Recent Advances in Understanding Pemphigus and Bullous Pemphigoid

Proteomic changes related to actin cytoskeleton function in the skin of vildagliptin-treated mice

BACKGROUND

Vildagliptin, a dipeptidyl peptidase-4 inhibitor (DPP-4i) is a widely used type 2 diabetes medication that is associated with an up-to 10-fold increased risk for the development of bullous pemphigoid (BP), an autoimmune skin disease. The mechanism by which vildagliptin promotes the development of BP remains unknown.

OBJECTIVE

To elucidate effects of vildagliptin treatment on the mouse cutaneous proteome.

METHODS

We analyzed the cutaneous proteome of nondiabetic mice treated for 12 weeks with vildagliptin using label-free shotgun mass spectrometry (MS), two-dimensional difference gel electrophoresis (2D-DIGE), immunohistochemistry, immunoblotting, and quantitative real-time polymerase chain reaction.

RESULTS

Although vildagliptin treatment did not cause any clinical signs or histological changes in the skin, separate MS and 2D-DIGE analyses revealed altered cutaneous expression of several proteins, many of which were related to actin cytoskeleton remodeling. Altogether 18 proteins were increased and 40 were decreased in the vildagliptin-treated mouse skin. Both methods revealed increased levels of beta-actin and C->U-editing enzyme APOBEC2 in vildagliptin-treated mice. However, elevated levels of a specific moesin variant in vildagliptin-treated animals were only detected with 2D-DIGE. Immunohistochemical staining showed altered cutaneous expression of DPP-4, moesin, and galectin-1. The changed proteins detected by MS and 2D-DIGE were linked to actin cytoskeleton remodeling, transport, cell movement and organelle assembly.

CONCLUSION

Vildagliptin treatment alters the cutaneous proteome of nondiabetic mice even without clinical signs in the skin. Cytoskeletal changes in the presence of other triggering factors may provoke a break of immune tolerance and further promote the development of BP.

Comparison of gut microbiota dysbiosis between pemphigus vulgaris and bullous pemphigoid

OBJECTIVE

Pemphigus vulgaris (PV) and bullous pemphigoid (BP) are two prevalent bullous diseases. Previous studies found that the antibodies of BP could be expressed in the intestinal epithelium and BP was tightly related to inflammatory bowel disease. Therefore, gut microbiota might also play an important role in bullous disease. However, the specific relationship between gut microbiota and bullous diseases remains unknown. Our study aimed to investigate the potential role of gut microbiota in the development and progression of different bullous diseases.

METHODS

We conducted a prospective and observational cohort study at Peking Union Medical College Hospital. Untreated BP and PV patients were recruited, along with healthy controls (HC) who were spouses or caregivers of these patients. Fecal samples were collected, followed by 16S rRNA gene sequencing. Bioinformatics analyses were performed to assess the composition and function of gut microbiota.

RESULTS

A total of 38 HC, 32 BP, and 19 PV patients were enrolled in this study. Compared to HC, BP, and PV exhibited a distinct gut microbiota composition, especially BP. The gut microbiota changes were mainly observed in the phylum Bacteroidetes, Firmicutes, and Proteobacteria. The ratio of Faecalibacterium to Escherichia-Shigella (F/E ratio) had a considerable predictive value (AUC: 0.705) for recognizing BP from PV. The levels of Faecalibacterium and Enterobacter were correlated to the anti-BP 180 and anti-desmoglein 3. Microbial functional prediction revealed elevated activity in pathways related to gut microbiota translocation significantly increased in BP patients, indicating a potential pathogenetic role in BP.

CONCLUSIONS

Our study suggests that the composition of gut microbiota is specific in different bullous diseases and the role of gut microbiota differs. Gut microbiota could help distinguish BP and PV, and might play a role in the pathogenesis of different bullous diseases.

Pemphigus and pemphigoid are associated with Alzheimer's disease in older adults: evidence from the US Nationwide inpatient sample 2016-2018

BACKGROUND

Pemphigus and pemphigoid are rare autoimmune skin disorders caused by autoantibodies against structural proteins and characterized by blistering of the skin and/or mucous membranes. Associations have been noted between skin diseases and Alzheimer's dementia (AD). Dementia is a neurological disorder of progressive cognitive impairment with increasing incidence among older adults. This study aimed to assess the potential associations between pemphigus, pemphigoid and AD in a large, nationally representative US cohort.

