Transgenes delivered by lentiviral vector are suppressed in human embryonic stem cells in a promoter-dependent manner

Transcriptional Silencing of Moloney Murine Leukemia Virus in Human Embryonic Carcinoma Cells

Embryonic carcinoma (EC) cells are malignant counterparts of embryonic stem (ES) cells and serve as useful models for investigating cellular differentiation and human embryogenesis. Though the susceptibility of murine EC cells to retroviral infection has been extensively analyzed, few studies of retrovirus infection of human EC cells have been performed. We tested the susceptibility of human EC cells to transduction by retroviral vectors derived from three different retroviral genera. We show that human EC cells efficiently express reporter genes delivered by vectors based on human immunodeficiency virus type 1 (HIV-1) and Mason-Pfizer monkey virus (M-PMV) but not Moloney murine leukemia virus (MLV). In human EC cells, MLV integration occurs normally, but no viral gene expression is observed. The block to MLV expression of MLV genomes is relieved upon cellular differentiation. The lack of gene expression is correlated with transcriptional silencing of the MLV promoter through the deposition of repressive histone marks as well as DNA methylation. Moreover, depletion of SETDB1, a histone methyltransferase, resulted in a loss of transcriptional silencing and upregulation of MLV gene expression. Finally, we provide evidence showing that the lack of MLV gene expression may be attributed in part to the lack of MLV enhancer function in human EC cells.

IMPORTANCE

Human embryonic carcinoma (EC) cells are shown to restrict the expression of murine leukemia virus genomes but not retroviral genomes of the lentiviral or betaretroviral families. The block occurs at the level of transcription and is accompanied by the deposition of repressive histone marks and methylation of the integrated proviral DNA. The host machinery required for silencing in human EC cells is distinct from that in murine EC cell lines: the histone methyltransferase SETDB1 is required, but the widely utilized corepressor TRIM28/Kap1 is not. A transcriptional enhancer element from the Mason-Pfizer monkey virus can override the silencing and promote transcription of chimeric proviral DNAs. The findings reveal novel features of human EC gene regulation not present in their murine counterparts.

Lent-On-Plus Lentiviral vectors for conditional expression in human stem cells

Conditional transgene expression in human stem cells has been difficult to achieve due to the low efficiency of existing delivery methods, the strong silencing of the transgenes and the toxicity of the regulators. Most of the existing technologies are based on stem cells clones expressing appropriate levels of tTA or rtTA transactivators (based on the TetR-VP16 chimeras). In the present study, we aim the generation of Tet-On all-in-one lentiviral vectors (LVs) that tightly regulate transgene expression in human stem cells using the original TetR repressor. By using appropriate promoter combinations and shielding the LVs with the Is2 insulator, we have constructed the Lent-On-Plus Tet-On system that achieved efficient transgene regulation in human multipotent and pluripotent stem cells. The generation of inducible stem cell lines with the Lent-ON-Plus LVs did not require selection or cloning, and transgene regulation was maintained after long-term cultured and upon differentiation toward different lineages. To our knowledge, Lent-On-Plus is the first all-in-one vector system that tightly regulates transgene expression in bulk populations of human pluripotent stem cells and its progeny.

A dual molecular analogue tuner for dissecting protein function in mammalian cells

Loss-of-function studies are fundamental for dissecting gene function. Yet, methods to rapidly and effectively perturb genes in mammalian cells, and particularly in stem cells, are scarce. Here we present a system for simultaneous conditional regulation of two different proteins in the same mammalian cell. This system harnesses the plant auxin and jasmonate hormone-induced degradation pathways, and is deliverable with only two lentiviral vectors. It combines RNAi-mediated silencing of two endogenous proteins with the expression of two exogenous proteins whose degradation is induced by external ligands in a rapid, reversible, titratable and independent manner. By engineering molecular tuners for NANOG, CHK1, p53 and NOTCH1 in mammalian stem cells, we have validated the applicability of the system and demonstrated its potential to unravel complex biological processes.

Loss-of-function approaches are fundamental for dissecting the roles played by genes but methods to simultaneously perturb several proteins in the same mammalian cell are scarce. Here the authors harness the plant auxin and jasmonate hormone-degradation pathways and RNAi technology, to control the levels of two proteins and validate its application in stem cells.

Single-Cell-State Culture of Human Pluripotent Stem Cells Increases Transfection Efficiency

Efficient gene transfer into human pluripotent stem cells (hPSCs) holds great promise for regenerative medicine and pharmaceutical development. In the past decade, various methods were developed for gene transfer into hPSCs; however, hPSCs form tightly packed colonies, making gene transfer difficult. In this study, we established a stable culture method of hPSCs at a single-cell state to reduce cell density and investigated gene transfection efficiency followed by gene editing efficiency. hPSCs cultured in a single-cell state were transfected using nonliposomal transfection reagents with plasmid DNA or mRNA encoding enhanced green fluorescent protein. We found that most cells (DNA > 90%; mRNA > 99%) were transfected without the loss of undifferentiated PSC marker expression or pluripotency. Moreover, we demonstrated an efficient gene editing method using transcription activator-like effector nucleases (TALENs) targeting the adenomatous polyposis coli (APC) gene. Our new method may improve hPSC gene transfer techniques, thus facilitating their use for human regenerative medicine.

Improving the Gene Transfection in Human Embryonic Stem Cells: Balancing with Cytotoxicity and Pluripotent Maintenance

Manipulation of genes in human embryonic stem cells (hESCs) is imperative for their highly potential applications; however, the transduction efficiency remains very low. Although existing evidence revealed the type, size, and zeta potential of vector affect gene transfection efficiency in cells, the systematic study in hESCs is scarce. In this study, using poly(amidoamine) (PAMAM) dendrimers ended with amine, hydroxyl, or carboxyl as model, we tested the influences of size and surface group as well as cytotoxicity and endocytosis on hESC gene transfection. We found that in culture medium of mTeSR the particle sizes of G5, G7, G4.5COOH, and G5OH were around 5 nm and G1 had a smaller size of 3.14 nm. G5 and G7 had a slight and significant positive zeta potential, respectively, whereas G1 was slightly negative, and G4.5COOH and G5OH were significantly negative. We demonstrated that only amine-terminated dendrimers accomplished gene transfection in hESCs, which is greater than that from Lipofectamine 2000 transfection. Ten micromolar G5 had the greatest efficiency and was better than 1000 μM G1. Only a low concentration (0.5 and 1 μM) of G7 realized gene delivery. Amine-ended dendrimers, especially with higher generations, were detrimental to the growth and pluripotent maintenance of hESCs. In contrast, similarly sized hydroxyl- and carboxyl-terminated dendrimers exerted much lower cytotoxicity, in which carboxyl-terminated dendrimer maintained pluripotency of hESCs. We also confirmed the endocytosis into and significant exocytosis from hESCs using FITC-labeled G5 dendrimer. These results suggested that careful considerations of size, concentration, and zeta potential, particularly the identity and position of groups, as well as minimized exocytosis in the design of a vector for hESC gene delivery are necessary, which helps to better design an effective vector in hESC gene transduction.

