2. No physical contraindications to stem cell donation (i.e. severe atherosclerosis, auto-immune disease, cerebrovascular accident, prior malignancy. Patients with severe atherosclerosis by history will receive a cardiology consult and be judged eligible on a case by case basis. The exclusion of patients with a prior malignancy will be evaluated on a case by case basis. If it is felt by the investigators that the risk of potential transfer of malignant cells is far outweighed by the potential benefit of the procedure the patient may be eligible to serve as a donor. Persons with a history of non-hematologic malignancy must have undergone potentially curative therapy for that malignancy and 1) have had no evidence of that disease for 5 years, and/or 2) be deemed at low risk for recurrence (less than or equal to 20% at 5 years). Such persons will be considered eligible for stem cell donation at the discretion of the principal investigator, who will evaluate the possible benefit to the potential transplant recipient and the risk of disease transmission in consultation with Department of Transfusion Medicine staff. Prospective donors with a history of non-hematologic malignancy who have received potentially curative therapy and are in remission, but whose estimated risk of recurrence is greater than 20% at 5 years, will be considered on an individual basis in consultation with the NCI IRB. Any prospective transplant recipient whose donor has a history of malignancy will be counseled about the theoretical risk of transmission of cancer from the donor to the recipient.