METHODS

All data of hospitalized patients aged 60 years or older were extracted from the US Nationwide Inpatient Sample (NIS) database 2016-2018. Patients with a history of head trauma, diagnosis of vascular dementia, history of cerebrovascular disease, or malformation of cerebral vessels were excluded. The study population was divided into those with and without pemphigus (cohort 1) and with and without pemphigoid (cohort 2).

RESULTS

Pemphigus was independently associated with a 69% increased risk of AD. Adults ≥80 years old with pemphigus were 72% more likely to develop AD than adults without pemphigus. Women with pemphigus were 78% more likely to develop AD than women without pemphigus. On the other hand, pemphigoid was independently associated with a 39% increased risk for AD and subjects ≥80 years with pemphigoid were 40% more likely to have AD than those without pemphigoid. Females with pemphigoid were 63% more likely to have AD than those without pemphigoid. Moreover, Hispanic older adults with pemphigus were 3-times more likely to have AD than those without pemphigoid.

CONCLUSIONS

Pemphigus and pemphigoid were both independently associated with AD in older adults, especially among females and octogenarians. Further studies addressing the etiology and mechanisms underlying these associations are highly warranted.

Pemphigus and pemphigoids: Clinical presentation, diagnosis and therapy

Pemphigus and pemphigoid are two potentially life-threatening groups of autoimmune diseases, characterized by autoantibodies targeting structural components of desmosomes or hemidesmosomes, respectively. Affected patients typically show itchy/painful plaques or blistering skin lesions and/or impairing mucosal blistering and erosions, which may strongly impact their quality of life. Since the milestone work of Walter Lever in 1953, who differentiated these two groups of diseases by histopathological analysis of the level of antibody-mediated skin cleavage, enormous progresses occurred. Achievements made in laboratory diagnostics now allow to identify antigen specific structural proteins of the skin that are targeted by pathogenic autoantibodies. These progresses were accompanied by an increased understanding of the pathogenesis of these diseases thanks to the establishment of animal models reproducing disease and on studies on skin and blood of affected individuals, which have been leading to novel and disease-specific treatments. Yet, given their phenotypical overlap with more common dermatological diseases, correct diagnosis and appropriate treatment are often delayed, in some cases leading to irreversible sequelae, including organ dysfunction (i.e., loss of vision in mucous membrane pemphigoid). Here, we provide a concise overview of the clinical appearance, diagnosis and therapeutic management of pemphigus and pemphigoid diseases.

Pemphigus- und Pemphigoid-Erkrankungen: Klinik, Diagnostik und Therapie: Pemphigus and pemphigoids: Clinical presentation, diagnosis and therapy

Pemphigus und Pemphigoid sind seltene Autoimmunkrankheiten der Haut mit potenziell lebensbedrohlichem Verlauf. Autoantikörper gegen epidermale und junktionale Strukturproteine (Desmosomen sowie Hemidesmosomen) führen bei Betroffenen typischerweise zu juckenden, schmerzhaften Plaques oder Blasen an der Haut und/oder Blasenbildung und Erosionen der Schleimhäute mit möglicher Einschränkung der Lebensqualität. Seit der bahnbrechenden Arbeit von Walter Lever im Jahr 1953, dem es gelang, mittels histopathologischer Untersuchung diese beiden Krankheitsgruppen anhand des Musters der Antikörper‐vermittelten Blasenbildung zu differenzieren, wurden enorme Fortschritte im Verständnis der Erkrankungen erzielt. Die Errungenschaften in der Labordiagnostik ermöglichten die Identifikation von Zielstrukturen zur präzisen Unterscheidung verschiedener Varianten der bullösen Autoimmunerkrankungen. Diese Fortschritte gingen dank der Entwicklung von Tiermodellen mit einem besseren Verständnis der Pathogenese einher. Außerdem haben Studien an Haut und Blut betroffener Patienten zu neuen und krankheitsspezifischen Behandlungen geführt. Aufgrund ihrer Seltenheit und der klinischen Ähnlichkeit mit anderen dermatologischen Erkrankungen verzögern sich die korrekte Diagnosestellung und die Einleitung einer entsprechenden Therapie häufig, was in einigen Fällen zu irreversiblen Folgeerscheinungen, einschließlich Funktionsstörungen von Organen (zum Beispiel Verlust des Sehvermögens beim Schleimhautpemphigoid) führt. Wir geben hier einen Überblick über das klinische Erscheinungsbild, den Diagnosealgorithmus und das therapeutische Management von Pemphigus‐ und Pemphigoid‐Erkrankungen.

