ABSTRACT

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.

SummaryWe previously reported that embryonic stem (ES) cells cultured on M15 cells, a mesoderm-derived supportive cell line, were efficiently differentiated towards an endodermal fate, finally adopting the specific lineages of various digestive organs such as the pancreas and liver. We show here that the endoderm-inducing activity of M15 cells is in part mediated through the extracellular matrices, and that laminin 5 is one of the crucial components. In an attempt to establish a feeder-free ES-cell procedure for pancreatic differentiation, we used a synthesized basement membrane (sBM) substratum using an HEK293 cell line stably expressing laminin-511. On the sBM, mouse ES or induced pluripotent stem (iPS) cells sequentially differentiated into the definitive endoderm, pancreatic progenitor cells, and then insulin-expressing pancreatic b-cells in vitro. Knockdown of ES cells with integrin b1 (Itgb1) reduces differentiation towards pancreatic cells. Heparan sulfate proteoglycan 2 (HSPG2) knockdown and heparitinase treatment synergistically decreased the number of Pdx1-expressing cells. These findings indicate that components of the basement membrane have an important role in the differentiation of definitive endoderm lineages. This novel procedure will be useful for the study of pancreatic differentiation of ES or iPS cells and the generation of potential sources of surrogate cells for regenerative medicine.

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The derivation of mature functional cholangiocytes from human pluripotent stem cells (hPSCs) provides a model for studying the pathogenesis of cholangiopathies and for developing therapies to treat them. Current differentiation protocols are not efficient and give rise to cholangiocytes that are not fully mature, limiting their therapeutic applications. Here, we generate functional hPSC-derived cholangiocytes that display many characteristics of mature bile duct cells including high levels of cystic fibrosis transmembrane conductance regulator (CFTR) and the presence of primary cilia capable of sensing flow. With this level of maturation, these cholangiocytes are amenable for testing the efficacy of cystic fibrosis drugs and for studying the role of cilia in cholangiocyte development and function. Transplantation studies show that the mature cholangiocytes generate ductal structures in the liver of immunocompromised mice indicating that it may be possible to develop cell-based therapies to restore bile duct function in patients with biliary disease.

Humanized-liver mice, in which the liver has been repopulated with human hepatocytes, have been used to study aspects of human liver physiology such as drug metabolism, toxicology and hepatitis infection. However, the procurement of human hepatocytes is a major problem in producing humanized-liver mice because of the finite nature of the patient-derived resource.In order to overcome this limitation, the human hepatic cell line HepaRG® were evaluated as promising donor cells for liver reconstitution in the TK-NOG mouse model.We demonstrate that, in vivo, transplanted confluent culture or differentiated HepaRG® cells proliferated and differentiated toward both hepatocyte-like and biliary-like cells within the recipient liver. In contrast, proliferative HepaRG® cells could engraft TK-NOG mouse liver but could differentiate only toward biliary-like cells. The differentiation to hepatocyte-like cells was characterized by the detection of human albumin in the recipient mouse serum and was confirmed by immunohistochemical staining for human leukocyte antigen, human albumin, cytochrome P450 3A4, and multidrug resistance-associated protein 2. Biliary-like cells were characterized by positive staining for cytokeratin-19.These results indicated that the differentiated HepaRG® cells are a possible cell source for generating humanized-liver mice, which are a useful model for in vivo studies of liver physiology.

The use of human induced pluripotent stem cells (hiPSCs) and recent advances in cell engineering have opened new prospects for cell‐based therapy. However, there are concerns that must be addressed prior to their broad clinical applications and a major concern is tumorigenicity. Suicide gene approaches could eliminate wayward tumor‐initiating cells even after cell transplantation, but their efficacy remains controversial. Another concern is the safety of genome editing. Our knowledge of human genomic safe harbors (GSHs) is still insufficient, making it difficult to predict the influence of gene integration on nearby genes. Here, we showed the topological architecture of human GSH candidates, AAVS1 , CCR5 , human ROSA26 , and an extragenic GSH locus on chromosome 1 (Chr1‐eGSH). Chr1‐eGSH permitted robust transgene expression, but a 2 Mb‐distant gene within the same topologically associated domain showed aberrant expression. Although knockin iPSCs carrying the suicide gene, herpes simplex virus thymidine kinase ( HSV‐TK ), were sufficiently sensitive to ganciclovir in vitro, the resulting teratomas showed varying degrees of resistance to the drug in vivo. Our findings suggest that the Chr1‐eGSH is not suitable for therapeutic gene integration and highlight that topological analysis could facilitate exploration of human GSHs for regenerative medicine applications. Our data indicate that the HSV‐TK/ganciclovir suicide gene approach alone may be not an adequate safeguard against the risk of teratoma, and suggest that the combination of several distinct approaches could reduce the risks associated with cell therapy. stem cells translational medicine 2019;8:627&638

Although progresses in developing differentiation procedures have been achieved, it remains challenging to generate hES/iPS cell-derived mature hepatocytes. We performed knock-in of a monomeric Kusabira orange (mKO1) cassette in the albumin (ALB) gene, in human embryonic stem (hES) cells and induced pluripotent stem (hiPS) cells, with the use of the helper-dependent adenovirus vector (HDAdV). Upon induction into the hepatic lineages, these knock-in hES/iPS cells differentiated into cells that displayed several known hepatic functions. The mKO1 knock-in (ALB/mKo1) hES/hiPS cells were used to visualize hepatic differentiation in vitro. mKO1 reporter expression recapitulated endogenous ALB transcriptional activity. ALB/mKo1 [Hi] population isolated by flow cytometry was confirmed to be enriched with ALB mRNA. Expression profile analyses revealed that characteristic hepatocyte genes and genes related to drug metabolism and many aspects of liver function were highly enriched in the ALB/mKo1 [Hi] population. Our data demonstrate that ALB/mKo1 knock-in hES/iPS cells are valuable resources for monitoring in vitro hepatic differentiation, isolation and analyses of hES and hiPS cells-derived hepatic cells that actively transcribing ALB. These knock-in hES/iPS cell lines could provide further insights into the mechanism of hepatic differentiation and molecular signatures of the hepatic cells derived from hES/iPS cells.