Identification of normal and neoplastic stem cells by the multicolor lineage tracing methods

Adult stem cells and embryonic (ES) and induced pluripotent stem (iPS) cells are two major focus areas of stem cell research. Studies on adult stem cells are important not only as sources for regenerative medicine but for analyzing the mechanisms of tissue homeostasis, tissue repair after injury, cancinogenesis, and aging. On the other hand, ES and iPS cells are mainly important for regenerative medicine. However, many adult stem cells, especially those in low‐turnover tissues, have remained unidentified. We have been working on the development of methods using multiple fluorescent markers, to improve the accuracy of lineage‐tracing analyses of adult stem cells and their fetal progenitors. With this method, we were able to identify lingual epithelial stem cells (LESCs). By using the same strategy, we could potentially identify candidate cancer stem cells. In this review, we would like to introduce how the multicolor lineage tracing method could be used in various stem cell studies.     

Reprogramming to iPS cells and their subsequent hematopoietic differentiation is more efficient from MEFs than from preB cells

Efficiencies of the generation of induced pluripotent stem (iPS) cells from either mouse embryonic fibroblasts (MEF) or from mouse fetal liver (FL) derived preB cells and their hematogenic potencies were compared. In 10 days approximately 2% of the MEFs transduced with Sox-2, Oct-4 and Klf-4 developed to iPS cells, while only 0.01% of transduced FL-preB cells yielded iPS cells, and only after around 3 weeks. Subsequently, the generated iPS cells were induced to differentiate into hematopoietic cells in vitro. On day 5 of differentiation MEF-iPS yielded numbers and percentages of Flk-1(+) mesodermal-like cells comparable to those developed from embryonic stem (ES) cells. Compared to ES cells further differentiation to hematopoietic and lymphopoietic cells was reduced, possibly because of persistent expression of the reprogramming factors. By contrast, FL-iPS cells developed lower numbers and percentages of Flk-1(+) cells, and no significant further development to hematopoietic or lymphopoietic cells could be induced. These results indicate that the efficiencies of iPS generation and subsequent hematopoietic development depends on the type of differentiated cell from which iPS cells are generated.     

The generation of iPS cells using non-viral magnetic nanoparticle based transfection

Induced pluripotent stem (iPS) cells have been generated from various somatic cells; however, a major restriction of the technology is the use of potentially harmful genome-integrating viral DNAs. Here, without a viral vector, we generated iPS cells from fibroblasts using a non-viral magnetic nanoparticle-based transfection method that employs biodegradable cationic polymer PEI-coated super paramagnetic nanoparticles (NP). Our findings support the possible use of transient expression of iPS genes in somatic cells by magnet-based nanofection for efficient generation of iPS cells. Results of dynamic light scattering (DLS) analysis and TEM analyses demonstrated efficient conjugation of NP with iPS genes. After transfection, nanofection-mediated iPS cells showed ES cell-like characteristics, including expression of endogenous pluripotency genes, differentiation of three germ layer lineages, and formation of teratomas. Our results demonstrate that magnet-based nanofection may provide a safe method for use in generation of virus-free and exogenous DNA-free iPS cells, which will be crucial for future clinical applications in the field of regenerative medicine.     

Application of iPS Cells in Dental Bioengineering and Beyond

The stem-cell-based tissue-engineering approaches are widely applied in establishing functional organs and tissues for regenerative medicine. Successful generation of induced pluripotent stem cells (iPS cells) and rapid progress of related technical platform provide great promise in the development of regenerative medicine, including organ regeneration. We have previously reported that iPS cells could be an appealing stem cells source contributing to tooth regeneration. In the present paper, we mainly review the application of iPS technology in dental bioengineering and discuss the challenges for iPS cells in the whole tooth regeneration.     

iPS cells: a more critical review

Over the past 20 months, reports claiming the generation of induced pluripotent stem (iPS) cells with characteristics identical to those of embryonic stem (ES) cells from nonembryonic tissue have captured great attention in both the scientific community and the general public. In the light of the continuing controversy over the use of ES cells, these reports have profound ramifications. This review calls into question the validity of many claims made in these reports--claims that have led to the rapid and premature acceptance of using iPS cells as a viable alternative to using normal stem cells for regenerative therapy. How convincing is the evidence supporting the various claims made for the iPS cells? Are there other more plausible explanations for the same observations? What are these iPS cells? Are they really safe for therapeutic use? Should the iPS technique be considered, in the absence of any direct evidence for induction and reprogramming, as a realistic alternative for somatic cell nuclear transfer (SCNT) to generate ES-like cells? This review attempts to encourage reflections on and offer alternative views for key aspects of iPS cells and studies.     

