A defined, feeder-free, serum-free system to generate in vitro hematopoietic progenitors and differentiated blood cells from hESCs and hiPSCs

Improving hematopoietic differentiation from human induced pluripotent stem cells by the modulation of Hippo signaling with a diarylheptanoid derivative

BACKGROUND

The diarylheptanoid ASPP 049 has improved the quality of adult hematopoietic stem cell (HSC) expansion ex vivo through long-term reconstitution in animal models. However, its effect on hematopoietic regeneration from human induced pluripotent stem cells (hiPSCs) is unknown.

METHOD

We utilized a defined cocktail of cytokines without serum or feeder followed by the supplementation of ASPP 049 to produce hematopoietic stem/progenitor cells (HSPCs). Flow cytometry and trypan blue exclusion analysis were used to identify nonadherent and adherent cells. Nonadherent cells were harvested to investigate the effect of ASPP 049 on multipotency using LTC-IC and CFU assays. Subsequently, the mechanism of action was explored through transcriptomic profiles, which were validated by qRT-PCR, immunoblotting, and immunofluorescence analysis.

RESULT

The supplementation of ASPP 049 increased the number of phenotypically defined primitive HSPCs (CD34+CD45+CD90+) two-fold relative to seeded hiPSC colonies, indicating enhanced HSC derivation from hiPSCs. Under ASPP 049-supplemented conditions, we observed elevated HSPC niches, including CD144+CD73- hemogenic- and CD144+CD73+ vascular-endothelial progenitors, during HSC differentiation. Moreover, harvested ASPP 049-treated cells exhibited improved self-renewal and a significantly larger proportion of different blood cell colonies with unbiased lineages, indicating enhanced HSC stemness properties. Transcriptomics and KEGG analysis of sorted CD34+CD45+ cells-related mRNA profiles revealed that the Hippo signaling pathway is the most significant in responding to WWTR1/TAZ, which correlates with the validation of the protein expression. Interestingly, ASPP 049-supplemented HSPCs upregulated 11 genes similarly to umbilical cord blood-derived HSPCs.

CONCLUSION

These findings suggest that ASPP 049 can improve HSC-generating protocols with proliferative potentials, self-renewal ability, unbiased differentiation, and a definable mechanism of action for the clinical perspective of hematopoietic regenerative medicine.

Modelling Takenouchi-Kosaki syndrome using disease-specific iPSCs

Takenouchi-Kosaki Syndrome (TKS) is a congenital multi-organ disorder caused by the de novo missense mutation c.191A > G p. Tyr64Cys (Y64C) in the CDC42 gene. We previously elucidated the functional abnormalities and thrombopoietic effects of Y64C using HEK293 and MEG01 cells. In the present study, we used iPSCs derived from TKS patients to model the disease and successfully recapitulated macrothrombocytopenia, a prominent TKS phenotype. The megakaryopoietic differentiation potential of TKS-iPSCs and platelet production capacity were examined using an efficient platelet production method redesigned from existing protocols. The results obtained showed that TKS-iPSCs produced fewer hematopoietic progenitor cells, exhibited defective megakaryopoiesis, and released platelets with an abnormally low count and giant morphology. We herein report the first analysis of TKS-iPSC-derived megakaryocytes and platelets, and currently utilize this model to perform drug evaluations for TKS. Therefore, our simple yet effective differentiation method, which mimics the disease in a dish, is a feasible strategy for studying hematopoiesis and related diseases.

Human Endometrium Derived Induced Pluripotent Stem Cells Are Amenable to Directed Erythroid Differentiation

BACKGROUND

A protocol for using human endometrium derived induced pluripotent stem cells (iPSCs) to derive hematopoietic and erythroid lineages will be elaborated, through a two-phase culture system.

METHODS

Discarded endometrial tissues were obtained from women receiving hysterectomy in their 4th to 5th decade due to benign uterine conditions. pCE-Sox2, Oct4, Klf4, L-Myc and Lin28 episomal vectors were used to electrotransfect the endometrial stromal cells. The first 8 days involves commitment to hematopoietic stem cells through embryoid body with robust expansion on murine bone marrow stromal cells. The second phase involves feeder free conditions with hydrocortisone, stem cell factor, interleukin-3, and recombinant EPO. After 22 days of feeder free culture, the expression profiles of CD235a+, CD34+, CD43+ and CD 71+ were analyzed by flow cytometry and Wright-Giemsa staining for differential counting. The oxygen carrying capacity of cultured RBCs was measured using a hemoxanalyser.

RESULTS

As a result of inducing these cells via co-culture with murine stromal fibroblasts, all endometrium derived iPSCs were differentiated into erythroblasts with a stable yield of approximately 80% for polychromatic and orthochromatic normoblasts. The protocol for complete induction of erythroid lineage cells starting from human endometrial tissue via iPS cells has been optimized.

CONCLUSION

Successful directed erythroid differentiation has occurred from human endometrium-derived iPS cells. A comprehensive process of actually deriving iPS cells using discarded surgical hysterectomy specimens to the erythroid fate has significance in that the scope of using human iPSC cell lines for tissue regeneration could be expanded in the future.

Assembling the Puzzle Pieces. Insights for in Vitro Bone Remodeling

As a highly dynamic organ, bone changes during throughout a person's life. This process is referred to as 'bone remodeling' and it involves two stages - a well-balanced osteoclastic bone resorption and an osteoblastic bone formation. Under normal physiological conditions bone remodeling is highly regulated that ensures tight coupling between bone formation and resorption, and its disruption results in a bone metabolic disorder, most commonly osteoporosis. Though osteoporosis is one of the most prevalent skeletal ailments that affect women and men aged over 40 of all races and ethnicities, currently there are few, if any safe and effective therapeutic interventions available. Developing state-of-the-art cellular systems for bone remodeling and osteoporosis can provide important insights into the cellular and molecular mechanisms involved in skeletal homeostasis and advise better therapies for patients. This review describes osteoblastogenesis and osteoclastogenesis as two vital processes for producing mature, active bone cells in the context of interactions between cells and the bone matrix. In addition, it considers current approaches in bone tissue engineering, pointing out cell sources, core factors and matrices used in scientific practice for modeling bone diseases and testing drugs. Finally, it focuses on the challenges that bone regenerative medicine is currently facing.

Evaluation of 2D and 3D Erythroid Differentiation Protocols Using Sickle Cell Disease and Healthy Donor Induced Pluripotent Stem Cells

BACKGROUND

Sickle cell disease (SCD) is a highly prevalent genetic disease caused by a point mutation in the HBB gene, which can lead to chronic hemolytic anemia and vaso-occlusive events. Patient-derived induced pluripotent stem cells (iPSCs) hold promise for the development of novel predictive methods for screening drugs with anti-sickling activity. In this study, we evaluated and compared the efficiency of 2D and 3D erythroid differentiation protocols using a healthy control and SCD-iPSCs.

METHODS

iPSCs were subjected to hematopoietic progenitor cell (HSPC) induction, erythroid progenitor cell induction, and terminal erythroid maturation. Differentiation efficiency was confirmed by flow cytometry analysis, colony-forming unit (CFU) assay, morphological analyses, and qPCR-based gene expression analyses of HBB and HBG2.

