Sirolimus for acute pemphigus vulgaris: a case report and discussion of dualistic action providing for both immunosuppression and keratinocyte protection

Mechanisms of Resistance to Rituximab Used for the Treatment of Autoimmune Blistering Diseases

Autoimmune blistering diseases represent a group of chronic severe, disabling, and potentially fatal disorders of the skin and/or mucous membranes, primarily mediated by pathogenic auto-antibodies. Despite their rarity, these diseases are associated with significant morbidity and mortality and profound negative impact on the patient's quality of life and impose a considerable economic burden. Rituximab, an anti-CD-20 monoclonal antibody, represents the first line of therapy for pemphigus, regardless of severity and a valuable off-label therapeutic alternative for subepidermal autoimmune blistering diseases as it ensures high rates of rapid, long-lasting complete remission. Nevertheless, disease recurrence is the rule, all patients requiring maintenance therapy with rituximab eventually. While innate resistance to rituximab in pemphigus patients is exceptional, acquired resistance is frequent and may develop even in patients with initial complete response to rituximab, representing a real challenge for physicians. We discuss the various resistance mechanisms and their complex interplay, as well as the numerous therapeutic alternatives that may be used to circumvent rituximab resistance. As no therapeutic measure is universally efficient, individualization of rituximab treatment regimen and tailored adjuvant therapies in refractory autoimmune blistering diseases are mandatory.

Unbiased screening identifies regulators of cell-cell adhesion and treatment options in pemphigus

Cell-cell junctions, and specifically desmosomes, are crucial for robust intercellular adhesion. Desmosomal function is compromised in the autoimmune blistering skin disease pemphigus vulgaris. We combine whole-genome knockout screening and a promotor screen of the desmosomal gene desmoglein 3 in human keratinocytes to identify novel regulators of intercellular adhesion. Kruppel-like-factor 5 (KLF5) directly binds to the desmoglein 3 regulatory region and promotes adhesion. Reduced levels of KLF5 in patient tissue indicate a role in pemphigus vulgaris. Autoantibody fractions from patients impair intercellular adhesion and reduce KLF5 levels in in vitro and in vivo disease models. These effects were dependent on increased activity of histone deacetylase 3, leading to transcriptional repression of KLF5. Inhibiting histone deacetylase 3 increases KLF5 levels and protects against the deleterious effects of autoantibodies in murine and human pemphigus vulgaris models. Together, KLF5 and histone deacetylase 3 are regulators of desmoglein 3 gene expression and intercellular adhesion and represent potential therapeutic targets in pemphigus vulgaris.

Systematic review of sirolimus in dermatological conditions

Sirolimus is a mammalian target of rapamycin inhibitor (mTORI) with anti-proliferative, antiangiogenic and immunosuppressive properties. While approved in Australia as an anti-rejection medication for renal transplant patients, there is mounting evidence regarding the utility of oral and topical sirolimus in treating a plethora of dermatological conditions or conditions with cutaneous manifestations. Our aim was to present an overview of the evidence for current usage and breadth of the application of sirolimus in dermatology. We carried out a systematic review of all the literature published up to 31 August 2019 on oral and topical sirolimus with respect to dermatological conditions or conditions otherwise relevant to dermatology. While 3368 papers were initially produced in our search, 238 papers met our inclusion criteria and were examined in our review. The conditions examined were categorised into genodermatoses (9 conditions), infection (1 condition), inflammatory/autoimmune (10 conditions), neoplasm (3 conditions) and vascular (17 conditions). We extracted data on first author, publication year, journal, characteristics of the study and study patients, condition, drug modalities, drug efficacy, side effects, blood level of mTORI, co-interventions and follow-up. While there is level 1 evidence for the efficacy of sirolimus in conditions such as tuberous sclerosis complex (TSC) and GVHD prophylaxis, for many other conditions, the evidence is limited to level 4 evidence. Regarding oral systemic therapy, dosing regimens varied with the most common for children 0.8mg/m² twice daily and for adults 1 mg twice daily. Doses were often adjusted to reach a typical trough level of between 5 and 15 ng/mL, though targets often varied. In the overall majority of cases, side effects were minimal or tolerable, including mucositis, cytopenias, lipid abnormalities and nausea/vomiting, and only a few cases had to stop due to adverse effects. Regarding topical therapy, concentration of formulations varied from 0.1% to 1% and were compounded into creams, ointments or gels and administered typically once or twice per day. The most common side effect was skin irritation. There were a number of limitations to our study. In particular, many of the published studies were case reports or case series with no comparator arm, leading to susceptibility of bias in conclusions drawn, in particular a high likelihood of publication bias. Given the heterogeneity amongst studies, comparisons or aggregation of results was difficult. There continues to be growing use of oral and topical sirolimus in dermatological conditions. It provides new therapeutic options to patients where previous therapies have either failed or are limited due to toxicity. However, further studies are warranted.

