Enriched Levels of Erythropoietin in Human Umbilical Cord Blood Stimulate Hematopoietic Progenitor Cells

Abstract

Human umbilical cord blood (CB) is a recognized source of hematopoietic tissues for transplantation, the treatment of malignancies and gene therapy, among other potential clinical applications. A rich network of hematopoietic cytokines and growth factors possessing stimulatory effects on primitive hematopoietic stem/progenitor cells further characterizes fetal CB. To better elucidate these complex interactions and properties, we compared the hematopoietic activities of CB and normal human peripheral blood (PB), by examining growth/survival of normal hematopoietic progenitors and erythropoietin-dependent UT-7/EPO cells. Colony-forming activity assays of normal bone marrow (BM) BFU-E and CFU-GM showed that CB significantly enhanced progenitor cell growth in comparison to PB. Apoptosis was determined by enumerating APO 2.7 mAb stained cells using flow cytometry. UT-7/EPO cell cultures subjected to PB exhibited a four-fold higher rate of apoptosis than CB exposed cultures, indicating that CB markedly suppressed apoptosis in this human leukemic cell line. Immunoprecipitation of UT-7/EPO cell lysates and immunodetection of the anti-phosphotyrosine Ab (4G10), revealed that CB induced tyrosine phosphorylation of three proteins, with approximate molecular masses of 160, 117.5 and 80 kDa. The 80 kDa protein corresponds to the previously reported molecular mass for the Epo receptor, suggesting that erythropoietin is enriched in CB compared with adult PB.