- Ages =< 50 years of age with hematologic diseases treatable by allogeneic HCT who through pre-existing medical conditions or prior therapy are considered to be at high risk for regimen related toxicity associated with a conventional transplant (> 40% risk of transplant-related mortality [TRM]) or those patients who refuse a conventional HCT; transplants must be approved for these inclusion criteria by both the participating institution's patient review committee such as the Patient Care Conference (PCC at the Fred Hutchinson Cancer Research Center [FHCRC]) and by the principal investigator at the collaborating center; patients =< 50 years of age who have received previous high-dose transplantation do not require patient review committee approval; all children < 12 years must be discussed with the FHCRC primary investigator (PI) prior to registration