Biologics in autoimmune bullous diseases: Current scenario

Autoimmune bullous diseases can be intraepidermal (pemphigus group of disorders) or subepidermal (pemphigoid group of disorders). The treatment of these disorders chiefly comprises corticosteroids and immunosuppressant adjuvants like azathioprine and mycophenolate mofetil. Autoantibodies are the main mediators of these diseases. Rituximab, a chimeric anti-CD20 monoclonal antibody targeting B-cells, has emerged as an excellent treatment option for refractory pemphigus vulgaris in the last decade. Since then, many new biologics have been proposed/explored for managing autoimmune bullous diseases. These hold potential for greater efficacy and lesser adverse effects than conventional immunosuppressants. In this review, we discuss the role of various biologics in the treatment of autoimmune bullous diseases, followed by a brief discussion on the drawbacks to their use and new developments in this area.

Pemphigus: Current and Future Therapeutic Strategies

Pemphigus encompasses a heterogeneous group of autoimmune blistering diseases, which affect both mucous membranes and the skin. The disease usually runs a chronic-relapsing course, with a potentially devastating impact on the patients' quality of life. Pemphigus pathogenesis is related to IgG autoantibodies targeting various adhesion molecules in the epidermis, including desmoglein (Dsg) 1 and 3, major components of desmosomes. The pathogenic relevance of such autoantibodies has been largely demonstrated experimentally. IgG autoantibody binding to Dsg results in loss of epidermal keratinocyte adhesion, a phenomenon referred to as acantholysis. This in turn causes intra-epidermal blistering and the clinical appearance of flaccid blisters and erosions at involved sites. Since the advent of glucocorticoids, the overall prognosis of pemphigus has largely improved. However, mortality persists elevated, since long-term use of high dose corticosteroids and adjuvant steroid-sparing immunosuppressants portend a high risk of serious adverse events, especially infections. Recently, rituximab, a chimeric anti CD20 monoclonal antibody which induces B-cell depletion, has been shown to improve patients' survival, as early rituximab use results in higher disease remission rates, long term clinical response and faster prednisone tapering compared to conventional immunosuppressive therapies, leading to its approval as a first line therapy in pemphigus. Other anti B-cell therapies targeting B-cell receptor or downstream molecules are currently tried in clinical studies. More intriguingly, a preliminary study in a preclinical mouse model of pemphigus has shown promise regarding future therapeutic application of Chimeric Autoantibody Receptor T-cells engineered using Dsg domains to selectively target autoreactive B-cells. Conversely, previous studies from our group have demonstrated that B-cell depletion in pemphigus resulted in secondary impairment of T-cell function; this may account for the observed long-term remission following B-cell recovery in rituximab treated patients. Likewise, our data support the critical role of Dsg-specific T-cell clones in orchestrating the inflammatory response and B-cell activation in pemphigus. Monitoring autoreactive T-cells in patients may indeed provide further information on the role of these cells, and would be the starting point for designating therapies aimed at restoring the lost immune tolerance against Dsg. The present review focuses on current advances, unmet challenges and future perspectives of pemphigus management.

Differential expression of mTOR signaling pathway proteins in lichen planopilaris and frontal fibrosing alopecia

