Thrombopoietin is synergistic with other cytokines for expansion of cord blood progenitor cells

We investigated the effects of recombinant human thrombopoietin (TPO) in co mbination with various cytokines including erythropoietin (EPO), interleuki n-3 (IL-3), interleukin-6 (IL-6), and stem cell factor (SCP) on megakaryopo iesis, and the expansion of CD34(+)CD41a(+) cells from human cord blood CD3 4(+) cells with these cytokines under serum-free conditions. Human cord blo od CD34+ cells were cultured in Megacult(TM) (Stem Cell Technologies Inc. V ancouver, Canada) in the presence of recombinant growth factors. Colony-for ming unit-megakaryocyte (CFU-M) colonies were counted on day 14. CD34(+)CD4 1a(+) and CD34-CD41a(+) cell expansion was analyzed using a serum-free liqu id culture system for 7 days with recombinant growth factors. TPO alone had a concentration-dependent effect on megakaryocyte colony growth. At concen trations above 1 ng/ml, TPO supported significant CPU-Meg colony formation in a concentration-dependent manner. The combination of TPO plus other cyto kines, including EPO, IL-3, and SCP, resulted in a synergistic enhancement of the number of CPU-Meg colonies, but IL-6 failed to enhance the effect of TPO. The number of CD41a(+) cells increased after 7 days in liquid culture of human cord blood CD34(+) cells with various cytokines (EPO, IL-3, IL-6, SCP) combined with TPO, but SCP plus TPO only resulted in a significant sy nergistic increment of CD34(+)CD41a(+) cells compared with TPO alone. The r esults of the present study indicate that EPO, IL-3, and SCP can be synergi stic with TPO to stimulate proliferation of CPU-Meg and suggest that SCP pl us TPO can expand CD34(+)CD41a(+) cells to effect the rapid recovery of pla telets in patients following stem cell transplantation.