- All patients 2 years old or over with SAA who have failed initial immunosuppression with r-ATG/CsA and are not candidates for a matched sibling marrow transplantation will be considered for enrollment. Patients who have a suitable matched sibling donor will be referred for consideration of allogeneic bone marrow transplantation. Patients not willing to undergo transplantation will be considered for enrollment. Eligibility will be determined on another screening Hematology Branch protocol (97-H-0041) or another active Hematology branch protocol. The time between determination of eligibility and signing consent to participate on this protocol and initiate treatment on this protocol will not exceed 90 days.