Dysregulation of the mammalian target of rapamycin (mTOR) signaling pathway has a variety of effects on the immune system and stem cell proliferation. Lichen planopilaris (LPP) and frontal fibrosing alopecia (FFA) are inflammatory scalp conditions resulting in permanent alopecia, which are thought to be related to stem cell damage. Here we investigate the expression of mTOR signaling pathway proteins in human hair follicles of LPP and FFA patients. The expression of mTOR pathway proteins in biopsy specimens from lesional and non-lesional scalp areas of eight LPP and five FFA patients were compared to control scalp biopsies from patients undergoing surgical excisions of sebaceous cysts. We performed immunohistochemical evaluation using a panel of antibodies including mTOR, phospho-mTOR (Ser2448), phospho-p70S6K (Thr389), phospho-4EBP1 (Thr37146), and phospho-tuberin (T1462), as well as Western blot analysis for phospho-p70S6K (Thr389) expression. All evaluated mTOR pathway proteins were similarly expressed in the control and patient non-lesional scalps. While mTOR expression did not show significant alterations between the groups, p-mTOR, p-p70S6K, p-4EBP1, and p-tuberin expressions decreased in the interfollicular epidermis in the lesional scalps of patients. p-p70S6K and p-4EBP1 expression decreased in the outer root sheath (ORS) and inner root sheath (IRS) of the bulge of hair follicles in the lesional scalps of patients. p-mTOR and p-p70S6K expression increased in the lower follicle ORS and bulb of the hair follicles, and p-4EBP1 expression decreased in the bulb of the hair follicles in the lesional scalps of patients. Phospho-tuberin expression increased in the IRS of the bulge and lower follicle ORS of the hair follicles in the lesional scalps of patients, whereas its expression decreased in the bulb. Our results indicate that the mTOR signaling pathway proteins are localized throughout normal hair follicles and that expression of mTOR signaling pathway proteins is altered in the hair follicles of LPP and FFA patients. Further research is required to understand the mechanism by which mTOR operates in the pathogenesis of these diseases.

Stat3 regulates desmoglein 3 transcription in epithelial keratinocytes

Pemphigus vulgaris (PV) is an epithelial blistering disease caused by autoantibodies to the desmosomal cadherin desmoglein 3 (DSG3). Glucocorticoids improve disease within days by increasing DSG3 gene transcription, although the mechanism for this observation remains unknown. Here, we show that DSG3 transcription in keratinocytes is regulated by Stat3. Treatment of primary human keratinocytes (PHKs) with hydrocortisone or rapamycin, but not the p38 MAPK inhibitor SB202190, significantly increases DSG3 mRNA and protein expression and correspondingly reduces phospho-S727 Stat3. Stat3 inhibition or shRNA-knockdown also significantly increases DSG3 mRNA and protein levels. Hydrocortisone- or rapamycin-treated PHKs demonstrate increased number and length of desmosomes by electron microscopy and are resistant to PV IgG-induced loss of cell adhesion, whereas constitutive activation of Stat3 in PHKs abrogates DSG3 upregulation and inhibits hydrocortisone and rapamycin's therapeutic effects. Topical hydrocortisone, rapamycin, or Stat3 inhibitor XVIII prevents autoantibody-induced blistering in the PV passive transfer mouse model, correlating with increased epidermal DSG3 expression and decreased phospho-S727 Stat3. Our data indicate that glucocorticoids and rapamycin upregulate DSG3 transcription through inhibition of Stat3. These studies explain how glucocorticoids rapidly improve pemphigus and may also offer novel insights into the physiologic and pathophysiologic regulation of desmosomal cadherin expression in normal epidermis and epithelial carcinomas.

Elucidation of the mTOR Pathway and Therapeutic Applications in Dermatology

The member of the phosphatidylinositol 3-kinase family, mammalian target of rapamycin, is involved in modulating inflammatory response and regulating cellular processes associated with growth, differentiation, and angiogenesis. Recent years have seen major advances in our understanding of the mammalian target of rapamycin signaling pathway and the implication of this pathway in multiple genetic and inflammatory diseases and tumors. The development of the mammalian target of rapamycin inhibitors has given rise to new treatment approaches that have led to substantially improved outcomes in many diseases. In this article, we review the role of the mammalian target of rapamycin signaling pathway in the different skin diseases with which it has been associated, examine the therapeutic applications of drugs targeting this pathway, and provide an overview of current trends and future directions in research.

Advances in the therapeutic use of mammalian target of rapamycin (mTOR) inhibitors in dermatology

Significant developments in the use of mammalian target of rapamycin (mTOR) inhibitors (mTORIs) as immunosuppressant and antiproliferative agents have been made. Recent advances in the understanding of the mTOR signaling pathway and its downstream effects on tumorigenesis and vascular proliferation have broadened the clinical applications of mTORIs in many challenging disorders such as tuberous sclerosis complex, pachyonychia congenita, complex vascular anomalies, and inflammatory dermatoses. Systemic mTORI therapy has shown benefits in these areas, but is associated with significant side effects that sometimes necessitate drug holidays. To mitigate the side effects of systemic mTORIs for dermatologic applications, preliminary work to assess the potential of percutaneous therapy has been performed, and the evidence suggests that percutaneous delivery of mTORIs may allow for effective long-term therapy while avoiding systemic toxicities. Additional large placebo-controlled, double-blinded, randomized studies are needed to assess the efficacy, safety, duration, and tolerability of topical treatments. The objective of this review is to provide updated information on the novel use of mTORIs in the management of many cutaneous disorders.

