Hyper-IL-6 (H-IL-6), a Fusion Protein of Soluble IL-6 Receptor (Sil-6R), and Interleukin-6 (IL-6), Acts Synergistic with Thrombopoietin (TPO) and Stem Cell Factor (SCF) in Expanding Megakaryocyte Progenitors from Human Cd34++/Cd90+ Cell

Abstract

It has been shown that signalings from c-kit and gpl30, the signal-transducing receptor component of the IL6 receptor, act synergistic for the ex-vivo expansion of multipotential hematopoietic progenitors. A similar synergistic effect has been demonstrated for signalings from c-kit, c-mpl, and flt3. While c-kit is activated by stem cell factor (SCF), gpl30 can be activated by the complex of soluble IL-6 receptor (sIL-6R) and interleukin-6 (IL-6). Recently, a bioactive designer cytokine, H-IL-6, a fusion protein consisting of SIL-6R and IL-6 linked by a flexible peptide chain has been shown to expand human hematopoietic colony-forming cells. We tested the activity of H-IL-6 alone and in combination with TPO, SCF, and the flt3 ligand (FL) on mobilized purified human primitive CD34++/CD90+ progenitor cells in a 7 day serum-free liquid culture system. Apart from a moderate expansion of CD34+ cells (2.5-fold to 3.5-fold) the most striking effects of H-IL-6 were observed in megakaryopoiesis. In contrast to TPO, H-IL-6 alone was not sufficient for survival or proliferation of CD34++/CD90+ progenitor cells. Yet the combination of H-IL-6 and TPO expanded CD41+ cells to the same extent as did the combination of TPO + SCF (20-fold). A maximum yield of megakaryocyte progenitors (more than 50-fold) was obtained with the combination of H-IL-6, TPO, and SCF.