The study is a randomized, two-arm, trial in which 2/3 of participants will receive the study drug, while the remaining 1/3 will receive a placebo (a pretend medicine that does nothing). The group you are assigned to is decided by chance (as by the toss of a coin or drawing straws). Neither you nor your doctor will be able to choose which group you are in. Also, neither you nor the researchers will know which group you are in. Participants will take rituximab, or the placebo, once a week during the first 4 weeks in the study. It will be given as an intravenous infusion at a clinical center.