Single-cell analyses and machine learning define hematopoietic progenitor and HSC-like cells derived from human PSCs.

Hematopoietic stem and progenitor cells (HSPCs) develop in distinct waves at various anatomical sites during embryonic development. The in vitro differentiation of human pluripotent stem cells (hPSCs) recapitulates some of these processes; however, it has proven difficult to generate functional hematopoietic stem cells (HSCs). To define the dynamics and heterogeneity of HSPCs that can be generated in vitro from hPSCs, we explored single-cell RNA sequencing (scRNAseq) in combination with single-cell protein expression analysis. Bioinformatics analyses and functional validation defined the transcriptomes of naïve progenitors and erythroid-, megakaryocyte-, and leukocyte-committed progenitors, and we identified CD44, CD326, ICAM2/CD9, and CD18, respectively, as markers of these progenitors. Using an artificial neural network that we trained on scRNAseq derived from human fetal liver, we identified a wide range of hPSC-derived HSPCs phenotypes, including a small group classified as HSCs. This transient HSC-like population decreased as differentiation proceeded, and was completely missing in the data set that had been generated using cells selected on the basis of CD43 expression. By comparing the single-cell transcriptome of in vitro-generated HSC-like cells with those generated within the fetal liver, we identified transcription factors and molecular pathways that can be explored in the future to improve the in vitro production of HSCs.

Concise review: programming human pluripotent stem cells into blood.

Blood disorders are treated with cell therapies including haematopoietic stem cell (HSC) transplantation as well as platelet and red blood cell transfusions. However the source of cells is entirely dependent on donors, procedures are susceptible to transfusion-transmitted infections and serious complications can arise in recipients due to immunological incompatibility. These problems could be alleviated if it was possible to produce haematopoietic cells in vitro from an autologous and renewable cell source. The production of haematopoietic cells in the laboratory from human induced pluripotent stem cells (iPSCs) may provide a route to realize this goal but it has proven challenging to generate long-term reconstituting HSCs. To date, the optimization of differentiation protocols has mostly relied on the manipulation of extrinsic signals to mimic the in vivo environment. We review studies that have taken an alternative approach to modulate intrinsic signals by enforced expression of transcription factors. Single and combinations of multiple transcription factors have been used in a variety of contexts to enhance the production of haematopoietic cells from human pluripotent stem cells. This programming approach, together with the recent advances in the production and use of synthetic transcription factors, holds great promise for the production of fully functional HSCs in the future.

Analysis of the Spatiotemporal Development of Hematopoietic Stem and Progenitor Cells in the Early Human Embryo.

Definitive hematopoietic stem cells (HSCs) first emerge in the aorta-gonad-mesonephros (AGM) region in both mice and humans. An ex vivo culture approach has enabled recapitulation and analysis of murine HSC development. Knowledge of early human HSC development is hampered by scarcity of tissue: analysis of both CFU-C and HSC development in the human embryo is limited. Here, we characterized the spatial distribution and temporal kinetics of CFU-C development within early human embryonic tissues. We then sought to adapt the murine ex vivo culture system to recapitulate human HSC development. We show robust expansion of CFU-Cs and maintenance, but no significant expansion, of human HSCs in culture. Furthermore, we demonstrate that HSCs emerge predominantly in the middle section of the dorsal aorta in our culture system. We conclude that there are important differences between early mouse and human hematopoiesis, which currently hinder the quest to recapitulate human HSC development ex vivo.

Conference report: the third BIRAX Regenerative Medicine Conference.

The third Britain/Israel Research and Academic Exchange Partnership Regenerative Medicine conference was recently held in Oxford (UK). This conference report summarizes highlights from the scientific program. There is a particular emphasis on internationally collaborative projects funded by this initiative, the young researchers' symposium, and a lively panel session focused on the relationships between industry and academia.

Enforced Expression of HOXB4 in Human Embryonic Stem Cells Enhances the Production of Hematopoietic Progenitors but Has No Effect on the Maturation of Red Blood Cells.

