- Design: Participants will be referred to the NIH Clinical Center (CC) from participating hospitals or will be recruited by advertisements through CNRM Recruitment core to receive EPO or placebo. Telephone screening will be carried out to determine tentative eligibility. At the baseline visit, participants will be screened, consented and randomized 2:1 to receive either EPO or placebo with a dose of 40,000 IU EPO subcutaneously (s.c.) (n=20) once weekly for 4 weeks or placebo (n=10). Each participant will have 6 outpatient visits (visits 1-6) performed at the NIH CC. Placebo or active drug will be administered s.c. based on the randomization at visits 1-4; blood will be collected for EPC assays and safety laboratory measurements during each visit. Brain MRI and neuropsychological tests will be performed during visit 1 (before administering EPO or placebo), and visit 5 (one week after final drug administration) and visit 6 (6 months after study enrollment).