Rapid and efficient reprogramming of human fetal and adult blood CD34+ cells into mesenchymal stem cells with a single factor. Cell Res. 2013;23:658-672. [PMID: 23478301 PMCID: PMC3641600 DOI: 10.1038/cr.2013.40]

Progress and emerging techniques for biomaterial-based derivation of mesenchymal stem cells (MSCs) from pluripotent stem cells (PSCs)

The use of mesenchymal stem cells (MSCs) for clinical purposes has skyrocketed in the past decade. Their multilineage differentiation potentials and immunomodulatory properties have facilitated the discovery of therapies for various illnesses. MSCs can be isolated from infant and adult tissue sources, which means they are easily available. However, this raises concerns because of the heterogeneity among the various MSC sources, which limits their effective use. Variabilities arise from donor- and tissue-specific differences, such as age, sex, and tissue source. Moreover, adult-sourced MSCs have limited proliferation potentials, which hinders their long-term therapeutic efficacy. These limitations of adult MSCs have prompted researchers to develop a new method for generating MSCs. Pluripotent stem cells (PSCs), such as embryonic stem cells and induced PSCs (iPSCs), can differentiate into various types of cells. Herein, a thorough review of the characteristics, functions, and clinical importance of MSCs is presented. The existing sources of MSCs, including adult- and infant-based sources, are compared. The most recent techniques for deriving MSCs from iPSCs, with a focus on biomaterial-assisted methods in both two- and three-dimensional culture systems, are listed and elaborated. Finally, several opportunities to develop improved methods for efficiently producing MSCs with the aim of advancing their various clinical applications are described.

Reprogramming of human peripheral blood mononuclear cells into induced mesenchymal stromal cells using non-integrating vectors

Mesenchymal stromal cells (MSCs) have great value in cell therapies. The MSC therapies have many challenges due to its inconsistent potency and limited quantity. Here, we report a strategy to generate induced MSCs (iMSCs) by directly reprogramming human peripheral blood mononuclear cells (PBMCs) with OCT4, SOX9, MYC, KLF4, and BCL-XL using a nonintegrating episomal vector system. While OCT4 was not required to reprogram PBMCs into iMSCs, omission of OCT4 significantly impaired iMSC functionality. The omission of OCT4 resulted in significantly downregulating MSC lineage specific and mesoderm-regulating genes, including SRPX, COL5A1, SOX4, SALL4, TWIST1. When reprogramming PBMCs in the absence of OCT4, 67 genes were significantly hypermethylated with reduced transcriptional expression. These data indicate that transient expression of OCT4 may serve as a universal reprogramming factor by increasing chromatin accessibility and promoting demethylation. Our findings represent an approach to produce functional MSCs, and aid in identifying putative function associated MSC markers.

A review of literature: role of long noncoding RNA TPT1-AS1 in human diseases

Human diseases are multifactorial processes mainly driven by the intricate interactions of genetic and environmental factors. Long noncoding RNAs (lncRNAs) represent a type of non-coding RNAs with more than 200 nucleotides. Multiple studies have demonstrated that the dysregulation of lncRNAs is associated with complex biological as well as pathological processes through various mechanism, especially the regulation of gene transcription and related signal transduction pathways. Moreover, an increasing number of studies have explored lncRNA-based clinical applications in different diseases. For instance, the lncRNA Tumor Protein Translationally Controlled 1 (TPT1) Antisense RNA 1 (TPT1-AS1) was found to be dysregulated in several types of disease and strongly associated with patient prognosis and diverse clinical features. Recent studies have also documented that TPT1-AS1 modulates numerous biological processes through multiple mechanisms, including cell proliferation, apoptosis, autophagy, invasion, migration, radiosensitivity, chemosensitivity, stemness, and extracellular matrix (ECM) synthesis. Furthermore, TPT1-AS1 was regarded as a promising biomarker for the diagnosis, prognosis and treatment of several human diseases. In this review, we summarize the role of TPT1-AS1 in human diseases with the aspects of its expression, relevant clinical characteristics, molecular mechanisms, biological functions, and subsequent clinical applications.

Mesenchymal Stem Cell-Derived Exosomes as a Novel Strategy for the Treatment of Intervertebral Disc Degeneration

Intervertebral disc degeneration (IVDD) has been reported to be the most prevalent contributor to low back pain, posing a significant strain on the healthcare systems on a global scale. Currently, there are no approved therapies available for the prevention of the progressive degeneration of intervertebral disc (IVD); however, emerging regenerative strategies that aim to restore the normal structure of the disc have been fundamentally promising. In the last decade, mesenchymal stem cells (MSCs) have received a significant deal of interest for the treatment of IVDD due to their differentiation potential, immunoregulatory capabilities, and capability to be cultured and regulated in a favorable environment. Recent investigations show that the pleiotropic impacts of MSCs are regulated by the production of soluble paracrine factors. Exosomes play an important role in regulating such effects. In this review, we have summarized the current treatments for disc degenerative diseases and their limitations and highlighted the therapeutic role and its underlying mechanism of MSC-derived exosomes in IVDD, as well as the possible future developments for exosomes.