Development of Feeder-Free Culture Systems for Generation of ckit+sca1+ Progenitors from Mouse iPS Cells

Patient-specific therapeutic cells derived from induced pluripotent stem (iPS) cells may bypass the ethical issues associated with embryonic stem (ES) cells and avoid potential immunological reactions associated with allogenic transplantation. It is critical, for the ultimate clinical applicability of iPS cell-derived therapies, to establish feeder-free cultures that ensure efficient differentiation of iPS cells into therapeutic progenitors. It is also necessary to understand if iPS cell-derived progenitors differ from those derived from ES cells. In this study, we compared the efficiency of three different feeder-free cultures for differentiating mouse iPS cells into ckit+sca1+ hematopoietic progenitor cells (HPCs) and compared how differentiation and functionality varies between ES and iPS cells. Our results indicated that both iPS and ES cells can be efficiently differentiated into HPCs in suspension cultures supplemented with secretion factors from mouse bone marrow stromal cells (OP9-DL1 conditioned medium). The functionality of these cells was demonstrated by differentiation into CD11c+ dendritic cells (DCs). Both ES and iPS-derived DCs expressed activation molecules (CD86, CD80) in response to LPS stimulation and stimulated T cell proliferation in a mixed lymphocyte reaction (MLR). Extensive quantitative RT-PCR studies were used to study the differences in gene expression profiles of ckit+sca1+ cells generated from the various culture systems as well as differences between ES-derived and iPS-derived cells. We conclude that a feeder-free system using stromal conditioned medium can efficiently generate HPCs as well as functional DCs from iPS cells and the generated cells have similar gene expression profile as those from ES cells.     

Highly efficient induction of primate iPS cells by combining RNA transfection and chemical compounds

Induced pluripotent stem (iPS) cells hold great promise for regenerative medicine and the treatment of various diseases. Before proceeding to clinical trials, it is important to test the efficacy and safety of iPS cell‐based treatments using experimental animals. The common marmoset is a new world monkey widely used in biomedical studies. However, efficient methods that could generate iPS cells from a variety of cells have not been established. Here, we report that marmoset cells are efficiently reprogrammed into iPS cells by combining RNA transfection and chemical compounds. Using this novel combination, we generate transgene integration‐free marmoset iPS cells from a variety of cells that are difficult to reprogram using conventional RNA transfection method. Furthermore, we show this is similarly effective for human and cynomolgus monkey iPS cell generation. Thus, the addition of chemical compounds during RNA transfection greatly facilitates reprogramming and efficient generation of completely integration‐free safe iPS cells in primates, particularly from difficult‐to‐reprogram cells.     

Molecular Pathways Governing Development of Vascular Endothelial Cells from ES/iPS Cells

Assembly of complex vascular networks occurs in numerous biological systems through morphogenetic processes such as vasculogenesis, angiogenesis and vascular remodeling. Pluripotent stem cells such as embryonic stem (ES) and induced pluripotent stem (iPS) cells can differentiate into any cell type, including endothelial cells (ECs), and have been extensively used as in vitro models to analyze molecular mechanisms underlying EC generation and differentiation. The emergence of these promising new approaches suggests that ECs could be used in clinical therapy. Much evidence suggests that ES/iPS cell differentiation into ECs in vitro mimics the in vivo vascular morphogenic process. Through sequential steps of maturation, ECs derived from ES/iPS cells can be further differentiated into arterial, venous, capillary and lymphatic ECs, as well as smooth muscle cells. Here, we review EC development from ES/iPS cells with special attention to molecular pathways functioning in EC specification.     

Cord Blood Stem Cells: A Review of Potential Neurological Applications

It is estimated that as many as 128M individuals in the United States, or 1 in 3 people, might benefit from regenerative medicine therapy. Many of these usages include applications that affect the nervous system, including cerebral palsy, stroke, spinal cord injury and neurodegenerative disease such as Parkinson’s. The numbers of such individuals affected range from 10,000 (for cerebral palsy) to 700,000 annually (for stroke) at a cost of more than $65B. For the foreseeable future, regenerative medicine entrée to the clinic will depend upon the development of adult or non-embryonic stem (ES) cell therapies. Currently, non-ES cells easily available in large numbers from affected individuals can be found in the bone marrow, adipose tissue and umbilical cord blood (CB). It is our belief that CB stem cells are the best alternative to ES cells as these stem cells can be used to derive tissues from the mesodermal, endodermal and ectodermal germ lineages. CB contains a mixture of different types of stem cells in numbers not seen in any other location including embryonic-like stem cells, hematopoietic stem cells, endothelial stem cells, epithelial stem cells, mesenchymal stem cells and unrestricted somatic stem cells. This review will summarize the findings reported in the literature with regards to the use of CB stem cells to neurological applications including in vitro work, pre-clinical animal studies, and patient clinical trials.     

Hope and limits in cell therapies]

The hematopoietic system is one of the best characterized human cellular system in which a multipotent adult stem cell is at the origin of all the cells of a tissue. These last years, the use of stem cells has given rise to many hopes in regenerative medicine, especially in diseases without efficient therapies. However the hematopoietic system in which stem cell transplantation has entered in clinical practice for many years has also shown the limits of these approaches. Especially the in vitro manipulation of hematopoietic stem cells remains a challenge which requires more fundamental knowledge on the biology of stem cells including self renewal and homing. Knowledge for other tissue system is even more preliminary but the same experimental strategy used for hematopoietic stem cell can be translated and may accelerate their use in cell therapies. Characterization of human adult pluripotent stem cells and the generation of human ES cells capable to differentiate towards several tissues have led to new hopes but the road to their use in therapies may be long and will require a lot of investment in basic biology.