ALS Patient Stem Cells for Unveiling Disease Signatures of Motoneuron Susceptibility: Perspectives on the Deadly Mitochondria, ER Stress and Calcium Triad

Amyotrophic lateral sclerosis (ALS) is a largely sporadic progressive neurodegenerative disease affecting upper and lower motoneurons (MNs) whose specific etiology is incompletely understood. Mutations in superoxide dismutase-1 (SOD1), TAR DNA-binding protein 43 (TARDBP/TDP-43) and C9orf72, have been identified in subsets of familial and sporadic patients. Key associated molecular and neuropathological features include ubiquitinated TDP-43 inclusions, stress granules, aggregated dipeptide proteins from mutant C9orf72 transcripts, altered mitochondrial ultrastructure, dysregulated calcium homeostasis, oxidative and endoplasmic reticulum (ER) stress, and an unfolded protein response (UPR). Such impairments have been documented in ALS animal models; however, whether these mechanisms are initiating factors or later consequential events leading to MN vulnerability in ALS patients is debatable. Human induced pluripotent stem cells (iPSCs) are a valuable tool that could resolve this “chicken or egg” causality dilemma. Relevant systems for probing pathophysiologically affected cells from large numbers of ALS patients and discovering phenotypic disease signatures of early MN susceptibility are described. Performing unbiased ‘OMICS and high-throughput screening in relevant neural cells from a cohort of ALS patient iPSCs, and rescuing mitochondrial and ER stress impairments, can identify targeted therapeutics for increasing MN longevity in ALS.

Transition toward Human Cytomegalovirus Susceptibility in Early Human Embryonic Stem Cell-Derived Neural Precursors

Congenital human cytomegalovirus (HCMV) infection is associated with neurodevelopmental disabilities. To dissect the earliest events of infection in the developing human brain, we studied HCMV infection during controlled differentiation of human embryonic stem cells (hESC) into neural precursors. We traced a transition from viral restriction in hESC, mediated by a block in viral binding, toward HCMV susceptibility in early hESC-derived neural precursors. We further revealed the role of platelet-derived growth factor receptor alpha (PDGFRα) as a determinant of the developmentally acquired HCMV susceptibility.

Post-transcriptional gene silencing, transcriptional gene silencing and human immunodeficiency virus

While human immunodeficiency virus 1 (HIV-1) infection is controlled through continuous, life-long use of a combination of drugs targeting different steps of the virus cycle, HIV-1 is never completely eradicated from the body. Despite decades of research there is still no effective vaccine to prevent HIV-1 infection. Therefore, the possibility of an RNA interference (RNAi)-based cure has become an increasingly explored approach. Endogenous gene expression is controlled at both, transcriptional and post-transcriptional levels by non-coding RNAs, which act through diverse molecular mechanisms including RNAi. RNAi has the potential to control the turning on/off of specific genes through transcriptional gene silencing (TGS), as well as fine-tuning their expression through post-transcriptional gene silencing (PTGS). In this review we will describe in detail the canonical RNAi pathways for PTGS and TGS, the relationship of TGS with other silencing mechanisms and will discuss a variety of approaches developed to suppress HIV-1 via manipulation of RNAi. We will briefly compare RNAi strategies against other approaches developed to target the virus, highlighting their potential to overcome the major obstacle to finding a cure, which is the specific targeting of the HIV-1 reservoir within latently infected cells.

Efficient production of T cells from mouse pluripotent stem cells by controlled expression of Lhx2

LIM-homeobox transcription factor Lhx2 induces ex vivo amplification of adult hematopoietic stem cells (HSCs) in mice. We previously showed that engraftable HSC-like cells are generated from mouse embryonic stem cells (ESCs) and induced pluripotent stem cells by enforced expression of Lhx2. However, when these HSC-like cells were transplanted into irradiated congenic mice, donor-derived T cells were barely detectable, whereas other lineages of hematopoietic cells were continuously produced. Here we investigated T-cell differentiation potential of the Lhx2-induced HSC-like cells using ESCs carrying doxycycline (dox)-inducible Lhx2 expression cassette. Dox-mediated over-expression of Lhx2 conferred a self-renewing activity to ESC-derived c-Kit(+) CD41(+) embryonic hematopoietic progenitor cells (HPCs), thereby converting them to HSC-like cells. When these HSC-like cells were transplanted into irradiated immunodeficient mice and they were supplied with a dox-containing water, CD4/8 double negative T cells were detected in their thymi. Once the Lhx2 expression was terminated, differentiation of CD4/8 double positive and single positive T cells was initiated in the thymi of transplanted mice and mature T cells were released in the peripheral blood. These results showed that engraftable HSC-like cells with full hematopoietic potential can be obtained from ESCs by the conditional expression of Lhx2.

[Pluripotent stem cells as a source for T cell research and clinical application]

Recently, promising clinical outcomes of cancer immunotherapy including administration of an anti PD-1 antibody targeting for T cell reactivation has gained particular attention worldwide. Adoptive cell therapy with tumor infiltrating lymphocytes and TCR/CAR (Chimeric Antigen Receptor) transgenic T cells are also under development. Although it has become clearer that the efficacy of adoptive cell therapy correlate with the quality of infusing T cells, antigen specific T cells in patients with chronic infection and cancer have been exhausted. We have succeeded to generate rejuvenated antigen specific T cells by reprogramming to pluripotency and differentiation. In this article, we introduce fundamentals of this technology and describe its potential for adoptive cell therapy in the future.

