Vascular niche induction of hematopoietic progenitors from pluripotent stem cells

Pluripotent stem cells (PSC) represent an alternative source of hematopoietic stem cells (HSCs). Clinical translation is impeded by limited engraftment of human (h)PSC-multipotent progenitor cells (MPP). This barrier suggests that additional cues are required for definitive hematopoiesis. We hypothesized that vascular niche producing Notch ligands Jagged-1 (JAG1) and Delta-like ligand-4 (DLL4) would drive definitive hematopoiesis. To test our hypothesis, hes2 human embryonic stem cells (hESC) 2 and Macaca nemestrina (Mn) iPSC line-7 were differentiated with cytokines ± endothelial cells (EC), which express JAG1 and DLL4. EC co-culture supported emergence of 8-fold more CD34+CD45+ cells compared to co-culture with cytokines ± ECs with JAG1 or DLL4 knockdown. EC-induced cells exhibit Notch activation and express HSC-specific targets of Notch signaling RUNX1 and GATA2. EC-induced PSC-MPP engraft at a higher level in NSG mice compared to cytokine-induced cells (10% >5 months), and selection increased engraftment (30%). Long-term engraftment and the myeloid-to-lymphoid ratio achieved with vascular niche induction is similar to levels achieved for cord blood MPP and up to 20-fold higher than hPSC-MPP engraftment. Our findings identify a previously underappreciated role for endothelial Notch ligands in PSC definitive hematopoiesis and production of long-term engrafting CD34+ cells and suggest they are critical for HSC emergence. Overall design: Transcriptome sequencing of Macaca nemestrina (Mn) iPSCs