Divergent in situ expression of IL-31 and IL-31RA between bullous pemphigoid and pemphigus vulgaris

Bullous pemphigoid (BP) and pemphigus vulgaris (PV) are two major autoimmune blistering skin diseases. Unlike PV, BP is accompanied by intense pruritus, suggesting possible involvement of the pruritogenic cytokine IL-31. However, the underlying mechanisms of the clinical difference between BP and PV in terms of pruritus are not fully understood. To compare the expression levels of IL-31 and its receptor IL-31RA in the lesional skin, including peripheral nerves in BP and PV patients, immunohistochemical staining for IL-31 and IL-31RA was performed in skin samples of BP and PV patients and healthy controls (HC). The IL-31RA-expressing area in epidermis and peripheral nerves was analysed using ImageJ and the percentage of positive cells for IL-31/IL-31RA in dermal infiltrating cells was manually quantified. Quantitative analyses revealed that IL-31/IL-31RA expressions in the epidermis and dermal infiltrate were significantly increased in BP compared to PV and HC. The difference between BP and PV became more obvious when advanced bullous lesions were compared. Peripheral nerves in BP lesions presented significantly higher IL-31RA expression compared to PV lesions. In conclusion, we found significantly augmented expressions of IL-31/IL-31RA in BP lesions, including peripheral nerves, in comparison to PV. These results suggest a possible contribution of IL-31/IL-31RA signalling to the difference between BP and PV in the facilitation of pruritus and local skin inflammation, raising the possibility of therapeutic targeting of the IL-31/IL-31RA pathway in BP patients.

Targeting type 2 inflammation in bullous pemphigoid: current and emerging therapeutic approaches

Bullous pemphigoid (BP) is one of the most common autoimmune bullous diseases and mainly affects an elderly population with multi-morbidity. Due to the frailty of many BP patients, existing treatment options are limited. The blisters associated with BP result from IgG and IgE autoantibodies binding to the central components of hemidesmosome, BP180, and BP230, stimulating a destructive inflammatory process. The known characteristic features of BP, such as intense pruritus, urticarial prodrome, peripheral eosinophilia, elevated IgE, as well as recent expanding evidence from in vitro and in vivo studies implicate type 2 inflammation as an important driver of BP pathogenesis. Type 2 inflammation is an inflammatory pathway involving a subset of CD4+ T cells that secrete IL-4, IL-5, and IL-13, IgE-secreting B cells, and granulocytes, such as eosinophils, mast cells, and basophils. It is believed that effectors in type 2 inflammation may serve as novel and effective treatment targets for BP. This review focuses on recent understandings of BP pathogenesis with a particular emphasis on the role of type 2 inflammation. We summarize current clinical evidence of using rituximab (B-cell depletion), omalizumab (anti-IgE antibody), and dupilumab (anti-IL-4/13 antibody) in the treatment of BP. The latest advances in emerging targeted therapeutic approaches for BP treatment are also discussed.

Associations between bullous pemphigoid and hematological diseases: Literature review on mechanistic connections and possible treatments

Bullous pemphigoid is an autoimmune blistering disorder that primarily occurs in elderly patients. Reports indicate that BP coexists with various hematological diseases, including acquired hemophilia A, hypereosinophilic syndrome, aplastic anemia, autoimmune thrombocytopenia, and hematological malignancies. Early identification of these comorbidities contributes to a better control and reduced mortality. This article details the atypical clinical manifestations of BP when associated with hematological diseases, specific diagnostic strategies, underlying mechanistic connections, and possible treatments. Cross-reactivity between autoantibodies and exposed abnormal epitopes, shared cytokines and immune cells, together with genetic susceptibility are the most common connections between BP and hematological diseases. Patients were most often successfully treated with oral steroids combined with medications specifically targeting the hematological disorders. However, the individual comorbidities require specific considerations.

Clinical severity scores as a guide for prediction of initial treatment responses in pemphigus and pemphigoid patients

