Ex Vivo Expansion of Hematopoietic Stem Cells from Human Umbilical Cord Blood-derived CD34⁺ Cells Using Valproic Acid

Umbilical cord blood (UCB) units provide an alternative source of human hematopoietic stem cells (HSCs) for patients who require allogeneic bone marrow transplantation. While UCB has several unique advantages, the limited numbers of HSCs within each UCB unit limits their use in regenerative medicine and HSC transplantation in adults. Efficient expansion of functional human HSCs can be achieved by ex vivo culturing of CD34⁺ cells isolated from UCBs and treated with a deacetylase inhibitor, valproic acid (VPA). The protocol detailed here describes the culture conditions and methodology to rapidly isolate CD34⁺ cells and expand to a high degree a pool of primitive HSCs. The expanded HSCs are capable of establishing both short-term and long-term engraftment and are able to give rise to all types of differentiated hematopoietic cells. This method also holds potential for clinical application in autologous HSC gene therapy and provides an attractive approach to overcome the loss of functional HSCs associated with gene editing.