About 1 month after the transplant, you will be randomly assigned (as in the toss of a coin) to 1 of 2 new groups (Group A and Group B). Group A will receive rituximab by vein over 5-7 hours, once every 3 months, starting 3 months after the stem cell transplant. You will receive rituximab for the first 18 months after the stem cell transplant. Group B will not receive rituximab. You will have an equal chance of being in each group.