EXTENSIVE AMPLIFICATION AND SELF-RENEWAL OF HUMAN PRIMITIVE HEMATOPOIETIC STEM-CELLS FROM CORD-BLOOD

The use of umbilical cord blood as a source of marrow repopulating cel ls for the treatment of pediatric malignancies has been established. G iven the general availability, the ease of procurement, and progenitor content, cord blood is an attractive alternative to bone marrow or gr owth factor mobilized peripheral blood cells as a source of transplant able hematopoietic tissue. However, there is a major potential limitat ion to the widespread use of card blood as a source of hematopoietic s tem cells for marrow replacement and gene therapy. There may be enough hematopoietic stem cells to reconstitute children, but the ability to engraft an adult might require ex vivo manipulations, We describe an in vitro system in which the growth of cord blood CD34(+) cells is sus tained and greatly expanded for more than 6 months by the simple combi nation of two hematopoietic growth factors. Progenitors and cells belo nging to all hematopoietic lineages are continuously and increasingly generated (the number of colony-forming unit-granulocyte-macrophage [C FU-GM] present at the end of 6 months of culture are well over 2,000,0 00-foId the CFU-GM present at the beginning of the culture). Very prim itive hematopoietic progenitors, including long-term culture-initiatin g cells (LTC-ICs) and blast cell colony-forming units, are also greatl y expanded (after 20 weeks of liquid culture, LTC-IC number is over 20 0,000-foId the initial number). The extremely prolonged maintenance an d the massive expansion of these progenitors, which share many similar ities with murine long-term repopulating cells, suggest that extensive renewal and little differentiation take place. This system might prov e useful in diverse clinical settings involving treatment of grown-up children and adults with transplantation of normal or genetically mani pulated hematopoietic stem cells. (C) 1997 by The American Society of Hematology.