, and EBA pathogenesis has been studied in various disease models. Previous studies suggested that, following binding of autoantibodies to type VII collagen, activation of complement, cytokine release, neutrophil migration, Fcγ receptors (FcgRs) and metalloproteinases play important roles in induction of subepidermal blisters. In this issue of the Journal of Pathology, Kasperkiewicz and colleagues reveal important roles of activating FcgRIV and inhibitory FcgRIIB in EBA pathogenesis that were recognized by conducting elegant studies using both genetic analysis and functional animal model methods. The expression equilibrium of the activating and inhibitory FcgRs can be modulated towards the inhibitory FcgRIIB by IVIG therapy, resulting in beneficial clinical effects of IVIG in EBA and other autoimmune skin-blistering diseases.