A major limitation in the ex vivo expansion of harvested human hematopoietic stem-progenitor cells (HSPCs) is the rapid differentiation of HSPCs at the expense of the most primitive pluripotent HSCs. A culture system that expands both short-term progenitor cells and long-term repopulating HSCs could benefit translational research and clinical applications such as HSC transplantation and gene therapies. To address this challenge, we developed CTS StemPro™ HSC Expansion Medium, a xeno-free, serum-free medium designed with regulatory compliance in mind. Using a Design of Experiments approach, media constituents were systematically modified and each iteration was evaluated with the goal to maximize ex vivo expansion of hematopoietic stem-progenitor cell (HSPC) immunophenotypes.

 

CTS StemPro HSC Expansion Medium supplemented with FLT3L, SCF (also known as KITL), TPO, IL-3, and IL-6 (“FST36”) expands human CD34+ cells from mobilized peripheral blood, cord blood, and bone marrow. For example, primary human CD34+ cells from mobilized peripheral blood cultured for 7 days in FST36-containing CTS StemPro™ HSC Expansion Medium resulted in a ~100-fold increase in the number of CD34+CD45+Lin- cells and a ~2000-fold increase in the number of CD34+Lin-CD90+CD45RA- cells (an early HSPC immunophenotype), compared to uncultured cells. Expanded CD34+ cells maintained key HSC characteristics including in vitro differentiation into erythroid and non-erythroid cell colonies and expression of high levels of aldehyde dehydrogenase. Importantly, in vivo transplantation studies indicate that the expanded CD34+ cells can engraft into the bone marrow of immuno-deficient mice. In addition, utilizing liposome-mediated electroporation to deliver Cas9 RNPs (500 ng 1.4 kb GFP), we observed indel rates of up to 60% and a knock-in rate of 10% in cultured CD34+ cells. Both cultured CD34+ cells and PBMCs demonstrated a high reprogramming efficiency (~0.3%) with the CytoTune®-iPS Sendai Reprogramming Kit.

 

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