Emerging Treatments in Pemphigus: Is Healing an Achievable Goal?

Subtype transition from pemphigus vulgaris to pemphigus foliaceus

The pathophysiology of many dermatological diseases is complex. While some of these diseases are complicated by the involvement of multiple unidentified factors, others only appear to be complex because we do not understand the underlying principles and logic. Once their logic emerges, one can appreciate the beauty of nature and its elegant order. Fifty years ago, pemphigus was viewed as a complex disease. In 1964, Beutner and Jordon (1) discovered circulating immunoglobulin G (IgG) autoantibodies against the keratinocyte cell surface in the sera of pemphigus vulgaris (PV) patients, which opened up the modern history of pemphigus. In the late 1970s and early 1980s, the autoantibodies in pemphigus were shown to be pathogenic in that they induced blister formation in skin organ cultures (2,3) and following a passive transfer of IgG from pemphigus patients to neonatal mice (4). In the mid- and late 1980s, the target antigens of pemphigus were identified by immunochemical methods, such as immunoprecipitation and immunoblotting, as the 160- and 130-kDa glycoproteins for pemphigus foliaceus (PF) and PV, respectively (5–9). In the early 1990s, the isolation of cDNA using the technology of molecular biology revealed the 160- and 130-kDa antigens as desmoglein (Dsg)1 and Dsg3, respectively, which are cadherin-type cell–cell adhesion molecules that are expressed in the skin and mucous membranes (10–12). These findings, as well as the findings discussed below, have clarified the basic pathophysiology of pemphigus, and the clinical phenotype and localization of blister formation are logically explained by the anti-Dsg antibody profile and the expression pattern of Dsg isoforms in the skin and mucous membranes (Dsg compensation theory) (13–15). There are always exceptions to the general rule. However, the exceptions do not necessarily validate an alternative theory, supported by a minimal amount of solid evidence (16–19). A simple disease does not have to be explained by a complex theory. Compelling lines of evidence, collected not only from patient serology studies, but also from experiments with mouse models, genetic abrasion, Dsg1-specific protease and specific monoclonal or single-chain antibodies, support the theory that autoimmunity to Dsg is the principal cause of pemphigus pathogenesis. The following representative data corroborate this established theory (20). Anti-Dsg1 IgG autoantibodies have been found in patients with PF, but not in normal individuals (9,21–25). Anti-Dsg3 IgG autoantibodies have been found in patients with PV, but not in normal individuals (8,9,12,24–27). When monitored in individual patients, the titres of serum anti-Dsg1 and anti-Dsg3 IgG autoantibodies, as measured by indirect immunofluorescence or enzyme-linked immunosorbent assay, generally correlate with disease activity (24,28,29). Patients with mucosal dominant-type PV have only anti-Dsg3 IgG autoantibodies, while patients with mucocutaneous-type PV have anti-Dsg3 IgG and anti-Dsg1 IgG autoantibodies (30–33). Pemphigus subtype transition is accompanied by changes in the anti-Dsg antibody profiles. For example, when patients show clinical transition from PF to PV, anti-Dsg1 IgG is detected in the PF stage and anti-Dsg3 IgG is detected in the PV stage (34–38). IgG prepared from PF sera induced blisters with typical PF histology when passively transferred to neonatal mice (39). Removal of anti-Dsg1 IgG autoantibodies by immunoadsorption with baculovirus-expressed recombinant extracellular domain of Dsg1 (rDsg1) abolished the blister-forming activity of PF sera (40,41). Purified anti-Dsg1 IgG on rDsg1 from PF sera induced blisters with the typical histology (40). IgG prepared from PV sera induced blisters with typical histology when passively transferred to neonatal mice (4). Removal of anti-Dsg3 IgG by immunoadsorption with rDsg3 abolished the pathogenic activity of PV sera (26). Anti-Dsg3 and anti-Dsg1 IgG autoantibodies were necessary for efficient PV blister formation in the skin of neonatal mice (13). IgG prepared from the sera of patients with paraneoplastic pemphigus (PNP), which is another subtype of pemphigus that occurs with neoplasm, induces blisters when passively transferred to neonatal mice (42). Removal of anti-Dsg3 and anti-Dsg1 IgG autoantibodies by immunoadsorption abolished the blister-forming activity of the PNP sera (43). Specific inactivation of Dsg3 by genetic ablation of the DSG3 gene in mice resulted in a strikingly similar phenotype to that of mucosal dominant-type PV patients who carry anti-Dsg3 IgG autoantibodies alone (44). The exfoliative toxins (ETs), ETA, ETB and ETD, which are produced by Staphylococcus aureus, specifically cleave Dsg1 and induce blisters with identical histology to the PF blisters in humans and mice (45–47). Furthermore, patients with bullous impetigo caused by ETs and patients with PF show similar clinical manifestations (48). The anti-Dsg3 IgG mouse monoclonal antibody AK23 induces virtually the same PV phenotype as that of PV model mice or Dsg3−/− mice, with typical histology (49,50). The epitope of AK23 has been mapped to the N-terminal adhesive interface of Dsg3, which in functional terms is the most important part of the molecule. Single-chain monoclonal anti-Dsg antibodies isolated from a PV patient by phage display induced blisters that were histologically similar to those seen in pemphigus patients (51). The Dsg compensation theory is still under development. Anti-Dsg IgG antibodies do not necessarily possess equal pathogenic strength; some antibodies are more potent than others in blister-forming ability (50,51). Thus, the pathogenic potential of a given antibody constitutes an additional factor for explaining pemphigus cases that do not fall into classical forms of pemphigus (35,52–55). Cross-reactivity among Dsg isoforms also has to be considered. A subset of the anti-Dsg1 IgG antibodies cross-reacts with another isoform of Dsg, Dsg4, although the Dsg4/Dsg1-cross-reactive IgG has no significant pathogenic effect (56). Single-chain antibodies that react with both Dsg1 and Dsg3 have been isolated and shown to induce PV blisters in neonatal mice (51). We believe that the Dsg compensation theory will continue to provide a solid basis for a better understanding of the pathophysiological mechanism of blister formation in pemphigus.

