Teratoma formation by human embryonic stem cells is site dependent and enhanced by the presence of Matrigel

The potential for immunogenicity of autologous induced pluripotent stem cell-derived therapies

Induced pluripotent stem cell (iPSC) technology offers the promise of immune-matched cell therapies for a wide range of diseases and injuries. It is generally assumed that cells derived from autologous iPSCs will be immune-privileged. However, there are reasons to question this assumption, including recent studies that have tested iPSC immunogenicity in various ways with conflicting results. Understanding the risk of an immune response and developing strategies to minimize it will be important steps before clinical testing. Here, we review the evidence for autologous iPSC immunogenicity, its potential causes, and approaches for assessment and mitigation.

Mesenchymal stem cell-conditioned medium enhances osteogenic and chondrogenic differentiation of human embryonic stem cells and human induced pluripotent stem cells by mesodermal lineage induction

Human mesenchymal stem cells (hMSCs) have the ability to differentiate into mesenchymal lineages. In this study, we hypothesized that treatment of embryoid bodies (EBs) composed of either human embryonic stem cells (hESCs) or human induced pluripotent stem cells (hiPSCs) with a hMSC-conditioned medium (CM) can stimulate the induction of the mesodermal lineage and subsequent differentiation toward the osteogenic and chondrogenic lineage. Quantitative real-time reverse transcription-polymerase chain reaction (qRT-PCR) analysis indicated that the hMSC-CM treatment increased gene expression related to the mesodermal lineage and decreased gene expression related to the endodermal and ectodermal lineage in EBs. Fourteen days after culturing the mesodermal lineage-induced EBs in the osteogenic or chondrogenic differentiation medium, we observed enhanced osteogenic and chondrogenic differentiation compared with untreated EBs, as evaluated using qRT-PCR, cytochemistry, immunocytochemistry, and flow cytometry. This method may be useful for enhancing the osteogenic or chondrogenic differentiation of hESCs or hiPSCs.

ADAR1 is involved in the regulation of reprogramming human fibroblasts to induced pluripotent stem cells

Adenosine-to-inosine (A-to-I) RNA editing is a post-transcriptional, site-specific modification process that is catalyzed by Adenosine Deaminase Acting on RNA (ADAR) gene family members. Since ADARs act on double-stranded RNA, most A-to-I editing occurs within repetitive elements, particularly Alu elements, as the result of the inherent property of these sequences to fold and form double strands. ADAR1-mediated A-to-I RNA editing was recently implicated in the regulation of human embryonic stem cells (hESCs). Spontaneous and neuronal differentiation of hESC was shown to result in a decrease in A-to-I editing levels. Knockdown of ADAR1 in hESCs results in an elevation of the expression of differentiation-related genes. In addition, we found that hESCs over-expressing ADAR1 could not be generated. The current study shows that the editing levels of induced pluripotent stem cells (iPSCs) change throughout reprogramming, from a source cell level to a level similar to that of hESCs. Up- or down-regulation of the ADAR1 level in human foreskin fibroblast (HFF) cells before induction of reprogramming results in varied reprogramming efficiencies. Furthermore, HFF-iPSC early clones derived from source cells in which the ADAR1 level was down-regulated lose their iPSC properties shortly after iPSC colony formation and instead exhibit characteristics of cancer cells. Taken together, our results imply a role for ADAR1 in the regulation of pluripotency induction as well as in the maintenance of early iPSC properties.

Genetic correction of stem cells in the treatment of inherited diseases and focus on xeroderma pigmentosum

Somatic stem cells ensure tissue renewal along life and healing of injuries. Their safe isolation, genetic manipulation ex vivo and reinfusion in patients suffering from life threatening immune deficiencies (for example, severe combined immunodeficiency (SCID)) have demonstrated the efficacy of ex vivo gene therapy. Similarly, adult epidermal stem cells have the capacity to renew epidermis, the fully differentiated, protective envelope of our body. Stable skin replacement of severely burned patients have proven life saving. Xeroderma pigmentosum (XP) is a devastating disease due to severe defects in the repair of mutagenic DNA lesions introduced upon exposure to solar radiations. Most patients die from the consequences of budding hundreds of skin cancers in the absence of photoprotection. We have developed a safe procedure of genetic correction of epidermal stem cells isolated from XP patients. Preclinical and safety assessments indicate successful correction of XP epidermal stem cells in the long term and their capacity to regenerate a normal skin with full capacities of DNA repair.

Development of Experimental Tumors Formed by Mouse and Human Embryonic Stem and Teratocarcinoma Cells after Subcutaneous and Intraperitoneal Transplantations into Immunodeficient and Immunocompetent Mice

Pluripotent stem cells represent an attractive cell source for regenerative medicine. However, the risk of teratoma formation after transplantation restricts their clinical application. Therefore, to adequately evaluate the potential risk of tumorigenicity after cell transplantation into human tissues, effective animal transplantation assays need to be developed. We performed a multiparameter (cell number, transplantation site, cell type, host) comparative analysis of the efficiency of tumor development after transplantation of mouse and human embryonic stem (ES) cells and their malignant counterparts, teratocarcinoma (EC) cells, into animal recipients and revealed several key correlations. We found that the efficiency of tumor growth was higher after intra-peritoneal than after subcutaneous transplantations of all cell lines studied. The minimal cell numbers sufficient for tumor growth in immunodeficient nude mice were 100-fold lower for intraperitoneal than for subcutaneous transplantations of mouse and human ES cells (103 vs. 105 and 104 vs. 106, respectively). Moreover, mouse ES and EC cells formed tumors in immunodeficient and immunocompetent mice more effectively than human ES and EC cells. After intraperitoneal transplantation of 103, 104, and 105 mouse ES cells, teratomas developed in 83%, 100%, and 100% of nude mice, whereas after human ES cell transplantation, teratomas developed in 0%, 17%, and 60%, respectively. In addition, malignant mouse and human EC cells initiated tumor growth after intraperitoneal transplantation significantly faster and more effectively than ES cells. Mouse and human ES cells formed different types of teratomas containing derivatives of three germ layers but different numbers of undifferentiated cells. ES cell-like sublines with differentiation potential similar to the parental cell line were recloned only from mouse, but not from human, ES cell teratomas. These findings provide new information about the possibility and efficiency of tumor growth after transplantation of pluripotent stem cells. This information allows one to predict and possibly prevent the possible risks of tumorigenicity that could arise from stem cell therapeutics.