Derivation of Ringed Seal (Phoca hispida) Induced Multipotent Stem Cells

Induced pluripotent stem (iPS) cells have been produced just for a few species among order Carnivora: snow leopard, Bengal tiger, serval, jaguar, cat, dog, ferret, and American mink. We applied the iPS cell derivation protocol to the ringed seal (Phoca hispida) fibroblasts. The resulting cell line had the expression of pluripotency marker gene Rex1. Differentiation in embryoid body-like structures allowed us to register expression of AFP, endoderm marker, and Cdx2, trophectoderm marker, but not neuronal (ectoderm) markers. The cells readily differentiated into adipocytes and osteocytes, mesoderm cell types of origin. Transcriptome analysis allowed us to conclude that the cell line does not resemble human pluripotent cells, and, therefore, most probably is not pluripotent. Thus, we produced ringed seal multipotent stem cell line capable of differentiation into adipocytes and osteocytes.

Mesenchymal Stem Cell and MicroRNA Therapy of Musculoskeletal Diseases

The therapeutic effects of mesenchymal stem cells (MSCs) in musculoskeletal diseases (MSDs) have been verified in many human and animal studies. Although some tissues contain MSCs, the number of cells harvested from those tissues and rate of proliferation in vitro are not enough for continuous transplantation. In order to produce and maintain stable MSCs, many attempts are made to induce differentiation from pluripotent stem cells (iPSCs) into MSCs. In particular, it is also known that the paracrine action of stem cell-secreted factors could promote the regeneration and differentiation of target cells in damaged tissue. MicroRNAs (miRNAs), one of the secreted factors, are small non-coding RNAs that regulate the translation of a gene. It is known that miRNAs help communication between stem cells and their surrounding niches through exosomes to regulate the proliferation and differentiation of stem cells. While studies have so far been underway targeting therapeutic miRNAs of MSDs, studies on specific miRNAs secreted from MSCs are still minimal. Hence, our ultimate goal is to obtain sufficient amounts of exosomes from iPSC-MSCs and develop them into therapeutic agents, furthermore to select specific miRNAs and provide safe cell-free clinical setting as a cell-free status with purpose of delivering them to target cells. This review article focuses on stem cell therapy on MSDs, specific microRNAs regulating MSDs and updates on novel approaches.

Effects of DLX3 on the osteogenic differentiation of induced pluripotent stem cell‑derived mesenchymal stem cells

Osteoporosis is a disease characterized by the degeneration of bone structure and decreased bone mass. Induced pluripotent stem cell-derived mesenchymal stem cells (iPSC-MSCs) have multiple advantages that make them ideal seed cells for bone regeneration, including high-level proliferation, multi-differentiation potential and favorable immune compatibility. Distal-less homeobox (DLX)3, an important member of the DLX family, serves a crucial role in osteogenic differentiation and bone formation. The present study aimed to evaluate the effects of DLX3 on the proliferation and osteogenic differentiation of human iPSC-MSCs. iPSC-MSCs were induced from iPSCs, and identified via flow cytometry. Alkaline phosphatase (ALP), Von Kossa, Oil Red O and Alcian blue staining methods were used to evaluate the osteogenic, adipogenic and chondrogenic differentiation of iPSC-MSCs. DLX3 overexpression plasmids were constructed and transfected into iPSC-MSCs to generate iPSC-MSC-DLX3. iPSC-MSC-GFP was used as the control. Reverse transcription-quantitative PCR (RT-qPCR) and western blotting were performed to measure the expression of DLX3 2 days after transfection. Subsequently, cell proliferation was assessed using a Cell Counting Kit-8 assay on days 1, 3, 5 and 7. RT-qPCR and western blotting were used to analyze osteogenic-related gene and protein expression levels on day 7. ALP activity and mineralized nodules were assessed via ALP staining on day 14. Statistical analysis was performed using an unpaired Student's t-test. Flow cytometry results demonstrated that iPSC-MSCs were positive for CD73, CD90 and CD105, but negative for CD34 and CD45. iPSC-MSC-DLX3 had significantly lower proliferation compared with iPSC-MSC-GFP on days 5 and 7 (P<0.05). mRNA expression levels of osteogenic markers, such as ALP, osteopenia (OPN), osteocalcin (OCN) and Collagen Type I (COL-1), were significantly increased in iPSC-MSC-DLX3 compared with iPSC-MSC-GFP on day 7 (P<0.05). Similarly, the protein expression levels of ALP, OCN, OPN and COL-1 were significantly increased in iPSC-MSC-DLX3 compared with iPSC-MSC-GFP on day 7 (P<0.05). The number of mineralized nodules in iPSC-MSC-DLX3 was increased compared with that in iPSC-MSC-GFP on day 14 (P<0.05). Thus, the present study demonstrated that DLX3 serves a negative role in proliferation, but a positive role in the osteogenic differentiation of iPSC-MSCs. This may provide novel insight for treating osteoporosis.