RESULTS

Both 2D and 3D differentiation protocols led to the induction of CD34⁺/CD43⁺ HSPCs. The 3D protocol showed good efficiency (>50%) and high productivity (45-fold) for HSPC induction and increased the frequency of BFU-E, CFU-E, CFU-GM, and CFU-GEMM colonies. We also produced CD71⁺/CD235a⁺ cells (>65%) with a 630-fold cell expansion relative to that at the beginning of the 3D protocol. After erythroid maturation, we observed 95% CD235a⁺/DRAQ5- enucleated cells, orthochromatic erythroblasts, and increased expression of fetal HBG2 compared to adult HBB.

CONCLUSION

A robust 3D protocol for erythroid differentiation was identified using SCD-iPSCs and comparative analyses; however, the maturation step remains challenging and requires further development.

Human Embryonic Stem Cells as a Model for Hematopoietic Stem Cell Differentiation and Viral Infection

Pluripotent human embryonic stem cell (hESC) lines are a valuable in vitro tool to differentiate specific cell lineages, including cells from all three germ layers, i.e., neuronal cells, myocytes, and hematopoietic cells, including progenitors (described here), lymphoid cells, and myeloid cells. However, dramatically different cell subtypes and functional properties of specific cells can arise depending on the differentiation technique used. We previously optimized hematopoietic stem cell differentiation from two different NIH-approved hESC lines to generate CD34+ hematopoietic progenitor cells (HPCs). Infection of these HPCs with a common herpesvirus (human cytomegalovirus) results in maintenance of viral latency, capability of viral reactivation, recapitulation of viral mutant phenotypes, and virus-induced myelosuppression of hematopoietic differentiation. However, different HPC subpopulations support different viral latency and reactivation phenotypes, and different hESC-to-HPC differentiation methods alter the ratio of stem cell subsets. In addition, differences in differentiation methods are dependent on both protocol/reagents and user techniques. Here, we report a simplified and optimized method to generate large numbers of CD34+ HPCs with consistent phenotypes and demonstrate a comparison of several common methods that can be used to control the ratio of available HPC subpopulations. A key aspect of this approach is that we achieve consistency in differentiation across users in different laboratories and, importantly, among newly trained individuals. © 2022 The Authors. Current Protocols published by Wiley Periodicals LLC. Basic Protocol 1: Maintenance of human embryonic stem cells (hESCs) Basic Protocol 2: Differentiation of hESCs to hematopoietic progenitor cells (HPCs) Basic Protocol 3: Downstream functional differentiation of hESC-derived HPCs to mature lineages Support Protocol 1: Freezing and testing frozen batches of hESCs Support Protocol 2: Counting hESCs Support Protocol 3: Phenotyping by flow cytometry.

Dendritic cell differentiation from human induced pluripotent stem cells: challenges and progress

Dendritic cells (DCs) are the major antigen-presenting cells of the immune system responsible for initiating and coordinating immune responses. These abilities provide potential for several clinical applications, such as the development of immunogenic vaccines. However, difficulty in obtaining DCs from conventional sources, such as bone marrow (BM), peripheral blood (PBMC), and cord blood (CB), is a significantly hinders routine application. The use of human induced pluripotent stem cells (hiPSCs) is a valuable alternative for generating sufficient numbers of DCs to be used in basic and pre-clinical studies. Despite the many challenges that must be overcome to achieve an efficient protocol for obtaining the major DC types from hiPSCs, recent progress has been made. Here we review the current state of developing DCs from hiPSCs, as well as the key elements required to enable the routine use of hiPSC-derived DCs in pre-clinical and clinical assays.

Selection of O-negative induced pluripotent stem cell clones for high-density red blood cell production in a scalable perfusion bioreactor system

Objectives

Large‐scale generation of universal red blood cells (RBCs) from O‐negative (O‐ve) human induced pluripotent stem cells (hiPSCs) holds the potential to alleviate worldwide shortages of blood and provide a safe and secure year‐round supply. Mature RBCs and reticulocytes, the immature counterparts of RBCs generated during erythropoiesis, could also find important applications in research, for example in malaria parasite infection studies. However, one major challenge is the lack of a high‐density culture platform for large‐scale generation of RBCs in vitro.

Materials and Methods

We generated 10 O‐ve hiPSC clones and evaluated their potential for mesoderm formation and erythroid differentiation. We then used a perfusion bioreactor system to perform studies with high‐density cultures of erythroblasts in vitro.

Results

Based on their tri‐lineage (and specifically mesoderm) differentiation potential, we isolated six hiPSC clones capable of producing functional erythroblasts. Using the best performing clone, we demonstrated the small‐scale generation of high‐density cultures of erythroblasts in a perfusion bioreactor system. After process optimization, we were able to achieve a peak cell density of 34.7 million cells/ml with 92.2% viability in the stirred bioreactor. The cells expressed high levels of erythroblast markers, showed oxygen carrying capacity, and were able to undergo enucleation.

Conclusions

This study demonstrated a scalable platform for the production of functional RBCs from hiPSCs. The perfusion culture platform we describe here could pave the way for large volume‐controlled bioreactor culture for the industrial generation of high cell density erythroblasts and RBCs.

Harnessing the Power of Induced Pluripotent Stem Cells and Gene Editing Technology: Therapeutic Implications in Hematological Malignancies

In vitro modeling of hematological malignancies not only provides insights into the influence of genetic aberrations on cellular and molecular mechanisms involved in disease progression but also aids development and evaluation of therapeutic agents. Owing to their self-renewal and differentiation capacity, induced pluripotent stem cells (iPSCs) have emerged as a potential source of short in supply disease-specific human cells of the hematopoietic lineage. Patient-derived iPSCs can recapitulate the disease severity and spectrum of prognosis dictated by the genetic variation among patients and can be used for drug screening and studying clonal evolution. However, this approach lacks the ability to model the early phases of the disease leading to cancer. The advent of genetic editing technology has promoted the generation of precise isogenic iPSC disease models to address questions regarding the underlying genetic mechanism of disease initiation and progression. In this review, we discuss the use of iPSC disease modeling in hematological diseases, where there is lack of patient sample availability and/or difficulty of engraftment to generate animal models. Furthermore, we describe the power of combining iPSC and precise gene editing to elucidate the underlying mechanism of initiation and progression of various hematological malignancies. Finally, we discuss the power of iPSC disease modeling in developing and testing novel therapies in a high throughput setting.