Toward the use of endometrial and menstrual blood mesenchymal stem cells for cell-based therapies

INTRODUCTION

Bone marrow is a widely used source of mesenchymal stem cells (MSCs) for cell-based therapies. Recently, endometrium - the highly regenerative lining of the uterus - and menstrual blood have been identified as more accessible sources of MSCs. These uterine MSCs include two related cell types: endometrial MSCs (eMSCs) and endometrial regenerative cells (ERCs).

AREAS COVERED

The properties of eMSCs and ERCs and their application in preclinical in vitro and in vivo studies for pelvic organ prolapse, heart disorders and ischemic conditions are reviewed. Details of the first clinical Phase I and Phase II studies will be provided.

EXPERT OPINION

The authors report that eMSCs and ERCs are a readily available source of adult stem cells. Both eMSCs and ERCs fulfill the key MSC criteria and have been successfully used in preclinical models to treat various diseases. Data on clinical trials are sparse. More research is needed to determine the mechanism of action of eMSCs and ERCs in these regenerative medicine models and to determine the long-term benefits and any adverse effects after their administration.

Human umbilical cord mesenchymal stem cells support nontumorigenic expansion of human embryonic stem cells

The expansion of pluripotent human embryonic stem cells (hESCs) requires a culture on feeder layers of mouse embryonic fibroblasts (MEFs). The culture model often causes immunogenic contaminations such as xenocarbohydrate, and inevitably forms teratoma in vivo. This study tested human umbilical cord-derived mesenchymal stem cells (HUCMSCs) as the feeder for hESCs. Wharton's jelly-derived HUCMSCs showed characteristics of MSCs and were easily maintained in a culture for over 20 passages. Under the mitomycin-inhibited HUCMSC feeder, hESCs maintained the features of embryonic stem cells (pluripotency and maintenance of normal karyotypes) after a prolonged culture of more than 20 passages. Notably, in extensive trials, no teratoma was formed in xenograft in NOD/SCID mice, but subsequent resumption of teratoma formation was noted upon transient coculturing with MEFs. Interestingly, among the four pluripotency-conferring genes, MYC and OCT4 were found to be downregulated in hESCs cocultured with HUCMSCs. Results of this study supported a nontumorigenic sustained culture of hESCs and did not form teratoma in vivo.

Formation of human prostate epithelium using tissue recombination of rodent urogenital sinus mesenchyme and human stem cells

Progress in prostate cancer research is severely limited by the availability of human-derived and hormone-naïve model systems, which limit our ability to understand genetic and molecular events underlying prostate disease initiation. Toward developing better model systems for studying human prostate carcinogenesis, we and others have taken advantage of the unique pro-prostatic inductive potential of embryonic rodent prostate stroma, termed urogenital sinus mesenchyme (UGSM). When recombined with certain pluripotent cell populations such as embryonic stem cells, UGSM induces the formation of normal human prostate epithelia in a testosterone-dependent manner. Such a human model system can be used to investigate and experimentally test the ability of candidate prostate cancer susceptibility genes at an accelerated pace compared to typical rodent transgenic studies. Since Human embryonic stem cells (hESCs) can be genetically modified in culture using inducible gene expression or siRNA knock-down vectors prior to tissue recombination, such a model facilitates testing the functional consequences of genes, or combinations of genes, which are thought to promote or prevent carcinogenesis. The technique of isolating pure populations of UGSM cells, however, is challenging and learning often requires someone with previous expertise to personally teach. Moreover, inoculation of cell mixtures under the renal capsule of an immunocompromised host can be technically challenging. Here we outline and illustrate proper isolation of UGSM from rodent embryos and renal capsule implantation of tissue mixtures to form human prostate epithelium. Such an approach, at its current stage, requires in vivo xenografting of embryonic stem cells; future applications could potentially include in vitro gland formation or the use of induced pluripotent stem cell populations (iPSCs).

Lessons from human teratomas to guide development of safe stem cell therapies

The potential for the formation of teratomas or other neoplasms is a major safety roadblock to clinical application of pluripotent stem cell therapies. Preclinical assessment of the risk of tumor formation in this context poses considerable scientific and regulatory challenges, especially because animal xenograft models may not properly reflect the long-term tumorigenic potential of human cells. A better understanding of the biology of spontaneously occurring teratomas and related tumors in humans can help to guide efforts to assess and minimize the potential hazards of embryonic stem cell or induced pluripotent stem cell therapeutics. Here we review the features of teratomas derived experimentally from human pluripotent stem cells and argue that they most closely resemble spontaneous benign teratomas that occur early in both mouse and human life. The natural history and pathology of these spontaneously occurring teratomas provide important clues for preclinical safety assessment and patient monitoring in trials of stem cell therapies.

mRNA transfection-based, feeder-free, induced pluripotent stem cells derived from adipose tissue of a 50-year-old patient

Induced pluripotent stem cells (iPSC) have successfully been derived from somatic fibroblasts through transfection of synthetic modified mRNA encoding transcription factors. This technique obviates the use of recombinant DNA and viral vectors in cellular reprogramming. The present study derived iPSC from adipose-derived mesenchymal stem cells (of a 50-year-old female patient) by utilizing a similar technique, but with defined culture medium without feeder cells, during both reprogramming and propagation. Clonal selection was performed to yield 12 putative iPSC lines from individual colonies of nascent reprogrammed cells, starting from 150,000 cells. However, only seven lines maintained their undifferentiated state after 10 continuous serial passages. These seven lines were then subjected to a rigorous battery of analyses to confirm their identity as iPSC. These tests included immunostaining, flow cytometry, qRT-PCR, in vitro differentiation assay, and teratoma formation assay within SCID mice. Positive results were consistently observed in all analyses, thus verifying the cells as fully reprogrammed iPSC. While all 7 iPSC lines displayed normal karyogram up to passage 13, chromosomal anomalies occurred in 4 of 7 lines with extended in vitro culture beyond 24 serial passages. Only three lines retained normal karyotype of 46,XX. The remaining four lines displayed mosaicism of normal and abnormal karyotypes. Hence, this study successfully derived iPSC from abundant and easily accessible adipose tissues of a middle-aged patient; utilizing a mRNA-based integration-free technique under feeder-free conditions. This is a step forward in translating iPSC into personalized regenerative medicine within the clinic.

