Epigenetic Aberrations Are Not Specific to Transcription Factor-Mediated Reprogramming

Double sperm cloning (DSC) is a promising strategy in mammalian genetic engineering and stem cell research

Embryonic stem cells (ESCs) derived from somatic cell nuclear transfer (SCNT) and induced pluripotent stem cells (iPSCs) are promising tools for meeting the personalized requirements of regenerative medicine. However, some obstacles need to be overcome before clinical trials can be undertaken. First, donor cells vary, and the reprogramming procedures are diverse, so standardization is a great obstacle regarding SCNT and iPSCs. Second, somatic cells derived from a patient may carry mitochondrial DNA mutations and exhibit telomere instability with aging or disease, and SCNT-ESCs and iPSCs retain the epigenetic memory or epigenetic modification errors. Third, reprogramming efficiency has remained low. Therefore, in addition to improving their success rate, other alternatives for producing ESCs should be explored. Producing androgenetic diploid embryos could be an outstanding strategy; androgenic diploid embryos are produced through double sperm cloning (DSC), in which two capacitated sperms (XY or XX, sorted by flow cytometer) are injected into a denucleated oocyte by intracytoplasmic sperm injection (ICSI) to reconstruct embryo and derive DSC-ESCs. This process could avoid some potential issues, such as mitochondrial interference, telomere shortening, and somatic epigenetic memory, all of which accompany somatic donor cells. Oocytes are naturally activated by sperm, which is unlike the artificial activation that occurs in SCNT. The procedure is simple and practical and can be easily standardized. In addition, DSC-ESCs can overcome ethical concerns and resolve immunological response matching with sperm providers. Certainly, some challenges must be faced regarding imprinted genes, epigenetics, X chromosome inactivation, and dosage compensation. In mice, DSC-ESCs have been produced and have shown excellent differentiation ability. Therefore, the many advantages of DSC make the study of this process worthwhile for regenerative medicine and animal breeding.

Induced pluripotent stem cells reprogrammed from primary dendritic cells provide an abundant source of immunostimulatory dendritic cells for use in immunotherapy

Cell types differentiated from induced pluripotent stem cells (iPSCs) are frequently arrested in their development program, more closely resembling a fetal rather than an adult phenotype, potentially limiting their utility for downstream clinical applications. The fetal phenotype of iPSC‐derived dendritic cells (ipDCs) is evidenced by their low expression of MHC class II and costimulatory molecules, impaired secretion of IL‐12, and poor responsiveness to conventional maturation stimuli, undermining their use for applications such as immune‐oncology. Given that iPSCs display an epigenetic memory of the cell type from which they were originally derived, we investigated the feasibility of reprogramming adult DCs to pluripotency to determine the impact on the phenotype and function of ipDCs differentiated from them. Using murine bone marrow‐derived DCs (bmDCs) as proof of principle, we show here that immature DCs are tractable candidates for reprogramming using non‐integrating Sendai virus for the delivery of Oct4, Sox2, Klf4, and c‐Myc transcription factors. Reprogramming efficiency of DCs was lower than mouse embryonic fibroblasts (MEFs) and highly dependent on their maturation status. Although control iPSCs derived from conventional MEFs yielded DCs that displayed a predictable fetal phenotype and impaired immunostimulatory capacity in vitro and in vivo, DCs differentiated from DC‐derived iPSCs exhibited a surface phenotype, immunostimulatory capacity, and responsiveness to maturation stimuli indistinguishable from the source DCs, a phenotype that was retained for 15 passages of the parent iPSCs. Our results suggest that the epigenetic memory of iPSCs may be productively exploited for the generation of potently immunogenic DCs for immunotherapeutic applications.

DNA methylation and transcriptional trajectories during human development and reprogramming of isogenic pluripotent stem cells

Determining cell identity and maturation status of differentiated pluripotent stem cells (PSCs) requires knowledge of the transcriptional and epigenetic trajectory of organs during development. Here, we generate a transcriptional and DNA methylation atlas covering 21 organs during human fetal development. Analysis of multiple isogenic organ sets shows that organ-specific DNA methylation patterns are highly dynamic between week 9 (W9) and W22 of gestation. We investigate the impact of reprogramming on organ-specific DNA methylation by generating human induced pluripotent stem cell (hiPSC) lines from six isogenic organs. All isogenic hiPSCs acquire DNA methylation patterns comparable to existing hPSCs. However, hiPSCs derived from fetal brain retain brain-specific DNA methylation marks that seem sufficient to confer higher propensity to differentiate to neural derivatives. This systematic analysis of human fetal organs during development and associated isogenic hiPSC lines provides insights in the role of DNA methylation in lineage commitment and epigenetic reprogramming in humans.While DNA methylation and gene expression data are widely available for animal models, comprehensive data from human development is rarer. Here, the authors generated transcriptional and DNA methylation data from 21 organs during human development and 6 isogenic induced pluripotent stem cell lines.

Molecular Obstacles to Clinical Translation of iPSCs

The ability to reprogram somatic cells into induced pluripotent stem cells (iPSCs) using defined factors provides new tools for biomedical research. However, some iPSC clones display tumorigenic and immunogenic potential, thus raising concerns about their utility and safety in the clinical setting. Furthermore, variability in iPSC differentiation potential has also been described. Here we discuss whether these therapeutic obstacles are specific to transcription-factor-mediated reprogramming or inherent to every cellular reprogramming method. Finally, we address whether a better understanding of the mechanism underlying the reprogramming process might improve the fidelity of reprogramming and, therefore, the iPSC quality.

Therapeutics from Adult Stem Cells and the Hype Curve

The Gartner curve for regenerative and stem cell therapeutics is currently climbing out of the "trough of disillusionment" and into the "slope of enlightenment". Understanding that the early years of stem cell therapy relied on the model of embryonic stem cells (ESCs), and then moved into a period of the overhype of induced pluripotent stem cells (iPSCs), instead of using the model of 40 years of success, i.e. adult stem cells used in bone marrow transplants, the field of stem cell therapy has languished for years, trying to move beyond the early and poorly understood success of bone marrow transplants. Recent studies in the lab and clinic show that adult stem cells of various types, and the molecules that they release, avoid the issues associated with ESCs and iPSCs and lead to better therapeutic outcomes and into the slope of enlightenment.