Repetitive transfusion of platelets expressing HLA not corresponded to recipient matched often induces anti-HLA antibody-based undesired events including unresponsiveness in platelet transfusion therapy. It is desirable to use platelets derived from HLA-matched iPS cells. In this context, we have recently established an in vitro culture system whereby human pluripotent stem cells can be differentiated into'unique sac-like structures' (ES-/iPS-sacs) containing hematopoietic progenitors generating platelets. Among various iPS clones, we also found critical role of c-MYC in human megakaryopoiesis, leading to efficient platelet production with an intact in vivo functionality of hemostasis and thrombosis within the vessel. We propose that use of HLA-matched hiPS cells may be one of useful strategies for the treatment of thrombocytopenia in patients requiring repeated transfusion.

Liver transplants represent the only way to treat patients suffering from terminal liver failure, but they are associated with numerous problems, including a chronic shortage of donors, high cost, rejection, and side effects for the donor. It is anticipated that regenerative medicine will provide an alternative to liver transplants for such patients. An assortment of studies has documented their contribution in hepatogenic generation in vivo and in vitro. Preliminary results of only a few clinical studies on the administration of adult stem cells to liver cirrhotic patients seem to be very promising, but additional well-designed and controlled studies are needed. We herein present the current knowledge what we obtained from differentiation of functional hepatocytes from several types of stem cells.

Current stem cell therapy mainly targets diseases that can be treated by cell transplantation. The complexity of organogenesis hinders in vitro generation of organs derived from patient's pluripotent stem cells (PSCs), an ultimate goal of regenerative medicine. To address this issue, we attempted in vivo generation of PSC-derived pancreas using Pdx1(-/-) blastocysts(pancreatogenesis-disabled) and blastocyst complementation technique. When wild type rat PSCs were injected into mouse Pdx1(-/-) blastocysts, defective cells were totally replaced and pancreas was formed almost entirely by injected rat PSC derived cells. Chimeric mice of Pdx1(-/-) genotype survived to adulthood without any sign of diabetes. Generation of organs using blastocyst complementation in vivo provides a new strategy for understanding organogenesis and a novel approach for organ supply.

Human artificial chromosomes (HACs) exhibit several potential characteristics desired for an ideal gene delivery vector, including stable episomal maintenance and the capacity to carry large genomic loci with their regulatory elements, thus allowing the physiological regulation of the introduced gene. Stem cells, including hematopoietic stem cells, bone marrow-derived MSCs and iPS cells, can potentially avoid immune rejection due to their being obtained from the patient's own tissues. Recently, we succeeded the complete correction of a genetic deficiency in iPS cells derived from a human Duchenne muscular dystrophy patient using the HAC technology. Therefore, the combination of patient specific stem cells and HAC containing defective genes potentially represents a powerful tool for gene and cell therapies.

Pluripotent stem cells such as embryonic stem cells and induced pluripotent stem cells could be good sources for obtaining massive hematopoietic stem cells (HSC) and mature blood cells. Coculture with feeder cells and embryoid body formation are two major strategies to induce hematopoietic differentiation from pluripotent stem cells. Derivation of HSC with ability of reconstituting human hematopoiesis in immunodeficient mice has been achieved. It is also possible to generate mature blood cells such as neutrophils, erythrocytes, and platelets from pluripotent stem cells. Their morphologies, phenotypes, and functions are usually very similar to those of normal counterparts. However, a breakthrough is needed to overcome the issue of "yield", which still stands as a high barrier to reach clinical applications.

Although adult stem cells are generally known to generate the cell types of the tissue in which they reside, mesenchymal stem cells (MSCs) are unique in that they differentiate not only into the same mesodermal-lineage such as bone, cartilage, and adipocytes, but also into other lineages of ectodermal and endodermal cells. Furthermore, a subpopulation of MSCs are known to integrate into damaged sites, differentiate into cell types specific to the integrated tissue and contribute to the tissue repair. As MSCs comprise heterogeneous cell populations, however, the cells responsible for wide-ranging differentiation as well as for tissue repair have not been identified. Recent evidence suggests that a subpopulation of human MSCs, which were named Muse cells, were shown to have the ability to differentiate into trilineage cells and to function as tissue repairing cells in vivo. This review summarizes recent advances in MSC properties and discuss about future perspectives.

The use of mesenchymal stem cells (MSC) for tissue and organ regeneration offers advantages because the MSC contain multipotent progenitor cells and reported to be immunoprivileged as well as immunosuppressive. Therefore, cell therapy with allogeneic MSC has been reported as a promising treatment for severe acute graft versus host disease (GVHD). We reported a pilot study for GVHD treatments using a small number of allogeneic MSC. We also reported that MSC can show osteogenic differentiation capability when implanted in vivo as well as cultured in vitro. Based on these findings, we attempted to use allogeneic MSC for the treatment of genetic disorder of hypophosphatasia patient. Present paper summarizes our clinical experiences of allogeneic MSC for the purpose of regenerative medicine.