HDAC inhibitors improve CRISPR-mediated HDR editing efficiency in iPSCs

Genome-edited human induced pluripotent stem cells (iPSCs) hold great promise for therapeutic applications. However, low editing efficiency has hampered the applications of CRISPR-Cas9 technology in creating knockout and homology-directed repair (HDR)-edited iPSC lines, particularly for silent genes. This is partially due to chromatin compaction, inevitably limiting Cas9 access to the target DNA. Among the six HDAC inhibitors we examined, vorinostat, or suberoylanilide hydroxamic acid (SAHA), led to the highest HDR efficiency at both open and closed loci, with acceptable toxicity. HDAC inhibitors equally increased non-homologous end joining (NHEJ) editing efficiencies (∼50%) at both open and closed loci, due to the considerable HDAC inhibitor-mediated increase in Cas9 and sgRNA expression. However, we observed more substantial HDR efficiency improvement at closed loci relative to open chromatin (2.8 vs. 1.7-fold change). These studies provide a new strategy for HDR-editing of silent genes in iPSCs.

Loss of β-Actin Leads to Accelerated Mineralization and Dysregulation of Osteoblast-Differentiation Genes during Osteogenic Reprogramming

Actin plays fundamental roles in both the cytoplasm and the cell nucleus. In the nucleus, β-actin regulates neuronal reprogramming by consolidating a heterochromatin landscape required for transcription of neuronal gene programs, yet it remains unknown whether it has a role in other differentiation models. To explore the potential roles of β-actin in osteogenesis, β-actin wild-type (WT) and β-actin knockout (KO) mouse embryonic fibroblasts (MEFs) are reprogrammed to osteoblast-like cells using small molecules in vitro. It is discovered that loss of β-actin leads to an accelerated mineralization phenotype (hypermineralization), accompanied with enhanced formation of extracellular hydroxyapatite microcrystals, which originate in the mitochondria in the form of microgranules. This phenotype is a consequence of rapid upregulation of mitochondrial genes including those involved in oxidative phosphorylation (OXPHOS) in reprogrammed KO cells. It is further found that osteogenic gene programs are differentially regulated between WT and KO cells, with clusters of genes exhibiting different temporal expression patterns. A novel function for β-actin in osteogenic reprogramming through a mitochondria-based mechanism that controls cell-mediated mineralization is proposed.

Glycogen synthase kinase 3β inhibitor- CHIR 99021 augments the differentiation potential of mesenchymal stem cells

AIM

Mesenchymal stem cells (MSCs) are immunomodulatory, non-teratogenic and multipotent alternatives to embryonic or induced pluripotent stem cells (ESCs or iPSCs). However, the potency of MSCs is not equivalent to the pluripotency of ESCs or iPSCs. We used CHIR 99021 to improve current protocols and methods of differentiation for the enhanced transdifferentiation potency of MSCs.

MAIN METHODS

We used Flurescence activated cell sorter (FACS) for MSC immunophenotyping and biochemical assay for demonstrating the trilineage potential of MSCs. We used real-time polymerase chain reaction, immunocytochemistry and Western blotting assay for analyzing the expression of lineage-specific markers.

KEY FINDINGS

CHIR 99021 treatment of MSCs resulted in enhanced transdifferentiation into neurological, hepatogenic and cardiomyocyte lineages with standardized protocols of differentiation. CHIR 99021-treated MSCs showed increased nuclear localization of β-catenin. These MSCs showed a significantly increased deposition of active histone marks (H3K4Me3, H3K36Me3), whereas no change was observed in repressive marks (H3K9Me3, H3K27Me3). Differential methylation profiling showed demethylation of the transcription factor OCT4 promoter region with subsequent analysis revealing increased gene expression and protein content. The HLA-DR antigen was absent in CHIR 99021-treated MSCs and their differentiated cell types, indicating their immune-privileged status. Karyotyping analysis showed that CHIR 99021-treated MSCs were genomically stable. Teratoma analysis of nude mice injected with CHIR 99021-treated MSCs showed the increased presence of cell types of mesodermal origin at the site of injection.

SIGNIFICANCE

MSCs pretreated with CHIR 99021 can be potent, abundant alternative sources of stem cells with enhanced differentiation capabilities that are well suited to cell-based regenerative therapy.