A 3-D hydrogel based system for hematopoietic differentiation and its use in modeling down syndrome associated transient myeloproliferative disorder

Induced pluripotent stem cells (iPSCs) provide an extraordinary tool for disease modeling owing to their potential to differentiate into the desired cell type. The differentiation of iPSCs is typically performed on 2-dimensional monolayers of stromal cell or animal tissue derived extracellular matrices. Recent advancements in disease modeling have utilized iPSCs in 3-dimensional (3D) cultures to study diseases such as muscular dystrophy, cardiomyopathy, and pulmonary fibrosis. However, these approaches are yet to be explored in modeling the hematological malignancies. Transient myeloproliferative disorder (TMD) is a preleukemic stage, which is induced in 10-20% of children with trisomy 21 possessing the pathognomonic mutation in the transcription factor GATA1. In this study, we established a synthetic 3D iPSC culture system for modeling TMD via hematopoietic differentiation of customized iPSCs. A chemically cross-linkable PEG hydrogel decorated with integrin binding peptide was found to be permissive of hematopoietic differentiation of iPSCs. It provided a cost-effective system for the generation of hematopoietic stem and progenitor cells (HSPCs) with higher yield of early HSPCs compared to traditional 2D culture on Matrigel coated dishes. Characterization of the HSPCs produced from the iPSC lines cultured in 3D showed that the erythroid population was reduced whereas the megakaryoid and myeloid populations were significantly increased in GATA1 mutant trisomic line compared to disomic or trisomic lines with wild-type GATA1, consistent with TMD characteristics. In conclusion, we have identified a cost-effective tunable 3D hydrogel system to model TMD.

Recapitulative haematopoietic development of human pluripotent stem cells in the absence of exogenous haematopoietic cytokines

To improve the recapitulative quality of human pluripotent stem cell (hPSC) differentiation, we removed exogenous haematopoietic cytokines from the defined differentiation system. Here, we show that endogenous stimuli and VEGF are sufficient to induce robust hPSC-derived haematopoiesis, intensive generation of haematopoietic progenitors, maturation of blood cells and the emergence of definitive precursor cells including those that phenotypically identical to early human embryonic haematopoietic stem cells (HSCs). Moreover, the cytokine-free system produces significantly higher numbers of haematopoietic progenitors compared to the published protocols. The removal of cytokines revealed a broad developmental potential of the early blood cells, stabilized the hPSC-derived definitive precursors and led to spontaneous activation of inflammatory signalling. Our cytokine-free protocol is simple, efficient, reproducible and applicable for embryonic stem cells (ESCs) and induced PSCs. The spectrum of recapitulative features of the novel protocol makes the cytokine-free differentiation a preferred model for studying the early human haematopoietic development.

MYB bi-allelic targeting abrogates primitive clonogenic progenitors while the emergence of primitive blood cells is not affected

MYB is a key regulator of definitive hematopoiesis and it is dispensable for the development of primitive hematopoietic cells in vertebrates. In order to delineate definitive versus primitive hematopoiesis during differentiation of human embryonic stem cells, we have introduced reporters into the MYB locus and inactivated the gene by bi-allelic targeting. In order to recapitulate the early developmental events more adequately, mutant and wild-type human embryonic stem cell lines were differentiated in defined culture conditions without the addition of hematopoietic cytokines. The differentiation of the reporter cell lines demonstrated that MYB is specifically expressed throughout emerging hematopoietic cell populations. Here we show that the disruption of the MYB gene leads to severe defects in the development and proliferation of primitive hematopoietic progenitors while the emergence of primitive blood cells is not affected. We also provide evidence that MYB is essential for neutrophil and T-cell development and the upregulation of innate immunity genes during hematopoietic differentiation. Our results suggest that the endothelial origin of primitive blood cells is direct and does not include the intermediate step of primitive hematopoietic progenitors.

The Opportunities and Challenges regarding Induced Platelets from Human Pluripotent Stem Cells

As a standard clinical treatment, platelet transfusion has been employed to prevent hemorrhage in patients with thrombocytopenia or platelet dysfunctions. Platelets also show therapeutic potential for aiding liver regeneration and bone healing and regeneration and for treating dermatological conditions. However, the supply of platelets rarely meets the rising clinical demand. Other issues, including short shelf life, strict storage temperature, and allogeneic immunity caused by frequent platelet transfusions, have become serious challenges that require the development of high-yielding alternative sources of platelets. Human pluripotent stem cells (hPSCs) are an unlimited substitution source for regenerative medicine, and patient-derived iPSCs can provide novel research models to explore the pathogenesis of some diseases. Many studies have focused on establishing and modifying protocols for generating functional induced platelets (iPlatelets) from hPSCs. To reach high efficiency production and eliminate the exogenous antigens, media supplements and matrix have been optimized. In addition, the introduction of some critical transgenes, such as c-MYC, BMI1, and BCL-XL, can also significantly increase hPSC-derived platelet production; however, this may pose some safety concerns. Furthermore, many novel culture systems have been developed to scale up the production of iPlatelets, including 2D flow systems, 3D rotary systems, and vertical reciprocal motion liquid culture bioreactors. The development of new gene-editing techniques, such as CRISPR/Cas9, can be used to solve allogeneic immunity of platelet transfusions by knocking out the expression of B2M. Additionally, the functions of iPlatelets were also evaluated from multiple aspects, including but not limited to morphology, structure, cytoskeletal organization, granule content, DNA content, and gene expression. Although the production and functions of iPlatelets are close to meeting clinical application requirements in both quantity and quality, there is still a long way to go for their large-scale production and clinical application. Here, we summarize the diverse methods of platelet production and update the progresses of iPlatelets. Furthermore, we highlight recent advances in our understanding of key transcription factors or molecules that determine the platelet differentiation direction.

Rapid and Reproducible Differentiation of Hematopoietic and T Cell Progenitors From Pluripotent Stem Cells

Cell therapy using T cells has revolutionized medical care in recent years but limitations are associated with the difficulty of genome editing of the cells, the production of a sufficient number of cells and standardization of the product. Human pluripotent stem cells (hPSCs) can self-renew and differentiate into T cells to provide a standardized homogenous product of defined origin in indefinite quantity, therefore they are of great potential to alleviate limitations of therapeutic T cell production. The differentiation of hPSCs takes place in two steps: first the induction of hematopoietic stem/progenitor cells (HSPCs), then the induction of lymphopoiesis by Notch signaling. However, the differentiation of T cells from hPSCs can be difficult and lack reproducibility. One parameter that needs to be better assessed is the potential of DLL1 vs. DLL4 ligands of the Notch pathway to induce T cells. In addition, culture of hPSCs is labor-intensive and not compatible with GMP production, especially when they are cultured on feeder cells. Thus, the definition of a robust GMP-compatible differentiation protocol from hPSCs cultured in feeder-free conditions would increase the accessibility to off-the-shelf hematopoietic and T cell progenitors derived from hPSCs. In this article, we describe an efficient, rapid and reproducible protocol for the generation of hematopoietic and T cell progenitors in two steps: (1) generation of HSPCs from embryoid bodies (EB) in serum free medium and GMP-compatible feeder-free systems, (2) directed differentiation of hPSC-derived HSPCs into T-cell progenitors in the presence of bone marrow stromal cells expressing Notch-ligands OP9-DLL1 vs. OP9-DLL4.