Compared with other ‘model’ disorders of organ-specific autoimmunity, such as multiple sclerosis, myasthenia gravis or insulin-dependent diabetes mellitus, the pathogenesis of pemphigus is by far unravelled to the greatest extent (1,2). However, the ambitious endeavour to provide a pathogenetic concept that fits for all the clinical variations of pemphigus demonstrates that, apart from the definition of common major autoantigens, the relative contribution of additional factors may vary interindividually. Several brilliant achievements of the past years have helped to dissect crucial events in the effector phase of the immune pathogenesis of pemphigus, even though several aspects in the aetiology and molecular effects leading to autoimmune loss of epidermal adhesion are not yet fully understood. Immunogenetically, there is a clear-cut association of pemphigus with distinct human leukocyte antigen (HLA) class II alleles that have been shown to be critical for T-cell recognition of autoantigenic peptides of desmoglein (Dsg)3 and Dsg1, an initial event required for T-cell-dependent induction and perpetuation of autoantibody production (2–4). The relevance of this concept is supported by the finding that healthy carriers of pemphigus-associated HLA class II alleles have also autoreactive T cells of identical epitope specificity and similar frequency as patients with pemphigus (4–7). We have shown that Dsg3-specific, T-cell-driven peripheral tolerance is at least one mechanism which regulates the clinical outcome of pemphigus by preventing the activation of Dsg3-specific, autoaggressive B cells (7–9). Several human studies in pemphigus vulgaris (PV) and pemphigus foliaceus (PF) (including the endemic variant, fogo selvagem) have shown that, in general, immunoglobulin G (IgG) autoantibody titres against Dsg3 and Dsg1 relate to the clinical activity and phenotype of PV and PF, respectively (10,11), and that their therapeutic removal is of clinical benefit in PV (12,13). Even though there is a proof that the overall picture of the Dsg compensation theory is valid (11), there are several evidences that autoantibody specificities (i.e. Dsg1 vs Dsg3 reactivity) and titres do not always relate to the clinical phenotype and activity of pemphigus (14,15). With regard to intramolecular epitope spreading, there is strong evidence that polyclonal Dsg-specific IgG autoantibodies in the patients’ sera recognize both pathogenic and non-pathogenic epitopes located in the ectodomains of Dsg3 and Dsg1 (16). Experimental in vitro and in vivo data demonstrate that IgG against the NH2-terminal domain of Dsg3 is pathogenic, while IgG against other epitopes requires the presence of autoantibodies targeting additional epitopes resulting in a pathogenic synergism of ‘semipathogenic’ autoantibodies (17–19). This contention is also supported by serological analyses in PV patients showing (i) that IgG against the NH2-terminal aa1–161 relates to disease activity (20) and (i) that the presence of several domain-specific IgG autoantibodies against the Dsg3 ectodomain relates to disease activity in PV (21). In fogo selvagem, the endemic variant of PF, pathogenic IgG autoantibodies against the putative autoantigen, Dsg1, target its NH2-terminus, while patients’ relatives or individuals who develop disease later on have autoantibodies that target ‘non-pathogenic’ regions in the COOH-terminus of the Dsg1 ectodomain (22). Current evidence favours the concept that Dsg1 and Dsg3 are the principal autoantigens in most clinical variants of pemphigus, even though the relative contribution of additional desmosomal (i.e. desmocollins, plakins) and non-desmosomal autoantigens (pemphaxin, α9-acetylcholine receptor) remains a matter of debate (23,24). The critical role of Dsg3 in epidermal adhesion of mucosal and stratified squamous epithelia has been clearly shown in a Dsg3-deficient animal (25). However, we would like to challenge the concept that Dsg-specific autoantibodies alone are the principal effectors in pemphigus because patients on treatment with the anti-CD20 monoclonal antibody, rituximab, frequently show a clinical response despite the persistence of high autoantibody titres (26). Our group has observed in rituximab-treated PV patients that, upon depletion of B cells, the frequencies of autoreactive T helper 1 and 2 cells were immediately reduced to background levels (27). This was not the case with T helper cells responsive to an unrelated antigen, suggesting that rituximab acted specifically on autoreactive T cells which may also be critically involved in the effector phase of PV, apart from their helper function to autoaggressive B cells (28,29). Along this line, therapeutic blockade with infliximab, a monoclonal antibody against the proinflammatory cytokine, tumor necrosis factor-α, which is mainly produced by effector T cells, leads to an immediate amelioration of PV, despite the persistence of tissue-bound and circulating IgG autoantibodies (30). While this may not suffice to demote Dsg-specific autoantibodies to the inferior role of ‘witnesses of disease’, it clearly questions whether these autoantibodies alone are the principal effectors of PV immunopathogenesis.

