Gelclair at Conditioning or After Oral Mucositis Diagnosed vs. Magic Mouth Wash in Stem Cell Transplant Recipients

Adult patients at high risk for developing OM receiving one of the following myeloablative (MA) pre-transplant conditioning regimens prior to allogeneic transplant along with methotrexate (MTX) as part of graft vs. host disease (GVHD) prophylaxis meeting all other eligibility criteria will be enrolled: * FluBu based regimens: either fludarabine: 30 mg/m\^2 x 4 days and busulfan 0.8 mg/kg IV q6h x 4 days; both given daily starting at day -4 OR fludarabine: 40 mg/m\^2 and busulfan: 3.2 mg/kg both given daily on days -6 through -3. * Bu/Cy: busulfan, 0.8 mg/kg IV q6h x 4 days (-7 through -4); cyclophosphamide: 60 mg/kg IV once on days -3 and -2 * Cy/TBI: Cyclophosphamide, 60 mg/kg IV given twice between days -3 and -1 and TBI fractionated (generally over 3 days) for a total of 12Gy GVHD Prophylaxis: • Regimens including methotrexate (MTX; 15 mg/m\^2 planned to be given on days 1, 3, 6 and 11); addition of other agents given along with MTX (e.g., tacrolimus, sirolimus) is acceptable. Duration of treatment: * Arm 1: GEL treatment a minimum of 4x/day initiated from 1st day of conditioning through OM resolution (G0), up to a maximum of 20d. * Arms 2 (GEL) and 3 (MMW): Treatment a minimum of 4x/day initiated when G1 or G2 OM diagnosed during observation period (through Day +14 relative to stem cell infusion) through OM resolution (G0), up to a maximum of 20d.