These studies are designed to evaluate the relative efficiency of gene transfer into primitive human hematopoietic cells by comparing lentiviral and foamy virus vectors as vehicles for transfer and expression of globin genes. Normal volunteers will serve as research participants. Each will receive a 4 day course of Granulocyte-Colony Stimulating Factor (G-CSF) after which a peripheral blood apheresis will be performed to recover a mononuclear cell population enriched in primitive hematopoietic cells. The stem and progenitor cells will be purified by selection based on expression of the CD34 antigen. The CD34+ population will be cultured in vitro with various cytokines and transduced with vector particles. The efficiency of gene transfer will be evaluated in the transduced CD34+ population, in progenitors contained within that population by culture in semisolid media and in cells capable of establishing human hematopoiesis in immunodeficient mice. The level of transgene expression will be evaluated in mature hematopoietic lineages that develop in vitro or in immunodeficient mice.