Characterization of intracellular buffering power in human induced pluripotent stem cells and the loss of pluripotency is delayed by acidic stimulation and increase of NHE1 activity

The homeostasis of intracellular pH (pH_i ) affects many cellular functions. Our previous study has established a functional and molecular model of the active pH_i regulators in human induced pluripotent stem cells (hiPSCs). The aims of the present study were to further quantify passive pH_i buffering power (β) and to investigate the effects of extracellular pH and Na⁺ -H⁺ exchanger 1 (NHE1) activity on pluripotency in hiPSCs. pH_i was detected by microspectrofluorimetry with pH-sensitive dye-BCECF. Western blot, immunofluorescence staining, and flow cytometry were used to detect protein expression and pluripotency. Our study in hiPSCs showed that (a) the value of total (β_tot ), intrinsic (β_i ), and CO₂ -dependent ( β C O 2 ) buffering power all increased while pH_i increased; (b) during the spontaneous differentiation for 4 days, the β values of β_tot and β C O 2 changed in a tendency of decrease, despite the absence of statistical significance; (c) an acidic cultured environment retained pluripotency and further upregulated expression and activity of NHE1 during spontaneous differentiation; (d) inhibition on NHE1 activity promoted the loss of pluripotency. In conclusion, we, for the first time, established a quantitative model of passive β during differentiation and demonstrated that maintenance of NHE1 at a higher level was of critical importance for pluripotency retention in hiPSCs.

TALEN-mediated biallelic inactivation of MYB in human embryonic stem cell lines WAe001-A-45 and WAe001-A-46

MYB/c-MYB is a proto-oncogene encoding a helix-turn-helix transcription factor that plays a critical role in controlling proliferation and multilineage differentiation of hematopoietic progenitor and stem cells. Deregulation of MYB expression is associated with several types of leukemias and lymphomas. In an attempt to explore the role of the gene in the early human hematopoiesis, we have achieved bi-allelic targeting of MYB in human embryonic stem cells (hESCs) by TALEN-mediated homologous recombination. Furthermore, the gene targeting introduced eYFP Venus reporter gene into the MYB locus to delineate the expression pattern of MYB. The resulting two cell lines, WAe001-A-45 and WAe001-A-46, passed the standard assays for human pluripotent stem cells. Hematopoietic differentiation of these cell lines provides a model to study the role of MYB in human hematopoietic development.

Generation of RUNX1-null reporter human embryonic stem cell line GIBHe008-A

RUNX1/AML1/CBFA2 (runt-related transcription factor 1/acute myeloid leukemia 1 protein/core-binding factor subunit alpha-2), is a transcription factor that plays a critical role in the development of normal hematopoiesis. RUNX1 is also essential for the development of immune cells and sensory neurons. Chromosomal translocations involving the gene have been associated with several types of leukemia. To investigate the role of RUNX1 in human hematopoietic development we generated RUNX1-null human embryonic stem cell reporter line GIBHe008-A by TALEN mediated homologous recombination. This cell line GIBHe008-A was subjected to detailed characterization by standard assays for human pluripotent stem cells. It provides an ideal model to study the role of RUNX1 in the hESC-derived developmental models.

Ex Vivo Models of Chronic Granulomatous Disease

Induced pluripotent stem cells (iPSCs) are pluripotent stem cells that can be established from dedifferentiation of all somatic cell types by epigenetic phenomena. iPSCs can be differentiated into any mature cells like neurons, hepatocytes, or pancreatic cells that have not been easily available to date. Thus, iPSCs are widely used for disease modeling, drug discovery, and cell therapy development. Here, we describe a protocol to obtain human mature and functional neutrophils and macrophages as ex vivo models of X-linked chronic granulomatous disease (X-CGD). This method can be applied to model the other genetic forms of CGD. We also describe methods for testing the characteristics and functions of neutrophils and macrophages by morphology, phagocytosis assay, release of granule markers or cytokines, cell surface markers, and NADPH oxidase activity.

Recent Updates on Induced Pluripotent Stem Cells in Hematological Disorders

Over the past decade, enormous progress has been made in the field of induced pluripotent stem cells (iPSCs). Patients' somatic cells such as skin fibroblasts or blood cells can be used to generate disease-specific pluripotent stem cells, which have unlimited proliferation and can differentiate into all cell types of the body. Human iPSCs offer great promises and opportunities for treatments of degenerative diseases and studying disease pathology and drug screening. So far, many iPSC-derived disease models have led to the discovery of novel pathological mechanisms as well as new drugs in the pipeline that have been tested in the iPSC-derived cells for efficacy and potential toxicities. Furthermore, recent advances in genome editing technology in combination with the iPSC technology have provided a versatile platform for studying stem cell biology and regenerative medicine. In this review, an overview of iPSCs, patient-specific iPSCs for disease modeling and drug screening, applications of iPSCs and genome editing technology in hematological disorders, remaining challenges, and future perspectives of iPSCs in hematological diseases will be discussed.

Differentiation of Human-Induced Pluripotent Stem Cells to Macrophages for Disease Modeling and Functional Genomics

Macrophages play important roles in many diseases. We describe a protocol and the associated resources for the differentiation of human induced pluripotent stem cell-derived macrophages (IPSDM) and their applications in understanding human macrophage physiology and relevant diseases. The protocol uses an embryoid body-based approach with a combination of serum-free condition for hematopoiesis specification, followed by adherent culture with serum and M-CSF for myeloid expansion and macrophage maturation. The protocol produced an almost pure culture of CD45⁺ /CD18⁺ macrophages yielding up to 2 × 10⁷ cells per 6-well plate of iPSCs within 24 days, demonstrating high efficiency, purity, and scalability. The IPSDM and monocyte-derived macrophages (HMDM) cultured in the same medium were compared at morphological, functional and transcriptomic levels by RNA-sequencing. IPSDM and HMDM showed broadly similar profiles of coding transcriptome, alternative splicing events, and long noncoding RNAs, with advantages and successful applications in disease modeling using patients-derived and CRISPR-edited iPSC lines. © 2018 by John Wiley & Sons, Inc.

Biphasic modulation of insulin signaling enables highly efficient hematopoietic differentiation from human pluripotent stem cells

Background

Hematopoietic lineage cells derived from human pluripotent stem cells (hPSCs) hold great promise for the treatment of hematological diseases and providing sufficient cells for immune therapy. However, a simple, cost-effective method to generate large quantities of hematopoietic stem/progenitor cells (HSPCs) is not yet available.

Methods

We established a monolayer, chemically defined culture system to induce hematopoietic differentiation from hPSCs in 8 days.

Results

We found that insulin-free medium allowed hPSCs to leave pluripotency promptly and preferably enter the vascular lineage. Addition of insulin during the later stage of differentiation was essential for the efficient induction of hemogenic endothelium and the emergence of large numbers of CD34⁺CD43⁺ HSPCs, while no insulin condition preferably permits endothelial differentiation. Global transcriptome profiling revealed that HSPCs differentiated using our protocol were similar to embryoid body-derived HSPCs. HSPCs obtained from our differentiation system formed robust erythroid, granulocyte and monocyte/macrophage colonies in CFU assay, and can be induced to generate functional macrophages with robust phagocytic ability.

Conclusion

Our results demonstrated that proper manipulation of insulin-mTOR signaling can greatly facilitate HSPC formation. This finding can be further exploited to formulate cost-effective differentiation medium to generate large quantities of cells of desired blood lineages for regenerative medicine.

Electronic supplementary material

The online version of this article (10.1186/s13287-018-0934-x) contains supplementary material, which is available to authorized users.