Mucopolysaccharidosis enzyme production by bone marrow and dental pulp derived human mesenchymal stem cells

Mucopolysaccharidoses (MPS) are inherited metabolic disorders that arise from a complete loss or a reduction in one of eleven specific lysosomal enzymes. MPS children display pathology in multiple cell types leading to tissue and organ failure and early death. Mesenchymal stem cells (MSCs) give rise to many of the cell types affected in MPS, including those that are refractory to current treatment protocols such as hematopoietic stem cell (HSC) based therapy. In this study we compared multiple MPS enzyme production by bone marrow derived (hBM) and dental pulp derived (hDP) MSCs to enzyme production by HSCs. hBM MSCs produce significantly higher levels of MPS I, II, IIIA, IVA, VI and VII enzyme than HSCs, while hDP MSCs produce significantly higher levels of MPS I, IIIA, IVA, VI and VII enzymes. Higher transfection efficiency was observed in MSCs (89%) compared to HSCs (23%) using a lentiviral vector. Over-expression of four different lysosomal enzymes resulted in up to 9303-fold and up to 5559-fold greater levels in MSC cell layer and media respectively. Stable, persistent transduction of MSCs and sustained over-expression of MPS VII enzyme was observed in vitro. Transduction of MSCs did not affect the ability of the cells to differentiate down osteogenic, adipogenic or chondrogenic lineages, but did partially delay differentiation down the non-mesodermal neurogenic lineage.

Viral expression cassette elements to enhance transgene target specificity and expression in gene therapy

Over the last five years, the number of clinical trials involving AAV (adeno-associated virus) and lentiviral vectors continue to increase by about 150 trials each year. For continued success, AAV and lentiviral expression cassettes need to be designed to meet each disease's specific needs. This review discusses how viral vector expression cassettes can be engineered with elements to enhance target specificity and increase transgene expression. The key differences relating to target specificity between ubiquitous and tissue-specific promoters are discussed, as well as how endogenous miRNAs and their target sequences have been used to restrict transgene expression. Specifically, relevant studies indicating how cis-acting elements such as introns, WPRE, polyadenylation signals, and the CMV enhancer are highlighted to show their utility for enhancing transgene expression in gene therapy applications. All discussion bears in mind that expression cassettes have space constraints. In conclusion, this review can serve as a menu of vector genome design elements and their cost in terms of space to thoughtfully engineer viral vectors for gene therapy.

A simple and efficient system for regulating gene expression in human pluripotent stem cells and derivatives

Regulatable transgene expression in human pluripotent stem cells (hPSCs) and their progenies is often necessary to dissect gene function in a temporal and spatial manner. However, hPSC lines with inducible transgene expression, especially in differentiated progenies, have not been established due to silencing of randomly inserted genes during stem cell expansion and/or differentiation. Here, we report the use of transcription activator-like effector nucleases-mediated targeting to AAVS1 site to generate versatile conditional hPSC lines. Transgene (both green fluorescent protein and a functional gene) expression in hPSCs and their derivatives was not only sustained but also tightly regulated in response to doxycycline both in vitro and in vivo. We modified the donor construct so that any gene of interest can be readily inserted to produce hPSC lines with conditional transgene expression. This technology will substantially improve the way we study human stem cells.

Cell replacement therapies: is it time to reprogram?

Hematopoietic stem cell transplantations have become a very successful therapeutic approach to treat otherwise life-threatening blood disorders. It is thought that stem cell transplantation may also become a feasible treatment option for many non-blood-related diseases. So far, however, the limited availability of human leukocyte antigen-matched donors has hindered development of some cell replacement therapies. The Nobel-prize rewarded finding that pluripotency can be induced in somatic cells via expression of a few transcription factors has led to a revolution in stem cell biology. The possibility to change the fate of somatic cells by expressing key transcription factors has been used not only to generate pluripotent stem cells, but also for directly converting somatic cells into fully differentiated cells of another lineage or more committed progenitor cells. These approaches offer the prospect of generating cell types with a specific genotype de novo, which would circumvent the problems associated with allogeneic cell transplantations. This technology has generated a plethora of new disease-specific research efforts, from studying disease pathogenesis to therapeutic interventions. Here we will discuss the opportunities in this booming field of cell biology and summarize how the scientists in the Netherlands have joined efforts in one area to exploit the new technology.

Stable enhanced green fluorescent protein expression after differentiation and transplantation of reporter human induced pluripotent stem cells generated by AAVS1 transcription activator-like effector nucleases

Human induced pluripotent stem (hiPS) cell lines with tissue-specific or ubiquitous reporter genes are extremely useful for optimizing in vitro differentiation conditions as well as for monitoring transplanted cells in vivo. The adeno-associated virus integration site 1 (AAVS1) locus has been used as a "safe harbor" locus for inserting transgenes because of its open chromatin structure, which permits transgene expression without insertional mutagenesis. However, it is not clear whether targeted transgene expression at the AAVS1 locus is always protected from silencing when driven by various promoters, especially after differentiation and transplantation from hiPS cells. In this paper, we describe a pair of transcription activator-like effector nucleases (TALENs) that enable more efficient genome editing than the commercially available zinc finger nuclease at the AAVS1 site. Using these TALENs for targeted gene addition, we find that the cytomegalovirus-immediate early enhancer/chicken β-actin/rabbit β-globin (CAG) promoter is better than cytomegalovirus 7 and elongation factor 1α short promoters in driving strong expression of the transgene. The two independent AAVS1, CAG, and enhanced green fluorescent protein (EGFP) hiPS cell reporter lines that we have developed do not show silencing of EGFP either in undifferentiated hiPS cells or in randomly and lineage-specifically differentiated cells or in teratomas. Transplanting cardiomyocytes from an engineered AAVS1-CAG-EGFP hiPS cell line in a myocardial infarcted mouse model showed persistent expression of the transgene for at least 7 weeks in vivo. Our results show that high-efficiency targeting can be obtained with open-source TALENs and that careful optimization of the reporter and transgene constructs results in stable and persistent expression in vitro and in vivo.

