All treatment will be given at M. D. Anderson. First, you will be given chemotherapy to increase the number of stem cells in your blood stream. This chemotherapy will include the drugs ifosfamide, etoposide, and rituximab. You will receive a higher dose of rituximab than is standard of care. The drug ifosfamide will be started on Day 2 and will be given as a continuous injection into a vein over 72 hours. The drug etoposide will also be started on Day 2 and will be given by vein over 2 hours every 12 hours. Rituximab will be given by vein over 4-6 hours on Days 1 and 8. To help decrease the risk of developing side effects caused by the chemotherapy, you will be given fluids by vein and a drug called mesna. Mesna will be given by vein over 24 hours after treatment with ifosfamide is finished. You will have to stay in the hospital for 4-6 days for this part of the treatment.