Pemphigus and pemphigoid are autoimmune blistering diseases that affect mucosa and skin. Several clinical scoring systems, including the pemphigus disease area index (PDAI) and the bullous pemphigoid disease area index (BPDAI), have been validated for managing disease activity and severity. Current guidelines recommend that treatment response be evaluated with clinical scores and that additional second-line therapies be considered if initial treatment is insufficient for disease control. However, there have been few studies analyzing correlations between PDAI/BPDAI transitions and initial treatment effects. To investigate whether PDAI/BPDAI transitions during the treatment initiation phase correlate with initial treatment responses and whether such information can be used as a guide for necessary additional treatment, we retrospectively analyzed 67 pemphigus patients and 47 pemphigoid patients who received initial treatment at Keio University between 2012 and 2018. The clinical symptoms were evaluated weekly with PDAI/BPDAI. The patients were divided into two groups: in group A, disease was controlled only with oral corticosteroids and immunosuppressants (initial treatment), whereas in group B additional therapies were required due to insufficient responses. In pemphigus, the PDAI ratio of day 7/day 0 was significantly reduced in group A compared to group B (0.548 vs 0.761, P < 0.01) after initial treatment had started. In pemphigoid, the ratios of day 7/day 0 of BPDAI (erosion/blister) and BPDAI (urticaria/erythema) significantly decreased in group A compared to group B (0.565 vs 0.901 and 0.350 vs 0.760, respectively, P < 0.05). Receiver operating characteristic analyses on PDAI, BPDAI (erosion/blister) and BPDAI (urticaria/erythema) revealed that the cut-off values in the ratios of day 7/day 0 were 0.762, 0.675, and 0.568, respectively. Our results suggest that PDAI/BPDAI transitions during the initial phase of the treatments may be useful to predict the outcome of the treatment provided and the necessity of additional therapies to achieve disease control.

Dipeptidyl Peptidase 4 Inhibitor‒Associated Bullous Pemphigoid Is Characterized by an Altered Expression of Cytokines in the Skin

Dipeptidyl peptidase 4 inhibitors (DPP4is), commonly used drugs for treatment of type 2 diabetes, increase the risk for bullous pemphigoid (BP). Currently, the mechanism leading to the loss of immunological tolerance of the cutaneous adhesion molecule BP180 as well as similarities and differences in disease progression between DPP4i-associated BP (DPP4i-BP) and DPP4i-independent regular BP are largely unknown. We analyzed the expression of 32 cytokines and two proteases by Luminex and ELISA assays in samples taken from lesional and nonlesional skin of patients with regular BP or DPP4i-BP and healthy controls. Cytokines mediating B-cell survival and targeting such as BAFF, CCL4, CXCL12, and IL-6 were expressed at a higher level in the lesional regular BP skin than the levels in the lesional DPP4i-BP skin. The DPP4i-BP samples had increased levels of eosinophilic cytokines CCL1, CCL17, CCL26, and IL-5, which correlated with the serum level of anti-BP180 NC16A IgG autoantibodies. The mRNA expression of BAFF, IL6, CCL1, CCL17, CCL26, and IL5 measured by qPCR correlated with the protein levels. Taken together, the cutaneous cytokine profiles were found to provide distinctive molecular fingerprints between regular BP and DPP4i-BP.

The efficacy of adding oral sodium cromoglycate to stable treatment for controlling bullous pemphigoid-related pruritus: A retrospective study

Introduction

Bullous pemphigoid (BP) is the most common autoimmune subepidermal blistering disease which mainly affects the elderly. It manifests as severe pruritus, urticarial plaques, and tense bullae and is associated with significant mortality. Therapy options for itch in BP patients are limited, mainly because the pathogenesis of itch in BP remains unclear. Sodium cromoglycate was commonly used in the past as an inhaled drug for the management of bronchial asthma and as an oral treatment for children with urticaria pigmentosa. In this study we sought to assess its efficacy in reducing BP associated itch.

Objective

Assessing the efficacy of oral sodium cromoglycate in reducing BP-related pruritus after stabilization of disease activity.

Methods

We retrospectively reviewed the medical records of patients with a confirmed diagnosis of BP who were treated with sodium cromoglycate. Patient reported outcome measures (PROM) including: BPDAI pruritus, ABQOL and TABQOL, and BPDAI activity score were compared at two points in time: before commencing treatment with sodium cromoglycate or before commencing maximal dose of this treatment, and at least 4 weeks after treatment commencement.

Results

A total of 21 patients met the inclusion criteria. After at least 4 weeks of treatment with oral sodium cromoglycate BPDAI pruritus, ABQOL and TABQOL scores were statistically significantly decreased compared to the scores prior to treatment commencement, P < 0.000, P < 0.008, and P < 0.004, respectively.

Discussion

Oral treatment with sodium cromoglycate for the management of pruritus in BP patients may be beneficial, however, further prospective studies are required to better assess its efficacy.

Checkpoint inhibitor-associated bullous cutaneous immune-related adverse events: a multicentre observational study

BACKGROUND

Checkpoint inhibitor (CPI) therapy has significantly improved overall survival in several cancers including metastatic melanoma (MM) and in the adjuvant setting. Cutaneous immune-related adverse events (irAEs) secondary to CPIs are commonly observed; however, autoimmune blistering disorders such as bullous pemphigoid (BP) are rare.

OBJECTIVES

To review the prevalence, incidence risk, clinicopathological features and management of toxicity in bullous cutaneous irAEs associated with CPI therapy.