Commonly used thiol-containing antioxidants reduce cardiac differentiation and alter gene expression ratios of sarcomeric isoforms

Reactive oxygen species (ROS) scavengers such as beta-mercaptoethanol (BME) and monothiol glycerol (MTG) are extensively used in stem cell research to prevent cellular oxidative stress. However, how these antioxidant supplements impact stem cell cardiac differentiation, a process regulated by redox-signaling remains unknown. In this study, we found that removal of BME from the conventional high-glucose, serum-based differentiation medium improved cardiac differentiation efficiency by 2-3 fold. BME and MTG treatments during differentiation significantly reduced mRNA expression of cardiac progenitor markers (NKX2.5 and ISL1) as well as sarcomeric markers (MLC2A, MLC2V, TNNI3, MYH6 and MYH7), suggesting reduced cardiomyogenesis by BME or MTG. Moreover, BME and MTG altered the expression ratios between the sarcomeric isoforms. In particular, TNNI3 to TNNI1 ratio and MLC2V to MLC2A ratio were significantly lower in BME or MTG treated cells than untreated cells, implying altered cardiomyocyte phenotype and maturity. Lastly, BME and MTG treatments resulted in less frequent beating, slower contraction and relaxation velocities than untreated cells. Interestingly, none of the above-mentioned effects was observed with Trolox, a non-thiol based antioxidant, despite its strong antioxidant activity. This work demonstrates that commonly used antioxidant supplements may cause considerable changes to cellular redox state and the outcome of differentiation.

Efficient production of erythroid, megakaryocytic and myeloid cells, using single cell-derived iPSC colony differentiation

Hematopoietic differentiation of human induced pluripotent stem cells (iPSCs) provide opportunities not only for fundamental research and disease modelling/drug testing but also for large-scale production of blood effector cells for future clinical application. Although there are multiple ways to differentiate human iPSCs towards hematopoietic lineages, there is a need to develop reproducible and robust protocols. Here we introduce an efficient way to produce three major blood cell types using a standardized differentiation protocol that starts with a single hematopoietic initiation step. This system is feeder-free, avoids EB-formation, starts with a hematopoietic initiation step based on a novel single cell-derived iPSC colony differentiation and produces multi-potential progenitors within 8-10 days. Followed by lineage-specific growth factor supplementation these cells can be matured into well characterized erythroid, megakaryocytic and myeloid cells with high-purity, without transcription factor overexpression or any kind of pre-purification step. This standardized differentiation system provides a simple platform to produce specific blood cells in a reproducible manner for hematopoietic development studies, disease modelling, drug testing and the potential for future therapeutic applications.

Defined Serum-Free Medium for Bioreactor Culture of an Immortalized Human Erythroblast Cell Line

Anticipated shortages in donated blood supply have prompted investigation of alternative approaches for in vitro production of red blood cells (RBCs), such as expansion of conditional immortalization erythroid progenitors. However, there is a bioprocessing challenge wherein factors promoting maximal cell expansion and growth-limiting inhibitory factors are yet to be investigated. The authors use an erythroblast cell line (ImEry) derived from immortalizing CD71+CD235a+ erythroblast from adult peripheral blood for optimization of expansion culture conditions. Design of experiments (DOE) is used in media formulation to explore relationships and interactive effects between factors which affect cell expansion. Our in-house optimized medium formulation produced significantly higher cell densities (3.62 ± 0.055) × 10⁶  cells mL^-1 , n = 3) compared to commercial formulations (2.07 ± 0.055) × 10⁶  cells mL^-1 , n = 3; at 209 h culture). Culture media costs per unit of blood is shown to have a 2.96-3.09 times cost reduction. As a proof of principle for scale up, ImEry are expanded in a half-liter stirred-bioreactor under controlled settings. Growth characteristics, metabolic, and molecular profile of the cells are evaluated. ImEry has identical O₂ binding capacity to adult erythroblasts. Amino acid supplementation results in further yield improvements. The study serves as a first step for scaling up erythroblast expansion in controlled bioreactors.

Functional characterization of human pluripotent stem cell-derived arterial endothelial cells

Here, we report the derivation of arterial endothelial cells from human pluripotent stem cells that exhibit arterial-specific functions in vitro and in vivo. We combine single-cell RNA sequencing of embryonic mouse endothelial cells with an EFNB2-tdTomato/EPHB4-EGFP dual reporter human embryonic stem cell line to identify factors that regulate arterial endothelial cell specification. The resulting xeno-free protocol produces cells with gene expression profiles, oxygen consumption rates, nitric oxide production levels, shear stress responses, and TNFα-induced leukocyte adhesion rates characteristic of arterial endothelial cells. Arterial endothelial cells were robustly generated from multiple human embryonic and induced pluripotent stem cell lines and have potential applications for both disease modeling and regenerative medicine.

Generation of hematopoietic stem cells from human embryonic stem cells using a defined, stepwise, serum-free, and serum replacement-free monolayer culture method

Background

Embryonic stem cells (ESCs) can be expanded infinitely in vitro and have the potential to differentiate into hematopoietic stem cells (HSCs); thus, they are considered a useful source of cells for HSC production. Although several technical in vitro methods for engineering HSCs from pluripotent stem cells have been developed, clinical application of HSCs engineered from pluripotent stem cells is restricted because of the possibility of xenogeneic contamination resulting from the use of murine materials.

Methods

Human ESCs (CHA-hES15) were cultured on growth factor-reduced Matrigel-coated dishes in the mTeSR1 serum-free medium. When the cells were 70% confluent, we initiated HSC differentiation by three methods involving (1) knockout serum replacement (KSR), cytokines, TGFb1, EPO, and FLT3L; (2) KSR, cytokines, and bFGF; or (3) cytokines and bFGF.

Results

Among the three differentiation methods, the minimal number of cytokines without KSR resulted in the greatest production of HSCs. The optimized method resulted in a higher proportion of CD34⁺CD43⁺ hematopoietic progenitor cells (HPCs) and CD34⁺CD45⁺ HPCs compared to the other methods. In addition, the HSCs showed the potential to differentiate into multiple lineages of hematopoietic cells in vitro.

Conclusion

In this study, we optimized a two-step, serum-free, animal protein-free, KSR-free, feeder-free, chemically defined monolayer culture method for generation of HSCs and hematopoietic stem and progenitor cells (HSPCs) from human ESCs.

Pyrimidoindole derivative UM171 enhances derivation of hematopoietic progenitor cells from human pluripotent stem cells

In the field of hematopoietic regeneration, deriving hematopoietic stem cells (HSCs) from pluripotent stem cells with engraftment potential is the central mission. Unstable hematopoietic differentiation protocol due to variation factors such as serums and feeder cells, remains a major technical issue impeding the screening of key factors for the derivation of HSCs. In combination with hematopoietic cytokines, UM171 has the capacity to facilitate the maintenance and expansion of human primary HSCs in vitro. Here, using a serum-free, feeder-free, and chemically defined induction protocol, we observed that UM171 enhanced hematopoietic derivation through the entire process of hematopoietic induction in vitro. UM171 facilitated generation of robust CD34⁺CD45⁺ derivatives that formed more and larger sized CFU-GM as well as larger sized CFU-Mix. In our protocol, the derived hematopoietic progenitors failed to engraft in NOG mice, indicating the absence of long-term HSC from these progenitors. In combination with other factors and protocols, UM171 might be broadly used for hematopoietic derivation from human pluripotent stem cells in vitro.

