Expansion of haematopoietic stem cells from normal donors and bone marrow failure patients by recombinant hoxb4

We produced six versions of recombinant human hoxb4 proteins and evaluated their effectiveness in expanding human hematopoietic stem and progenitor cells in vitro and in vivo. An N-terminal-tat and C-terminal histidine-tagged version of hoxb4 (T-hoxb4-H) had the highest activity in expanding colony forming cells (CFCs) and long-term culture-initiating cells (LTC-ICs) when used at 50nM concentration in cell culture. Human cord blood CD34+ cells cultured with 50nM T-hoxb4-H had a significant increase in severe-combined immunodeficient mouse-repopulating cells (SRCs). In a mouse model of immune-mediated BM failure, T-hoxb4-H showed an additive effect with cyclosporine in alleviating pancytopenia. In addition, T-hoxb4-H expanded CFC and LTC-IC on BM samples from patients with refractory severe aplastic anemia and myelodysplastic syndromes: after culturing with 50nM T-hoxb4-H for four days, BM cells from 10 of the 11 patients showed increases in CFC and LTC-IC, and the increase in LTC-IC was statistically significant in samples from 4 patients. Recombinant human hoxb4 could be a promising therapeutic agent for BM failure.