Fast and efficient multitransgenic modification of human pluripotent stem cells

Human pluripotent stem cells (hPSCs) represent a prime cell source for pharmacological research and regenerative therapies because of their extensive expansion potential and their ability to differentiate into essentially all somatic lineages in vitro. Improved methods to stably introduce multiple transgenes into hPSCs will promote, for example, their preclinical testing by facilitating lineage differentiation and purification in vitro and the subsequent in vivo monitoring of respective progenies after their transplantation into relevant animal models. To date, the establishment of stable transgenic hPSC lines is still laborious and time-consuming. Current limitations include the low transfection efficiency of hPSCs via nonviral methods, the inefficient recovery of genetically engineered clones, and the silencing of transgene expression. Here we describe a fast, electroporation-based method for the generation of multitransgenic hPSC lines by overcoming the need for any preadaptation of conventional hPSC cultures to feeder-free conditions before genetic manipulation. We further show that the selection for a single antibiotic resistance marker encoded on one plasmid allowed for the stable genomic (co-)integration of up to two additional, independent expression plasmids. The method thereby enables the straightforward, nonviral generation of valuable multitransgenic hPSC lines in a single step. Practical applicability of the method is demonstrated for antibiotic-based lineage enrichment in vitro and for sodium iodide symporter transgene-based in situ cell imaging after intramyocardial cell infusion into explanted pig hearts.

Hypoxia-inducible factors have distinct and stage-specific roles during reprogramming of human cells to pluripotency

Pluripotent stem cells have distinct metabolic requirements, and reprogramming cells to pluripotency requires a shift from oxidative to glycolytic metabolism. Here, we show that this shift occurs early during reprogramming of human cells and requires hypoxia-inducible factors (HIFs) in a stage-specific manner. HIF1α and HIF2α are both necessary to initiate this metabolic switch and for the acquisition of pluripotency, and the stabilization of either protein during early phases of reprogramming is sufficient to induce the switch to glycolytic metabolism. In contrast, stabilization of HIF2α during later stages represses reprogramming, partly because of the upregulation of TNF-related apoptosis-inducing ligand (TRAIL). TRAIL inhibits induced pluripotent stem cell (iPSC) generation by repressing apoptotic caspase 3 activity specifically in cells undergoing reprogramming but not human embryonic stem cells (hESCs), and inhibiting TRAIL activity enhances human iPSC generation. These results shed light on the mechanisms underlying the metabolic shifts associated with the acquisition of a pluripotent identity during reprogramming.

Transduction of murine embryonic stem cells by magnetic nanoparticle-assisted lentiviral gene transfer

Genetic modification of embryonic stem (ES) cells is a valuable technique when combined with cell replacement strategies. Obtaining stable transgene expression and low-cytotoxicity lentiviral transduction of ES cells is advantageous. It has been shown that the efficiency of transfection and transduction approaches can be increased by magnetic nanoparticles (MNPs). Here, we present a protocol for MNP-assisted lentiviral transduction of adherent mouse ES cells. The application of MNPs increased transduction efficiency and provided the opportunity of cell positioning by a magnetic field.

Optimizing retroviral gene expression for effective therapies

With their ability to integrate their genetic material into the target cell genome, retroviral vectors (RV) of both the gamma-retroviral (γ-RV) and lentiviral vector (LV) classes currently remain the most efficient and thus the system of choice for achieving transgene retention and therefore potentially long-term expression and therapeutic benefit. However, γ-RV and LV integration comes at a cost in that transcription units will be present within a native chromatin environment and thus be subject to epigenetic effects (DNA methylation, histone modifications) that can negatively impact on their function. Indeed, highly variable expression and silencing of γ-RV and LV transgenes especially resulting from promoter DNA methylation is well documented and was the cause of the failure of gene therapy in a clinical trial for X-linked chronic granulomatous disease. This review will critically explore the use of different classes of genetic control elements that can in principle reduce vector insertion site position effects and epigenetic-mediated silencing. These transcriptional regulatory elements broadly divide themselves into either those with a chromatin boundary or border function (scaffold/matrix attachment regions, insulators) or those with a dominant chromatin remodeling and transcriptional activating capability (locus control regions,, ubiquitous chromatin opening elements). All these types of elements have their strengths and weaknesses within the constraints of a γ-RV and LV backbone, showing varying degrees of efficacy in improving reproducibility and stability of transgene function. Combinations of boundary and chromatin remodeling; transcriptional activating elements, which do not impede vector production; transduction efficiency; and stability are most likely to meet the requirements within a gene therapy context especially when targeting a stem cell population.

Enhanced Non-Viral Gene Delivery to Human Embryonic Stem Cells via Small Molecule-Mediated Transient Alteration of Cell Structure

Non-viral gene delivery into human embryonic stem cells (hESCs)is an important tool for controlling cell fate. However, the delivery efficiency remains low due in part to the tight colony structure of the cells which prevents effective exposure towards delivery vectors. We herein report a novel approach to enhance non-viral gene delivery to hESCs by transiently altering the cell and colony structure. (R)-(+)-trans-4-(1-aminoethyl)-N-(4-pyridyl)cyclohexanecarboxamide (Y-27632), a small molecule that inhibits the rho-associated protein kinase pathway, is utilized to induce transient colony spreading which leads to increased transfection efficiency by 1.5 to 2 folds in a spectrum of non-viral transfection reagents including Lipofectamine 2000 and Fugene HD. After removal of Y-27632 post-transfection, cells can revert back to its normal state and do not show alteration of pluripotency. This approach provides a simple, effective tool to enhance non-viral gene delivery into adherent hESCs for genetic manipulation.

Reprogramming adipose tissue-derived mesenchymal stem cells into pluripotent stem cells by a mutant adeno-associated viral vector

Induced pluripotent stem (iPS) cells have great potential for personalized regenerative medicine. Although several different methods for generating iPS cells have been reported, improvement of safety and efficiency is imperative. In this study, we tested the feasibility of using a triple tyrosine mutant AAV2 (Y444+500+730F) vector, designated AAV2.3m, to generate iPS cells. We developed a polycistronic rAAV2.3m vector expressing three reprogramming factors, Klf4, Oct4, and Sox2, and then used this vector to infect mouse adipose-derived mesenchymal stem cells (AT-MSCs) to induce the generation of iPS cells. We demonstrated that (1) the triple tyrosine mutant AAV2 vector is able to reprogram mouse adult adipose tissue-derived stem cells into the pluripotent state. Those rAAV2.3m-derived iPS (rAAV2.3m-iPS) cells express endogenous pluripotency-associated genes including Oct4, Sox2, and SSEA-1, and form teratomas containing multiple tissues in vivo; (2) c-myc, an oncogene, is dispensable in rAAV2.3m-mediated cellular reprogramming; and (3) transgene expression is undetectable after reprogramming, whereas vector DNA is detectable, indicating that transgenes are silenced. These results indicated the rAAV vector may have some advantages in generating iPS cells.