Distinct gene expression program dynamics during erythropoiesis from human induced pluripotent stem cells compared with adult and cord blood progenitors

BACKGROUND

Human-induced pluripotent stem cells (hiPSCs) are a potentially invaluable resource for regenerative medicine, including the in vitro manufacture of blood products. HiPSC-derived red blood cells are an attractive therapeutic option in hematology, yet exhibit unexplained proliferation and enucleation defects that presently preclude such applications. We hypothesised that substantial differential regulation of gene expression during erythroid development accounts for these important differences between hiPSC-derived cells and those from adult or cord-blood progenitors. We thus cultured erythroblasts from each source for transcriptomic analysis to investigate differential gene expression underlying these functional defects.

RESULTS

Our high resolution transcriptional view of definitive erythropoiesis captures the regulation of genes relevant to cell-cycle control and confers statistical power to deploy novel bioinformatics methods. Whilst the dynamics of erythroid program elaboration from adult and cord blood progenitors were very similar, the emerging erythroid transcriptome in hiPSCs revealed radically different program elaboration compared to adult and cord blood cells. We explored the function of differentially expressed genes in hiPSC-specific clusters defined by our novel tunable clustering algorithms (SMART and Bi-CoPaM). HiPSCs show reduced expression of c-KIT and key erythroid transcription factors SOX6, MYB and BCL11A, strong HBZ-induction, and aberrant expression of genes involved in protein degradation, lysosomal clearance and cell-cycle regulation.

CONCLUSIONS

Together, these data suggest that hiPSC-derived cells may be specified to a primitive erythroid fate, and implies that definitive specification may more accurately reflect adult development. We have therefore identified, for the first time, distinct gene expression dynamics during erythroblast differentiation from hiPSCs which may cause reduced proliferation and enucleation of hiPSC-derived erythroid cells. The data suggest several mechanistic defects which may partially explain the observed aberrant erythroid differentiation from hiPSCs.

A portable platform for stepwise hematopoiesis from human pluripotent stem cells within PET-reinforced collagen sponges

Various systems for differentiating hematopoietic cells from human pluripotent stem cells (PSCs) have been developed, although none have been fully optimized. In this report, we describe the development of a novel three-dimensional system for differentiating hematopoietic cells from PSCs using collagen sponges (CSs) reinforced with poly(ethylene terephthalate) fibers as a scaffold. PSCs seeded onto CSs were differentiated in a stepwise manner with appropriate cytokines under serum-free and feeder-free conditions. This process yielded several lineages of floating hematopoietic cells repeatedly for more than 1 month. On immunohistochemical staining, we detected CD34+ cells and CD45+ cells in the surface and cavities of the CS. Taking advantage of the portability of this system, we were able to culture multiple CSs together floating in medium, making it possible to harvest large numbers of hematopoietic cells repeatedly. Given these findings, we suggest that this novel three-dimensional culture system may be useful in the large-scale culture of PSC-derived hematopoietic cells.

Superior Red Blood Cell Generation from Human Pluripotent Stem Cells Through a Novel Microcarrier-Based Embryoid Body Platform

In vitro generation of red blood cells (RBCs) from human embryonic stem cells and human induced pluripotent stem cells appears to be a promising alternate approach to circumvent shortages in donor-derived blood supplies for clinical applications. Conventional methods for hematopoietic differentiation of human pluripotent stem cells (hPSC) rely on embryoid body (EB) formation and/or coculture with xenogeneic cell lines. However, most current methods for hPSC expansion and EB formation are not amenable for scale-up to levels required for large-scale RBC generation. Moreover, differentiation methods that rely on xenogenic cell lines would face obstacles for future clinical translation. In this study, we report the development of a serum-free and chemically defined microcarrier-based suspension culture platform for scalable hPSC expansion and EB formation. Improved survival and better quality EBs generated with the microcarrier-based method resulted in significantly improved mesoderm induction and, when combined with hematopoietic differentiation, resulted in at least a 6-fold improvement in hematopoietic precursor expansion, potentially culminating in a 80-fold improvement in the yield of RBC generation compared to a conventional EB-based differentiation method. In addition, we report efficient terminal maturation and generation of mature enucleated RBCs using a coculture system that comprised primary human mesenchymal stromal cells. The microcarrier-based platform could prove to be an appealing strategy for future scale-up of hPSC culture, EB generation, and large-scale generation of RBCs under defined and xeno-free conditions.

High-Efficiency Serum-Free Feeder-Free Erythroid Differentiation of Human Pluripotent Stem Cells Using Small Molecules

This article describes a highly efficient, fully feeder-free, serum-free method for erythroid differentiation of induced pluripotent stem cells and human embryonic stem cells, including a clinical-grade line, that is amenable to scale-up and as such will be of significant value for basic and translational studies of hematopoiesis and erythropoiesis.

This article describes a good manufacturing practice (GMP)-compatible, feeder-free and serum-free method to produce large numbers of erythroid cells from human pluripotent stem cells (hPSCs), either embryonic or induced. This multistep protocol combines cytokines and small molecules to mimic and surpass the early stages of development. It produces, without any selection or sorting step, a population of cells in which 91.8% ± 5.4% express CD34 at day 7, 98.6% ± 1.3% express CD43 at day 10, and 99.1% ± 0.95% of cells are CD235a positive by day 31 of the differentiation process. Moreover, this differentiation protocol supports extensive expansion, with a single hPSC producing up to 150 hematopoietic progenitor cells by day 10 and 50,000–200,000 erythroid cells by day 31. The erythroid cells produced exhibit a definitive fetal hematopoietic type, with 90%–95% fetal globin and variable proportion of embryonic and adult globin at the protein level. The presence of small molecules during the differentiation protocol has quantitative and qualitative effects; it increases the proportion of adult globin and decreases the proportion of embryonic globin. Given its level of definition, this system provides a powerful tool for investigation of the mechanisms governing early hematopoiesis and erythropoiesis, including globin switching and enucleation. The early stages of the differentiation protocol could also serve as a starting point for the production of endothelial cells and other hematopoietic cells, or to investigate the production of long-term reconstituting hematopoietic stem cells from hPSCs.

Significance

This differentiation protocol allows the production of a large amount of erythroid cells from pluripotent stem cells. Its efficiency is compatible with that of in vitro red blood cell production, and it can be a considerable asset for studying developmental erythropoiesis and red blood cell enucleation, thereby aiding both basic and translational research. In addition to red cells, the early stages of the protocol could also be used as a starting point for the large-scale production of other hematopoietic cell types, including the ultimate goal of generating long-term reconstituting hematopoietic stem cells.