UNLABELLED: : We have developed a robust, Good Manufacturing Practice-compatible differentiation protocol capable of producing scalable quantities of red blood cells (RBCs) from human pluripotent stem cells (hPSCs). However, translation of this protocol to the clinic has been compromised because the RBCs produced are not fully mature; thus, they express embryonic and fetal, rather than adult globins, and they do not enucleate efficiently. Based on previous studies, we predicted that activation of exogenous HOXB4 would increase the production of hematopoietic progenitor cells (HPCs) from hPSCs and hypothesized that it might also promote the production of more mature, definitive RBCs. Using a tamoxifen-inducible HOXB4-ER(T2) expression system, we first demonstrated that activation of HOXB4 does increase the production of HPCs from hPSCs as determined by colony-forming unit culture activity and the presence of CD43(+)CD34(+) progenitors. Activation of HOXB4 caused a modest, but significant, increase in the proportion of immature CD235a(+)/CD71(+) erythroid cells. However, this did not result in a significant increase in more mature CD235a(+)/CD71(-) cells. RBCs produced in the presence of enhanced HOXB4 activity expressed embryonic (ε) and fetal (γ) but not adult (ß) globins, and the proportion of enucleated cells was comparable to that of the control cultures. We conclude that programming with the transcription factor HOXB4 increases the production of hematopoietic progenitors and immature erythroid cells but does not resolve the inherent challenges associated with the production of mature adult-like enucleated RBCs. SIGNIFICANCE: As worldwide blood donations decrease and transfusable transmitted infections increase, intense interest has ensued in deriving red blood cells (RBCs) in vitro from alternative sources such as pluripotent stem cells. A translatable protocol was developed to generate RBCs; however, these RBCs have an immature phenotype. It was hypothesized that the transcription factor HOXB4 could enhance their production and maturation. Although HOXB4 increased the production of erythroid progenitors, it did not promote their maturation. Despite the remaining challenges, a robust system has been established to test other candidates and add to the knowledge base in this field.

Cigarette smoke extract (CSE) delays NOD2 expression and affects NOD2/RIPK2 interactions in intestinal epithelial cells.

BACKGROUND: Genetic and environmental factors influence susceptibility to Crohn's disease (CD): NOD2 is the strongest individual genetic determinant and smoking the best-characterised environmental factor. Carriage of NOD2 mutations predispose to small-intestinal, stricturing CD, a phenotype also associated with smoking. We hypothesised that cigarette smoke extract (CSE) altered NOD2 expression and function in intestinal epithelial cells. METHODS AND FINDINGS: Intestinal epithelial cell-lines (SW480, HT29, HCT116) were stimulated with CSE and nicotine (to mimic smoking) ±TNFα (to mimic inflammation). NOD2 expression was measured by qRT-PCR and western blotting; NOD2-RIPK2 interactions by co-immunoprecipitation (CoIP); nuclear NFκB-p65 by ELISA; NFκB activity by luciferase reporter assays and chemokines (CCL20, IL8) in culture supernatants by ELISA. In SW480 and HT29 cells the TNFα-induced NOD2 expression at 4 hours was reduced by CSE (p = 0.0226), a response that was dose-dependent (p = 0.003) and time-dependent (p = 0.0004). Similar effects of CSE on NOD2 expression were seen in cultured ileal biopsies from healthy individuals. In SW480 cells CSE reduced TNFα-induced NFκB-p65 translocation at 15 minutes post-stimulation, upstream of NOD2. Levels of the NOD2-RIPK2 complex were no different at 8 hours post-stimulation with combinations of CSE, nicotine and TNFα, but at 18 hours it was increased in cells stimulated with TNFα+CSE but decreased with TNFα alone (p = 0.0330); CSE reduced TNFα-induced NFκB activity (p = 0.0014) at the same time-point. At 24 hours, basal CCL20 and IL8 (p<0.001 for both) and TNFα-induced CCL20 (p = 0.0330) production were decreased by CSE. CSE also reduced NOD2 expression, CCL20 and IL8 production seen with MDP-stimulation of SW480 cells pre-treated with combinations of TNFα and CSE. CONCLUSIONS: CSE delayed TNFα-induced NOD2 mRNA expression and was associated with abnormal NOD2/RIPK2 interaction, reduced NFκB activity and decreased chemokine production. These effects may be involved in the pathogenesis of small-intestinal CD and may have wider implications for the effects of smoking in NOD2-mediated responses.