Intracerebral transplantation of differentiated human embryonic stem cells to hemiparkinsonian monkeys

To explore stem cell therapy for Parkinson's disease (PD), three adult rhesus monkeys were first rendered hemiparkinsonian by unilateral intracarotid 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) infusion. Five months postinfusion, they were given MRI-guided stereotaxic intrastriatal and intranigral injections of green fluorescent protein (GFP)-labeled cultures of dopaminergic neurons derived from human embryonic stem cells (DA-hES cells). The animals were immunosuppressed using daily oral cyclosporine (CsA). Three months later, viable grafts were observed at the injection sites in one animal, while no obvious grafts were present in the other two monkeys. The surviving grafts contained numerous GFP-positive cells that were positively labeled for nestin and MAP2 but not for glial fibrillary acidic protein (GFAP), NeuN, or tyrosine hydroxylase (TH). The grafted areas in all animals showed dense staining for GFAP, CD68, and CD45. These results indicated that xenografts of human stem cell derivatives in CsA-suppressed rhesus brain were mostly rejected. Our study suggests that immunological issues are obstacles for preclinical evaluation of hES cells and that improved immunosuppression paradigms and/or alternative cell sources that do not elicit immune rejection are needed for long-term preclinical studies.

Porcine synapsin 1: SYN1 gene analysis and functional characterization of the promoter

Synapsin 1 (SYN1) is a phosphoprotein involved in nerve signal transmission. The porcine SYN1 promoter orthologue was cloned and characterized to provide a means of expressing a transgene specifically in neurons. The nucleotide sequence of the promoter displayed a high degree of conservation of elements responsible for neuron-specific expression. Expression analysis of SYN1 demonstrated presence of transcript during embryonic development. Analysis of GFP expression in transgenic zebrafish embryos suggests that the pig SYN1 promoter directs expression in neuronal cells. Thus, the SYN1 promoter is a good candidate for use in the generation of pig models of human neurodegenerative disorders.

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The porcine synapsin1 (SYN1) promoter was cloned and characterized.

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SYN1 mRNA expression is detected in brain during embryo development.

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The SYN1 gene is mapped to pig chromosome X.

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Porcine SYN1 directs GFP expression in neuronal cells of transgenic zebrafish.

Improved Method of Producing Human Neural Progenitor Cells of High Purity and in Large Quantities from Pluripotent Stem Cells for Transplantation Studies

Transplantation of human neural progenitor cells (hNPCs) is a promising therapeutic approach for various diseases of the central nervous system (CNS). Reliable testing of hNPC transplantation in animal models of neurological diseases requires that these cells can be produced in sufficient amounts, show consistent homogeneity as a neural cell population, and be reliably labeled for in vivo tracking. In addition, the cells should be characterized as being at the optimal state of differentiation favoring successful engraftment. Here, we show that high numbers of purified hNPCs can be produced from human embryonic stem cells (hESCs) by manually selecting specifically sized and shaped spheres followed by fluorescence-activated cell sorting based on the relative cell size. In addition, we report that labeling of hNPCs with ultra-small superparamagnetic iron oxide (USPIO) particles does not affect the cellular morphology or growth. More importantly, we show that the transduction with lentiviral vector encoding green fluorescent protein (GFP) decreases the neurality of the cell population. We conclude that our cost-effective protocol of generating hNPCs is widely applicable for preclinical studies on CNS disorders. This improved method of producing large quantities of high-purity hNPCs maybe useful also when generating hNPCs from human induced pluripotent stem (hiPS) cell lines. However, caution should be used when lenti-GFP transduction is applied for hNPC labeling.

Baculoviral transduction facilitates TALEN-mediated targeted transgene integration and Cre/LoxP cassette exchange in human-induced pluripotent stem cells

Safety and reliability of transgene integration in human genome continue to pose challenges for stem cell-based gene therapy. Here, we report a baculovirus-transcription activator-like effector nuclease system for AAVS1 locus-directed homologous recombination in human induced pluripotent stem cells (iPSCs). This viral system, when optimized in human U87 cells, provided a targeted integration efficiency of 95.21% in incorporating a Neo-eGFP cassette and was able to mediate integration of DNA insert up to 13.5 kb. In iPSCs, targeted integration with persistent transgene expression was achieved without compromising genomic stability. The modified iPSCs continued to express stem cell pluripotency markers and maintained the ability to differentiate into three germ lineages in derived embryoid bodies. Using a baculovirus-Cre/LoxP system in the iPSCs, the Neo-eGFP cassette at the AAVS1 locus could be replaced by a Hygro-mCherry cassette, demonstrating the feasibility of cassette exchange. Moreover, as assessed by measuring γ-H2AX expression levels, genome toxicity associated with chromosomal double-strand breaks was not detectable after transduction with moderate doses of baculoviral vectors expressing transcription activator-like effector nucleases. Given high targeted integration efficiency, flexibility in transgene exchange and low genome toxicity, our baculoviral transduction-based approach offers great potential and attractive option for precise genetic manipulation in human pluripotent stem cells.