Neural nitric oxide synthase participates in pemphigus vulgaris acantholysis through upregulation of Rous sarcoma, mammalian target of rapamycin and focal adhesion kinase

Pemphigus vulgaris (PV) is an autoimmune blistering skin disease characterized by suprabasal acantholysis produced as a consequence of desmoglein (Dsg) and non-Dsg autoantibodies binding to several targeting molecules localized on the membrane of keratinocytes. Nitric oxide (NO) may exert a pathogenic function in several immunological processes. We have previously demonstrated that neural nitric oxide synthase (nNOS) plays part in PV acantholysis. Also, our group has described a relevant role for HER [human epidermal growth factor receptor (EGFR) related] isoforms and several kinases such as Src (Rous sarcoma), mammalian target of rapamycin (mTOR) and focal adhesion kinase (FAK), as well as caspases in PV development. Using a passive transfer mouse model of PV, we aimed to investigate the relationship between the increase in nNOS and EGFR, Src, mTOR and FAK kinase upregulation observed in PV lesions. Our results revealed a new function for nNOS, which contributes to EGFR-mediated PV acantholysis through the upregulation of Src, mTOR and FAK. In addition, we found that nNOS participates actively in PV at least in part by increasing caspase-9 and caspase-3 activities. These findings underline the important issue that in PV acantholysis, caspase activation is a nNOS-linked process downstream of Src, mTOR and FAK kinase upregulation.

Urban legends: pemphigus vulgaris

Pemphigus vulgaris (PV) is the most common type of pemphigus. PV pathogenesis is still debated, and treatment remains challenging. We investigated five controversial topics: (1) What are the target antigens in PV? (2) Do desmogleins adequately address PV pathophysiology? (3) How does acantholysis occur in PV? (4) Is PV still a lethal disease? (5) What is the role of rituximab (RTX) in PV treatment? Results from extensive literature searches suggested the following: (1) Target antigens of PV include a variety of molecules and receptors that are not physically compartmentalized within the epidermis. (2) PV is caused by a variety of autoantibodies to keratinocyte self-antigens, which concur to cause blistering by acting synergistically. (3) The concept of apoptolysis distinguishes the unique mechanism of autoantibody-induced keratinocyte damage in PV from other known forms of cell death. (4) PV remains potentially life-threatening largely because of treatment side effects, but it is uncertain which therapies carry the highest likelihood of lethal risk. (5) RTX is a very promising treatment option in patients with widespread recalcitrant or life-threatening PV. RTX's cost is an issue, its long-term side effects are still unknown, and randomized controlled trials are needed to establish the optimal dosing regimen.

Pemphigus autoimmunity: hypotheses and realities

The goal of contemporary research in pemphigus vulgaris and pemphigus foliaceus is to achieve and maintain clinical remission without corticosteroids. Recent advances of knowledge on pemphigus autoimmunity scrutinize old dogmas, resolve controversies, and open novel perspectives for treatment. Elucidation of intimate mechanisms of keratinocyte detachment and death in pemphigus has challenged the monopathogenic explanation of disease immunopathology. Over 50 organ-specific and non-organ-specific antigens can be targeted by pemphigus autoimmunity, including desmosomal cadherins and other adhesion molecules, PERP cholinergic and other cell membrane (CM) receptors, and mitochondrial proteins. The initial insult is sustained by the autoantibodies to the cell membrane receptor antigens triggering the intracellular signaling by Src, epidermal growth factor receptor kinase, protein kinases A and C, phospholipase C, mTOR, p38 MAPK, JNK, other tyrosine kinases, and calmodulin that cause basal cell shrinkage and ripping desmosomes off the CM. Autoantibodies synergize with effectors of apoptotic and oncotic pathways, serine proteases, and inflammatory cytokines to overcome the natural resistance and activate the cell death program in keratinocytes. The process of keratinocyte shrinkage/detachment and death via apoptosis/oncosis has been termed apoptolysis to emphasize that it is triggered by the same signal effectors and mediated by the same cell death enzymes. The natural course of pemphigus has improved due to a substantial progress in developing of the steroid-sparing therapies combining the immunosuppressive and direct anti-acantholytic effects. Further elucidation of the molecular mechanisms mediating immune dysregulation and apoptolysis in pemphigus should improve our understanding of disease pathogenesis and facilitate development of steroid-free treatment of patients.