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Hemogenic endothelial (HE) cells are specialized endothelial cells to give rise to hematopoietic stem/progenitor cells during hematopoietic development. The underlying mechanisms that regulate endothelial-to-hematopoietic transition (EHT) of human HE cells are not fully understand. Here, we identified platelet endothelial aggregation receptor-1 (PEAR1) as a novel regulator of early hematopoietic development in human pluripotent stem cells (hPSCs). We found that the expression of PEAP1 was elevated during hematopoietic development. A subpopulation of PEAR1

Hematopoietic differentiation of human pluripotent stem cells (hPSCs) requires orchestration of dynamic cell and gene regulatory networks but often generates blood cells that lack natural function. Here, we performed extensive single-cell transcriptomic analyses to map fate choices and gene expression patterns during hematopoietic differentiation of hPSCs and showed that oxidative metabolism was dysregulated during in vitro directed differentiation. Applying hypoxic conditions at the stage of endothelial-to-hematopoietic transition in vitro effectively promoted the development of arterial specification programs that governed the generation of hematopoietic progenitor cells (HPCs) with functional T cell potential. Following engineered expression of the anti-CD19 chimeric antigen receptor, the T cells generated from arterial endothelium-primed HPCs inhibited tumor growth both in vitro and in vivo. Collectively, our study provides benchmark datasets as a resource to further understand the origins of human hematopoiesis and represents an advance in guiding in vitro generation of functional T cells for clinical applications.

The cover image is based on the Original Manuscript Vitronectin‐activated αvβ3 and αvβ5 integrin signalling specifies haematopoietic fate in human pluripotent stem cells by Jun Shen et al., https://doi.org/10.1111/cpr.13012. [Image: see text]

Objectives Vitronectin (VTN) has been widely used for the maintenance and expansion of human pluripotent stem cells (hPSCs) as feeder‐free conditions. However, the effect of VTN on hPSC differentiation remains unclear. Here, we investigated the role of VTN in early haematopoietic development of hPSCs. Materials and Methods A chemically defined monolayer system was applied to study the role of different matrix or basement membrane proteins in haematopoietic development of hPSCs. The role of integrin signalling in VTN‐mediated haematopoietic differentiation was investigated by integrin antagonists. Finally, small interfering RNA was used to knock down integrin gene expression in differentiated cells. Results We found that the haematopoietic differentiation of hPSCs on VTN was far more efficient than that on Matrigel that is also often used for hPSC culture. VTN promoted the fate determination of endothelial‐haematopoietic lineage during mesoderm development to generate haemogenic endothelium (HE). Moreover, we demonstrated that the signals through αvβ3 and αvβ5 integrins were required for VTN‐promoted haematopoietic differentiation. Blocking αvβ3 and αvβ5 integrins by the integrin antagonists impaired the development of HE, but not endothelial‐to‐haematopoietic transition (EHT). Finally, both αvβ3 and αvβ5 were confirmed acting synergistically for early haematopoietic differentiation by knockdown the expression of αv, β3 or β5. Conclusion The established VTN‐based monolayer system of haematopoietic differentiation of hPSCs presents a valuable platform for further investigating niche signals involved in human haematopoietic development., Compared with Matrigel (MTG), vitronectin (VTN) was required for the mesoderm to acquire higher endothelial‐hematopoietic potential. The promoting effect of VTN on early hematopoiesis was dependent on αvβ3 and αvβ5 integrins. Inhibition of αvβ3 and αvβ5 impaired HE development without affecting EHT.

Human pluripotent stem cells (hPSCs) provide a powerful platform for generating functional hematopoietic cells for blood disease modeling and therapeutic testing. However, the quantity and quality of hPSC-derived blood cells remain to be improved. Here, by performing extensive single-cell transcriptomic analyses to map fate choices and gene expression programs during hematopoietic differentiation of hPSCs, we construct the first hematopoietic landscape of hPSCs at the single-cell level and identify strategies to promote hematopoietic progenitor (HP) generation from hPSCs with functional T cell potential. By focusing specifically on cell populations and molecular events involved in endothelial-to-hematopoietic transition (EHT), we compared the difference of early hematopoiesis between hPSCs and human embryos (Yang Zeng et al. Cell Research. 2019) and found aerobic metabolism was dysregulated during in-vitro-directed differentiation. The decreased oxygen metabolism program was further deciphered as a key molecular event occurred during the EHT. Providing hypoxia at the stage of EHT enhanced hematopoietic differentiation of hPSCs via specifying arterial programs, including arterial hemogenic endothelium (AHE) and arterial endothelium cells (AE). To further determine the effect of AE on hematopoietic development, we isolated AE, venous endothelium and mesenchymal cells identified in our single-cell transcriptomic analyses and cocultured them with AHE respectively for HP generation. AE were finally validated as a critical regulator of definitive HP specification with more T cell potential. T cells generated from AE-primed HPs (AE-T) were highly functional and exhibited polyfunctional production of interferon (IFN)-γ, tumor necrosis factor alpha (TNF-α), and IL-2 in response to phorbol 12-myristate 13-acetate (PMA) and ionomycin. To further evaluate the function of AE-T, we engineered T cells with CD19-CAR. The in vitro cytotoxicity of CAR-engineered AE-T was performed both in CD19+ cell lines (Nalm-6 and Raji) and human primary B-ALL samples. The efficacy of CAR-engineered AE-T in vivo was evaluated in a mouse xenograft model inoculated intravenously with luciferase-expressing Nalm-6 cells. Similar to CD19 CAR-transduced peripheral blood T cells, the AE-T potently inhibited tumor growth both in vitro and in vivo. Collectively, our study provides benchmark datasets to understand the origins of human hematopoiesis and presents an advance for guiding the generation of functional T cells in vitro for clinical applications. Disclosures No relevant conflicts of interest to declare.

Human pluripotent stem cells (hPSCs) provide a powerful platform for studying the dynamic molecular network towards hematopoiesis. To date, a comprehensive roadmap at single-cell level for hPSC-derived hematopoietic differentiation has not been established. Here, we performed single-cell transcriptomic analyses to map gene expression programs during hematopoietic differentiation of hPSCs, from which new strategies to improve in vitro hematopoietic differentiation may be thus developed. We firstly established a serum-free, stroma-free and chemically defined monolayer system for hematopoietic differentiation of hPSCs, which enabled single-cell transcriptomic analysis. Through identifying sequential molecular events, we generated a time-course gene expression profile revealing the temporally restricted expression dynamics of stage-specific genes associated with hematopoietic cell fate choices. To better understand the lineage trajectories and gene regulatory networks governing diversification of cell fates, we established transcription factor regulatory networks predicting developmental fate choices during hematopoietic differentiation. By pseudotime analysis, we constructed the endothelial-hematopoietic trajectory revealing a novel hematopoietic development model that hemogenic endothelium initiated first and then differentiated into arteries and veins, whereas arteries had the ability to promote endothelial-to-hematopoietic transition. Moreover, we found that the genes related to aerobic metabolism were significantly decreased in hematopoietic cells and hypoxia-primed hematopoietic differentiation showed higher potency for generating more hematopoietic lineages. Further studies showed that hypoxia enhanced hematopoietic differentiation by promoting the development of arterial endothelium, rather than directly acting on hemogenic endothelium.