Evaluation of long-term transgene expression in piggyBac-modified human T lymphocytes

The piggyBac transposon system is a promising nonviral method to genetically modify T cells for immunotherapeutic applications. To evaluate the regulation and stability of transgene expression in human T cells modified with piggyBac-transposons, peripheral blood mononuclear cells were nucleofected with transposase and an enhanced green fluorescence protein (eGFP)-expressing transposon. Single-cell clones that were subsequently stimulated and expanded exhibited homogenous eGFP expression for >26 weeks in culture. CD3 stimulation of the T-cell receptor together with CD28-mediated costimulation resulted in an approximate 10-fold transient increase in eGFP expression, but immunomodulatory cytokines, including interferon-γ, interleukin-12, interleukin-4, and transforming growth factor-β, did not alter transgene expression in actively dividing, activated, or resting T cells. Epigenetic modification with 5-azacytidine or trichostatin-A increased transgene expression indicating that piggyBac-mediated transgene expression could be modulated by methylation or histone acetylation, respectively. We performed transposon copy number analysis of populations of stably transfected T cells, comparing transposon plasmids of 5.6 and 3.5 kb. The smaller vector achieved an average of 22 transposon copies per cell, whereas the larger vector achieved 1.6 copies/cell, implying that transposon copy number can be engineered to be low or high depending on the vector used. Our results provide important insight into the ability of piggyBac to achieve stable genetic modification of T cells for immunotherapy applications and how transgene expression might be regulated by TCR activation, cytokines, and epigenetic mechanisms.

Induced pluripotent stem cell-derived neural cells survive and mature in the nonhuman primate brain

The generation of induced pluripotent stem cells (iPSCs) opens up the possibility for personalized cell therapy. Here, we show that transplanted autologous rhesus monkey iPSC-derived neural progenitors survive for up to 6 months and differentiate into neurons, astrocytes, and myelinating oligodendrocytes in the brains of MPTP-induced hemiparkinsonian rhesus monkeys with a minimal presence of inflammatory cells and reactive glia. This finding represents a significant step toward personalized regenerative therapies.

Significant differences in genotoxicity induced by retrovirus integration in human T cells and induced pluripotent stem cells

Retrovirus is frequently used in the genetic modification of mammalian cells and the establishment of induced pluripotent stem cells (iPSCs) via cell reprogramming. Vector-induced genotoxicity could induce profound effect on the physiology and function of these stem cells and their differentiated progeny. We analyzed retrovirus-induced genotoxicity in somatic cell Jurkat and two iPSC lines. In Jurkat cells, retrovirus frequently activated host gene expression and gene activation was not dependent on the distance between the integration site and the transcription start site of the host gene. In contrast, retrovirus frequently down-regulated host gene expression in iPSCs, possibly due to the action of chromatin silencing that spreads from the provirus to the nearby host gene promoter. Our data raises the issue that some of the phenotypic variability observed among iPSC clones derived from the same parental cell line may be caused by retrovirus-induced gene expression changes rather than by the reprogramming process itself. It also underscores the importance of characterizing retrovirus integration and carrying out risk assessment of iPSCs before they can be applied in basic research and clinics.

Differentiation and lineage commitment of murine embryonic stem cells into insulin producing cells

Pluripotent embryonic stem (ES) cells and induced pluripotent stem (iPS) cells recently developed in our laboratory can be used to generate the much needed insulin producing cells (IPCs) for the treatment of type 1 diabetes. However, currently available differentiation protocols generate IPCs at a very low frequency. More importantly, it is difficult to purify the IPCs from the mixed cell population due to the lack of well characterized pancreatic beta cell-specific cell surface markers. Subsequently, multiple studies have been published with limited success. A major cause for these poor results is an inadequate Pdx1 expression in the embryoid body (EB) or definitive endoderm (DE)-derived precursors. Here we investigated whether ectopic expression of pancreatic and duodenal homeobox 1 (Pdx1), an essential pancreatic transcription factor, in mouse ES cells leads to enhanced differentiation into IPCs. Here we describe a new approach for the generation of glucose responsive IPCs using ES cells ectopically expressing pancreatic and duodenal homeobox 1 (Pdx1) and paired box gene 4 (Pax4).

Fluorescence microscopy-based high-throughput screening for factors involved in gene silencing

Gene silencing in eukaryotes is a highly controlled process. It involves the concerted action of histone and DNA-modifying enzymes as well as transcription factors and chromatin-associated proteins. To understand how epigenetic gene silencing is regulated, it is important to identify the factors involved in this process. Here we describe an assay that allows high-throughput screening for factors involved in gene silencing. This assay exploits the susceptibility of the viral cytomegalovirus (CMV) promoter to epigenetic silencing in embryonic stem cells (ESCs) and uses reporter constructs with an optical readout to determine the gene silencing potential of candidate factors. This approach allows to study mechanisms and kinetics of gene silencing in living cells and to evaluate the role of DNA methyltransferases, histone-modifying enzymes, and other chromatin-associated factors during gene silencing.

The impact of cHS4 insulators on DNA transposon vector mobilization and silencing in retinal pigment epithelium cells

DNA transposons have become important vectors for efficient non-viral integration of transgenes into genomic DNA. The Sleeping Beauty (SB), piggyBac (PB), and Tol2 transposable elements have distinct biological properties and currently represent the most promising transposon systems for animal transgenesis and gene therapy. A potential obstacle, however, for persistent function of integrating vectors is transcriptional repression of the element and its genetic cargo. In this study we analyze the insulating effect of the 1.2-kb 5'-HS4 chicken β-globin (cHS4) insulator element in the context of SB, PB, and Tol2 transposon vectors. By examining transgene expression from genomically inserted transposon vectors encoding a marker gene driven by a silencing-prone promoter, we detect variable levels of transcriptional silencing for the three transposon systems in retinal pigment epithelium cells. Notably, the PB system seems less vulnerable to silencing. Incorporation of cHS4 insulator sequences into the transposon vectors results in 2.2-fold and 1.5-fold increased transgene expression levels for insulated SB and PB vectors, respectively, but an improved persistency of expression was not obtained for insulated transgenes. Colony formation assays and quantitative excision assays unveil enhanced SB transposition efficiencies by the inclusion of the cHS4 element, resulting in a significant increase in the stable transfection rate for insulated SB transposon vectors in human cell lines. Our findings reveal a positive impact of cHS4 insulator inclusion for SB and PB vectors in terms of increased transgene expression levels and improved SB stable transfection rates, but also the lack of a long-term protective effect of the cHS4 insulator against progressive transgene silencing in retinal pigment epithelium cells.

Intra-articular injection of mesenchymal stem cells expressing coagulation factor ameliorates hemophilic arthropathy in factor VIII-deficient mice

BACKGROUND

Transplantation of cells overexpressing a target protein represents a viable gene therapeutic approach for treating hemophilia. Here, we focused on the use of autologous mesenchymal stem cells (MSCs) expressing coagulation factor for the treatment of coagulation factor VIII (FVIII) deficiency in mice.

