Wiskott-Aldrich syndrome iPS cells produce megakaryocytes with defects in cytoskeletal rearrangement and proplatelet formation

Understanding immunoactinopathies: A decade of research on WAS gene defects

Immunoactinopathies caused by mutations in actin-related proteins are a growing group of inborn errors of immunity (IEI). Immunoactinopathies are caused by a dysregulated actin cytoskeleton and affect hematopoietic cells especially because of their unique capacity to survey the body for invading pathogens and altered self, such as cancer cells. These cell motility and cell-to-cell interaction properties depend on the dynamic nature of the actin cytoskeleton. Wiskott-Aldrich syndrome (WAS) is the archetypical immunoactinopathy and the first described. WAS is caused by loss-of-function and gain-of-function mutations in the actin regulator WASp, uniquely expressed in hematopoietic cells. Mutations in WAS cause a profound disturbance of actin cytoskeleton regulation of hematopoietic cells. Studies during the last 10 years have shed light on the specific effects on different hematopoietic cells, revealing that they are not affected equally by mutations in the WAS gene. Moreover, the mechanistic understanding of how WASp controls nuclear and cytoplasmatic activities may help to find therapeutic alternatives according to the site of the mutation and clinical phenotypes. In this review, we summarize recent findings that have added to the complexity and increased our understanding of WAS-related diseases and immunoactinopathies.

In vitro systems to study inborn errors of immunity using human induced pluripotent stem cells

In the last two decades, the exponential progress in the field of genetics could reveal the genetic impact on the onset and progression of several diseases affecting the immune system. This knowledge has led to the discovery of more than 400 monogenic germline mutations, also known as “inborn errors of immunity (IEI)”. Given the rarity of various IEI and the clinical diversity as well as the limited available patients’ material, the continuous development of novel cell-based in vitro models to elucidate the cellular and molecular mechanisms involved in the pathogenesis of these diseases is imperative. Focusing on stem cell technologies, this review aims to provide an overview of the current available in vitro models used to study IEI and which could lay the foundation for new therapeutic approaches. We elaborate in particular on the use of induced pluripotent stem cell-based systems and their broad application in studying IEI by establishing also novel infection culture models. The review will critically discuss the current limitations or gaps in the field of stem cell technology as well as the future perspectives from the use of these cell culture systems.

Atopic Dermatitis-like Genodermatosis: Disease Diagnosis and Management

Eczema is a classical characteristic not only in atopic dermatitis but also in various genodermatosis. Patients suffering from primary immunodeficiency diseases such as hyper-immunoglobulin E syndromes, Wiskott-Aldrich syndrome, immune dysregulation, polyendocrinopathy, enteropathy, X-linked syndrome, STAT5B deficiency, Omenn syndrome, atypical complete DiGeorge syndrome; metabolic disorders such as acrodermatitis enteropathy, multiple carboxylase deficiency, prolidase deficiency; and other rare syndromes like severe dermatitis, multiple allergies and metabolic wasting syndrome, Netherton syndrome, and peeling skin syndrome frequently perform with eczema-like lesions. These genodermatosis may be misguided in the context of eczematous phenotype. Misdiagnosis of severe disorders unavoidably affects appropriate treatment and leads to irreversible outcomes for patients, which underlines the importance of molecular diagnosis and genetic analysis. Here we conclude clinical manifestations, molecular mechanism, diagnosis and management of several eczema-related genodermatosis and provide accessible advice to physicians.

Wiskott-Aldrich syndrome protein forms nuclear condensates and regulates alternative splicing

The diverse functions of WASP, the deficiency of which causes Wiskott-Aldrich syndrome (WAS), remain poorly defined. We generated three isogenic WAS models using patient induced pluripotent stem cells and genome editing. These models recapitulated WAS phenotypes and revealed that WASP deficiency causes an upregulation of numerous RNA splicing factors and widespread altered splicing. Loss of WASP binding to splicing factor gene promoters frequently leads to aberrant epigenetic activation. WASP interacts with dozens of nuclear speckle constituents and constrains SRSF2 mobility. Using an optogenetic system, we showed that WASP forms phase-separated condensates that encompasses SRSF2, nascent RNA and active Pol II. The role of WASP in gene body condensates is corroborated by ChIPseq and RIPseq. Together our data reveal that WASP is a nexus regulator of RNA splicing that controls the transcription of splicing factors epigenetically and the dynamics of the splicing machinery through liquid-liquid phase separation.