Immunogenicity of pluripotent stem cells and their derivatives

The ability of pluripotent stem cells to self-renew and differentiate into all somatic cell types brings great prospects to regenerative medicine and human health. However, before clinical applications, much translational research is necessary to ensure that their therapeutic progenies are functional and nontumorigenic, that they are stable and do not dedifferentiate, and that they do not elicit immune responses that could threaten their survival in vivo. For this, an in-depth understanding of their biology, genetic, and epigenetic make-up and of their antigenic repertoire is critical for predicting their immunogenicity and for developing strategies needed to assure successful long-term engraftment. Recently, the expectation that reprogrammed somatic cells would provide an autologous cell therapy for personalized medicine has been questioned. Induced pluripotent stem cells display several genetic and epigenetic abnormalities that could promote tumorigenicity and immunogenicity in vivo. Understanding the persistence and effects of these abnormalities in induced pluripotent stem cell derivatives is critical to allow clinicians to predict graft fate after transplantation, and to take requisite measures to prevent immune rejection. With clinical trials of pluripotent stem cell therapy on the horizon, the importance of understanding immunologic barriers and devising safe, effective strategies to bypass them is further underscored. This approach to overcome immunologic barriers to stem cell therapy can take advantage of the validated knowledge acquired from decades of hematopoietic stem cell transplantation.

Basal expression of pluripotency-associated genes can contribute to stemness property and differentiation potential

Pluripotency and stemness is believed to be associated with high Oct-3/4, Nanog, and Sox-2 (ONS) expression. Similar to embryonic stem cells (ESCs), high ONS expression eventually became the measure of pluripotency in any cell. The threshold expression of ONS genes that underscores pluripotency, stemness, and differentiation potential is still unclear. Therefore, we raised a question as to whether pluripotency and stemness is a function of basal ONS gene expression. To prove this, we carried out a comparative study between basal ONS expressing NIH3T3 cells with pluripotent mouse bone marrow mesenchymal stem cells (mBMSC) and mouse ESC. Our studies on cellular, molecular, and immunological biomarkers between NIH3T3 and mBMSC demonstrated stemness property of undifferentiated NIH3T3 cells that was similar to mBMSC and somewhat close to ESC as well. In vivo teratoma formation with all three germ layer derivatives strengthen the fact that these cells in spite of basal ONS gene expression can differentiate into cells of multiple lineages without any genetic modification. Conclusively, our novel findings suggested that the phenomenon of pluripotency which imparts ability for multilineage cell differentiation is not necessarily a function of high ONS gene expression.

Side scatter intensity is highly heterogeneous in undifferentiated pluripotent stem cells and predicts clonogenic self-renewal

In culture, human pluripotent stem cells (PSCs) are phenotypically (for instance, the SSEA3 expression level) and functionally (capacity to survive after single-cell dissociation) heterogeneous. We report here that the side scatter (SSC) signal measured by flow cytometry, a variable correlated with membrane irregularity and cell granularity, is very high in PSCs, even higher than in blood polymorphonuclear cells, and markedly heterogeneous. Moreover, SSC intensity rapidly and strongly decreases upon PSC differentiation into any of the three germ layers. PSCs with high SSC (HSSC cells) or low SSC (LSSC cells) values both express pluripotency markers, but HSSC cells are characterized by more frequent simultaneous expression of the membrane pluripotency factors SSEA3, SSEA4, TRA-1-81, TRA-1-60, and CD24 and by a higher mitochondrial content. Functionally, HSSC cells are more likely to generate colonies upon single-cell passage than LSSC cells. SSC monitoring might provide a simple, but robust and rapid method to estimate pluripotency variations in culture and unveils a new phenotypic and functional heterogeneity in PSCs.

Goat embryonic stem-like cell derivation and characterization

Embryonic stem (ES) cells are derived from the inner cell masses of preimplantation embryos. ES cells are pluripotent cells with the capacity for long-term propagation and broad differentiation plasticity. These cells have an exceptional functional feature in that they can differentiate into all tissues and organs, including germ cells. Established ES cell lines have been generated in mouse, human, and nonhuman primate but derivation of ES cells in farm animals has been problematic. Several ES-like cell lines from farm animals have been reported to exhibit properties of pluripotency in vitro. However, only a few of them morphologically resemble ES cells, or express markers that are associated with established ES cell lines from mouse and humans. Methods for derivation, propagation, and differentiation of ES cells from domestic animals have not been fully established. In this chapter, we describe methods for isolation of goat ES (gES) cell lines from in vivo-derived blastocysts and characterization of markers indicative of pluripotency. In addition, we outline differentiation of gES cells into all three germ layers in vivo by forming teratomas as a hallmark of pluripotency.

Transplantation of osteogenically differentiated mouse iPS cells for bone repair

Induced pluripotent stem (iPS) cells are a type of undifferentiated cell that can be obtained from differentiated cells and have the pluripotent potential to differentiate into the musculoskeletal system, the myocardium, vascular endothelial cells, neurons, and hepatocytes. We therefore cultured mouse iPS cells in a DMEM containing 15% FBS, 10(-7) M dexamethasone, 10 mM β-glycerophosphate, and 50 μg/ml ascorbic acid for 3 weeks, in order to induce bone differentiation, and studied the expression of the bone differentiation markers Runx2 and osteocalcin using RT-PCR in a time-dependent manner. Osteocalcin, a bone differentiation marker in bone formation, exhibited the highest expression in the third week. In addition, the deposition of calcium nodules was observed using Alizarin red S staining. iPS cells cultured for bone differentiation were transplanted into severe combined immunodeficiency (SCID) mice, and the osteogenic potential exhibited after 4 weeks was studied. When bone differentiation-induced iPS cells were transplanted into SCID mice, bone formation was confirmed in soft X-ray images and tissue specimens. However, teratoma formation was confirmed in 20% of the transplanted models. When mouse iPS cells were treated with irradiation of 2 Gray (Gy) prior to transplantation, teratoma formation was inhibited. When mouse iPS cells treated in a likewise manner were xenotransplanted into rats, bone formation was confirmed but teratoma formation was not observed. It is believed that irradiation before transplantation is an effective way to inhibit teratoma formation.

Toward personalized cell therapies by using stem cells: seven relevant topics for safety and success in stem cell therapy

Stem cells, both embryonic and adult, due to the potential for application in tissue regeneration have been the target of interest to the world scientific community. In fact, stem cells can be considered revolutionary in the field of medicine, especially in the treatment of a wide range of human diseases. However, caution is needed in the clinical application of such cells and this is an issue that demands more studies. This paper will discuss some controversial issues of importance for achieving cell therapy safety and success. Particularly, the following aspects of stem cell biology will be presented: methods for stem cells culture, teratogenic or tumorigenic potential, cellular dose, proliferation, senescence, karyotyping, and immunosuppressive activity.

