EFFECT OF RECOMBINANT ERYTHROPOIETIN IN INTERACTION WITH STROMAL FACTORS ON CORD-BLOOD HEMATOPOIESIS

To investigate the effect of recombinant erythropoietin (Epo) on primi tive human hematopoietic progenitor cells, we cultured cord blood mono nuclear cells (CBMNC) and CB CD34(+) cells in a Dexter-type long-term culture system (LTC), to which various concentrations of Epo were adde d at day 0 or 7, with or without direct contact with irradiated alloge neic human marrow stromal layers. In regular stroma-contact cultures, when CBMNC were inoculated, the addition of Epo at 1 to 10 U/mL induce d a significant increase in LTC-initiating cells (LTC-IC), particularl y in the myeloid component, compared with the control without Epo. Sig nificantly more LTC-IC were generated by the delayed addition of Epo o n day 7 than on day 0. On the other hand, when CD34(+) cells were inoc ulated, physiologic concentrations of Epo (0.1 U/mL) induced a more th an twofold increase in LTC-IC, which was attributed equally to both th e myeloid and erythroid lineages, only when added on day 0. In stroma- noncontact cultures, which were created using a Transwell 0.4-mu m mic roporous membrane filter, dose-dependent suppression of the myeloid co mponent of LTC-IC was observed with a higher concentration of Epo (1 t o 100 U/mL) when CBMNC was inoculated. On the other hand, without Epo, fourfold more LTC-IC was generated from CD34(+) cells in stroma-nonco ntact than in stroma-contact cultures, which was then significantly au gmented by the addition of Epo (0.1 or 10 U/mL) on day 0. This increas e was due to both the myeloid and erythroid lineages. A higher concent ration of Epo (100 U/mL) resulted in a decrease in LTC-IC, mainly in m yeloid progeny, in all of the culture conditions. Hence, Epo may play an important physiologic role in the maintenance and proliferation of immature stem/progenitor cells, in close interaction with factors from marrow stromal cells. (C) 1996 by The American Society of Hematology.