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Autoantibodies in the Autoimmune Disease Pemphigus Foliaceus Induce Blistering via p38 Mitogen-Activated Protein Kinase-Dependent Signaling in the Skin

Epitope Spreading Is Rarely Found in Pemphigus Vulgaris by Large-Scale Longitudinal Study Using Desmoglein 2–Based Swapped Molecules

Pemphigus is a life-threatening autoimmune blistering disease. Patient characteristics, treatment courses, and outcomes remain unclear owing to its rarity. To describe the background, treatment, and outcomes of pemphigus, we identified 2598 patients with pemphigus vulgaris and 1186 patients with pemphigus foliaceus from a nationwide inpatient database in Japan. Patients with pemphigus vulgaris were younger (62 vs 72 years, P< 0.001), had fewer comorbidities, and were more likely to be admitted to high-volume hospitals (38% vs 30%, P< 0.001) than those with pemphigus foliaceus. Patients with pemphigus vulgaris had undergone more aggressive treatment, including steroid pulse therapy, intravenous immunoglobulin, or plasmapheresis, compared with those with pemphigus foliaceus (48% vs 42%, P= 0.001); specifically, in patients aged <70 years, the pemphigus vulgaris group was more likely to undergo aggressive treatment than the pemphigus foliaceus group (52% vs 45%), whereas there was no significant difference in patients aged ≥70 years (40% vs 40%). Immunosuppressive agents (30% vs 26%, P= 0.015) and analgesics, including opioids (45% vs 36%, P< 0.001), were used more frequently, whereas topical corticosteroids were used less frequently (32% vs 48%, P< 0.001) in patients with pemphigus vulgaris compared with those with pemphigus foliaceus. In-hospital mortality was lower in patients with pemphigus vulgaris than in those with pemphigus foliaceus (2.2% vs 4.0%, P= 0.002); in the comparison stratified by age, the mortality was equivalent among the two groups (0.6% in patients aged <70 years and 6.1% in those aged ≥70 years). Overall, patients with pemphigus vulgaris had a 10-day longer hospitalization period and higher hospitalization costs than those with pemphigus foliaceus. Our findings provide useful information for understanding the current trends in the management of pemphigus in Japan.