Standardization of the teratoma assay for analysis of pluripotency of human ES cells and biosafety of their differentiated progeny

Teratoma tumor formation is an essential criterion in determining the pluripotency of human pluripotent stem cells. However, currently there is no consistent protocol for assessment of teratoma forming ability. Here we present detailed characterization of a teratoma assay that is based on subcutaneous co-transplantation of defined numbers of undifferentiated human embryonic stem cells (hESCs) with mitotically inactivated feeder cells and Matrigel into immunodeficient mice. The assay was highly reproducible and 100% efficient when 100,000 hESCs were transplanted. It was sensitive, promoting teratoma formation after transplantation of 100 hESCs, though larger numbers of animals and longer follow-up were required. The assay could detect residual teratoma forming cells within differentiated hESC populations however its sensitivity was decreased in the presence of differentiated cells. Our data lay the foundation, for standardization of a teratoma assay for pluripotency analysis. The assay can also be used for bio-safety analysis of pluripotent stem cell-derived differentiated progeny.

Efficient neuronal differentiation and maturation of human pluripotent stem cells encapsulated in 3D microfibrous scaffolds

Developing an efficient culture system for controlled human pluripotent stem cell (hPSC) differentiation into selected lineages is a major challenge in realizing stem cell-based clinical applications. Here, we report the use of chitin-alginate 3D microfibrous scaffolds, previously developed for hPSC propagation, to support efficient neuronal differentiation and maturation under chemically defined culture conditions. When treated with neural induction medium containing Noggin/retinoic acid, the encapsulated cells expressed much higher levels of neural progenitor markers SOX1 and PAX6 than those in other treatment conditions. Immunocytochemisty analysis confirmed that the majority of the differentiated cells were nestin-positive cells. Subsequently transferring the scaffolds to neuronal differentiation medium efficiently directed these encapsulated neural progenitors into mature neurons, as detected by RT-PCR and positive immunostaining for neuron markers βIII tubulin and MAP2. Furthermore, flow cytometry confirmed that >90% βIII tubulin-positive neurons was achieved for three independent iPSC and hESC lines, a differentiation efficiency much higher than previously reported. Implantation of these terminally differentiated neurons into SCID mice yielded successful neural grafts comprising MAP2 positive neurons, without tumorigenesis, suggesting a potential safe cell source for regenerative medicine. These results bring us one step closer toward realizing large-scale production of stem cell derivatives for clinical and translational applications.

Efficient derivation of human embryonic stem cell lines from discarded embryos through increases in the concentration of basic fibroblast growth factor

We describe the derivation and characterization of three novel human embryonic stem (hES) cell lines (YT1, YT2, YT3). One hES line (YT1) was obtained from six discarded blastocysts in a culture medium supplemented with 12 ng/ml basic fibroblast growth factor (bFGF), and two lines (YT2,YT3)were obtained from three discarded blastocysts in the same medium but supplemented with 16 ng/ml bFGF. These cell lines were derived by partial or whole embryo culture followed by further expansion after manual dissection of the passaged cells. These cells were passaged continuously for more than 6 or 8 months and possessed all of the typical features of pluripotent hES cell lines, such as typical morphological characteristics and the expression of hES-specific markers (TRA-1-60, TRA-1-81, SSEA-4, SSEA-3, alkaline phosphatase, Oct4, Nanog) and pluripotency-related genes (Oct4, Nanog, TDGF1, Sox2, EBAF, Thy-1, FGF4, Rex1). The lines maintained normal karyotypes after long-term cultivation. The karyotype of YT1 and YT3 was 46,XX, and that of YT2 was 46, XY. Pluripotency was confirmed by in vitro and in vivo differentiation, and genetic identity was demonstrated by DNA fingerprinting.Our results indicate that higher concentrations of bFGF at the early culture stage support efficient the hES cell derivation.

Derivation of stromal (skeletal and mesenchymal) stem-like cells from human embryonic stem cells

Derivation of bone forming cells (osteoblasts) from human embryonic stem cells (hESCs) is a prerequisite for their use in clinical applications. However, there is no standard protocol for differentiating hESCs into osteoblastic cells. The aim of this study was to identify the emergence of a human stromal (mesenchymal and skeletal) stem cell (hMSC)-like population, known to be osteoblastic cell precursors and to test their osteoblastic differentiation capacity in ex vivo cultures and in vivo. We cultured hESCs in a feeder-free environment using serum replacement and as suspension aggregates (embryoid bodies; hEBs). Over a 20 day developmental period, the hEBs demonstrated increasing enrichment for cells expressing hMSC markers: CD29, CD44, CD63, CD56, CD71, CD73, CD105, CD106, and CD166 as revealed by immunohistochemical staining and flow cytometry (fluorescence-activated cell sorting) analysis. Ex vivo differentiation of hEBs using bone morphogenic protein 2 (BMP2) combined with standard osteoblast induction medium led to weak osteoblastic induction. Conversely, subcutaneous in vivo implantation of day 20 hEBs in immune deficient mice, mixed with hydroxyapatite/tricalcium phosphate (HA/TCP) as an osteoconductive scaffold, revealed bone and cartilage, and fibrous tissue elements after 8 weeks. These tissues were of human origin and there was no evidence of differentiation to nonmesodermal tissues. hEBs implanted in the absence of HA/TCP formed vacuolated tissue containing glandular, fibrous and muscle-like tissue elements. Conversely, implantation of undifferentiated hESCs resulted in the formation of a teratoma containing a mixture of endodermal, mesodermal, and ectodermal tissues. Our study demonstrates that hMSC-like cells can be obtained from hESCs and they can be induced to form skeletal tissues in vivo when combined with HA/TCP. These findings are relevant for tissue engineering and suggest that differentiated hEBs can provide an unlimited source for functional osteogenic cells.

In vivo differentiation potential of buffalo (Bubalus bubalis) embryonic stem cell

Embryonic stem cells (ESCs) derived from inner cell mass (ICM) of mammalian blastocyst are having indefinite proliferation and differentiation capability for any type of cell lineages. In the present study, ICMs of in vitro-derived buffalo blastocysts were cultured into two different culture systems using buffalo fetal fibroblast as somatic cell support and Matrigel as synthetic support to obtain pluripotent buffalo embryonic stem cell (buESC) colonies. Pluripotency of the ESCs were characterised through pluripotency markers whereas, their differentiation capability was assessed by teratoma assay using immuno-compromised mice. Cumulus ooccyte complexes from slaughter house-derived ovaries were subjected to in vitro maturation, in vitro fertilization and in vitro culture to generate blastocysts. Total 262 blastocysts were derived through IVEP with 11.83 % (31/262) hatching rate. To generate buESCs, 15 ICMs from hatched blastocysts were cultured on mitomycin-C-treated homologous fetal fibroblast feeder layer, whereas the leftover 16 ICMs were cultured on extra-cellular matrix (Matrigel). No significant differences were observed for primary ESCs colony formation between two culture systems. Primary colonies as well as passaged ESCs were characterised by alkaline phosphatase staining, karyotyping and expression of transcription-based stem cell markers, OCT-4 and cell surface antigens SSEA-4 and TRA-1-60. Batch of ESCs found positive for pluripotency markers and showing normal karyotype after fifteenth passage were inoculated into eight immuno-compromised mice through subcutaneous and intramuscular route. Subcutaneous route of inoculation was found to be better than intramuscular route. Developed teratomas were excised surgically and subjected to histological analysis. Histological findings revealed presence of all the three germinal layer derivatives in teratoma sections. Presence of germinal layer derivatives were further confirmed by reverse transcriptase-polymerase chain reaction for the presence of differentiation markers like nerve cell adhesion molecule, fetal liver kinase-1 and alpha-feto protein for ectoderm, mesoderm and endoderm, respectively.