Hematopoietic Cells from Pluripotent Stem Cells: Hope and Promise for the Treatment of Inherited Blood Disorders

Inherited blood disorders comprise a large spectrum of diseases due to germline mutations in genes with key function in the hematopoietic system; they include immunodeficiencies, anemia or metabolic diseases. For most of them the only curative treatment is bone marrow transplantation, a procedure associated to severe complications; other therapies include red blood cell and platelet transfusions, which are dependent on donor availability. An alternative option is gene therapy, in which the wild-type form of the mutated gene is delivered into autologous hematopoietic stem cells using viral vectors. A more recent therapeutic perspective is gene correction through CRISPR/Cas9-mediated gene editing, that overcomes safety concerns due to insertional mutagenesis and allows correction of base substitutions in large size genes difficult to incorporate into vectors. However, applying this technique to genomic disorders caused by large gene deletions is challenging. Chromosomal transplantation has been proposed as a solution, using a universal source of wild-type chromosomes as donor, and induced pluripotent stem cells (iPSCs) as acceptor. One of the obstacles to be addressed for translating PSC research into clinical practice is the still unsatisfactory differentiation into transplantable hematopoietic stem or mature cells. We provide an overview of the recent progresses in this field and discuss challenges and potential of iPSC-based therapies for the treatment of inherited blood disorders.

Induced Pluripotent Stem Cells as a Tool for Modeling Hematologic Disorders and as a Potential Source for Cell-Based Therapies

The breakthrough in human induced pluripotent stem cells (hiPSCs) has revolutionized the field of biomedical and pharmaceutical research and opened up vast opportunities for drug discovery and regenerative medicine, especially when combined with gene-editing technology. Numerous healthy and patient-derived hiPSCs for human disease modeling have been established, enabling mechanistic studies of pathogenesis, platforms for preclinical drug screening, and the development of novel therapeutic targets/approaches. Additionally, hiPSCs hold great promise for cell-based therapy, serving as an attractive cell source for generating stem/progenitor cells or functional differentiated cells for degenerative diseases, due to their unlimited proliferative capacity, pluripotency, and ethical acceptability. In this review, we provide an overview of hiPSCs and their utility in the study of hematologic disorders through hematopoietic differentiation. We highlight recent hereditary and acquired genetic hematologic disease modeling with patient-specific iPSCs, and discuss their applications as instrumental drug screening tools. The clinical applications of hiPSCs in cell-based therapy, including the next-generation cancer immunotherapy, are provided. Lastly, we discuss the current challenges that need to be addressed to fulfill the validity of hiPSC-based disease modeling and future perspectives of hiPSCs in the field of hematology.

Mutated JAK2 signal transduction in human Induced Pluripotent Stem Cell (iPSC)-derived Megakaryocytes

Janus kinase 2 (JAK2) gene mutations are the main drivers for polycythemia vera (PV) and essential thrombocythemia (ET). The mechanisms of single altered gene causing two different diseases are unclear. Additionally, novel treatments specifically targeting mutated JAK2 proteins are needed. In this study, the induced pluripotent stem cells (iPSCs) were virally transduced to express wild-type JAK2 (JAK2WT), JAK2p.V617F (JAK2V617F) or JAK2p.N542_E543del (JAK2exon12) under a doxycycline-inducible system. The modified iPSCs which were differentiated into megakaryocytes in the presence vs. absence of doxycycline were compared to ensure that the differences were solely from mutated JAK2 expressions. The JAK2V617-expressing iPSCs yielded significantly higher numbers of megakaryocytes consistent with the ET phenotype, while there was no enhancement by JAK2exon12 expression compatible with the pure erythrocytosis in humans. Capillary Western analyses revealed significantly greater JAK2 phosphorylation in iPSCs carrying JAK2V617F but not in JAK2WT and JAK2exon12 iPSCs. Activation of STAT3, STAT5 and AKT was increased by JAK2V617F, while they were decreased in JAK2exon12 iPSCs. Notably, interferon alpha and/or arsenic trioxide inhibited megakaryocytes proliferation and reduced JAK2, STAT3, STAT5 and AKT phosphorylation in mutant JAK2-expressing iPSCs compared with those without induction. In conclusion, JAK2V617F expression in iPSCs preferentially promoted megakaryocytes with a signaling profile distinctive from JAK2exon12 expression. Treatments with interferon alpha or arsenic trioxide preferentially suppressed the mutated over wild-type JAK2 signaling. This iPSC model is helpful in mechanistic studies and novel therapy screen for myeloproliferative neoplasm.

