*4.2.2 Anti-CD20*

Rituximab (RTX) is a well-known monoclonal antibody directed against CD20. It causes the depletion of mature and memory B cells through several mechanisms such as CDC and ADCC. For many years, it has been used to treat B cell hematological malignancies and autoimmune diseases such as- rheumatoid arthritis (RA), and pemphigus vulgaris [46]. Due to the autoimmune nature of CSU, it seems reasonable that the reduction of memory B cells and a subsequent decrease of the autoantibodies due to Rituximab, could well become a beneficial treatment option, particularly in autoimmune CSU. So far, only five patients in whom severe CSU refractory to immunosuppressive treatments, have been treated with rituximab [47–51]. The treatment regimen in these patients was either as used in lymphoma (375 mg/m2 weekly for 4 weeks) or as used in the RA protocol (two doses of 1000 mg with a 2-week interval). Four patients responded well to this treatment, and only one failed. However, a phase I/II open-label trial (NCT00216762) was terminated due to safety concerns. To date, there are no ongoing clinical trials on Rituximab in CSU patients. It appears that Rituximab could be reserved for future use as an alternative treatment option in patients with very severe, and treatmentresistant CSU.