Astrocytes generated from patient induced pluripotent stem cells recapitulate features of Huntington's disease patient cells

Background

Huntington’s Disease (HD) is a devastating neurodegenerative disorder that clinically manifests as motor dysfunction, cognitive impairment and psychiatric symptoms. There is currently no cure for this progressive and fatal disorder. The causative mutation of this hereditary disease is a trinucleotide repeat expansion (CAG) in the Huntingtin gene that results in an expanded polyglutamine tract. Multiple mechanisms have been proposed to explain the preferential striatal and cortical degeneration that occurs with HD, including non-cell-autonomous contribution from astrocytes. Although numerous cell culture and animal models exist, there is a great need for experimental systems that can more accurately replicate the human disease. Human induced pluripotent stem cells (iPSCs) are a remarkable new tool to study neurological disorders because this cell type can be derived from patients as a renewable, genetically tractable source for unlimited cells that are difficult to acquire, such as neurons and astrocytes. The development of experimental systems based on iPSC technology could aid in the identification of molecular lesions and therapeutic treatments.

Results

We derived iPSCs from a father with adult onset HD and 50 CAG repeats (F-HD-iPSC) and his daughter with juvenile HD and 109 CAG repeats (D-HD-iPSC). These disease-specific iPSC lines were characterized by standard assays to assess the quality of iPSC lines and to demonstrate their pluripotency. HD-iPSCs were capable of producing phenotypically normal, functional neurons in vitro and were able to survive and differentiate into neurons in the adult mouse brain in vivo after transplantation. Surprisingly, when HD-iPSCs were directed to differentiate into an astrocytic lineage, we observed the presence of cytoplasmic, electron clear vacuoles in astrocytes from both F-HD-iPSCs and D-HD-iPSCs, which were significantly more pronounced in D-HD-astrocytes. Remarkably, the vacuolation in diseased astrocytes was observed under basal culture conditions without additional stressors and increased over time. Importantly, similar vacuolation phenotype has also been observed in peripheral blood lymphocytes from individuals with HD. Together, these data suggest that vacuolation may be a phenotype associated with HD.

Conclusions

We have generated a unique in vitro system to study HD pathogenesis using patient-specific iPSCs. The astrocytes derived from patient-specific iPSCs exhibit a vacuolation phenotype, a phenomenon previously documented in primary lymphocytes from HD patients. Our studies pave the way for future mechanistic investigations using human iPSCs to model HD and for high-throughput therapeutic screens.

Procedures for derivation and characterisation of human embryonic stem cells from Odense, Denmark

In 1998, a development occurred in stem cell biology with the first report of the derivation of a human embryonic stem cell (hESC) line. Since then a number of techniques have been used to derive and characterise hESCs. Here, we describe the derivation methods used by our laboratory for isolation of the ICM by immunosurgery and outgrowth of the whole blastocyst. We have added protocols for routine culture, passaging and cryopreservation of our hESC lines as well as the methods we have used for characterisation (flow cytometry, karyotyping, immunocytochemistry, in vitro and in vivo differentiation). Additionally, we have included gene sequences for PCR and an antibody list for immunocytochemistry.

Nonhuman primate induced pluripotent stem cells in regenerative medicine

Among the various species from which induced pluripotent stem cells have been derived, nonhuman primates (NHPs) have a unique role as preclinical models. Their relatedness to humans and similar physiology, including central nervous system, make them ideal for translational studies. We review here the progress made in deriving and characterizing iPS cell lines from different NHP species. We focus on iPS cell lines from the marmoset, a small NHP in which several human disease states can be modeled. The marmoset can serve as a model for the implementation of patient-specific autologous cell therapy in regenerative medicine.

Generation of disease-specific induced pluripotent stem cells from patients with different karyotypes of Down syndrome

Introduction

Down syndrome (DS), a major cause of mental retardation, is caused by trisomy of some or all of human chromosome 21 and includes three basic karyotypes: trisomy 21, translocation, and mosaicism. The derivation of DS-specific induced pluripotent stem cells (iPSCs) provides us novel DS models that can be used to determine the DS mechanism and to devise therapeutic approaches for DS patients.

Methods

In the present study, fibroblasts from patients with DS of various karyotypes were reprogrammed into iPSCs via the overexpression of four factors: OCT4, SOX2, KLF4, and c-MYC, by using lentiviral vectors. The abilities of the iPSC-DS in the self-renewal and pluripotency in vitro and in vivo were then examined.

Results

The iPSC-DS showed characteristics similar to those of human embryonic stem cells, particularly the morphology, surface marker (SSEA4, TRA-1-60, and TRA-1-81) expression, pluripotent-specific transcription-factor expression levels, and methylation status of the OCT4 promoter. The pluripotency of iPSC-DS was also tested in vitro and in vivo. Embryoid bodies were formed and showed the expression of differentiated markers for three germ layers. Furthermore, iPSC-DS formed classic teratomas when injected into nonobese diabetic-severe combined immunodeficient (NOD-SCID) mice.

Conclusions

iPSCs were generated from patients with DS. The iPSCs derived from different types of DS may be used in DS modeling, patient-care optimization, drug discovery, and eventually, autologous cell-replacement therapies.

[Embryonic stem cells in the treatment of severe cardiac insufficiency]

The experience accumulated in cardiac cell therapy suggests that regeneration of extensively necrotic myocardial areas is unlikely to be achieved by the sole paracrine effects of the grafted cells but rather requires the conversion of these cells into cardiomyocytes featuring the capacity to substitute for those which have been irreversibly lost. In this setting, the use of human pluripotent embryonic stem cells has a strong rationale. The experimental results obtained in animal models of myocardial infarction are encouraging. However, the switch to clinical applications still requires to address some critical issues, among which optimizing cardiac specification of the embryonic stem cells, purifying the resulting progenitor cells so as to graft a purified population devoid from any contamination by residual pluripotent cells which carry the risk of tumorigenesis and controlling the expected allogeneic rejection by clinically acceptable methods. If the solution to these problems is a pre-requisite, the therapeutic success of this approach will also depend on the capacity to efficiently transfer the cells to the target tissue, to keep them alive once engrafted and to allow them to spatially organize in such a way that they can contribute to the contractile function of the heart.