Viewpoint 6

Long-term complete remission of severe pemphigus vulgaris with monoclonal anti-CD20 antibody therapy and immunophenotype correlations

Pemphigus is a rare intraepidermal autoimmune bullous disease. Two major variants, pemphigus vulgaris (PV) and pemphigus foliaceus (PF), are distinguished. The aim of this study was to document the clinical and immunopathological findings in all pemphigus patients who were diagnosed in the Department of Dermatology at the University of Würzburg over the past 10 years. Based on a retrospective study, clinical and immunopathological findings in 48 patients with pemphigus were recorded. All patients had positive findings by direct and/or indirect immunofluorescence microscopy. Between January 1989 and August 1998, 48 patients were diagnosed with pemphigus at our institution; 31 patients had PV and 17 PF. The average age (+/- standard deviation) of PV patients was 55 (+/- 17) and of PF patients 60 (+/- 12) years. All PV patients showed involvement of mucous membranes and in 65% of cases, the skin was also involved. In contrast, PF patients had involvement only of the skin. By direct immunofluorescence microscopy, intercellular deposits of IgG and C3 were detected in 89% and 78% of PV cases, respectively. In PF, intercellular deposits of IgG were found in 94% and of C3 in 75% of cases. By indirect immunofluorescence microscopy on monkey esophagus, 94% of the PV and 88% of the PF patients revealed circulating serum antibodies. In 30 patients, we characterized the immune response by ELISA using recombinant desmoglein 1 and 3. All PF sera showed autoantibodies against desmoglein 1 and all PV sera against desmoglein 3. In PV with both mucous membrane and skin involvement, antibodies to both desmoglein 3 and 1 were detected. Our results confirm the correlation of the autoantibody profile with the clinical phenotype of pemphigus.

29 - Pemphigus

Pemphigus is a group of potentially fatal dermatological autoimmune disorders. Analysis of cases of pemphigus vulgaris (PV) and pemphigus foliaceus (PF) newly diagnosed and treated at the Department of Dermatology and Venereology, Medical University of Białystok, North-east Poland in years 2001-2018. A retrospective analysis and comparison of sociodemographic, epidemiological and clinical characteristics of PV and PF patients, including: age, gender, residency, initial severity of skin lesions, involvement of mucous membranes, co-morbidities and their treatment, efficacy of therapy. Sixty-two new cases - 41 (66.13%) of PV and 21 (33.87%) of PF were diagnosed. The average age of PV patients was 54.85±12.35 years and those of PF - 63.81±31.52 years, P<0.05. Females constituted 75.61% and 61.90% in PV and PF group, respectively. Majority of patients with PV were residents of urban and these with PF - of rural areas (70.73% and 66.67%, respectively). On admission, 14 patients with PV (34.15%) and 11 with PF (52.38%) had more than 30% of body surface area involved. In 22 (53.66%) PV mucous membrane (oropharyngeal cavity) was involved. Ten (24.39%) patients with PV and 12 (57.14%) - with PF had more than one concomitant disorder (P<0.05). In treatment prednisone in monotherapy or with additional immunosuppressive agent was mainly used. The disease relapsed within three years after achieving clinical and immunological remission in 29.27% of PV and in 38.10% of PF patients. PF patients are older than PV ones, more frequently live in rural areas, have more comorbidities. Females constitute majority of pemphigus patients. The disease may relapse in about one third of patients. Because of frequent comorbidities, also these related to pemphigus treatment, patients with pemphigus require complex and multispecialistic medical care.

Common Human Leukocyte Antigen Alleles in Pemphigus Vulgaris and Pemphigus Foliaceus Italian Patients

Obinutuzumab in a patient with chronic lymphocytic leukemia-associated paraneoplastic pemphigus

IgG Autoantibody Response against Keratinocyte Cadherins in Endemic Pemphigus Foliaceus (Fogo Selvagem)