Induced pluripotent stem (iPS) cells, which are generated from somatic cells, are expected to be a hopeful source for cell therapy to treat intractable diseases due to its unlimited proliferation potential, differentiation potentials and the capability of autotransplantation characteristics. In this review, we have summarized the extension of iPS cell researches into cell therapy and the new researches associated with iPS cell technology. However, transplantation of iPS cell-derived tissue is considered to have a risk of tumorigenesis which is one of the major hurdles of using pluripotent stem cell in clinical application. This review is also focused on new strategies for reducing a risk of tumorigenesis.

Research using human embryonic stem cell (hESC) lines has expanded dramatically because of two attractive capacity; self-renewal and differentiation into almost all cell types. For therapeutic purposes, many researchers are trying to establish methods for maintaining pluripotency in defined xeno-free conditions and scalable culture systems. Banking of hESC lines is important for the wide spread of personalized cell therapy and transplantation. We introduced the ongoing clinical trials using hESC-derived cells in patients with subacute spinal cord injury and Stargardt's macular dystrophy. We also discussed opportunities and an example for the use of hESC in drug discovery. Finally, we introduced transgenic hESC as a disease model.

Here, we summarize the history and current status of clinical applications of stem cells for regenerative medicine. Cultured autologous epidermal cells were successfully applied to treat human severe burn patients in 1980 for the first time ever. Then, several commercial tissue engineered products including skin and cartilage have been approved by the regulatory agencies, and many clinical trials are ongoing now in Europe and United States. Regenerative medicine achieved by tissue engineering with autologous and allogeneic stem cells including ES and iPS cells are highly promising, and more and more products are expected to come on the market in the near future.

A 44-year-old male patient was diagnosed with acute lymphoblastic leukemia (CD10+, CD19+, CD20 weak) and underwent unrelated bone marrow transplantation (uBMT) with a conditioning regimen of cyclophosphamide plus total body irradiation during first complete remission (CR). Twenty months post-uBMT, the serum creatinine level (Cre) increased gradually, up to ≥ 1.5 mg/dl at 23 months. Since the increase in Cre was observed continuously, imaging examinations were performed and showed significant bilateral enlargement of the kidneys. Renal biopsy showed diffuse invasion of TdT, CD10 and CD19 positive lymphoid cells in the tubulo-interstitial region. Since leukemia cells were observed in the bone marrow, it was diagnosed as relapse in the bone marrow and kidney. Following reinduction chemotherapy, both kidneys returned to normal size. The patient entered into a second CR, but relapse occurred 6 months thereafter. The patient underwent uBMT again with a reduced-intensity conditioning regimen and CR has been maintained up to 5 months post-second uBMT. Although it is considered rare for relapse to occur with diffuse enlargement of both kidneys, as shown in this case, it is important to confirm the state of the kidney by performing blood tests and image diagnosis during the early phase, when renal dysfunction of an uncertain cause occurs after transplantation.

Intravascular large B-cell lymphoma (IVLBCL) is a rare subtype of extranodal large B-cell lymphoma characterized by the growth of lymphoma cells only within the lumina of small vessels in various organs. IVLBCL is an intractable hematological disease, in particular, the high incidence of central nervous system (CNS) involvement is one of the causes of the poor prognosis of IVLBCL. Autologous stem cell transplantation (ASCT) is an effective therapeutic option for refractory or high-risk aggressive lymphoma. However, it is unknown whether ASCT is an effective treatment for CNS involvement of aggressive lymphoma including IVLBCL. We show a case of a 39-year-old woman with recurrent CNS involvement of IVLBCL receiving autologous peripheral blood stem cell transplantation (auto-PBSCT) preconditioned with high-dose thiotepa, busulfan, cyclophosphamide (TBC regimen). Culture-negative febrile neutropenia developed requiring antimicrobial therapy, but nonhematological adverse effects including stomatitis and neurotoxicity, with grade ≥ 3, were not observed. The patient achieved and has maintained complete remission (CR) for 24 months after TBC/auto-PBSCT and has survived for around 30 months from the diagnosis of the CNS recurrence. The clinical course of this case suggests that auto-PBSCT preconditioned with TBC could be one of the therapeutic options for the treatment of CNS involvement of IVLBCL.

Human induced pluripotent stem cells (hiPSCs) are expected to be used in various life science areas, ranging from basic research to medical applications. This article describes perspectives regarding the potential use of hiPSCs, especially in Japan, for manufacturing products related to regenerative medicine as well as for establishing cell-based assay/screening systems that can be used for effective and efficient assessment of candidates for new drugs. The applications of hiPSCs include the following: hiPSC-derived retinal pigment epithelial cells for treating age-related macular degeneration; potential corneal reconstruction by using a combination of various relevant hiPSC-derived differentiated cells; potential treatment of Parkinson's disease by using dopaminergic neurons generated from hiPSCs; potential treatment of spinal cord injury by using neural stem/progenitor cells generated from hiPSCs; potential treatment of chronic heart failure by using hiPSC-derived functional cardiomyocytes; and development of cell-based drug toxicity screening and drug effect assay systems involving cells such as cardiomyocytes, hepatocytes, and neural cells that are differentiated from hiPSCs and can be used in the early phase of new drug development. The current situation regarding the development of guidelines for ensuring the quality and safety of hiPSC-derived medicinal products has also been described.