Megakaryocyte Cytoskeletal Proteins in Platelet Biogenesis and Diseases

Thrombopoiesis governs the formation of blood platelets in bone marrow by converting megakaryocytes into long, branched proplatelets on which individual platelets are assembled. The megakaryocyte cytoskeleton responds to multiple microenvironmental cues, including chemical and mechanical stimuli, sustaining the platelet shedding. During the megakaryocyte's life cycle, cytoskeletal networks organize cell shape and content, connect them physically and biochemically to the bone marrow vascular niche, and enable the release of platelets into the bloodstream. While the basic building blocks of the cytoskeleton have been studied extensively, new sets of cytoskeleton regulators have emerged as critical components of the dynamic protein network that supports platelet production. Understanding how the interaction of individual molecules of the cytoskeleton governs megakaryocyte behavior is essential to improve knowledge of platelet biogenesis and develop new therapeutic strategies for inherited thrombocytopenias caused by alterations in the cytoskeletal genes.

Distinct effects of V617F and exon12-mutated JAK2 expressions on erythropoiesis in a human induced pluripotent stem cell (iPSC)-based model

Activating mutations affecting the JAK-STAT signal transduction is the genetic driver of myeloproliferative neoplasms (MPNs) which comprise polycythemia vera (PV), essential thrombocythemia (ET) and myelofibrosis. The JAK2p.V617F mutation can produce both erythrocytosis in PV and thrombocytosis in ET, while JAK2 exon 12 mutations cause only erythrocytosis. We hypothesized that these two mutations activated different intracellular signals. In this study, the induced pluripotent stem cells (iPSCs) were used to model JAK2-mutated MPNs. Normal iPSCs underwent lentiviral transduction to overexpress JAK2p.V617F or JAK2p.N542_E543del (JAK2exon12) under a doxycycline-inducible system. The modified iPSCs were differentiated into erythroid cells. Compared with JAK2V617F-iPSCs, JAK2exon12-iPSCs yielded more total CD71⁺GlycophorinA⁺ erythroid cells, displayed more mature morphology and expressed more adult hemoglobin after doxycycline induction. Capillary Western immunoassay revealed significantly higher phospho-STAT1 but lower phospho-STAT3 and lower Phospho-AKT in JAK2exon12-iPSCs compared with those of JAK2V617F-iPSCs in response to erythropoietin. Furthermore, interferon alpha and arsenic trioxide were tested on these modified iPSCs to explore their potentials for MPN therapy. Both agents preferentially inhibited proliferation and promoted apoptosis of the iPSCs expressing mutant JAK2 compared with those without doxycycline induction. In conclusion, the modified iPSC model can be used to investigate the mechanisms and search for new therapy of MPNs.

Role of Rho-GTPases in megakaryopoiesis

Megakaryocytes (MKs) are the bone marrow (BM) cells that generate blood platelets by a process that requires: i) polyploidization responsible for the increased MK size and ii) cytoplasmic organization leading to extension of long pseudopods, called proplatelets, through the endothelial barrier to allow platelet release into blood. Low level of localized RHOA activation prevents actomyosin accumulation at the cleavage furrow and participates in MK polyploidization. In the platelet production, RHOA and CDC42 play opposite, but complementary roles. RHOA inhibits both proplatelet formation and MK exit from BM, whereas CDC42 drives the development of the demarcation membranes and MK migration in BM. Moreover, the RhoA or Cdc42 MK specific knock-out in mice and the genetic alterations in their down-stream effectors in human induce a thrombocytopenia demonstrating their key roles in platelet production. A better knowledge of Rho-GTPase signalling is thus necessary to develop therapies for diseases associated with platelet production defects.