Embryonic stem cells for severe heart failure: why and how?

The experience accumulated in cardiac cell therapy suggests that regeneration of extensively necrotic myocardial areas is unlikely to be achieved by the sole paracrine effects of the grafted cells but rather requires the conversion of these cells into cardiomyocytes featuring the capacity to substitute for those which have been irreversibly lost. In this setting, the use of human pluripotent embryonic stem cells has a strong rationale. The experimental results obtained in animal models of myocardial infarction are encouraging. However, the switch to clinical applications still requires to address some critical issues, among which the optimization of the cardiac specification of the embryonic stem cells, the purification of the resulting progenitor cells so as to graft a purified population devoid from any contamination by residual pluripotent cells which carry the risk of tumorigenesis, and the control of the expected allogeneic rejection by clinically acceptable methods. If the solution to these problems is a prerequisite, the therapeutic success of this approach will also depend on the capacity to efficiently transfer the cells to the target tissue, to keep them alive once engrafted, and to allow them to spatially organize in such a way that they can contribute to the contractile function of the heart.

Protecting against wayward human induced pluripotent stem cells with a suicide gene

The generation of human induced pluripotent stem cells (hiPSCs) opens a prospect for regenerative medicine. However, transplantation of somatic cells derived from hiPSCs still harbor many risks such as cells' incorrect differentiation or over-proliferation, and the worst, tumor formation. Therefore, it's essential to ravel out these obstacles before their clinical application. Herein, we genetically modified hiPSCs and human embryonic stem cells (hESCs) with a truncated herpes simplex virus delta thymidine kinase (deltaTK) gene driven by EF1α or Nanog promoter to selectively ablate wayward pluripotent stem cells. The results showed that insertion of deltaTK gene did not alter their pluripotency and self-renewal capacity but rendered them sensitive to ganciclovir, which induced elimination of deltaTK(+) cells in vitro in a dose and time-dependent manner, most importantly, facilitated both prevention and ablation of tumors in vivo. Furthermore, comparative analysis between transduced hiPSCs and hESCs showed that there was no difference in ganciclovir sensitivity between them. This approach may help to develop safety strategies for clinical application of hiPSCs in regenerative medicine in the future.

Mouse and human pluripotent stem cells and the means of their myogenic differentiation

Pluripotent stem cells, such as embryonic stem cells and induced pluripotent stem cells, are an important tool in the studies focusing at the differentiation of various cell types, including skeletal myoblasts. They are also considered as a source of the cells that due to their pluripotent character and availability could be turned into any required tissue and then used in future in regenerative medicine. However, the methods of the derivation of some of cell types from pluripotent cells still need to be perfected. This chapter summarizes the history and current advancements in the derivation and testing of pluripotent stem cells-derived skeletal myoblasts. It focuses at the in vitro methods allowing the differentiation of stem cells grown in monolayer or propagated as embryoid bodies, and also at in vivo tests allowing the verification of the functionality of obtained skeletal myoblasts.

Early events in xenograft development from the human embryonic stem cell line HS181--resemblance with an initial multiple epiblast formation

Xenografting is widely used for assessing in vivo pluripotency of human stem cell populations. Here, we report on early to late events in the development of mature experimental teratoma from a well-characterized human embryonic stem cell (HESC) line, HS181. The results show an embryonic process, increasingly chaotic. Active proliferation of the stem cell derived cellular progeny was detected already at day 5, and characterized by the appearance of multiple sites of engraftment, with structures of single or pseudostratified columnar epithelium surrounding small cavities. The striking histological resemblance to developing embryonic ectoderm, and the formation of epiblast-like structures was supported by the expression of the markers OCT4, NANOG, SSEA-4 and KLF4, but a lack of REX1. The early neural marker NESTIN was uniformly expressed, while markers linked to gastrulation, such as BMP-4, NODAL or BRACHYURY were not detected. Thus, observations on day 5 indicated differentiation comparable to the most early transient cell populations in human post implantation development. Confirming and expanding on previous findings from HS181 xenografts, these early events were followed by an increasingly chaotic development, incorporated in the formation of a benign teratoma with complex embryonic components. In the mature HS181 teratomas not all types of organs/tissues were detected, indicating a restricted differentiation, and a lack of adequate spatial developmental cues during the further teratoma formation. Uniquely, a kinetic alignment of rare complex structures was made to human embryos at diagnosed gestation stages, showing minor kinetic deviations between HS181 teratoma and the human counterpart.

Potential of human embryonic stem cells in cartilage tissue engineering and regenerative medicine

The current surgical intervention of using autologous chondrocyte implantation (ACI) for cartilage repair is associated with several problems such as donor site morbidity, de-differentiation upon expansion and fibrocartilage repair following transplantation. This has led to exploration of the use of stem cells as a model for chondrogenic differentiation as well as a potential source of chondrogenic cells for cartilage tissue engineering and repair. Embryonic stem cells (ESCs) are advantageous, due to their unlimited self-renewal and pluripotency, thus representing an immortal cell source that could potentially provide an unlimited supply of chondrogenic cells for both cell and tissue-based therapies and replacements. This review aims to present an overview of emerging trends of using ESCs in cartilage tissue engineering and regenerative medicine. In particular, we will be focusing on ESCs as a promising cell source for cartilage regeneration, the various strategies and approaches employed in chondrogenic differentiation and tissue engineering, the associated outcomes from animal studies, and the challenges that need to be overcome before clinical application is possible.

Extra-embryonic human Wharton's jelly stem cells do not induce tumorigenesis, unlike human embryonic stem cells

Tumorigenesis is the major obstacle of tissues derived from human embryonic stem cells (ESC) and human induced pluripotent stem cell (IPSC) for transplantation therapy. This prompted a search for other sources of ESC. This study isolated and characterized stem cells from the extra-embryonic human umbilical cord Wharton's jelly (WJSC). These cells are non-controversial, available in abundance, proliferative, multipotent and hypoimmunogenic. However, their tumorigenic potential has not been properly addressed. Their tumour-producing capabilities were compared with human ESC using the immunodeficient mouse model. Unlabelled human ESC+matrigel (2×10(6)cells/site), labelled human WJSC (red fluorescent protein; 5×10(6)cells/site) and unlabelled human WJSC+matrigel (5×10(6)cells/site) were injected via three routes (s.c., i.m. and i.p.). Animals that received human ESC+matrigel developed teratomas in 6 weeks (s.c. 85%; i.m. 75%; i.p. 100%) that contained tissues of ectoderm, mesoderm and endoderm. No animal that received human WJSC developed tumours or inflammatory reactions at the injection sites when maintained for a prolonged period (20 weeks). Human WJSC produced increases in anti-inflammatory cytokines in contrast to human ESC, which increased pro-inflammatory cytokines. Human WJSC, being hypoimmunogenic and non-tumorigenic, have the potential for safe cell-based therapies.