Duchenne muscular dystrophy (DMD) is a devastating muscle disorder caused by mutations in the dystrophin gene. There is currently no effective treatment for DMD. Muscle satellite cells are tissue-specific stem cells found in the skeletal muscle; these cells play a central role in postnatal muscle growth and regeneration, and are, therefore, a potential source for stem cell therapy for DMD. However, transplantation of satellite cell-derived myoblasts has not yet been successful in humans. Patient-specific induced pluripotent stem (iPS) cells are expected to be a source for autologous cell transplantation therapy for DMD, because iPS cells can proliferate vigorously in vitro and can differentiate into multiple cell lineages both in vitro and in vivo. Here, we discuss the strategies to generate muscle stem cells from iPS cells. So far, the most promising method for generating muscle stem cells from iPS cells is the conditional overexpression of Pax3 or Pax7 in the differentiating mouse embryoid bodies. However, induction methods for human iPS cells have not yet been developed. Thus, iPS cells are expected to serve as an in vitro disease model system, which will enable us to determine the pathology of muscle diseases and develop pharmaceutical treatments.

Parkinson's disease has been so far commonly treated with medication therapy. Although the medication works effectively in the initial phase, it turns out to be less effective at the later stage of the disease. Recently, induced pluripotent stem (iPS) cells have attracted much attention because of their potential to cure diseases such as Parkinson's disease. Due to the accumulating clinical experiences of cell transplantation procedures with aborted fetal tissues, Parkinson's disease has become one of the most promising targets for the clinical application of this iPS cell technology. In this review, we will summarize the ongoing research in the field of iPS cells and Parkinson's disease. The method for establishing iPS cells has advanced rapidly that can be applied in the clinical stage in terms of avoiding the use of viral vectors, xenogenic materials, etc. The differentiation protocol to derive the dopamine neurons from iPS cells has also been improved. However, several issues, such as the risk of tumor formation and the poor survival of the grafted dopamine neurons in vivo remain to be solved before these cells can be used in the clinical settings. Other than cell transplantations, iPS cell technology can also provide a valuable platform for disease analysis and drug development with in vitro systems of human cells. Several lines of iPS cells have already been established from Parkinson's disease patients with either sporadic or genetic background. For patients to achieve maximum benefits of this technology, further research must be conducted in both fields, that is, cell transplantation and the disease modeling with patient-derived iPS cells.

Once the safety issue has been overcome, induced pluripotent stem cells (iPSCs), which do not entail ethical or immunological concerns, may become the preferred cell source for regenerative medicine. Various types of iPSCs have been established by different methods, and each type exhibits different biological properties. Before iPSC-based clinical applications can be initiated, detailed evaluations of the cells, including their differentiation potentials and tumorigenic activities in different contexts, should be investigated to establish their safety and effectiveness for cell transplantation therapies. Recently, we demonstrated the directed neural differentiation of mouse iPSCs and examined their therapeutic potential in a mouse spinal cord injury (SCI) model. Mouse iPSC-derived neural stem/progenitor cells (NS/PCs), which had been pre-evaluated as non-tumorigenic by their transplantation into nonobese diabetic-severe combined immunodeficiency (NOD-scid) mouse brain, were transplanted into the spinal cord 9 days after SCI. Mouse iPSC-derived NS/PCs differentiated into all three neural lineages without forming teratomas or other tumors. They also participated in re-myelination and induced the axonal re-growth, promoting motor functional recovery. Nevertheless, our results constitute only the first step toward clinical application. The safety and effectiveness of human iPSC-derived NS/PCs need to be more intensively investigated in future preclinical studies, for example, using non-human primate SCI models. In particular, human iPSCs established by delivering reprogramming factors using a safer method than retrovirus system, such as an integration-free virus system, virus-free system, or transgene-free system should be evaluated.

The discovery of the induced pluripotent stem (iPS) cell technology, which enables us to produce pluripotent stem cells by introducing a few genetic factors, commands considerable attention in the field of dentistry. These iPS cells may be of particular importance for developing innovative technologies to regenerate missing jaw bones and lost teeth, and there are expectations that several types of tissue stem cells and mucosal cells in the oral area can be used as an ideal iPS cell source. We previously reported that the gingiva, which is often resected during general dental treatments and treated as biomedical waste, is a promising source of iPS cells. In this review, the current trends in iPS cell research in dentistry are outlined, and future aspects of potential applications of the iPS cell technologies to dental treatments will be discussed.