METHODS

A multicentre, retrospective, observational study of CPI-associated bullous irAEs in adults with all cancers across four UK specialist centres between 2006 and 2019.

RESULTS

In total, 7391 patients were identified. CPI-associated bullous irAEs including BP (n = 16) occurred in 0·3% (n = 22). The median age of onset was 76 years, and there was a male predominance. Most patients had cutaneous melanoma (73%, n = 16), of which 81% (13 of 16) were BRAF wildtype. Grade 1, 2, 3 and 4 skin toxicity occurred in 9%, 45%, 41% and 5%, respectively. The mucosae were involved in 27%, and 25% of confirmed cases of BP did not present with bullae. The median time to onset of bullous irAEs was 12 months, with a median total symptom duration of 6 months. Single PD-1/PD-L1 agents had a longer time to onset of symptoms than combination therapy (median 12 vs. 7 months, respectively). Overall, 91%, 64% and 9% of patients required one, two or three lines of treatment, respectively. Two cases occurred after completion of CPIs (1 and 3 months). Of the 20 cases that presented while on CPIs this was permanently discontinued in 55% (11 of 20) and temporarily held in 20% (four of 20). In the four held cases of CPI, bullous eruption reflared in 50%.

CONCLUSIONS

CPI-associated bullous skin toxicity is a rare cutaneous irAE occurring in approximately 0·3% of cases over 13 years of treated patients in this series. Not all cases are diagnostic of BP, but management remains the same. There is a prolonged latency of onset compared with other cutaneous irAEs, with a median time of 12 months, and they can occur after cessation of therapy. Discontinuation of CPIs may be required. Recognizing bullous irAEs promptly and referral to dermatology are essential to optimize management and improve patient outcomes and tumour responses. What is already known about this topic? Checkpoint inhibitor (CPI)-associated bullous pemphigoid is a rare dermatological immune-related adverse event (irAE) that has been reported in small case series and reports. What does this study add? This is the largest multicentre, observational study conducted in the UK over the longest period of 13 years, which demonstrates an overall incidence of bullous cutaneous irAEs secondary to CPIs of 0·3%. Clinical presentation is variable, with one-quarter of patients with bullous pemphigoid presenting without bullae, and mucosal involvement was noted in 27%. Prolonged pruritus is frequently a prodromal symptom. The median time to diagnosis is 12 months and irAEs rarely present after cessation of treatment. Time to onset of symptoms is longer with a single CPI, but with a shorter duration of symptoms compared with combination CPI therapy. Most patients had cutaneous melanoma, of which 81% were BRAF wildtype.

Distinct impact of IgG subclass on autoantibody pathogenicity in different IgG4-mediated diseases

IgG4 is the least potent human IgG subclass for the FcγR-mediated antibody effector function. Paradoxically, IgG4 is also the dominant IgG subclass of pathogenic autoantibodies in IgG4-mediated diseases. Here, we show that the IgG subclass and Fc-FcγR interaction have a distinct impact on the pathogenic function of autoantibodies in different IgG4-mediated diseases in mouse models. While IgG4 and its weak Fc-FcγR interaction have an ameliorative role in the pathogenicity of anti-ADAMTS13 autoantibodies isolated from thrombotic thrombocytopenic purpura (TTP) patients, they have an unexpected exacerbating effect on anti-Dsg1 autoantibody pathogenicity in pemphigus foliaceus (PF) models. Strikingly, a non-pathogenic anti-Dsg1 antibody variant optimized for FcγR-mediated effector function can attenuate the skin lesions induced by pathogenic anti-Dsg1 antibodies by promoting the clearance of dead keratinocytes. These studies suggest that IgG effector function contributes to the clearance of autoantibody-Ag complexes, which is harmful in TTP, but beneficial in PF and may provide new therapeutic opportunity.

Use of gliptins reduces levels of SDF-1/CXCL12 in bullous pemphigoid and type 2 diabetes, but does not increase autoantibodies against BP180 in diabetic patients