METHODS AND RESULTS

Analysis of luciferase gene constructs driven by different promoters revealed that the plasminogen activator inhibitor-1 (PAI-1) gene promoter coupled with the cytomegalovirus promoter enhancer region was one of the most effective promoters for producing the target protein. MSCs transduced with the simian immunodeficiency virus (SIV) vector containing the FVIII gene driven by the PAI-1 promoter expressed FVIII for several months, and this expression was maintained after multiple mesenchymal lineage differentiation. Although intravenous injection of cell supernatant derived from MSCs transduced with an SIV vector containing the FVIII gene driven by the PAI-1 promoter significantly increased plasma FVIII levels, subcutaneous implantation of the MSCs resulted in a transient and weak increase in plasma FVIII levels in FVIII-deficient mice. Interestingly, intra-articular injection of the transduced MSCs significantly ameliorated the hemarthrosis and hemophilic arthropathy induced by knee joint needle puncture in FVIII-deficient mice. The therapeutic effects of a single intra-articular injection of transduced MSCs to inhibit joint bleeding persisted for at least 8 weeks after administration.

CONCLUSIONS

MSCs provide a promising autologous cell source for the production of coagulation factor. Intra-articular injection of MSCs expressing coagulation factor may offer an attractive treatment approach for hemophilic arthropathy.

Generation of a human embryonic stem cell line stably expressing high levels of the fluorescent protein mCherry

AIM

The generation and characterization of a human embryonic stem cell (hESC) line stably expressing red fluorescent mCherry protein.

METHODS

Lentiviral transduction of a ubiquitously-expressed human EF-1α promoter driven mCherry transgene was performed in MEL2 hESC. Red fluore-scence was assessed by immunofluorescence and flow cytometry. Pluripotency of stably transduced hESC was determined by immunofluorescent pluripotency marker expression, flow cytometry, teratoma assays and embryoid body-based differentiation followed by reverse transcriptase-polymerase chain reaction. Quantification of cell motility and survival was performed with time lapse microscopy.

RESULTS

Constitutively fluorescently-labeled hESCs are useful tools for facile in vitro and in vivo tracking of survival, motility and cell spreading on various surfaces before and after differentiation. Here we describe the generation and characterization of a hESC line (MEL2) stably expressing red fluorescent protein, mCherry. This line was generated by random integration of a fluorescent protein-expressing cassette, driven by the ubiquitously-expressed human EF-1α promoter. Stably transfected MEL2-mCherry hESC were shown to express pluripotency markers in the nucleus (POU5F1/OCT4, NANOG and SOX2) and on the cell surface (SSEA4, TRA1-60 and TG30/CD9) and were shown to maintain a normal karyotype in long-term (for at least 35 passages) culture. MEL2-mCherry hESC further readily differentiated into representative cell types of the three germ layers in embryoid body and teratoma based assays and, importantly, maintained robust mCherry expression throughout differentiation. The cell line was next adapted to single-cell passaging, rendering it compatible with numerous bioengineering applications such as measurement of cell motility and cell spreading on various protein modified surfaces, quantification of cell attachment to nanoparticles and rapid estimation of cell survival.

CONCLUSION

The MEL2-mCherry hESC line conforms to the criteria of bona fide pluripotent stem cells and maintains red fluorescence throughout differentiation, making it a useful tool for bioengineering and in vivo tracking experiments.

Human cardiac progenitor cells engineered with Pim-I kinase enhance myocardial repair

OBJECTIVES

The goal of this study was to demonstrate the enhancement of human cardiac progenitor cell (hCPC) reparative and regenerative potential by genetic modification for the treatment of myocardial infarction.

BACKGROUND

Regenerative potential of stem cells to repair acute infarction is limited. Improved hCPC survival, proliferation, and differentiation into functional myocardium will increase efficacy and advance translational implementation of cardiac regeneration.

METHODS

hCPCs isolated from the myocardium of heart failure patients undergoing left ventricular assist device implantation were engineered to express green fluorescent protein (hCPCe) or Pim-1-GFP (hCPCeP). Functional tests of hCPC regenerative potential were performed with immunocompromised mice by using intramyocardial adoptive transfer injection after infarction. Myocardial structure and function were monitored by echocardiographic and hemodynamic assessment for 20 weeks after delivery. hCPCe and hCPCeP expressing luciferase were observed by using bioluminescence imaging to noninvasively track persistence.

RESULTS

hCPCeP exhibited augmentation of reparative potential relative to hCPCe control cells, as shown by significantly increased proliferation coupled with amelioration of infarction injury and increased hemodynamic performance at 20 weeks post-transplantation. Concurrent with enhanced cardiac structure and function, hCPCeP demonstrated increased cellular engraftment and differentiation with improved vasculature and reduced infarct size. Enhanced persistence of hCPCeP versus hCPCe was revealed by bioluminescence imaging at up to 8 weeks post-delivery.

CONCLUSIONS

Genetic engineering of hCPCs with Pim-1 enhanced repair of damaged myocardium. Ex vivo gene delivery to modify stem cells has emerged as a viable option addressing current limitations in the field. This study demonstrates that efficacy of hCPCs from the failing myocardium can be safely and significantly enhanced through expression of Pim-1 kinase, setting the stage for use of engineered cells in pre-clinical settings.

Transposon-mediated BAC transgenesis in human ES cells

Transgenesis is a cornerstone of molecular biology. The ability to integrate a specifically engineered piece of DNA into the genome of a living system is fundamental to our efforts to understand life and exploit its implications for medicine, nanotechnology and bioprospecting. However, transgenesis has been hampered by position effects and multi-copy integration problems, which are mainly due to the use of small, plasmid-based transgenes. Large transgenes based on native genomic regions cloned into bacterial artificial chromosomes (BACs) circumvent these problems but are prone to fragmentation. Herein, we report that contrary to widely held notions, large BAC-sized constructs do not prohibit transposition. We also report the first reliable method for BAC transgenesis in human embryonic stem cells (hESCs). The PiggyBac or Sleeping Beauty transposon inverted repeats were integrated into BAC vectors by recombineering, followed by co-lipofection with the corresponding transposase in hESCs to generate robust fluorescent protein reporter lines for OCT4, NANOG, GATA4 and PAX6. BAC transposition delivers several advantages, including increased frequencies of single-copy, full-length integration, which will be useful in all transgenic systems but especially in difficult venues like hESCs.