PDGFB-expressing mesenchymal stem cells improve human hematopoietic stem cell engraftment in immunodeficient mice

The bone marrow (BM) niche regulates multiple hematopoietic stem cell (HSC) processes. Clinical treatment for hematological malignancies by HSC transplantation often requires preconditioning via total body irradiation, which severely and irreversibly impairs the BM niche and HSC regeneration. Novel strategies are needed to enhance HSC regeneration in irradiated BM. We compared the effects of EGF, FGF2, and PDGFB on HSC regeneration using human mesenchymal stem cells (MSCs) that were transduced with these factors via lentiviral vectors. Among the above niche factors tested, MSCs transduced with PDGFB (PDGFB-MSCs) most significantly improved human HSC engraftment in immunodeficient mice. PDGFB-MSC-treated BM enhanced transplanted human HSC self-renewal in secondary transplantations more efficiently than GFP-transduced MSCs (GFP-MSCs). Gene set enrichment analysis showed increased antiapoptotic signaling in PDGFB-MSCs compared with GFP-MSCs. PDGFB-MSCs exhibited enhanced survival and expansion after transplantation, resulting in an enlarged humanized niche cell pool that provide a better humanized microenvironment to facilitate superior engraftment and proliferation of human hematopoietic cells. Our studies demonstrate the efficacy of PDGFB-MSCs in supporting human HSC engraftment.

Generation of mesenchymal stem-like cells for producing extracellular vesicles

Mesenchymal stem cells (MSCs) are multipotent progenitor cells with therapeutic potential against autoimmune diseases, inflammation, ischemia, and metabolic disorders. Contrary to the previous conceptions, recent studies have revealed that the tissue repair and immunomodulatory functions of MSCs are largely attributed to their secretome, rather than their potential to differentiate into desired cell types. The composition of MSC secretome encompasses cytokines and growth factors, in addition to the cell-derived structures known as extracellular vesicles (EVs). EVs are membrane-enclosed nanoparticles that are capable of delivering biomolecules, and it is now believed that MSC-derived EVs are the major players that induce biological changes in the target tissues. Based on these EVs’ characteristics, the potential of EVs derived from MSC (MSC-EV) in terms of tissue regeneration and immune modulation has grown during the last decade. However, the use of MSCs for producing sufficient amount of EVs has not been satisfactory due to limitations in the cell growth and large variations among the donor cell types. In this regard, pluripotent stem cells (PSCs)-derived MSC-like cells, which can be robustly induced and expanded in vitro, have emerged as more accessible cell source that can overcome current limitations of using MSCs for EV production. In this review, we have highlighted the methods of generating MSC-like cells from PSCs and their therapeutic outcome in preclinical studies. Finally, we have also discussed future requirements for making this cell-free therapy clinically feasible.

Current Strategies to Generate Human Mesenchymal Stem Cells In Vitro

Mesenchymal stem cells (MSCs) are heterogeneous multipotent stem cells that are involved in the development of mesenchyme-derived evolving structures and organs during ontogeny. In the adult organism, reservoirs of MSCs can be found in almost all tissues where MSCs contribute to the maintenance of organ integrity. The use of these different MSCs for cell-based therapies has been extensively studied over the past years, which highlights the use of MSCs as a promising option for the treatment of various diseases including autoimmune and cardiovascular disorders. However, the proportion of MSCs contained in primary isolates of adult tissue biopsies is rather low and, thus, vigorous ex vivo expansion is needed especially for therapies that may require extensive and repetitive cell substitution. Therefore, more easily and accessible sources of MSCs are needed. This review summarizes the current knowledge of the different strategies to generate human MSCs in vitro as an alternative method for their applications in regenerative therapy.

MSX2 Initiates and Accelerates Mesenchymal Stem/Stromal Cell Specification of hPSCs by Regulating TWIST1 and PRAME

The gap in knowledge of the molecular mechanisms underlying differentiation of human pluripotent stem cells (hPSCs) into the mesenchymal cell lineages hinders the application of hPSCs for cell-based therapy. In this study, we identified a critical role of muscle segment homeobox 2 (MSX2) in initiating and accelerating the molecular program that leads to mesenchymal stem/stromal cell (MSC) differentiation from hPSCs. Genetic deletion of MSX2 impairs hPSC differentiation into MSCs. When aided with a cocktail of soluble molecules, MSX2 ectopic expression induces hPSCs to form nearly homogeneous and fully functional MSCs. Mechanistically, MSX2 induces hPSCs to form neural crest cells, an intermediate cell stage preceding MSCs, and further differentiation by regulating TWIST1 and PRAME. Furthermore, we found that MSX2 is also required for hPSC differentiation into MSCs through mesendoderm and trophoblast. Our findings provide novel mechanistic insights into lineage specification of hPSCs to MSCs and effective strategies for applications of stem cells for regenerative medicine.