The use of dipeptidyl peptidase 4 (DPP4) inhibitors, (also known as gliptins), is associated with an increased risk of bullous pemphigoid (BP), an autoimmune blistering skin disease. To explore the mechanism behind gliptin-associated BP we investigated circulating autoantibodies against the major BP autoantigen BP180 in serum samples from patients with type 2 diabetes (T2D) with preceding gliptin medication (n = 136) or without (n = 136). Sitagliptin was the most frequently prescribed gliptin (125/136 patients). Using an ELISA assay, we showed that IgG autoantibodies against the immunodominant NC16A domain of BP180 were found in 5.9% of gliptin treated and in 6.6% of non-gliptin treated T2D patients. We found that 28% of gliptin treated patients had IgG autoantibodies recognizing the native full-length BP180 in ELISA, but among non-gliptin treated the seropositivity was even higher, at 32%. Further ELISA analysis of additional serum samples (n = 57) found no major changes in the seropositivity against BP180 during a follow-up period of about nine years. In immunoblotting, full-length BP180 was recognized by 71% of gliptin treated and 89% of non-gliptin treated T2D patients, but only by 46% of the age-and sex-matched controls. The chemokine stromal derived factor-1(SDF-1/CXCL12) is one of the major substrates of DPP4. Immunostainings showed that the expression of SDF-1 was markedly increased in the skin of BP patients, but not affected by prior gliptin treatment. We found that the use of gliptins decreased the serum level of SDF-1α in both BP and T2D patients. Our results indicate that the autoantibodies against the linear full-length BP180 are common in patients with T2D, but seropositivity is unaffected by the use of sitagliptin.

Updated S2 K guidelines for the management of bullous pemphigoid initiated by the European Academy of Dermatology and Venereology (EADV)

BACKGROUND

Bullous pemphigoid (BP) is the most common autoimmune subepidermal blistering disease of the skin and mucous membranes. This disease typically affects the elderly and presents with itch and localized or, most frequently, generalized bullous lesions. A subset of patients only develops excoriations, prurigo-like lesions, and eczematous and/or urticarial erythematous lesions. The disease, which is significantly associated with neurological disorders, has high morbidity and severely impacts the quality of life.

OBJECTIVES AND METHODOLOGY

The Autoimmune blistering diseases Task Force of the European Academy of Dermatology and Venereology sought to update the guidelines for the management of BP based on new clinical information, and new evidence on diagnostic tools and interventions. The recommendations are either evidence-based or rely on expert opinion. The degree of consent among all task force members was included.

RESULTS

Treatment depends on the severity of BP and patients' comorbidities. High-potency topical corticosteroids are recommended as the mainstay of treatment whenever possible. Oral prednisone at a dose of 0.5 mg/kg/day is a recommended alternative. In case of contraindications or resistance to corticosteroids, immunosuppressive therapies, such as methotrexate, azathioprine, mycophenolate mofetil or mycophenolate acid, may be recommended. The use of doxycycline and dapsone is controversial. They may be recommended, in particular, in patients with contraindications to oral corticosteroids. B-cell-depleting therapy and intravenous immunoglobulins may be considered in treatment-resistant cases. Omalizumab and dupilumab have recently shown promising results. The final version of the guideline was consented to by several patient organizations.

CONCLUSIONS

The guidelines for the management of BP were updated. They summarize evidence- and expert-based recommendations useful in clinical practice.

Immunotherapy for Pemphigus: Present and Future

Pemphigus is a chronic and severe autoimmune bullous disease caused by autoantibodies targeting adhesion molecules between keratinocytes. It requires 2–3 years on average to manage the disease. To date, although Rituximab combined with short-term systemic glucocorticoids was accepted as first-line therapy, systemic glucocorticoids remain the primary therapeutic option for pemphigus patients, successfully decreasing morbidity and mortality from pemphigus. However, novel therapeutic strategies are desirable due to the low efficacy in some subset of patients and the long-term severe adverse effects of traditional therapies. Recently, immunotherapy has proved to be encouraging for disease control or cure. Based on the current understanding of the immune mechanisms of pemphigus, we review the immune targets and corresponding agents applied in practice or under clinical trials. The goals of the novel treatments are to improve the quality of life of pemphigus patients by improving efficacy and safety, minimizing side effects, achieving fast disease control, or curing the disease.

Translational autoimmunity in pemphigus and the role of novel Bruton tyrosine kinase inhibitors

Bruton tyrosine kinase (BTK) is involved in a multifarious inflammatory and autoimmune process. As a result, BTK has emerged as a promising novel remedial target for amalgamated autoimmune diseases. Medicament corporations have recently devoted considerable attention to the evolution of BTK inhibitors. Pemphigus is an uncommon and often fatal autoimmune illness. Blisters and erosions on cutaneous surfaces and mucous membranes are crippling symptoms of pemphigus vulgaris, which are caused by immunoglobulin G autoantibodies binding to keratinocyte proteins, resulting in keratinocyte adhesion defects. Although systemic corticosteroids and adjuvant medications are used to treat pemphigus, some patients are resistant to these. BTK inhibitors inhibit B-cell signaling, which is clinically useful in treating pemphigus. Assorted clinical trials are underway to assess the safety, tolerability, and pharmacokinetics of distinct BTK inhibitors, including PRN473 and remibrutinib. The current review evaluates translational autoimmunity in pemphigus and discusses BTK inhibitors in the treatment of pemphigus.