Abbreviations: AKT: Protein Kinase BARHGEF2: Rho/Rac Guanine Nucleotide Exchange Factor 2ARP2/3: Actin related protein 2/3BM: Bone marrowCDC42: Cell division control protein 42 homologCFU-MK: Colony-forming-unit megakaryocyteCIP4: Cdc42-interacting protein 4mDIA: DiaphanousDIAPH1; Protein diaphanous homolog 1ECT2: Epithelial Cell Transforming Sequence 2FLNA: Filamin AGAP: GTPase-activating proteins or GTPase-accelerating proteinsGDI: GDP Dissociation InhibitorGEF: Guanine nucleotide exchange factorHDAC: Histone deacetylaseLIMK: LIM KinaseMAL: Megakaryoblastic leukaemiaMARCKS: Myristoylated alanine-rich C-kinase substrateMKL: Megakaryoblastic leukaemiaMLC: Myosin light chainMRTF: Myocardin Related Transcription FactorOTT: One-Twenty Two ProteinPACSIN2: Protein Kinase C And Casein Kinase Substrate In Neurons 2PAK: P21-Activated KinasePDK: Pyruvate Dehydrogenase kinasePI3K: Phosphoinositide 3-kinasePKC: Protein kinase CPTPRJ: Protein tyrosine phosphatase receptor type JRAC: Ras-related C3 botulinum toxin substrate 1RBM15: RNA Binding Motif Protein 15RHO: Ras homologousROCK: Rho-associated protein kinaseSCAR: Suppressor of cAMP receptorSRF: Serum response factorSRC: SarcTAZ: Transcriptional coactivator with PDZ motifTUBB1: Tubulin β1VEGF: Vascular endothelial growth factorWAS: Wiskott Aldrich syndromeWASP: Wiskott Aldrich syndrome proteinWAVE: WASP-family verprolin-homologous proteinWIP: WASP-interacting proteinYAP: Yes-associated protein

Regulation of platelet numbers and sizes by signaling pathways

Either the glycoprotein (GP) Ib deficiency or hyper-function in humans can cause macrothrombocytopenia, the molecular mechanisms of which remain unclear. Herein, the investigations for disease pathogenesis were performed in the human induced pluripotent stem cell (hiPSC) model. The hiPSCs carrying a gain-of-function GP1BA p.M255V mutation which was described in platelet-type von Willebrand disease (PT-VWD) were generated using CRISPR/Cas9. The GP1BA-null hiPSCs were previously derived from a Bernard-Soulier syndrome (BSS) patient. After full megakaryocyte differentiation in culture, both hiPSC mutations showed large proplatelet tips under fluorescence microscopy and yielded fewer but larger platelets compared with those of wild-type cells. The Capillary Western analyses revealed the lower ERK1/2 activation and higher MLC2 (Myosin light chain 2) phosphorylation in megakaryocytes with mutated GPIb. Adding a mitogen-activated protein kinase (MAPK) pathway inhibitor to wild-type hiPSCs recapitulated the phenotypes of GPIb mutations and increased MLC2 phosphorylation. Notably, a ROCK inhibitor which could inhibit MLC2 phosphorylation rescued the macrothrombocytopenia phenotypes of both GPIb alterations and wild-type hiPSCs with a MAPK inhibitor. In conclusion, the genetically modified hiPSCs can be used to model disorders of proplatelet formation. Both loss- and gain-of-function GPIb reduced MAPK/ERK activation but enhanced ROCK/MLC2 phosphorylation resulting in dysregulated platelet generation.

Differentiation of human induced pluripotent stem cells into erythroid cells

During the last years, several strategies have been made to obtain mature erythrocytes or red blood cells (RBC) from the bone marrow or umbilical cord blood (UCB). However, UCB-derived hematopoietic stem cells (HSC) are a limited source and in vitro large-scale expansion of RBC from HSC remains problematic. One promising alternative can be human pluripotent stem cells (PSCs) that provide an unlimited source of cells. Human PSCs, including embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs), are self-renewing progenitors that can be differentiated to lineages of ectoderm, mesoderm, and endoderm. Several previous studies have revealed that human ESCs can differentiate into functional oxygen-carrying erythrocytes; however, the ex vivo expansion of human ESC-derived RBC is subjected to ethical concerns. Human iPSCs can be a suitable therapeutic choice for the in vitro/ex vivo manufacture of RBCs. Reprogramming of human somatic cells through the ectopic expression of the transcription factors (OCT4, SOX2, KLF4, c-MYC, LIN28, and NANOG) has provided a new avenue for disease modeling and regenerative medicine. Various techniques have been developed to generate enucleated RBCs from human iPSCs. The in vitro production of human iPSC-derived RBCs can be an alternative treatment option for patients with blood disorders. In this review, we focused on the generation of human iPSC-derived erythrocytes to present an overview of the current status and applications of this field.