Isolation and Characterisation of Mesenchymal Stem Cells from Rat Bone Marrow and the Endosteal Niche: A Comparative Study

Within bone, mesenchymal stromal cells (MSCs) exist within the bone marrow stroma (BM-MSC) and the endosteal niche, as cells lining compact bone (CB-MSCs). This study isolated and characterised heterogeneous MSC populations from each niche and subsequently investigated the effects of extensive cell expansion, analysing population doublings (PDs)/cellular senescence, colony-forming efficiencies (CFEs), MSC cell marker expression, and osteogenic/adipogenic differentiation. CB-MSCs and BM-MSCs demonstrated similar morphologies and PDs, reaching 100 PDs. Both populations exhibited consistent telomere lengths (12-17 kb), minimal senescence, and positive telomerase expression. CB-MSCs (PD15) had significantly lower CFEs than PD50. CB-MSCs and BM-MSCs both expressed MSC (CD73/CD90/CD105); embryonic (Nanog) and osteogenic markers (Runx2, osteocalcin) but no hematopoietic markers (CD45). CB-MSCs (PD15) strongly expressed Oct4 and p16INK4A. At early PDs, CB-MSCs possessed a strong osteogenic potency and low potency for adipogenesis, whilst BM-MSCs possessed greater overall bipotentiality for osteogenesis and adipogenesis. At PD50, CB-MSCs demonstrated reduced potency for both osteogenesis and adipogenesis, compared to BM-MSCs at equivalent PDs. This study demonstrates similarities in proliferative and mesenchymal cell characteristics between CB-MSCs and BM-MSCs, but contrasting multipotentiality. Such findings support further comparisons of human CB-MSCs and BM-MSCs, facilitating selection of optimal MSC populations for regenerative medicine purposes.

Efficient Generation of Chemically Induced Mesenchymal Stem Cells from Human Dermal Fibroblasts

Human mesenchymal stromal/stem cells (MSCs) are multipotent and currently undergoing hundreds of clinical trials for disease treatments. To date, no studies have generated induced MSCs from skin fibroblasts with chemicals or growth factors. Here, we established the first chemical method to convert primary human dermal fibroblasts into multipotent, induced MSC-like cells (iMSCs). The conversion method uses a defined cocktail of small molecules and growth factors, and it can achieve efficient conversion with an average rate of 38% in 6 days. The iMSCs have much higher clonogenicity than fibroblasts, and they can be maintained and expanded in regular MSC medium for at least 8 passages and further differentiated into osteoblasts, adipocytes, and chondrocytes. Moreover, the iMSCs can suppress LPS-mediated acute lung injury as effectively as bone marrow-derived mesenchymal stem cells. This finding may greatly benefit stem cell biology, cell therapy, and regenerative medicine.

Generation of Integration-free Induced Pluripotent Stem Cells from Human Peripheral Blood Mononuclear Cells Using Episomal Vectors

Induced Pluripotent Stem Cells (iPSCs) hold great promise for disease modeling and regenerative therapies. We previously reported the use of Episomal Vectors (EV) to generate integration-free iPSCs from peripheral blood mononuclear cells (PB MNCs). The episomal vectors used are DNA plasmids incorporated with oriP and EBNA1 elements from the Epstein-Barr (EB) virus, which allow for replication and long-term retainment of plasmids in mammalian cells, respectively. With further optimization, thousands of iPSC colonies can be obtained from 1 mL of peripheral blood. Two critical factors for achieving high reprogramming efficiencies are: 1) the use of a 2A "self-cleavage" peptide to link OCT4 and SOX2, thus achieving equimolar expression of the two factors; 2) the use of two vectors to express MYC and KLF4 individually. Here we describe a step-by-step protocol for generating integration-free iPSCs from adult peripheral blood samples. The generated iPSCs are integration-free as residual episomal plasmids are undetectable after five passages. Although the reprogramming efficiency is comparable to that of Sendai Virus (SV) vectors, EV plasmids are considerably more economical than the commercially available SV vectors. This affordable EV reprogramming system holds potential for clinical applications in regenerative medicine and provides an approach for the direct reprogramming of PB MNCs to integration-free mesenchymal stem cells, neural stem cells, etc.

Chemical Modulation of Cell Fate in Stem Cell Therapeutics and Regenerative Medicine

Regenerative medicine aims to repair and regenerate injured tissues and restore their impaired functions. Recent developments in stem cell biology have attracted significant interest in their applications in regenerative medicine. Chemical approaches using small molecules have yielded exciting results in induction and differentiation of pluripotent stem cells, lineage conversion of somatic cells, and ex vivo as well as in vivo modulation of adult stem cells. In this review, we discuss recent progress, new insights, and future challenges of the chemical approaches in stem cell biology and regenerative medicine.