Jekyll or Hyde: does Matrigel provide a more or less physiological environment in mammary repopulating assays?

In vivo transplantation is the current 'gold-standard' assay for evaluating mammary stem cell (MaSC) function. Matrigel, a reconstituted extracellular matrix derived from a mouse sarcoma line, is increasingly being utilized for mammary repopulating assays, although original studies were carried out in its absence. This matrix has also been shown to enhance tumor-initiating capacity. Whilst Matrigel increases the rate of engraftment by MaSCs, it also appears to promote progenitor activity that is distinct from bona fide stem cell activity. This caveat should be considered when interpreting mammary reconstitution assays that incorporate Matrigel, particularly when transplanting high cell numbers.

Effects of histocompatibility and host immune responses on the tumorigenicity of pluripotent stem cells

Pluripotent stem cells hold great promises for regenerative medicine. They might become useful as a universal source for a battery of new cell replacement therapies. Among the major concerns for the clinical application of stem cell-derived grafts are the risks of immune rejection and tumor formation. Pluripotency and tumorigenicity are closely linked features of pluripotent stem cells. However, the capacity to form teratomas or other tumors is not sufficiently described by inherited features of a stem cell line or a stem cell-derived graft. The tumorigenicity always depends on the inability of the recipient to reject the tumorigenic cells. This review summarizes recent data on the tumorigenicity of pluripotent stem cells in immunodeficient, syngeneic, allogeneic, and xenogeneic hosts. The effects of immunosuppressive treatment and cell differentiation are discussed. Different immune effector mechanisms appear to be involved in the rejection of undifferentiated and differentiated cell populations. Elements of the innate immune system, such as natural killer cells and the complement system, which are active also in syngeneic recipients, appear to preferentially reject undifferentiated cells. This effect could reduce the risk of tumor formation in immunocompetent recipients. Cell differentiation apparently increases susceptibility to rejection by the adaptive immune system in allogeneic hosts. The current data suggest that the immune system of the recipient has a major impact on the outcome of pluripotent stem cell transplantation, whether it is rejection, engraftment, or tumor development. This has to be considered when the results of experimental transplantation models are interpreted and even more when translation into clinics is planned.

Risk factors in the development of stem cell therapy

Stem cell therapy holds the promise to treat degenerative diseases, cancer and repair of damaged tissues for which there are currently no or limited therapeutic options. The potential of stem cell therapies has long been recognised and the creation of induced pluripotent stem cells (iPSC) has boosted the stem cell field leading to increasing development and scientific knowledge. Despite the clinical potential of stem cell based medicinal products there are also potential and unanticipated risks. These risks deserve a thorough discussion within the perspective of current scientific knowledge and experience. Evaluation of potential risks should be a prerequisite step before clinical use of stem cell based medicinal products.

The risk profile of stem cell based medicinal products depends on many risk factors, which include the type of stem cells, their differentiation status and proliferation capacity, the route of administration, the intended location, in vitro culture and/or other manipulation steps, irreversibility of treatment, need/possibility for concurrent tissue regeneration in case of irreversible tissue loss, and long-term survival of engrafted cells. Together these factors determine the risk profile associated with a stem cell based medicinal product. The identified risks (i.e. risks identified in clinical experience) or potential/theoretical risks (i.e. risks observed in animal studies) include tumour formation, unwanted immune responses and the transmission of adventitious agents.

Currently, there is no clinical experience with pluripotent stem cells (i.e. embryonal stem cells and iPSC). Based on their characteristics of unlimited self-renewal and high proliferation rate the risks associated with a product containing these cells (e.g. risk on tumour formation) are considered high, if not perceived to be unacceptable. In contrast, the vast majority of small-sized clinical trials conducted with mesenchymal stem/stromal cells (MSC) in regenerative medicine applications has not reported major health concerns, suggesting that MSC therapies could be relatively safe. However, in some clinical trials serious adverse events have been reported, which emphasizes the need for additional knowledge, particularly with regard to biological mechanisms and long term safety.

Sustained embryoid body formation and culture in a non-laborious three dimensional culture system for human embryonic stem cells

Pluripotent human embryonic stem cell (hESC) lines are a promising model system in developmental and tissue regeneration research. Differentiation of hESCs towards the three germ layers and finally tissue specific cell types is often performed through the formation of embryoid bodies (EBs) in suspension or hanging droplet culture systems. However, these systems are inefficient regarding embryoid body (EB) formation, structural support to the EB and long term differentiation capacity. The present study investigates if agarose, as a semi solid matrix, can facilitate EB formation and support differentiation of hESC lines. The results showed that agarose culture is able to enhance EB formation efficiency with 10% and increase EB growth by 300%. The agarose culture system was able to maintain expression of the three germ layers over 8 weeks of culture. All of the four hESC lines tested developed EBs in the agarose system although with a histological heterogeneity between cell lines as well as within cell lines. In conclusion, a 3-D agarose culture of spherical hESC colonies improves EB formation and growth in a cost effective, stable and non-laborious technique.

Selective isolation and differentiation of a stromal population of human embryonic stem cells with osteogenic potential

The derivation of osteogenic cells from human embryonic stem cells (hESC) has been hampered by the absence of easy and reproducible protocols. hESC grown in feeder-free conditions, often show a sub population of fibroblast-like, stromal cells growing between the colonies. Thus, we examined the possibility that these cells represent a population of stromal (mesenchymal) stem cells (hESC-stromal). Two in house derived hES cell lines (Odense3 and KMEB3) as well as an externally derived cell line (Hues8) were transitioned to feeder-free conditions. A sub population of fibroblast-like cells established between the hESC colonies were isolated by selective adherence to hyaluronic acid-coated plates (100 μg/ml) and were characterized using a combination of FACS analysis and staining. The cells were CD44(+), CD29(+), CD73(+), CD166(+), CD146(+), and CD105(+); and, Oct4⁻, CD34⁻, CD45⁻ and CXCR4⁻. When cultured in osteogenic differentiation media, up regulation of osteoblastic lineage markers (DLX5, MSX2, RUNX2, SPARC, ALP, COL1a1, BGLAP, IBSP, DCN, LOX-L4) and production of in vitro mineralized matrix was detected. hESC-stromal cells loaded on a carrier and implanted either subcutaneously or in a critical size calvarial defect in immune deficient mice for 10 weeks, resulted in new bone formation and partial repair of the calvarial defect. In conclusion, hESC-stromal can be isolated from hESC cultures and represent a good source for obtaining cells with osteogenic differentiation potential suitable for regenerative medicine protocols.

