Maintenance and enhancement of human peripheral blood mobilized stem/progenitor cell engraftment after ex vivo culture via an HDACi/SALL4 axis (3465)

Currently, there is a growing need for culturing hematopoietic stem/progenitor cells (HSPCs) in vitro for various clinical applications including gene therapy. Compared with cord blood (CB) CD34+ HSPCs, it is more challenging to maintain or expand CD34+ peripheral blood mobilized stem/progenitor cells (PBSCs) ex vivo. To fill this knowledge gap, we have systematically surveyed 466 small-molecule drug compounds for their potential in cytokine-dependent expansion of human CD34+CD90+ HSPCs. We found that epigenetic modifiers, especially histone deacetylase inhibitors (HDACis), could preferentially maintain and expand these cells. In particular, treatment of CD34+ PBSCs with a single dose of HDACi trichostatin A (TSA) at a concentration of 50 nmol/L ex vivo yielded the greatest expansion (11.7-fold) of CD34+CD90+ cells when compared with the control (dimethyl sulfoxide [DMSO] plus cytokines) group. Additionally, TSA-treated PBSC CD34+ cells had a statistically significant higher engraftment rate than the control-treated group in xenotransplantation experiments. Mechanistically, TSA treatment was associated with increased expression of HSPC-related genes such as GATA2 and SALL4. Furthermore, TSA-mediated CD34+CD90+ expansion was reduced by downregulation of SALL4 but not GATA2. Overall, we have developed a robust, short-term (5-day), PBSC ex vivo maintenance/expansion culture technique and found that the HDACi–TSA/SALL4 axis is important for the biological process.