SummaryMurine- and human-induced pluripotent stem cell-derived neural stem/progenitor cells (iPSC-NS/PCs) promote functional recovery following transplantation into the injured spinal cord in rodents and primates. Although remyelination of spared demyelinated axons is a critical mechanism in the regeneration of the injured spinal cord, human iPSC-NS/PCs predominantly differentiate into neurons both in vitro and in vivo. We therefore took advantage of our recently developed protocol to obtain human-induced pluripotent stem cell-derived oligodendrocyte precursor cell-enriched neural stem/progenitor cells and report the benefits of transplanting these cells in a spinal cord injury (SCI) model. We describe how this approach contributes to the robust remyelination of demyelinated axons and facilitates functional recovery after SCI.

SummaryNeural stem/progenitor cells (NS/PCs) derived from human induced pluripotent stem cells (hiPSCs) are considered to be a promising cell source for cell-based interventions that target CNS disorders. We previously reported that transplanting certain hiPSC-NS/PCs in the spinal cord results in tumor-like overgrowth of hiPSC-NS/PCs and subsequent deterioration of motor function. Remnant immature cells should be removed or induced into more mature cell types to avoid adverse effects of hiPSC-NS/PC transplantation. Because Notch signaling plays a role in maintaining NS/PCs, we evaluated the effects of γ-secretase inhibitor (GSI) and found that pretreating hiPSC-NS/PCs with GSI promoted neuronal differentiation and maturation in vitro, and GSI pretreatment also reduced the overgrowth of transplanted hiPSC-NS/PCs and inhibited the deterioration of motor function in vivo. These results indicate that pretreatment with hiPSC-NS/PCs decreases the proliferative capacity of transplanted hiPSC-NS/PCs, triggers neuronal commitment, and improves the safety of hiPSC-based approaches in regenerative medicine.

SummaryHuman induced pluripotent stem cells (iPSCs) are promising in regenerative medicine. However, the risks of teratoma formation and the overgrowth of the transplanted cells continue to be major hurdles that must be overcome. Here, we examined the efficacy of the inducible caspase-9 (iCaspase9) gene as a fail-safe against undesired tumorigenic transformation of iPSC-derived somatic cells. We used a lentiviral vector to transduce iCaspase9 into two iPSC lines and assessed its efficacy in vitro and in vivo. In vitro, the iCaspase9 system induced apoptosis in approximately 95% of both iPSCs and iPSC-derived neural stem/progenitor cells (iPSC-NS/PCs). To determine in vivo function, we transplanted iPSC-NS/PCs into the injured spinal cord of NOD/SCID mice. All transplanted cells whose mass effect was hindering motor function recovery were ablated upon transduction of iCaspase9. Our results suggest that the iCaspase9 system may serve as an important countermeasure against post-transplantation adverse events in stem cell transplant therapies.

The risk of tumorigenicity is a hurdle for regenerative medicine using induced pluripotent stem cells (iPSCs). Although teratoma formation is readily distinguishable, the malignant transformation of iPSC derivatives has not been clearly defined due to insufficient analysis of histology and phenotype. In the present study, we evaluated the histology of neural stem/progenitor cells (NSPCs) generated from integration-free human peripheral blood mononuclear cell (PBMC)-derived iPSCs (iPSC-NSPCs) following transplantation into central nervous system (CNS) of immunodeficient mice. We found that transplanted iPSC-NSPCs produced differentiation patterns resembling those in embryonic CNS development, and that the microenvironment of the final site of migration affected their maturational stage. Genomic instability of iPSCs correlated with increased proliferation of transplants, although no carcinogenesis was evident. The histological classifications presented here may provide cues for addressing potential safety issues confronting regenerative medicine involving iPSCs.Electronic supplementary materialThe online version of this article (doi:10.1186/s13041-016-0265-8) contains supplementary material, which is available to authorized users.

The resin-coating technique is one of the successful bonding techniques used for the indirect restorations. The dentin surfaces exposed after cavity preparation are coated with a thin film of a coating material or a dentin bonding system combined with a flowable composite resin. Resin coating can minimize pulp irritation and improve the bond strength between a resin cement and tooth structures. The technique can also be applied to endodontically treated teeth, resulting in prevention of coronal leakage of the restorations. Application of a resin coating to root surface provides the additional benefit of preventing root caries in elderly patients. Therefore, the coating materials have the potential to reinforce sound tooth ("Super Tooth" formation), leading to preservation of maximum tooth structures.