Hematopoietic stem cells (HSCs) are rare cells that have the unique ability to self-renew and differentiate into cells of all hematopoietic lineages. The lack of donors and current inability to rapidly and efficiently expand HSCs are key roadblocks in the development of successful cell therapies. Thus the challenge of ex-vivo human HSC expansion remains a fertile and critically important area of investigation. Here we show that either SALL4A- or B-transduced human HSCs obtained from the mobilized peripheral blood are capable of rapid and efficient expansion ex vivo by more than 10,000 fold for both CD34+/CD38- and CD34+/CD38+ cells in the presence of appropriate cytokines. We found that the expanded cells retained hematopoietic precursor cell immunophenotypes and morphology as well as normal in vitro or vivo potential for differentiation. The SALL4 mediated expansion was associated with enhanced stem cell engraftment and long-term repopulation capacity in vivo. In addition, we demonstrated that constitutive expression of SALL4 inhibited granulocytic differentiation and permitted expansion of undifferentiated cells in 32D myeloid progenitors, consistent with the known function of SALL4 in the ES (embryonic stem) cell system. Furthermore, a TAT-SALL4B fusion was able to rapidly expand CD34+ cells, and it is thus feasible to translate this study into the clinical setting. Our findings provide a new avenue for investigating mechanisms of stem cell self renewal and achieving clinically significant expansion of human HSCs.

  • Submitted January 31, 2011.
  • Accepted May 3, 2011.