Fetal hematopoietic stem cells: in vitro expansion and transduction using lentiviral vectors.

Abstract

Umbilical cord blood (CB), remaining in the placenta at delivery, is rich in hematopoietic stem and progenitor cells. Compared with adult peripheral blood, the content of CD34+ and CD34+CD38− cells in CB is approximately tenfold higher and thus comparable to adult bone marrow (Broxmeyer et al. 1989, 1990; Hao et al. 1995). Moreover, CB progenitors have high plating efficiency in clonogenic assays, they respond rapidly to cytokine stimulation in vitro and generate progeny comparable to that derived from bone marrow precursors (Emerson et al. 1985; Cardoso et al. 1993; Lansdorp et al. 1993). Due to these characteristics, CB has been recognized as an attractive alternative source of hematopoietic stem cells for transplantation (Cairo and Wagner 1997). Several hundreds of patients with hematological malignancies and genetic diseases affecting the hematopoietic system have been treated with CB from related as well as from unrelated donors (Gluckman et al. 1989, 1997; Rubinstein et al. 1998). Clinical results have shown that CB transplants engraft and sustain hematopoietic function. Survival rates are comparable to those after bone marrow transplantation. The main advantage of CB over adult hematopoietic tissue is immunologic immaturity of accessory cells in the graft, including a lower expression level of T cell-derived growth factors (Ehlers and Smith 1991; Harris et al. 1992; Sautois et al. 1997). In clinical practice, this results in reduced incidence and severity of graft-versus-host disease, and may allow a higher degree of human leukocyte antigen (HLA) disparity between donor and recipient (Rubinstein et al. 1998). While CB transplantation has proven feasible in pediatric patients, the number of stem cells in a CB graft may be insufficient to reconstitute an adult recipient. Therefore, efforts to expand pluripotent hematopoietic CB cells in vitro are under way. The most efficient amplification of hematopoietic cells from human CB has recently been described in cultures supplemented with thrombopoietin, and flt-3 ligand (Moore and Hoskins 1994; Piacibello et al. 1997).