Different Effects of sgRNA Length on CRISPR-mediated Gene Knockout Efficiency

CRISPR-Cas9 is a powerful genome editing technology, yet with off-target effects. Truncated sgRNAs (17nt) have been found to decrease off-target cleavage without affecting on-target disruption in 293T cells. However, the potency of 17nt sgRNAs relative to the full-length 20nt sgRNAs in stem cells, such as human mesenchymal stem cells (MSCs) and induced pluripotent stem cells (iPSCs), has not been assessed. Using a GFP reporter system, we found that both 17nt and 20nt sgRNAs expressed by lentiviral vectors induce ~95% knockout (KO) in 293T cells, whereas the KO efficiencies are significantly lower in iPSCs (60-70%) and MSCs (65-75%). Furthermore, we observed a decrease of 10-20 percentage points in KO efficiency with 17nt sgRNAs compared to full-length sgRNAs in both iPSCs and MSCs. Off-target cleavage was observed in 17nt sgRNAs with 1-2nt but not 3-4nt mismatches; whereas 20nt sgRNAs with up to 5nt mismatches can still induce off-target mutations. Of interest, we occasionally observed off-target effects induced by the 17nt but not the 20nt sgRNAs. These results indicate the importance of balancing on-target gene cleavage potency with off-target effects: when efficacy is a major concern such as genome editing in stem cells, the use of 20nt sgRNAs is preferable.

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.

The Importance of Ubiquitination and Deubiquitination in Cellular Reprogramming

Ubiquitination of core stem cell transcription factors can directly affect stem cell maintenance and differentiation. Ubiquitination and deubiquitination must occur in a timely and well-coordinated manner to regulate the protein turnover of several stemness related proteins, resulting in optimal embryonic stem cell maintenance and differentiation. There are two switches: an E3 ubiquitin ligase enzyme that tags ubiquitin molecules to the target proteins for proteolysis and a second enzyme, the deubiquitinating enzyme (DUBs), that performs the opposite action, thereby preventing proteolysis. In order to maintain stemness and to allow for efficient differentiation, both ubiquitination and deubiquitination molecular switches must operate properly in a balanced manner. In this review, we have summarized the importance of the ubiquitination of core stem cell transcription factors, such as Oct3/4, c-Myc, Sox2, Klf4, Nanog, and LIN28, during cellular reprogramming. Furthermore, we emphasize the role of DUBs in regulating core stem cell transcriptional factors and their function in stem cell maintenance and differentiation. We also discuss the possibility of using DUBs, along with core transcription factors, to efficiently generate induced pluripotent stem cells. Our review provides a relatively new understanding regarding the importance of ubiquitination/deubiquitination of stem cell transcription factors for efficient cellular reprogramming.

Bone Tissue Engineering: Past-Present-Future

Bone is one of the few tissues to display a true potential for regeneration. Fracture healing is an obvious example where regeneration occurs through tightly regulated sequences of molecular and cellular events which recapitulate tissue formation seen during embryogenesis. Still in some instances, bone regeneration does not occur properly (i.e. critical size lesions) and an appropriate therapeutic intervention is necessary. Successful replacement of bone by tissue engineering will likely depend on the recapitulation of this flow of events. In fact, bone regeneration requires cross-talk between microenvironmental factors and cells; for example, resident mesenchymal progenitors are recruited and properly guided by soluble and insoluble signaling molecules. Tissue engineering attempts to reproduce and to mimic this natural milieu by delivering cells capable of differentiating into osteoblasts, inducing growth factors and biomaterials to support cellular attachment, proliferation, migration, and matrix deposition. In the last two decades, a significant effort has been made by the scientific community in the development of methods and protocols to repair and regenerate tissues such as bone, cartilage, tendons, and ligaments. In this same period, great advancements have been achieved in the biology of stem cells and on the mechanisms governing "stemness". Unfortunately, after two decades, effective clinical translation does not exist, besides a few limited examples. Many years have passed since cell-based regenerative therapies were first described as "promising approaches", but this definition still engulfs the present literature. Failure to envisage translational cell therapy applications in routine medical practice evidences the existence of unresolved scientific and technical struggles, some of which still puzzle researchers in the field and are presented in this chapter.

Preclinical targeting of human T-cell malignancies using CD4-specific chimeric antigen receptor (CAR)-engineered T cells

Peripheral T-cell lymphomas (PTCLs) are aggressive lymphomas with no effective upfront standard treatment and ineffective options in relapsed disease, resulting in poorer clinical outcomes as compared with B-cell lymphomas. The adoptive transfer of T cells engineered to express chimeric antigen receptors (CARs) is a promising new approach for treatment of hematological malignancies. However, preclinical reports of targeting T-cell lymphoma with CARs are almost non-existent. Here we have designed a CAR, CD4CAR, which redirects the antigen specificity of CD8+ cytotoxic T cells to CD4-expressing cells. CD4CAR T cells derived from human peripheral blood mononuclear cells and cord blood effectively redirected T-cell specificity against CD4+ cells in vitro. CD4CAR T cells efficiently eliminated a CD4+ leukemic cell line and primary CD4+ PTCL patient samples in co-culture assays. Notably, CD4CAR T cells maintained a central memory stem cell-like phenotype (CD8+CD45RO+CD62L+) under standard culture conditions. Furthermore, in aggressive orthotropic T-cell lymphoma models, CD4CAR T cells efficiently suppressed the growth of lymphoma cells while also significantly prolonging mouse survival. Combined, these studies demonstrate that CD4CAR-expressing CD8+ T cells are efficacious in ablating malignant CD4+ populations, with potential use as a bridge to transplant or stand-alone therapy for the treatment of PTCLs.

