This study will test whether the immune-suppressing drug rituximab can increase blood counts and reduce the need for transfusions in patients with moderate aplastic anemia, pure red cell aplasia, or Diamond Blackfan anemia. These are rare and serious blood disorders in which the immune system turns against bone marrow cells, causing the bone marrow to stop producing red blood cells in patients with pure red cell aplasia and Diamond Blackfan anemia, and red blood cells, white blood cells and platelets in patients with aplastic anemia. Rituximab is a laboratory-made monoclonal antibody that recognizes and destroys white blood cells called lymphocytes that are responsible for destroying bone marrow cells in these diseases. The drug is currently approved by the Food and Drug Administration for treating patients with B-cell non-Hodgkin lymphoma, a disease of white blood cells.

This study will test whether the immune-suppressing drug rituximab can increase blood counts and reduce the need for transfusions in patients with moderate aplastic anemia, pure red cell aplasia, or Diamond Blackfan anemia. These are rare and serious blood disorders in which the immune system turns against bone marrow cells, causing the bone marrow to stop producing red blood cells in patients with pure red cell aplasia and Diamond Blackfan anemia, and red blood cells, white blood cells and platelets in patients with aplastic anemia. Rituximab is a laboratory-made monoclonal antibody that recognizes and destroys white blood cells called lymphocytes that are responsible for destroying bone marrow cells in these diseases. The drug is currently approved by the Food and Drug Administration for treating patients with B-cell non-Hodgkin lymphoma, a disease of white blood cells. Participants receive four doses of rituximab, once a week for 4 weeks through a needle in an arm vein. The infusion rate depends on how well the patient tolerates the drug. The first infusion usually takes 4 to 6 hours and the rest take 3 to 4 hours. The first and fourth infusions are given at NIH; the second and third may be given at NIH or by a patient's referring doctor. Patients who respond to rituximab but then relapse may receive one additional course of four doses. Patients may continue with transfusions and their current medications, including growth factors (e.g., Epogen and Neupogen) while on study, but may have to stop taking immunosuppressive drugs, such as prednisone or cyclosporine. Patients who must start another immunosuppressive medication are taken off rituximab and followed for safety with clinic visits one week and then once a month for 6 months after the first dose of rituximab. Patients have a blood test once a week while receiving rituximab to evaluate blood counts. After treatment is completed, patients are evaluated once a month until 6 months, then once a year until 3 years to monitor the response to treatment and any drug side effects. Patients are evaluated at NIH for the 3- and 6-month visits and the annual visits. They may be seen at NIH or by their referring doctors for the 1-, 2-, 4- and 5-month visits. A blood test is done at every visit, and a bone marrow aspiration and biopsy are done at the 3-month visit (and when clinically needed to evaluate the effect of rituximab on bone marrow cells).