Cord blood, which contains a high frequency of immature stem/progenitor cells with extensive proliferative and replating capacity in vitro was used as a clinical source of transplantable stem and progenitor cells. These cells can be efficiently transduced with new genetic material by using AAV or retroviral vectors. Using a recombinant AAV vector, high level expression of the lacZ gene under a CMV promoter was demonstrated in immature subsets of cord blood progenitor cells.