Generation and characterization of integration-free induced pluripotent stem cells from patients with autoimmune disease

Autoimmune diseases (AIDs), a heterogeneous group of immune-mediated disorders, are a major and growing health problem. Although AIDs are currently treated primarily with anti-inflammatory and immunosuppressive drugs, the use of stem cell transplantation in patients with AIDs is becoming increasingly common. However, stem cell transplantation therapy has limitations, including a shortage of available stem cells and immune rejection of cells from nonautologous sources. Induced pluripotent stem cell (iPSC) technology, which allows the generation of patient-specific pluripotent stem cells, could offer an alternative source for clinical applications of stem cell therapies in AID patients. We used nonintegrating oriP/EBNA-1-based episomal vectors to reprogram dermal fibroblasts from patients with AIDs such as ankylosing spondylitis (AS), Sjögren's syndrome (SS) and systemic lupus erythematosus (SLE). The pluripotency and multilineage differentiation capacity of each patient-specific iPSC line was validated. The safety of these iPSCs for use in stem cell transplantation is indicated by the fact that all AID-specific iPSCs are integrated transgene free. Finally, all AID-specific iPSCs derived in this study could be differentiated into cells of hematopoietic and mesenchymal lineages in vitro as shown by flow cytometric analysis and induction of terminal differentiation potential. Our results demonstrate the successful generation of integration-free iPSCs from patients with AS, SS and SLE. These findings support the possibility of using iPSC technology in autologous and allogeneic cell replacement therapy for various AIDs, including AS, SS and SLE.

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.

Engineering pulmonary vasculature in decellularized rat and human lungs

Bioengineered lungs produced from patient-derived cells may one day provide an alternative to donor lungs for transplantation therapy. Here we report the regeneration of functional pulmonary vasculature by repopulating the vascular compartment of decellularized rat and human lung scaffolds with human cells, including endothelial and perivascular cells derived from induced pluripotent stem cells. We describe improved methods for delivering cells into the lung scaffold and for maturing newly formed endothelium through co-seeding of endothelial and perivascular cells and a two-phase culture protocol. Using these methods we achieved ∼75% endothelial coverage in the rat lung scaffold relative to that of native lung. The regenerated endothelium showed reduced vascular resistance and improved barrier function over the course of in vitro culture and remained patent for 3 days after orthotopic transplantation in rats. Finally, we scaled our approach to the human lung lobe and achieved efficient cell delivery, maintenance of cell viability and establishment of perfusable vascular lumens.

In Vitro T-Cell Generation From Adult, Embryonic, and Induced Pluripotent Stem Cells: Many Roads to One Destination

T lymphocytes are critical mediators of the adaptive immune system and have the capacity to serve as therapeutic agents in the areas of transplant and cancer immunotherapy. While T cells can be isolated and expanded from patients, T cells derived in vitro from both hematopoietic stem/progenitor cells (HSPCs) and human pluripotent stem cells (hPSCs) offer great potential advantages in generating a self-renewing source of T cells that can be readily genetically modified. T-cell differentiation in vivo is a complex process requiring tightly regulated signals; providing the correct signals in vitro to induce T-cell lineage commitment followed by their development into mature, functional, single positive T cells, is similarly complex. In this review, we discuss current methods for the in vitro derivation of T cells from murine and human HSPCs and hPSCs that use feeder-cell and feeder-cell-free systems. Furthermore, we explore their potential for adoption for use in T-cell-based therapies.

The Use of Patient-Specific Induced Pluripotent Stem Cells (iPSCs) to Identify Osteoclast Defects in Rare Genetic Bone Disorders

More than 500 rare genetic bone disorders have been described, but for many of them only limited treatment options are available. Challenges for studying these bone diseases come from a lack of suitable animal models and unavailability of skeletal tissues for studies. Effectors for skeletal abnormalities of bone disorders may be abnormal bone formation directed by osteoblasts or anomalous bone resorption by osteoclasts, or both. Patient-specific induced pluripotent stem cells (iPSCs) can be generated from somatic cells of various tissue sources and in theory can be differentiated into any desired cell type. However, successful differentiation of hiPSCs into functional bone cells is still a challenge. Our group focuses on the use of human iPSCs (hiPSCs) to identify osteoclast defects in craniometaphyseal dysplasia. In this review, we describe the impact of stem cell technology on research for better treatment of such disorders, the generation of hiPSCs from patients with rare genetic bone disorders and current protocols for differentiating hiPSCs into osteoclasts.

Thymopentin enhances the generation of T-cell lineage derived from human embryonic stem cells in vitro

Thymopentin is a group of biologically active peptide secreted mainly by the epithelial cells of thymic cortex and medulla. Whether it promotes T cells production from human embryonic stem cells(hESCs) in vitro remains an elusive issue. In the present study, we develop a novel strategy that enhances T-cell lineage differentiation of hESCs in collagen matrix culture by sequential cytokine cocktails treatment combined with thymopentin stimulation. We observed that approximately 30.75% cells expressed CD34 on day 14 of the cultures and expressed the surface markers of erythroid, lymphoid and myeloid lineages. The results of colony assays and gene expressions by RT-PCR analysis also demonstrated that hematopoietic progenitor cells (HPCs) derived from hESCs were capable of multi-lineage differentiation. Further study revealed that culturing with thymopentin treatment, the CD34(+)CD45RA(+)CD7(+) cells sorted from HPCs expressed T-cell-related genes, IKAROS, DNTT, TCRγ and TCRβ, and T-cell surface markers, CD3, cytoplasmic CD3, CD5, CD27, TCRγδ, CD4 and CD8. The differentiated cells produced the cytokines including IFN-γ, IL-2 and TNF-α in response to stimulation, providing the evidence for T-cell function of these cells. In conclusion, thymopentin enhances T-cell lineage differentiation from hESCs in vitro by mimicking thymus peptide environment in vivo.

Tenascin C promotes hematoendothelial development and T lymphoid commitment from human pluripotent stem cells in chemically defined conditions

The recent identification of hemogenic endothelium (HE) in human pluripotent stem cell (hPSC) cultures presents opportunities to investigate signaling pathways that are essential for blood development from endothelium and provides an exploratory platform for de novo generation of hematopoietic stem cells (HSCs). However, the use of poorly defined human or animal components limits the utility of the current differentiation systems for studying specific growth factors required for HE induction and manufacturing clinical-grade therapeutic blood cells. Here, we identified chemically defined conditions required to produce HE from hPSCs growing in Essential 8 (E8) medium and showed that Tenascin C (TenC), an extracellular matrix protein associated with HSC niches, strongly promotes HE and definitive hematopoiesis in this system. hPSCs differentiated in chemically defined conditions undergo stages of development similar to those previously described in hPSCs cocultured on OP9 feeders, including the formation of VE-Cadherin⁺CD73⁻CD235a/CD43⁻ HE and hematopoietic progenitors with myeloid and T lymphoid potential.

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Hemogenic endothelium is generated in a completely defined xenogen-free system

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The system reproduces all stages of hematopoietic development

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Tenascin C enhances hematoendothelial development from pluripotent stem cells

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Tenesacin C uniquely supports T cell specification

Scalable generation of universal platelets from human induced pluripotent stem cells

Human induced pluripotent stem cells (iPSCs) provide a potentially replenishable source for the production of transfusable platelets. Here, we describe a method to generate megakaryocytes (MKs) and functional platelets from iPSCs in a scalable manner under serum/feeder-free conditions. The method also permits the cryopreservation of MK progenitors, enabling a rapid “surge” capacity when large numbers of platelets are needed. Ultrastructural/morphological analyses show no major differences between iPSC platelets and human blood platelets. iPSC platelets form aggregates, lamellipodia, and filopodia after activation and circulate in macrophage-depleted animals and incorporate into developing mouse thrombi in a manner identical to human platelets. By knocking out the β2-microglobulin gene, we have generated platelets that are negative for the major histocompatibility antigens. The scalable generation of HLA-ABC-negative platelets from a renewable cell source represents an important step toward generating universal platelets for transfusion as well as a potential strategy for the management of platelet refractoriness.