•

Pemphigus is severe, and potentially fatal B-cell-mediated autoimmune illness.

•Systemic corticosteroids are used to treat pemphigus, some patients are resistant.

•Bruton Tyrosine Kinase (BTK) is involved in a variety of auto-immune processes.

•As a result, BTK has emerged as a new therapeutic target including pemphigus.

•The current review evaluates the translational autoimmunity in pemphigus.

•This review also depicts the role of BTK inhibitors in treatment of pemphigus.

Pemphigus and Pemphigoid: From Disease Mechanisms to Druggable Pathways

Pemphigus and pemphigoid are paradigms for understanding the mechanisms of antibody-mediated autoimmune disease in humans. In pemphigus, IgG4-predominant autoantibodies cause intraepidermal blistering by direct interference with desmoglein interactions and subsequent disruption of desmosomes and signaling pathways. In pemphigoid, IgG1, IgG4, and IgE autoantibodies against basement membrane zone antigens directly interfere with hemidesmosomal adhesion, activating complement and Fc receptor‒mediated effector pathways. Unraveling disease mechanisms in pemphigus and pemphigoid has identified numerous opportunities for clinical trials, which hold promise to identify safer and more effective therapies for these potentially life-threatening diseases.

Bruton Tyrosine Kinase Inhibition and Its Role as an Emerging Treatment in Pemphigus

Bruton Tyrosine Kinase (BTK) has a key role in multiple pathways involved in inflammation and autoimmunity. Therefore, BTK has become a new therapeutic target for a group of hematologic and autoimmune disorders. The pharmaceutical industry has invested in the clinical development of BTK inhibitors during the last decade. Ibrutinib, for example, which was the first BTK inhibitor to be used in clinical trials, has two approved indications, mantle cell lymphoma and chronic lymphocytic leukemia, and remains under evaluation for additional indications. Rillzabrutinib (PRN1008) is a new, highly potent and selective inhibitor of BTK. Early studies performed in canine pemphigus demonstrated effectiveness. A proof-of-concept, multicenter, phase 2 trial has recently showed the efficacy and safety of oral rilzabrutinib in pemphigus vulgaris. In this mini review, we present evidence regarding the mechanisms affected by BTK inhibition and the concept of BTK inhibition as an emerging new treatment in pemphigus.

Pathogenic Activation and Therapeutic Blockage of FcαR-Expressing Polymorphonuclear Leukocytes in IgA Pemphigus

Pathomechanisms in IgA pemphigus are assumed to rely on Fc-dependent cellular activation by antigen-specific IgA autoantibodies; however, models for the disease and more detailed pathophysiologic data are lacking. In this study, we aimed to establish in vitro models of disease for IgA pemphigus, allowing us to study the effects of the interaction of anti-keratinocyte IgA with cell surface FcαRs. Employing multiple in vitro assays, such as a skin cryosection assay and a human skin organ culture model, in this study, we present mechanistic data for the pathogenesis of IgA pemphigus, mediated by anti-desmoglein 3 IgA autoantibodies. Our results reveal that this disease is dependent on FcαR-mediated activation of leukocytes in the epidermis. Importantly, this cell-dependent pathology can be dose-dependently abrogated by peptide-mediated inhibition of FcαR:IgA-Fc interaction, as confirmed in an additional model for IgA-dependent disease, that is, IgA vasculitis. These data suggest that IgA pemphigus can be modeled in vitro and that IgA pemphigus and IgA vasculitis are FcαR-dependent disease entities that can be specifically targeted in these experimental systems.

Evolving Mechanisms in the Pathophysiology of Pemphigus Vulgaris: A Review Emphasizing the Role of Desmoglein 3 in Regulating p53 and the Yes-Associated Protein

The immunobullous condition Pemphigus Vulgaris (PV) is caused by autoantibodies targeting the adhesion proteins of desmosomes, leading to blistering in the skin and mucosal membrane. There is still no cure to the disease apart from the use of corticosteroids and immunosuppressive agents. Despite numerous investigations, the pathological mechanisms of PV are still incompletely understood, though the etiology is thought to be multifactorial. Thus, further understanding of the molecular basis underlying this disease process is vital to develop targeted therapies. Ample studies have highlighted the role of Desmoglein-3 (DSG3) in the initiation of disease as DSG3 serves as a primary target of PV autoantibodies. DSG3 is a pivotal player in mediating outside-in signaling involved in cell junction remodeling, cell proliferation, differentiation, migration or apoptosis, thus validating its biological function in tissue integrity and homeostasis beyond desmosome adhesion. Recent studies have uncovered new activities of DSG3 in regulating p53 and the yes-associated protein (YAP), with the evidence of dysregulation of these pathways demonstrated in PV. The purpose of this review is to summarize the earlier and recent advances highlighting our recent findings related to PV pathogenesis that may pave the way for future research to develop novel specific therapies in curing this disease.

