Objectives: There is evidence that B lymphocytes play a role in the pathogenesis of systemic sclerosis (scleroderma). Stimulatory autoantibodies targeting and activating normal human fibroblasts in vitro have been demonstrated in sera from scleroderma patients. Rituximab is a monoclonal antibody which selectively targets and depletes CD20+ B lymphocytes. We investigated the biological effects of rituximab in six patients affected by scleroderma with severe skin involvement.
Methods: Six patients with severe skin fibrosis, unresponsive to immunosuppressive treatment, were treated with 375 mg/m2 per week of intravenous rituximab for a total of four doses. Serum stimulatory autoantibodies to the PDGF receptor were detected. Fibroblast activation was evaluated in fibroblasts grown from skin biopsies performed at baseline and at months 3 and 6 post-treatment. The modified Rodnan's skin score, health assessment questionnaire (HAQ) and visual analogic scale (VAS) for global wellness and B lymphocyte count were performed monthly.
Results: A significant reduction of anti-PDGF receptor autoantibodies was observed in the serum of all patients 3 months after treatment. Fibroblasts showed a significant downregulation of type I collagen gene expression and of the intracellular signalling triggered by anti-PDGFR autoantibodies. A decrease of the skin score and an improvement of disability indexes matched with the in vitro results. A single course of rituximab reduced scleroderma fibroblast activation in vitro and the serum levels of anti-PDGFR stimulatory autoantibodies.
Conclusions: These data provide further evidence of B-cell involvement in the pathogenesis of scleroderma. Targeting B cells may be a promising treatment for scleroderma patients, and controlled clinical trials are warranted.