Anti-IL-5 Therapy in Bullous Pemphigoid. Randomized, Placebo-controlled, Double-blind Study Evaluating the Effect of Anti-IL-5 Therapy in Patients With Bullous Pemphigoid.

Background

Bullous pemphigoid (BP) is the most common autoimmune blistering skin disease. It characteristically affects the elderly (>70 years) with an annual incidence of 5 to 35 per million. This is comparable with the incidence of eosinophilic esophagitis that we determined with approximately 14 per million. Eosinophilic esophagitis has been recognized as an emerging medical problem and, consequently, several studies with anti-IL-5-antibodies have been performed and are still ongoing. It should be noted, however, that, in contrast to eosinophilic esophagitis, the incidence of BP is dramatically increasing with an average of 17% per year. Moreover, with the increase of the proportion of the elderly in the industrialized world, the medical problems associated with BP will even be more visible in the near future. For instance, patients with BP have an increased mortality risk of 2.3. In the US, an increase in mortality of BP patients has been noticed from 1979 to 2002. Taken together, BP is a frequent disease that affects mostly the elderly.

BP often starts with extremely pruritic skin lesions resembling eczema or urticaria before vesicles and blisters arise. In 10-30% of patients, BP also involves the oral mucosa. Disease severity can be determined by means of the autoimmune bullous skin disorder intensity score (ABSIS) that evaluates the involved area as well as the disease activity. The disease is due to an autoimmune response to structural components of junctional adhesion complexes leading to the damage of the dermal-epidermal junction with subepidermal blister formation. Specifically, autoreactive B and T cell responses against the hemidesmosomal antigens BP180 and BP230 have been identified. Serum levels of autoantibodies to BP180 reflect the disease severity and activity. The T cells are memory CD4+ cells producing both Th1 and Th2 cytokines, mostly IL-4, IL-5 and IL-13. IL-5 as well as eotaxin are abundantly found in blister fluids. The production of IL-5 is indeed associated with blood eosinophilia and significant eosinophil infiltration in the skin of BP patients. Eosinophils are thought to be critically implicated in blister formation by releasing toxic granule proteins (ESP, MBP) and proteolytic enzymes.

Systemic corticosteroids have been widely used for the treatment of BP. Nevertheless, the use of steroids is limited by their side effects. in therapy-resistant cases, immunosuppressive drugs such as azathioprine, chlorambucil, cyclophosphamide, cyclosporine, methotrexate, mycophenolate mofetil are employed, but their corticosteroid-sparing effect and overall benefit in BP is highly disputed. 70% of the relapses are usually observed within three months, 85% within 6 months after stopping therapy.

Since eosinophils are characteristically found in the skin at early stages of the disease before blisters occur and contribute to tissue damage, targeting eosinophils by reducing their number and activation might thus be a promising alternative therapeutic approach. Anti-IL-5 antibody therapy has been shown to be effective in depleting eosinophils, e.g. in diseases such as eosinophilic esophagitis and hypereosinophilic syndrome.