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Large-scale production of platelets from human iPSCs under defined conditions

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iPSC platelets are functional both in vivo and in vitro

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Knockout of β2-microglobulin gene in iPSCs generates universal platelets

Continuous hypoxic culturing of human embryonic stem cells enhances SSEA-3 and MYC levels

Low oxygen tension (hypoxia) contributes critically to pluripotency of human embryonic stem cells (hESCs) by preventing spontaneous differentiation and supporting self-renewal. However, it is not well understood how hESCs respond to reduced oxygen availability and what are the molecular mechanisms maintaining pluripotency in these conditions. In this study we characterized the transcriptional and molecular responses of three hESC lines (H9, HS401 and HS360) on short (2 hours), intermediate (24 hours) and prolonged (7 days) exposure to low oxygen conditions (4% O₂). In response to prolonged hypoxia the expression of pluripotency surface marker SSEA-3 was increased. Furthermore, the genome wide gene-expression analysis revealed that a substantial proportion (12%) of all hypoxia-regulated genes in hESCs, were directly linked to the mechanisms controlling pluripotency or differentiation. Moreover, transcription of MYC oncogene was induced in response to continuous hypoxia. At the protein level MYC was stabilized through phosphorylation already in response to a short hypoxic exposure. Total MYC protein levels remained elevated throughout all the time points studied. Further, MYC protein expression in hypoxia was affected by silencing HIF2α, but not HIF1α. Since MYC has a crucial role in regulating pluripotency we propose that induction of sustained MYC expression in hypoxia contributes to activation of transcriptional programs critical for hESC self-renewal and maintenance of enhanced pluripotent state.

Hematopoietic specification from human pluripotent stem cells: current advances and challenges toward de novo generation of hematopoietic stem cells

Significant advances in cellular reprogramming technologies and hematopoietic differentiation from human pluripotent stem cells (hPSCs) have already enabled the routine production of multiple lineages of blood cells in vitro and opened novel opportunities to study hematopoietic development, model genetic blood diseases, and manufacture immunologically matched cells for transfusion and cancer immunotherapy. However, the generation of hematopoietic cells with robust and sustained multilineage engraftment has not been achieved. Here, we highlight the recent advances in understanding the molecular and cellular pathways leading to blood development from hPSCs and discuss potential approaches that can be taken to facilitate the development of technologies for de novo production of hematopoietic stem cells.

Hematopoietic cell differentiation from embryonic and induced pluripotent stem cells

Pluripotent stem cells, both embryonic stem cells and induced pluripotent stem cells, are undifferentiated cells that can self-renew and potentially differentiate into all hematopoietic lineages, such as hematopoietic stem cells (HSCs), hematopoietic progenitor cells and mature hematopoietic cells in the presence of a suitable culture system. Establishment of pluripotent stem cells provides a comprehensive model to study early hematopoietic development and has emerged as a powerful research tool to explore regenerative medicine. Nowadays, HSC transplantation and hematopoietic cell transfusion have successfully cured some patients, especially in malignant hematological diseases. Owing to a shortage of donors and a limited number of the cells, hematopoietic cell induction from pluripotent stem cells has been regarded as an alternative source of HSCs and mature hematopoietic cells for intended therapeutic purposes. Pluripotent stem cells are therefore extensively utilized to facilitate better understanding in hematopoietic development by recapitulating embryonic development in vivo, in which efficient strategies can be easily designed and deployed for the generation of hematopoietic lineages in vitro. We hereby review the current progress of hematopoietic cell induction from embryonic stem/induced pluripotent stem cells.

The human immunodeficiency virus, (HIV-1), pandemic: cellular therapies, stem cells and biobanking

The Human Immunodeficiency Virus, (HIV-1), has become a major global health threat with recent estimates suggesting that 68% of people living with HIV (PLWH) reside in Sub-Saharan Africa. The current strategies for containment of this disease in the absence of an effective vaccine are of concern in terms of long-term fiscal sustainability and cost effectiveness. HIV prevalence rates are set to rise, not because of increasing incidence but rather because of the effort involved in implementing the anti-retroviral (ARV) programmes, especially on the African continent. Even when sub-optimally delivered, these therapies will lead to a decrease in mortality rates and prevent early death from opportunistic infections. However, evidence is emerging for long-term systemic effects of chronic HIV infection in persons on ARV therapy, including increased incidence of Haematological abnormalities and malignancies.

Foundational concepts of cell fate conversion to the hematopoietic lineage

Direct conversion of cellular fate provides a potential approach to generate cells of the hematopoietic lineage without the requisite reversion to a pluripotent state via somatic cell reprogramming. The utilization of this technology has enabled transcription factor-mediated conversion of somatic cell types to primitive and mature hematopoietic cells. Recent studies demonstrate that the direct conversion of somatic cells to the hematopoietic lineage likely requires the use of pioneer transcription factors to establish an accessible chromatin state that is responsive to enforced expression of hematopoietic-specific transcription factors, in combination with appropriate culture conditions that facilitate reprogramming. Developing adaptable, experimental strategies that incorporate these parameters should enable the efficient generation of human hematopoietic cells with translational potential.

The role of induced pluripotent stem cells in research and therapy of primary immunodeficiencies

The advent of reprogramming technology has greatly advanced the field of stem cell biology and nurtured our hope to create patient specific renewable stem cell sources. While the number of reports of disease specific induced pluripotent stem cells is continuously rising, the field becomes increasingly more aware that induced pluripotent stem cells are not as similar to embryonic stem cells as initially assumed. Our state of the art understanding of human induced pluripotent stem cells, their capacity, their limitations and their promise as it pertains to the study and treatment of primary immunodeficiencies, is the content of this review.

Mechanism of action of HOXB4 on the hematopoietic differentiation of embryonic stem cells

Pluripotent stem cells can be differentiated into hematopoietic lineages in vitro and hold promise for the future treatment of hematological disease. Differentiation strategies involving defined factors in serum-free conditions have been successful in producing hematopoietic progenitors and some mature cell types from mouse and human embryonic stem cells and induced pluripotent cells. However, these precisely defined protocols are relatively inefficient and have not been used successfully to produce hematopoietic stem cells capable of multilineage long-term reconstitution of the hematopoietic system. More complex differentiation induction strategies including coculture with stromal cells derived from sites of hematopoietic activity in vivo and enforced expression of reprogramming transcription factors, such as HOXB4, have been required to increase the efficiency of the differentiation procedure and to produce these most potent hematopoietic stem cells. We review the studies that have used HOXB4 to improve hematopoietic differentiation from pluripotent cells focusing on studies that have provided some insight into its mechanism of action. A better understanding of the molecular pathways involved in the action of HOXB4 might lead to more defined culture systems and safer protocols for clinical translation.