Patients will be randomized to one of two treatments: dexamethasone 10 mg IV once daily and ondansetron 8 mg orally every 8 hours on each day of the preparative regimen plus one additional day vs. 7.5 mg IV once daily and ondansetron 8 mg orally every 8 hours on each day of the preparative regimen plus one additional day combined with aprepitant, 125 mg orally on the first day of their preparative regimen followed by 80 mg daily on each remaining day of the preparative regimen plus three additional days.