Generation of integration-free induced hepatocyte-like cells from mouse fibroblasts

The ability to generate integration-free induced hepatocyte-like cells (iHeps) from somatic fibroblasts has the potential to advance their clinical application. Here, we have generated integration-free, functional, and expandable iHeps from mouse somatic fibroblasts. To elicit this direct conversion, we took advantage of an oriP/EBNA1-based episomal system to deliver a set of transcription factors, Gata4, Hnf1a, and Foxa3, to the fibroblasts. The established iHeps exhibit similar morphology, marker expression, and functional properties to primary hepatocytes. Furthermore, integration-free iHeps prolong the survival of fumarylacetoacetate-hydrolase-deficient (Fah(-/-)) mice after cell transplantation. Our study provides a novel concept for generating functional and expandable iHeps using a non-viral, non-integrating, plasmid-based system that could facilitate their pharmaceutical and biomedical application.

From Skeletal Development to Tissue Engineering: Lessons from the Micromass Assay

Damage and degeneration of the skeletal elements due to disease, trauma, and aging lead to a significant health and economical burden. To reduce this burden, skeletal tissue engineering strategies aim to regenerate functional bone and cartilage in the adult body. However, challenges still exist. Such challenges involve the identification of the external cues that determine differentiation, how to control chondrocyte hypertrophy, and how to achieve specific tissue patterns and boundaries. To address these issues, it could be insightful to look at skeletal development, a robust morphogenetic process that takes place during embryonic development and is commonly modeled in vitro by the micromass assay. In this review, we investigate what the tissue engineering field can learn from this assay. By comparing embryonic skeletal precursor cells from different anatomic locations and developmental stages in micromass, the external cues that guide lineage commitment can be identified. The signaling pathways regulating chondrocyte hypertrophy, and the cues required for tissue patterning, can be elucidated by combining the micromass assay with genetic, molecular, and engineering tools. The lessons from the micromass assay are limited by two major differences between developmental and regenerative skeletogenesis: cell type and scale. We highlight an important difference between embryonic and adult skeletal progenitor cells, in that adult progenitors are not able to form mesenchymal condensations spontaneously. Also, the mechanisms of tissue patterning need to be adjusted to the larger tissue engineering constructs. In conclusion, mechanistic insights of skeletal tissue generation gained from the micromass model could lead to improved tissue engineering strategies and constructs.

Direct Conversion of Cord Blood CD34+ Cells Into Neural Stem Cells by OCT4

: Cellular reprogramming or conversion is a promising strategy to generate desired stem cell types from somatic cells. Neural stem cells (NSCs) have the potential to regenerate central nervous system tissue and repair damage in response to injury. However, NSCs are difficult to isolate from human tissues and expand in sufficient quantities for therapy. Here, we report a method to generate neural stem cells from cord blood CD34-positive cells by ectopic expression of OCT4 in a feeder-free system. The induced cells (iNSCs) show a characteristic NSC-like morphology and can be expanded in vitro for more than 20 passages. In addition, the iNSCs are positive for neural stem cell-specific markers such as Nestin and Musashi-1 and are similar in gene expression patterns to a human neural stem cell line. The iNSCs express distinct transcriptional factors for forebrain, hindbrain, and spinal cord regions. Upon differentiation, the iNSCs are able to commit into multilineage mature neural cells. Following in vivo introduction into NOD/SCID mice, iNSCs can survive and differentiate in the mouse brain 3 months post-transplantation. Alternatively, we were also able to derive iNSCs with an episomal vector expressing OCT4. Our results suggest a novel, efficient approach to generate neural precursor cells that can be potentially used in drug discovery or regenerative medicine for neurological disease and injury.

SIGNIFICANCE

This study describes a novel method to generate expandable induced neural stem cells from human cord blood cells in a feeder-free system by a single factor, OCT4. The data are promising for future applications that require the generation of large amounts of autologous neural stem cells in disease modeling and regenerative medicine.

Fate of graft cells: what should be clarified for development of mesenchymal stem cell therapy for ischemic stroke?

Mesenchymal stem cells (MSCs) are believed to be promising for cell administration therapy after ischemic stroke. Because of their advantageous characteristics, such as ability of differentiation into neurovascular lineages, avoidance of immunological problems, and abundance of graft cells in mesodermal tissues, studies regarding MSC therapy have increased recently. However, several controversies are yet to be resolved before a worldwide consensus regarding a standard protocol is obtained. In particular, the neuroprotective effects, the rate of cell migration to the lesion, and differentiation direction differ depending on preclinical observations. Analyses of these differences and application of recent developments in stem cell biology or engineering in imaging modality may contribute to identification of criteria for optimal stem cell therapy in which reliable protocols, which control cell quality and include safe administration procedures, are defined for each recovery phase after cerebral ischemia. In this mini review, we examine controversies regarding the fate of grafts and the prospects for advanced therapy that could be obtained through recent developments in stem cell research as direct conversion to neural cells.