The teratoma assay: an in vivo assessment of pluripotency

A teratoma is a nonmalignant tumor comprised of a disorganized mixture of cells and small foci of tissue comprised of cells from all three of the embryonic germ-layers. By definition, a cell is pluripotent if it can differentiate into cells derived from all three of the embryonic germ-layers: ectoderm, mesoderm, and endoderm. In the teratoma assay, putative pluripotent stem cells (PSCs) are implanted into an immune-compromised mouse where they may proliferate and differentiate to form a teratoma. The PSCs grow at the implantation site supported by a complex mixture of factors from the local milieu, as well as circulating factors that are vital components of normal mammalian physiology. After a predetermined time of 6-12 weeks or when the tumor has reached sufficient size, it is removed and subjected to histopathological analysis. The teratoma may be further processed by immunocytochemistry and gene expression profiling. This chapter describes methods to generate teratomas through the implantation of putative PSC lines in the SCID mouse. Implantation at the following sites is described: (1) intramuscular, (2) subcutaneous, (3) under the testis capsule, and (4) under the kidney capsule.

Current technology for the derivation of pluripotent stem cell lines from human embryos

Technology for the derivation, propagation, and characterization of pluripotent stem cell lines from the human embryo has undergone considerable refinement and improvement since the first published description of human embryonic stem cells in 1998. In particular, there has been extensive effort to optimize protocols and develop defined culture systems with a view toward future clinical applications of embryonic stem cell-derived products. Here, we review the current status of methodology for human embryonic stem cell derivation and culture, and we highlight the challenges that remain for workers in the field.

A defined glycosaminoglycan-binding substratum for human pluripotent stem cells

To exploit the full potential of human pluripotent stem cells for regenerative medicine, developmental biology, and drug discovery, defined culture conditions are needed. Media of known composition that maintain human embryonic stem (hES) cells have been developed, but finding chemically-defined, robust substrata has proved difficult. We employed an array of self-assembled monolayers to identify peptide surfaces that sustain pluripotent stem cell self-renewal. The effective substrates display heparin-binding peptides, which can interact with cell surface glycosaminoglycans, and can be used with a defined medium to culture hES cells for more than 3 months. The resulting cells maintain a normal karyotype and display high levels of pluripotency markers. The peptides are able to support growth of multiple (eight) pluripotent cell lines on a variety of scaffolds. Our results indicate that synthetic substrates that recognize cell surface glycans can facilitate the long-term culture of pluripotent stem cells.

Tumor-initiating and -propagating cells: cells that we would like to identify and control

Identification of the cell types capable of initiating and sustaining growth of the neoplastic clone in vivo is a fundamental problem in cancer research. It is likely that tumor growth can be sustained both by rare cancer stem-like cells and selected aggressive clones and that the nature of the mutations, the cell of origin, and its environment will contribute to tumor propagation. Genomic instability, suggested as a driving force in tumorigenesis, may be induced by genetic and epigenetic changes. The feature of self-renewal in stem cells is shared with tumor cells, and deviant function of the stem cell regulatory networks may, in complex ways, contribute to malignant transformation and the establishment of a cancer stem cell-like phenotype. Understanding the nature of the more quiescent cancer stem-like cells and their niches has the potential to develop novel cancer therapeutic protocols including pharmacological targeting of self-renewal pathways. Drugs that target cancer-related inflammation may have the potential to reeducate a tumor-promoting microenvironment. Because most epigenetic modifications may be reversible, DNA methylation and histone deacetylase inhibitors can be used to induce reexpression of genes that have been silenced epigenetically. Design of therapies that eliminate cancer stem-like cells without eliminating normal stem cells will be important. Further insight into the mechanisms by which pluripotency transcription factors (e.g., OCT4, SOX2, and Nanog), polycomb repressive complexes and microRNA balance selfrenewal and differentiation will be essential for our understanding of both embryonic differentiation and human carcinogenesis and for the development of new treatment strategies.

Strategies for ensuring that regenerative cardiomyocytes function properly and in cooperation with the host myocardium

In developed countries, in which people have nutrient-rich diets, convenient environments, and access to numerous medications, the disease paradigm has changed. Nowadays, heart failure is one of the major causes of death. In spite of this, the therapeutic efficacies of medications are generally unsatisfactory. Although whole heart transplantation is ideal for younger patients with heart failure, many patients are deemed to be unsuitable for this type of surgery due to complications and/or age. The need for therapeutic alternatives to heart transplantation is great. Regenerative therapy is a strong option. For this purpose, several cell sources have been investigated, including intrinsic adult stem or progenitor cells and extrinsic pluripotent stem cells. Most intrinsic stem cells seem to contribute to a regenerative environment via paracrine factors and/or angiogenesis, whereas extrinsic pluripotent stem cells are unlimited sources of cardiomyocytes. In this review, we summarize the various strategies for using regenerative cardiomyocytes including our recent progressions: non-genetic approaches for the purification of cardiomyocytes and efficient transplantation. We expect that use of intrinsic and extrinsic stem cells in combination will enhance therapeutic effectiveness.

Strategies for ensuring that regenerative cardiomyocytes function properly and in cooperation with the host myocardium

In developed countries, in which people have nutrient-rich diets, convenient environments, and access to numerous medications, the disease paradigm has changed. Nowadays, heart failure is one of the major causes of death. In spite of this, the therapeutic efficacies of medications are generally unsatisfactory. Although whole heart transplantation is ideal for younger patients with heart failure, many patients are deemed to be unsuitable for this type of surgery due to complications and/or age. The need for therapeutic alternatives to heart transplantation is great. Regenerative therapy is a strong option. For this purpose, several cell sources have been investigated, including intrinsic adult stem or progenitor cells and extrinsic pluripotent stem cells. Most intrinsic stem cells seem to contribute to a regenerative environment via paracrine factors and/or angiogenesis, whereas extrinsic pluripotent stem cells are unlimited sources of cardiomyocytes. In this review, we summarize the various strategies for using regenerative cardiomyocytes including our recent progressions: non-genetic approaches for the purification of cardiomyocytes and efficient transplantation. We expect that use of intrinsic and extrinsic stem cells in combination will enhance therapeutic effectiveness.