Ex Vivo Expansion of Human Serial Transplantable Haematopoietic Stem Cells

The scarcity of haematopoietic stem cells (HSCs) limits clinical HSC transplantation, a curative therapy for various blood disorders. Although substantial advances have been made in the ex vivo expansion of HSCs, the expansion of long-term (LT-) HSCs capable of sustaining serial and multilineage engraftment remains an unmet challenge. Here, we present a culture system that couples intrinsic HSC programming with extrinsic bone marrow (BM) niche factors to sustain human umbilical cord blood (UCB) and BM-derived LT-HSCs ex vivo. This platform, in combination with pyrimidoindole derivative UM729, synergistically expands LT-HSCs while preserving balanced multilineage potential, as validated against fresh UCB controls. Single-cell multiome sequencing revealed that this system preserves HSC identity at transcriptional and epigenetic levels. Furthermore, we identified correlations between transcriptional and epigenetic signatures in HSCs and their transplantation outcomes, suggesting their potential for prospectively assessing HSC functionality and heterogeneity. This platform and framework advance HSC biology with clinical implications.