Bullous pemphigoid in patients receiving peritoneal dialysis: a case series and a literature survey

Bullous pemphigoid (BP) is an autoimmune subepidermal blistering disease. Although several cases of BP in end-stage renal disease patients receiving peritoneal dialysis (PD) or hemodialysis have been reported, the incidence of BP in these patients remains unknown. We recently experienced three PD patients diagnosed with BP. The skin injury was likely to be a trigger of BP in all the three PD patients. Nifedipine and icodextrin exposures were possible factors directly or indirectly affecting the onset of BP, because they were common in the three cases. We also report that the incidence of BP in PD patients was 3/478.3 person-years in a single-center 10-year study. This case series with a literature survey describes that the skin and tissue injuries are potential triggers responsible for the onset of BP in dialysis patients and that the incidence of BP in these patients seems to be much higher than that in the general population.

[Paraneoplastic autoimmune dermatoses]

Paraneoplastic skin manifestations associated with malignancies are extremely polymorphous. Clinicians should be familiar with paraneoplastic dermatoses to establish an early diagnosis of the underlying neoplasm. Lack of familiarity with cutaneous clues for internal malignancies may delay diagnosis and treatment of cancer. In this review, we describe several paraneoplastic autoimmune dermatoses, including paraneoplastic autoimmune multiorgan syndrome, paraneoplastic bullous pemphigoid, and paraneoplastic dermatomyositis.

Milestones in Personalized Medicine in Pemphigus and Pemphigoid

Pemphigus and pemphigoid diseases are autoimmune bullous diseases characterized and caused by autoantibodies targeting adhesion molecules in the skin and/or mucous membranes. Personalized medicine is a new medical model that separates patients into different groups and aims to tailor medical decisions, practices, and interventions based on the individual patient`s predicted response or risk factors. An important milestone in personalized medicine in pemphigus and pemphigoid was achieved by verifying the autoimmune pathogenesis underlying these diseases, as well as by identifying and cloning several pemphigus/pemphigoid autoantigens. The latter has become the basis of the current, molecular-based diagnosis that allows the differentiation of about a dozen pemphigus and pemphigoid entities. The importance of autoantigen-identification in pemphigus/pemphigoid is further highlighted by the emergence of autoantigen-specific B cell depleting strategies. To achieve this goal, the chimeric antigen receptor (CAR) T cell technology, which is used for the treatment of certain hematological malignancies, was adopted, by generating chimeric autoantigen receptor (CAAR) T cells. In addition to these more basic science-driven milestones in personalized medicine in pemphigus and pemphigoid, careful clinical observation and epidemiology are again contributing to personalized medicine. The identification of clearly distinct clinical phenotypes in pemphigoid like the non-inflammatory and gliptin-associated bullous pemphigoid embodies a prominent instance of the latter. We here review these exciting developments in basic, translational, clinical, and epidemiological research in pemphigus and pemphigoid. Overall, we hereby aim to attract more researchers and clinicians to this highly interesting and dynamic field of research.

B-cell targeted therapies in pemphigus

Pemphigus is a rare autoimmune disease of the skin, characterized by autoantibodies targeting adhesion proteins of the epidermis, in particular desmoglein 3 and desmoglein 1, that cause the loss of cell-cell adhesion and the formation of intraepidermal blisters. Given that these autoantibodies are both necessary and sufficient for pemphigus to occur, the goal of pemphigus therapy is the elimination of autoreactive B-cells responsible for autoantibody production. Rituximab, an anti-CD20 monoclonal antibody, was the first targeted B-cell therapy approved for use in pemphigus and is now considered the frontline therapy for new onset disease. One limitation of this treatment is that it targets both autoreactive and non -autoreactive B-cells, which accounts for the increased risk of serious infections in treated patients. In addition, most rituximab-treated patients experience disease relapse, highlighting the need of new therapeutic options. This review provides a concise overview of rituximab use in pemphigus and discusses new B-cell and antibody-directed therapies undergoing investigation in clinical studies.