Tissue engineering and regenerative medicine: a year in review

It is an exciting time to be involved in tissue engineering and regenerative medicine (TERM) research. Despite its relative youth, the field is expanding fast and breaking new ground in both the laboratory and clinically. In this "Year in Review," we highlight some of the high-impact advances in the field. Building upon last year's article, we have identified the recent "hot topics" and the key publications pertaining to these themes as well as ideas that have high potential to direct the field. Based on a modified methodology grounded on last year's approach, we have identified and summarized some of the most impactful publications in five main themes: (1) pluripotent stem cells: efforts and hurdles to translation, (2) tissue engineering: complex scaffolds and advanced materials, (3) directing the cell phenotype: growth factor and biomolecule presentation, (4) characterization: imaging and beyond, and (5) translation: preclinical to clinical. We have complemented our review of the research directions highlighted within these trend-setting studies with a discussion of additional articles along the same themes that have recently been published and have yet to surface in citation analyses. We conclude with a discussion of some really interesting studies that provide a glimpse of the high potential for innovation of TERM research.

Semaphorin 3A induces mesenchymal-stem-like properties in human periodontal ligament cells

Periodontal ligament stem cells (PDLSCs) have recently been proposed as a novel option in periodontal regenerative therapy. However, one of the issues is the difficulty of stably generating PDLSCs because of the variation of stem cell potential between donors. Here, we show that Semaphorin 3A (Sema3A) can induce mesenchymal-stem-like properties in human periodontal ligament (PDL) cells. Sema3A expression was specifically observed in the dental follicle during tooth development and in parts of mature PDL tissue in rodent tooth and periodontal tissue. Sema3A expression levels were found to be higher in multipotential human PDL cell clones compared with low-differentiation potential clones. Sema3A-overexpressing PDL cells exhibited an enhanced capacity to differentiate into both functional osteoblasts and adipocytes. Moreover, PDL cells treated with Sema3A only at the initiation of culture stimulated osteogenesis, while Sema3A treatment throughout the culture had no effect on osteogenic differentiation. Finally, Sema3A-overexpressing PDL cells upregulated the expression of embryonic stem cell markers (NANOG, OCT4, and E-cadherin) and mesenchymal stem cell markers (CD73, CD90, CD105, CD146, and CD166), and Sema3A promoted cell division activity of PDL cells. These results suggest that Sema3A may possess the function to convert PDL cells into mesenchymal-stem-like cells.

Cellular reprogramming of human peripheral blood cells

Breakthroughs in cell fate conversion have made it possible to generate large quantities of patient-specific cells for regenerative medicine. Due to multiple advantages of peripheral blood cells over fibroblasts from skin biopsy, the use of blood mononuclear cells (MNCs) instead of skin fibroblasts will expedite reprogramming research and broaden the application of reprogramming technology. This review discusses current progress and challenges of generating induced pluripotent stem cells (iPSCs) from peripheral blood MNCs and of in vitro and in vivo conversion of blood cells into cells of therapeutic value, such as mesenchymal stem cells, neural cells and hepatocytes. An optimized design of lentiviral vectors is necessary to achieve high reprogramming efficiency of peripheral blood cells. More recently, non-integrating vectors such as Sendai virus and episomal vectors have been successfully employed in generating integration-free iPSCs and somatic stem cells.

Efficient generation of integration-free ips cells from human adult peripheral blood using BCL-XL together with Yamanaka factors

The ability to efficiently generate integration-free induced pluripotent stem cells (iPSCs) from the most readily available source-peripheral blood-has the potential to expedite the advances of iPSC-based therapies. We have successfully generated integration-free iPSCs from cord blood (CB) CD34(+) cells with improved oriP/EBNA1-based episomal vectors (EV) using a strong spleen focus forming virus (SFFV) long terminal repeat (LTR) promoter. Here we show that Yamanaka factors (OCT4, SOX2, MYC, and KLF4)-expressing EV can also reprogram adult peripheral blood mononuclear cells (PBMNCs) into pluripotency, yet at a very low efficiency. We found that inclusion of BCL-XL increases the reprogramming efficiency by approximately 10-fold. Furthermore, culture of CD3(-)/CD19(-) cells or T/B cell-depleted MNCs for 4-6 days led to the generation of 20-30 iPSC colonies from 1 ml PB, an efficiency that is substantially higher than previously reported. PB iPSCs express pluripotency markers, form teratomas, and can be induced to differentiate in vitro into mesenchymal stem cells, cardiomyocytes, and hepatocytes. Used together, our optimized factor combination and reprogramming strategy lead to efficient generation of integration-free iPSCs from adult PB. This discovery has potential applications in iPSC banking, disease modeling and regenerative medicine.