Establishment of clonal MIN-O transplant lines for molecular imaging via lentiviral transduction & in vitro culture

As the field of molecular imaging evolves and increasingly is asked to fill the discovery and validation space between basic science and clinical applications, careful consideration should be given to the models in which studies are conducted. The MIN-O mouse model series is an established in vivo model of human mammary precancer ductal carcinoma in situ with progression to invasive carcinoma. This series of transplant lines is propagated in vivo and experiments utilizing this model can be completed in non-engineered immune intact FVB/n wild type mice thereby modeling the tumor microenvironment with biological relevance superior to traditional tumor cell xenografts. Unfortunately, the same qualities that make this and many other transplant lines more biologically relevant than standard cell lines for molecular imaging studies present a significant obstacle as somatic genetic re-engineering modifications common to many imaging applications can be technically challenging. Here, we describe a protocol for the efficient lentiviral transduction of cell slurries derived from precancerous MIN-O lesions, in vitro culture of “MIN-O-spheres” derived from single cell clones, and the subsequent transplantation of these spheres to produce transduced sublines suitable for optical imaging applications. These lines retain the physiologic and pathologic properties, including multilineage differentiation, and complex microanatomic interaction with the host stroma characteristic of the MIN-O model. We also present the in vivo imaging and immunohistochemical analysis of serial transplantation of one such subline and detail the progressive multifocal loss of the transgene in successive generations.

A β-sheet structure interacting peptide for intracellular protein delivery into human pluripotent stem cells and their derivatives

The advance in stem cell research relies largely on the efficiency and biocompatibility of technologies used to manipulate stem cells. In our previous study, we had designed an amphipathic peptide RV24 that can deliver proteins into cancer cell lines efficiently without significant side effects. Encouraged by this observation, we moved forward to test whether RV24 could be used to deliver proteins into human embryonic stem cells and human induced pluripotent stem cells. RV24 successfully mediated protein delivery into these pluripotent stem cells, as well as their derivatives including neural stem cells and dendritic cells. Based on NMR studies and particle surface charge measurements, we proposed that hydrophobic domain of RV24 interacts with β-sheet structures of the proteins, followed by formation of "peptide cage" to facilitate delivery across cellular membrane. These findings suggest the feasibility of using amphipathic peptide to deliver functional proteins intracellularly for stem cell research.

Varicella-zoster virus infects human embryonic stem cell-derived neurons and neurospheres but not pluripotent embryonic stem cells or early progenitors

Pluripotent human stem cells are a powerful tool for the generation of differentiated cells that can be used for the study of human disease. We recently demonstrated that neurons derived from pluripotent human embryonic stem cells (hESC) can be infected by the highly host-restricted human alphaherpesvirus varicella-zoster virus (VZV), permitting the interaction of VZV with neurons to be readily evaluated in culture. In the present study, we examine whether pluripotent hESC and neural progenitors at intermediate stages of differentiation are permissive for VZV infection. We demonstrate here that VZV infection is blocked in naïve hESC. A block to VZV replication is also seen when a bacterial artificial chromosome (BAC) containing the VZV genome is transfected into hESC. In contrast, related alphaherpesviruses herpes simplex virus 1 (HSV-1) and pseudorabies virus (PrV) productively infect naïve hESC in a cell-free manner, and PrV replicates from a BAC transfected into hESC. Neurons differentiate from hESC via neural progenitor intermediates, as is the case in the embryo. The first in vitro stage at which permissiveness of hESC-derived neural precursors to VZV replication is observed is upon formation of "neurospheres," immediately after detachment from the inductive stromal feeder layer. These findings suggest that hESC may be useful in deciphering the yet enigmatic mechanisms of specificity of VZV infection and replication.

Human embryonic stem cell-derived neurons adopt and regulate the activity of an established neural network

Whether hESC-derived neurons can fully integrate with and functionally regulate an existing neural network remains unknown. Here, we demonstrate that hESC-derived neurons receive unitary postsynaptic currents both in vitro and in vivo and adopt the rhythmic firing behavior of mouse cortical networks via synaptic integration. Optical stimulation of hESC-derived neurons expressing Channelrhodopsin-2 elicited both inhibitory and excitatory postsynaptic currents and triggered network bursting in mouse neurons. Furthermore, light stimulation of hESC-derived neurons transplanted to the hippocampus of adult mice triggered postsynaptic currents in host pyramidal neurons in acute slice preparations. Thus, hESC-derived neurons can participate in and modulate neural network activity through functional synaptic integration, suggesting they are capable of contributing to neural network information processing both in vitro and in vivo.

An efficient vector system to modify cells genetically

The transfer of foreign genes into mammalian cells has been essential for understanding the functions of genes and mechanisms of genetic diseases, for the production of coding proteins and for gene therapy applications. Currently, the identification and selection of cells that have received transferred genetic material can be accomplished by methods, including drug selection, reporter enzyme detection and GFP imaging. These methods may confer antibiotic resistance, or be disruptive, or require special equipment. In this study, we labeled genetically modified cells with a cell surface biotinylation tag by co-transfecting cells with BirA, a biotin ligase. The modified cells can be quickly isolated for downstream applications using a simple streptavidin bead method. This system can also be used to screen cells expressing two sets of genes from separate vectors.

Current progress and challenges in HIV gene therapy

HIV-1 causes AIDS, a syndrome that affects millions of people globally. Existing HAART is efficient in slowing down disease progression but cannot eradicate the virus. Furthermore the severity of the side effects and the emergence of drug-resistant mutants call for better therapy. Gene therapy serves as an attractive alternative as it reconstitutes the immune system with HIV-resistant cells and could thereby provide a potential cure. The feasibility of this approach was first demonstrated with the 'Berlin patient', who was functionally cured from HIV/AIDS with undetectable HIV-1 viral load after transplantation of bone marrow harboring a naturally occurring CCR5 mutation that blocks viral entry. Here, we give an overview of the current status of HIV gene therapy and remaining challenges and obstacles.