Efficacy of romiplostim in treatment of thrombocytopenia in children with Wiskott-Aldrich syndrome

Wiskott-Aldrich syndrome (WAS) is a life-threatening primary immunodeficiency associated with bleeding of variable severity due to thrombocytopenia. Correction of the thrombocytopenia is of paramount importance for most WAS patients. We report a retrospective analysis of the safety and efficacy of romiplostim treatment in reducing thrombocytopenia and bleeding tendency in 67 children (median age 1·3 years) with genetically confirmed WAS, followed in eight months (range, 1-12 months). Complete or partial primary responses regarding platelet counts were observed in 22 (33%) and 18 (27%) subjects, respectively. Yet, even in the non-responder group, the risk of haemorrhagic events decreased significantly, to 21%, after the first month of treatment. The responses tended to be durable and stable over time, with no significant fluctuations in platelets counts. The results of this retrospective study of a large cohort of WAS patients demonstrates that romiplostim can be used to increase platelet counts and reduce the risks of life-threatening bleeding in WAS patients awaiting haematopoietic stem cell transplantation or forgoing the procedure for various reasons.

Induced Pluripotent Stem Cell Meets Severe Combined Immunodeficiency

Severe combined immunodeficiency (SCID) is classified as a primary immunodeficiency, which is characterized by impaired T-lymphocytes differentiation. IL2RG, IL7Ralpha, JAK3, ADA, RAG1/RAG2, and DCLE1C (Artemis) are the most defective genes in SCID. The most recent SCID therapies are based on gene therapy (GT) of hematopoietic stem cells (HSC), which are faced with many challenges. The new studies in the field of stem cells have made great progress in overcoming the challenges ahead. In 2006, Yamanaka et al. achieved "reprogramming" technology by introducing four transcription factors known as Yamanaka factors, which generate induced pluripotent stem cells (iPSC) from somatic cells. It is possible to apply iPSC-derived HSC for transplantation in patients with abnormality or loss of function in specific cells or damaged tissue, such as T-cells and NK-cells in the context of SCID. The iPSC-based HSC transplantation in SCID and other hereditary disorders needs gene correction before transplantation. Furthermore, iPSC technology has been introduced as a promising tool in cellular-molecular disease modeling and drug discovery. In this article, we review iPSC-based GT and modeling for SCID disease and novel approaches of iPSC application in SCID.

Modeling blood diseases with human induced pluripotent stem cells

Induced pluripotent stem cells (iPSCs) are derived from somatic cells through a reprogramming process, which converts them to a pluripotent state, akin to that of embryonic stem cells. Over the past decade, iPSC models have found increasing applications in the study of human diseases, with blood disorders featuring prominently. Here, we discuss methodological aspects pertaining to iPSC generation, hematopoietic differentiation and gene editing, and provide an overview of uses of iPSCs in modeling the cell and gene therapy of inherited genetic blood disorders, as well as their more recent use as models of myeloid malignancies. We also discuss the strengths and limitations of iPSCs compared to model organisms and other cellular systems commonly used in hematology research.

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.

Modulated expression of the HIV-1 2LTR zinc finger efficiently interferes with the HIV integration process

Lentiviral vectors have emerged as the most efficient system to stably transfer and insert genes into cells. By adding a tetracycline (Tet)-inducible promoter, transgene expression delivered by a lentiviral vector can be expressed whenever needed and halted when necessary. Here we have constructed a doxycycline (Dox)-inducible lentiviral vector which efficiently introduces a designed zinc finger protein, 2-long terminal repeat zinc-finger protein (2LTRZFP), into hematopoietic cell lines and evaluated its expression in pluripotent stem cells. As a result this lentiviral inducible system can regulate 2LTRZFP expression in the SupT1 T-cell line and in pluripotent stem cells. Using this vector, no basal expression was detected in the T-cell line and its induction was achieved with low Dox concentrations. Remarkably, the intracellular regulatory expression of 2LTRZFP significantly inhibited HIV-1 integration and replication in HIV-inoculated SupT1 cells. This approach could provide a potential tool for gene therapy applications, which efficiently control and reduce the side effect of therapeutic genes expression.

