Optimization of adenoviral gene transfer in human pluripotent stem cells.

Human pluripotent stem cells, such as embryonic stem cells and induced pluripotent stem cells, have the potential to differentiate into a wide variety of cells in vitro and have applications in basic developmental biology research and regenerative medicine. To understand the process of differentiation from pluripotent stem cells to functional cells, it is necessary to efficiently and safely transfer and express exogenous genes. We attempted to optimize the efficient transfer of genes into pluripotent stem cells using adenoviral vectors. Comparative study of the activities of three representative ubiquitously active promoters revealed that only the CA promoter allowed robust transgene expression in human pluripotent stem cells. In addition, we established a protocol that allowed us to efficiently introduce target genes and ensure their expression even in small numbers of cells. Adenoviral vector infection of pluripotent stem cells in single-cell suspension culture yielded high gene transfer efficiency with low cytotoxicity, without losing the undifferentiated state of the pluripotent stem cells. This optimized system will facilitate developmental biology research and regenerative medicine using pluripotent stem cells.

A Novel Construction of Lentiviral Vectors for Eliminating Tumorigenic Cells from Pluripotent Stem Cells.

The risk of tumor formation poses a challenge for human pluripotent stem cell (hPSC)-based transplantation therapy. Specific and total elimination of tumorigenic hPSCs by suicide genes (SGs) has not been achieved because no methodology currently exists for testing multiple candidate transgene constructs. Here, we present a novel method for efficient generation of tumorigenic cell-targeting lentiviral vectors (TC-LVs) with diverse promoters upstream of a fluorescent protein and SGs. Our two-plasmid system achieved rapid and simultaneous construction of different TC-LVs with different promoters. Ganciclovir (GCV) exerted remarkable cytotoxicity in herpes simplex virus thymidine kinase-transduced hPSCs, and high specificity for undifferentiated cells was achieved using the survivin promoter (TC-LV.Surv). Moreover, GCV treatment completely abolished teratoma formation by TC-LV.Surv-infected hPSCs transplanted into mice, without harmful effects. Thus, TC-LV can efficiently identify the best promoter and SG for specific and complete elimination of tumorigenic hPSCs, facilitating the development of safe regenerative medicine. Stem Cells 2018;36:230-239.

Viral Vector-Based Innovative Approaches to Directly Abolishing Tumorigenic Pluripotent Stem Cells for Safer Regenerative Medicine.

Human pluripotent stem cells (hPSCs) are a promising source of regenerative material for clinical applications. However, hPSC transplant therapies pose the risk of teratoma formation and malignant transformation of undifferentiated remnants. These problems underscore the importance of developing technologies that completely prevent tumorigenesis to ensure safe clinical application. Research to date has contributed to establishing safe hPSC lines, improving the efficiency of differentiation induction, and indirectly ensuring the safety of products. Despite such efforts, guaranteeing the clinical safety of regenerative medicine products remains a key challenge. Given the intrinsic genome instability of hPSCs, selective growth advantage of cancer cells, and lessons learned through failures in previous attempts at hematopoietic stem cell gene therapy, conventional strategies are unlikely to completely overcome issues related to hPSC tumorigenesis. Researchers have recently embarked on studies aimed at locating and directly treating hPSC-derived tumorigenic cells. In particular, novel approaches to directly killing tumorigenic cells by transduction of suicide genes and oncolytic viruses are expected to improve the safety of hPSC-based therapy. This article discusses the current status and future perspectives of methods aimed at directly eradicating undifferentiated tumorigenic hPSCs, with a focus on viral vector transduction.

Conditionally replicating adenovirus prevents pluripotent stem cell-derived teratoma by specifically eliminating undifferentiated cells.

Incomplete abolition of tumorigenicity creates potential safety concerns in clinical trials of regenerative medicine based on human pluripotent stem cells (hPSCs). Here, we demonstrate that conditionally replicating adenoviruses that specifically target cancers using multiple factors (m-CRAs), originally developed as anticancer drugs, may also be useful as novel antitumorigenic agents in hPSC-based therapy. The survivin promoter was more active in undifferentiated hPSCs than the telomerase reverse transcriptase (TERT) promoter, whereas both promoters were minimally active in differentiated normal cells. Accordingly, survivin-responsive m-CRA (Surv.m-CRA) killed undifferentiated hPSCs more efficiently than TERT-responsive m-CRAs (Tert.m-CRA); both m-CRAs exhibited efficient viral replication and cytotoxicity in undifferentiated hPSCs, but not in cocultured differentiated normal cells. Pre-infection of hPSCs with Surv.m-CRA or Tert.m-CRA abolished in vivo teratoma formation in a dose-dependent manner following hPSC implantation into mice. Thus, m-CRAs, and in particular Surv.m-CRAs, represent novel antitumorigenic agents that could facilitate safe clinical applications of hPSC-based regenerative medicine.

Novel Therapy for Atherosclerosis Using Recombinant Immunotoxin Against Folate Receptor ß-Expressing Macrophages.

BACKGROUND: Folate receptor ß (FRß) is induced during macrophage activation. A recombinant immunotoxin consisting of the truncated Pseudomonas exotoxin A (PE38) conjugated to an anti-FRß antibody (anti-FRß-PE38) has been reported to kill activated macrophages in inflammatory diseases. To elucidate the effect of an immunotoxin targeting FRß on atherosclerosis, we determined the presence of FRß-expressing macrophages in atherosclerotic lesions and administered the FRß immunotoxin in apolipoprotein E-deficient mice. METHODS AND RESULTS: The FRß-expressing macrophages were observed in atherosclerotic lesions of apolipoprotein E-deficient mice. At 15 or 35 weeks of age, the apolipoprotein E-deficient mice were divided into 3 groups and were intravenously administered 0.1 mg/kg of anti-FRß-PE38 (immunotoxin group), 0.1 mg/kg of PE38 (toxin group), or 0.1 mL of saline (control group) every 3 days, for a total of 5 times for each age group. The mice were analyzed at 21 or 41 weeks of age. Treatment with the immunotoxin resulted in 31% and 22% reductions in atherosclerotic lesions of the 21- and 41-week-old mice, respectively (P<0.05). Administration of immunotoxin reduced the numbers of FRß- and tumor necrosis factor-α-expressing macrophages, reduced cell proliferation, and increased the number of apoptotic cells (P<0.05). Real-time polymerase chain reaction demonstrated that the expression of FRß and tumor necrosis factor-α mRNA was significantly decreased in the immunotoxin group (P<0.05). CONCLUSIONS: These results suggest that FRß-expressing macrophages exist in the atherosclerotic lesions of apolipoprotein E-deficient mice and that FRß immunotoxin administration reduces the progression of atherosclerotic lesions in younger and older individuals. The recombinant FRß immunotoxin targeting activated macrophages could provide a novel therapeutic tool for atherosclerosis. (J Am Heart Assoc. 2012;1:e003079 doi: 10.1161/JAHA.112.003079.).