This study will last approximately two years and consist of 15 study visits. These visits will occur at screening, baseline, Days 0 and 14, and Months 1, 2, 3, 4, 6, 9, 12, 15, 18, 21, and 24. Participants will receive a single rituximab injection on Days 0 and 14. Medication history and blood tests will occur at every study visit. A physical exam, medical history, and urine tests will occur at most visits. For females, a pregnancy test will occur at selected visits.