Clinical Manifestations and Pathophysiological Mechanisms of the Wiskott-Aldrich Syndrome

The Wiskott-Aldrich syndrome (WAS) is a rare X-linked disorder originally described by Dr. Alfred Wiskott in 1937 and Dr. Robert Aldrich in 1954 as a familial disease characterized by infections, bleeding tendency, and eczema. Today, it is well recognized that the syndrome has a wide clinical spectrum ranging from mild, isolated thrombocytopenia to full-blown presentation that can be complicated by life-threatening hemorrhages, immunodeficiency, atopy, autoimmunity, and cancer. The pathophysiology of classic and emerging features is being elucidated by clinical studies, but remains incompletely defined, which hinders the application of targeted therapies. At the same time, progress of hematopoietic stem cell transplantation and gene therapy offer optimistic prospects for treatment options aimed at the replacement of the defective lymphohematopoietic system that have the potential to provide a cure for this rare and polymorphic disease.

Wiskott-Aldrich syndrome in a child presenting with macrothrombocytopenia

Wiskott-Aldrich syndrome (WAS) is a rare X-linked recessive disease resulting from variants in the WAS gene, characterized by a triad of immunodeficiency, eczema, and thrombocytopenia. Despite the fact that WAS is traditionally differentiated from immune thrombocytopenia (ITP) by small size of WAS platelets, in practice, microthrombocytopenia may occasionally not be present, and in certain cases, WAS patients exhibit some parallelism to ITP patients. We characterized one patient presenting with the classic form of the disease but increased mean platelet volume. Molecular studies revealed a novel hemizygous 1-bp deletion in WAS gene, c.802delC, leading to a frameshift and stop codon at amino acid 308 (p.Arg268Glyfs*40). Next-generation sequencing of a total of 70 additional genes known to harbor variants implicated in inherited platelet disorders did not identify additional defects. The pathogenesis of macrothrombocytopenia in this case is not known, but probably the coexistence of a still unidentified additional genetic variant might be involved.

Human induced pluripotent stem cells for monogenic disease modelling and therapy

Recent and advanced protocols are now available to derive human induced pluripotent stem cells (hiPSCs) from patients affected by genetic diseases. No curative treatments are available for many of these diseases; thus, hiPSCs represent a major impact on patient' health. hiPSCs represent a valid model for the in vitro study of monogenic diseases, together with a better comprehension of the pathogenic mechanisms of the pathology, for both cell and gene therapy protocol applications. Moreover, these pluripotent cells represent a good opportunity to test innovative pharmacological treatments focused on evaluating the efficacy and toxicity of novel drugs. Today, innovative gene therapy protocols, especially gene editing-based, are being developed, allowing the use of these cells not only as in vitro disease models but also as an unlimited source of cells useful for tissue regeneration and regenerative medicine, eluding ethical and immune rejection problems. In this review, we will provide an up-to-date of modelling monogenic disease by using hiPSCs and the ultimate applications of these in vitro models for cell therapy. We consider and summarize some peculiar aspects such as the type of parental cells used for reprogramming, the methods currently used to induce the transcription of the reprogramming factors, and the type of iPSC-derived differentiated cells, relating them to the genetic basis of diseases and to their inheritance model.

hiPSC-derived iMSCs: NextGen MSCs as an advanced therapeutically active cell resource for regenerative medicine

Mesenchymal stem cells (MSCs) are being assessed for ameliorating the severity of graft‐versus‐host disease, autoimmune conditions, musculoskeletal injuries and cardiovascular diseases. While most of these clinical therapeutic applications require substantial cell quantities, the number of MSCs that can be obtained initially from a single donor remains limited. The utility of MSCs derived from human‐induced pluripotent stem cells (hiPSCs) has been shown in recent pre‐clinical studies. Since adult MSCs have limited capability regarding proliferation, the quantum of bioactive factor secretion and immunomodulation ability may be constrained. Hence, the alternate source of MSCs is being considered to replace the commonly used adult tissue‐derived MSCs. The MSCs have been obtained from various adult and foetal tissues. The hiPSC‐derived MSCs (iMSCs) are transpiring as an attractive source of MSCs because during reprogramming process, cells undergo rejuvination, exhibiting better cellular vitality such as survival, proliferation and differentiations potentials. The autologous iMSCs could be considered as an inexhaustible source of MSCs that could be used to meet the unmet clinical needs. Human‐induced PSC‐derived MSCs are reported to be superior when compared to the adult MSCs regarding cell proliferation, immunomodulation, cytokines profiles, microenvironment modulating exosomes and bioactive paracrine factors secretion. Strategies such as derivation and propagation of iMSCs in chemically defined culture conditions and use of footprint‐free safer reprogramming strategies have contributed towards the development of clinically relevant cell types. In this review, the role of iPSC‐derived mesenchymal stromal cells (iMSCs) as an alternate source of therapeutically active MSCs has been described. Additionally, we also describe the role of iMSCs in regenerative medical applications, the necessary strategies, and the regulatory policies that have to be enforced to render iMSC's effectiveness in translational medicine.

