Rituximab in Autoimmune Hematologic Diseases: Not Just a Matter of B Cells

Rituximab, a chimeric monoclonal antibody that depletes B cells by binding to the CD20 cell-surface antigen, has been investigated extensively in autoimmune disorders. Following the encouraging results in immune thrombocytopenia (ITP), the use of this agent was explored in other autoimmune hematologic diseases, most notably autoimmune hemolytic anemia (AIHA) and thrombotic thrombocytopenic purpura (TTP), characterized by the presence of pathogenetic autoantibodies. Although randomized clinical trials are lacking, the cumulative data would suggest that rituximab has a beneficial role in their treatment. Response to B-cell–depleting therapy is actually associated with a significant decrease of circulating autoantibodies. However, several lines of evidence indicate that the T-cell compartment may also be modulated by these interventions. The doses and the duration of rituximab treatment in patients with autoimmune diseases are still unclear. The incidence of severe side effects is low but not insignificant. In particular, the risk of systemic infections and viral reactivation is a major concern.