ARM I: Patients undergo allogeneic hematopoietic stem cell transplant (HCT) at day 0. Patients with an HLA-matched unrelated donor receive mycophenolate mofetil orally (PO) on days 0 to 40, cyclosporine PO every 12 hours twice daily (BID) on days -3 to 96 then tapered to day 150, and sirolimus PO once daily (QD) on days -3 to day 150 then tapered to day 180. Patients with an HLA-mismatched donor receive mycophenolate mofetil PO on days 0-100 then tapered to day 150, cyclosporine PO BID on days -3 to 150 then tapered to day 180, and sirolimus PO QD on days -3 to 180 then tapered to day 365.