Human Umbilical Cord Blood-Derived Serum for Culturing the Supportive Feeder Cells of Human Pluripotent Stem Cell Lines

Although human pluripotent stem cells (hPSCs) can proliferate robustly on the feeder-free culture system, genetic instability of hPSCs has been reported in such environment. Alternatively, feeder cells enable hPSCs to maintain their pluripotency. The feeder cells are usually grown in a culture medium containing fetal bovine serum (FBS) prior to coculture with hPSCs. The use of FBS might limit the clinical application of hPSCs. Recently, human cord blood-derived serum (hUCS) showed a positive effect on culture of mesenchymal stem cells. It is interesting to test whether hUCS can be used for culture of feeder cells of hPSCs. This study was aimed to replace FBS with hUCS for culturing the human foreskin fibroblasts (HFFs) prior to feeder cell preparation. The results showed that HFFs cultured in hUCS-containing medium (HFF-hUCS) displayed fibroblastic features, high proliferation rates, short population doubling times, and normal karyotypes after prolonged culture. Inactivated HFF-hUCS expressed important genes, including Activin A, FGF2, and TGFβ1, which have been implicated in the maintenance of hPSC pluripotency. Moreover, hPSC lines maintained pluripotency, differentiation capacities, and karyotypic stability after being cocultured for extended period with inactivated HFF-hUCS. Therefore, the results demonstrated the benefit of hUCS for hPSCs culture system.

Absence of WASp Enhances Hematopoietic and Megakaryocytic Differentiation in a Human Embryonic Stem Cell Model

The Wiskott-Aldrich syndrome (WAS) is an X-linked primary immunodeficiency caused by mutations in the WAS gene and characterized by severe thrombocytopenia. Although the role of WASp in terminally differentiated lymphocytes and myeloid cells is well characterized, its role in early hematopoietic differentiation and in platelets (Plts) biology is poorly understood. In the present manuscript, we have used zinc finger nucleases targeted to the WAS locus for the development of two isogenic WAS knockout (WASKO) human embryonic stem cell lines (hESCs). Upon hematopoietic differentiation, hESCs-WASKO generated increased ratios of CD34⁺CD45⁺ progenitors with altered responses to stem cell factor compared to hESCs-WT. When differentiated toward the megakaryocytic linage, hESCs-WASKO produced increased numbers of CD34⁺CD41⁺ progenitors, megakaryocytes (MKs), and Plts. hESCs-WASKO-derived MKs and Plts showed altered phenotype as well as defective responses to agonist, mimicking WAS patients MKs and Plts defects. Interestingly, the defects were more evident in WASp-deficient MKs than in WASp-deficient Plts. Importantly, ectopic WAS expression using lentiviral vectors restored normal Plts development and MKs responses. These data validate the AND-1_WASKO cell lines as a human cellular model for basic research and for preclinical studies for WAS.

Cytoskeletal regulation of platelet formation: Coordination of F-actin and microtubules

Platelets are small, anucleate blood cells which play an important role in haemostasis. Thrombocytopenia is a condition where the platelet count falls below 150×10(9)/l and patients suffering from severe forms of this condition can experience life-threatening bleeds requiring platelet transfusions. Platelets are produced from large progenitor cells called megakaryocytes which are found in the bone marrow. The process of megakaryocyte maturation and the formation of proplatelets are essential steps in the production of mature platelets and both depend heavily on the actin and microtubule cytoskeletons. Understanding these processes is important for the development of in vitro platelet production which will help to treat thrombocytopenia as well as produce model systems for studying platelet-associated disorders. This review will highlight some of the recent advances in our understanding of the role of the cytoskeleton in platelet production, especially the key molecules and signalling pathways that regulate actin and microtubule crosstalk.