AbstractPriming haematopoietic stem/progenitor cells (HSPCs) in vitro with specific chromatin modifying agents and cytokines under serum-free-conditions significantly enhances engraftable HSC numbers. We extend these studies by culturing human CD133+ HSPCs on nanofibre scaffolds to mimic the niche for 5-days with the HDAC inhibitor Scriptaid and cytokines. Scriptaid increases absolute Lin−CD34+CD38−CD45RA−CD90+CD49f+ HSPC numbers, while concomitantly decreasing the Lin−CD38−CD34+CD45RA−CD90− subset. Hypothesising that Scriptaid plus cytokines expands the CD90+ subset without differentiation and upregulates CD90 on CD90− cells, we sorted, then cultured Lin−CD34+CD38−CD45RA−CD90− cells with Scriptaid and cytokines. Within 2-days and for at least 5-days, most CD90− cells became CD90+. There was no significant difference in the transcriptomic profile, by RNAsequencing, between cytokine-expanded and purified Lin−CD34+CD38−CD45RA−CD49f+CD90+ cells in the presence or absence of Scriptaid, suggesting that Scriptaid maintains stem cell gene expression programs despite expansion in HSC numbers. Supporting this, 50 genes were significantly differentially expressed between CD90+ and CD90− Lin−CD34+CD38−CD45RA−CD49f+ subsets in Scriptaid-cytokine- and cytokine only-expansion conditions. Thus, Scriptaid treatment of CD133+ cells may be a useful approach to expanding the absolute number of CD90+ HSC, without losing their stem cell characteristics, both through direct effects on HSC and potentially also conversion of their immediate CD90− progeny into CD90+ HSC.