Beginning at least 4 weeks after conventional-dose chemotherapy, patients receive non-myeloablative conditioning comprising fludarabine IV over 30 minutes on days -8 to -4, cyclophosphamide IV over 2 hours on days -3 to -2, and anti-thymocyte globulin IV over at least 4 hours on days -2 and -1. Patients undergo filgrastim (G-CSF)-mobilized allogeneic peripheral blood stem cell transplantation on day 0.