Phase II Trial of Pentostatin and Targeted Busulfan

"Pre-conditioning therapy:~All participants will receive pentostatin 4 mg/m\^2 on day -28. Patients may receive additional doses on days -21 \& -14 depending on cell counts.~Participant will receive pentostatin at a dose of 4 mg/m\^2 by intravenous infusion over 1-2 hours on days -4, -3."

"Pre-conditioning therapy:~Intravenous Busulfan (1st dose) at a dose of 200mg/m\^2 on day -4.~Intravenous Busulfan (2nd dose) will be administered on day (-2) to target a total AUC of 16,000 +/- 1600."

"Pre-conditioning therapy:~Patients with CD20+ expressing malignancies will be treated with rituximab at a dose of 375 mg/m\^2 according to prescribing and institutional guidelines."

Hematopoietic progenitor cells to be infused at least 36 hours after last dose of Busulfan.