Sustained response to low-dose rituximab in idiopathic autoimmune hemolytic anemia

OBJECTIVES: To evaluate the sustained response to low-dose (LD) rituximab in autoimmune hemolytic anemia (AIHA), the ex vivo effect on anti-RBC antibody production by mitogen-stimulated direct antiglobulin test (MS-DAT), and the in vitro dose effect of the drug on the production of anti-RBC antibodies. METHODS: Thirty two patients, 18 warm (W) AIHA and 14 cold hemagglutinin disease (CHD), were treated with LD rituximab (100 mg fixed dose ×4 weekly infusions) along with a short course of oral prednisone. Complete clinical examination, blood counts, and hemolytic markers were performed at enrollment and at month 6, 12, 24, and 36. RESULTS: Hematological parameters significantly improved at all time points compared to enrollment. The overall response was 90%, 100%, 100%, and 89% and the relapse-free survival 87%, 79%, 68%, and 68% at 6, 12, 24, and 36 months, respectively. Response rates were slightly better in WAIHA than in CHD, and relapse risk was greater in cold than warm forms (HR 2.1, 95% CI 0.6-7.9). Four patients were retreated (one patient twice), all achieving a response, lasting a median of 18 months (range 9-30). Treatment was well tolerated without adverse events or infections. Anti-RBC antibody production by MS-DAT significantly decreased over time. In vitro studies showed that rituximab effectively inhibited anti-RBC antibody production at 50 μg/mL, 1/6 of the drug concentration after therapy with standard doses. CONCLUSIONS: These data confirm that LD rituximab treatment is effective and induces sustained responses in AIHA, and that a lower dose of the drug is enough to down-regulate autoantibody production.