Comparison of gene-transfer efficiency in human embryonic stem cells

Lentiviral Transduction-based CRISPR/Cas9 Editing of Schistosoma mansoni Acetylcholinesterase

Background

Recent studies on CRISPR/Cas9-mediated gene editing in Schistosoma mansoni have shed new light on the study and control of this parasitic helminth. However, the gene editing efficiency in this parasite is modest.

Methods

To improve the efficiency of CRISPR/Cas9 genome editing in schistosomes, we used lentivirus, which has been effectively used for gene editing in mammalian cells, to deliver plasmid DNA encoding Cas9 nuclease, a sgRNA targeting acetylcholinesterase (SmAChE) and a mCherry fluorescence marker into schistosomes.

Results

MCherry fluorescence was observed in transduced eggs, schistosomula, and adult worms, indicating that the CRISPR components had been delivered into these parasite stages by lentivirus. In addition, clearly changed phenotypes were observed in SmAChE-edited parasites, including decreased SmAChE activity, reduced hatching ability of edited eggs, and altered behavior of miracidia hatched from edited eggs. Next-generation sequencing analysis demonstrated that the lentiviral transduction-based CRISPR/Cas9 gene modifications in SmAChE-edited schistosomes were homology-directed repair predominant but with much lower efficiency than that obtained using electroporation (data previously published by our laboratory) for the delivery of CRISPR components.

Conclusion

Taken together, electroporation is more efficient than lentiviral transduction in the delivery of CRISPR/Cas9 into schistosomes for programmed genome editing. The exploration of tactics for enhancing CRISPR/Cas9 gene editing provides the basis for the future improvement of programmed genome editing in S. mansoni.

Engineering CpG island DNA methylation in pluripotent cells through synthetic CpG-free ssDNA insertion

Cellular differentiation requires global changes to DNA methylation (DNAme), where it functions to regulate transcription factor, chromatin remodeling activity, and genome interpretation. Here, we describe a simple DNAme engineering approach in pluripotent stem cells (PSCs) that stably extends DNAme across target CpG islands (CGIs). Integration of synthetic CpG-free single-stranded DNA (ssDNA) induces a target CpG island methylation response (CIMR) in multiple PSC lines, Nt2d1 embryonal carcinoma cells, and mouse PSCs but not in highly methylated CpG island hypermethylator phenotype (CIMP)+ cancer lines. MLH1 CIMR DNAme spanned the CGI, was precisely maintained through cellular differentiation, suppressed MLH1 expression, and sensitized derived cardiomyocytes and thymic epithelial cells to cisplatin. Guidelines for CIMR editing are provided, and initial CIMR DNAme is characterized at TP53 and ONECUT1 CGIs. Collectively, this resource facilitates CpG island DNAme engineering in pluripotency and the genesis of novel epigenetic models of development and disease.

Genome Editing Using Cas9 Ribonucleoprotein Is Effective for Introducing PDGFRA Variant in Cultured Human Glioblastoma Cell Lines

Many variants of uncertain significance (VUS) have been detected in clinical cancer cases using next-generation sequencing-based cancer gene panel analysis. One strategy for the elucidation of VUS is the functional analysis of cultured cancer cell lines that harbor targeted gene variants using genome editing. Genome editing is a powerful tool for creating desired gene alterations in cultured cancer cell lines. However, the efficiency of genome editing varies substantially among cell lines of interest. We performed comparative studies to determine the optimal editing conditions for the introduction of platelet-derived growth factor receptor alpha (PDGFRA) variants in human glioblastoma multiforme (GBM) cell lines. After monitoring the copy numbers of PDGFRA and the expression level of the PDGFRα protein, four GBM cell lines (U-251 MG, KNS-42, SF126, and YKG-1 cells) were selected for the study. To compare the editing efficiency in these GBM cell lines, the modes of clustered regularly interspaced short palindromic repeat (CRISPR)-associated protein 9 (Cas9) delivery (plasmid vs. ribonucleoprotein (RNP)), methods of transfection (lipofection vs. electroporation), and usefulness of cell sorting were then evaluated. Herein, we demonstrated that electroporation-mediated transfer of Cas9 with single-guide RNA (Cas9 RNP complex) could sufficiently edit a target nucleotide substitution, irrespective of cell sorting. As the Cas9 RNP complex method showed a higher editing efficiency than the Cas9 plasmid lipofection method, it was the optimal method for single-nucleotide editing in human GBM cell lines under our experimental conditions.

Effect of Experimental Electrical and Biological Parameters on Gene Transfer by Electroporation: A Systematic Review and Meta-Analysis

The exact mechanisms of nucleic acid (NA) delivery with gene electrotransfer (GET) are still unknown, which represents a limitation for its broader use. Further, not knowing the effects that different experimental electrical and biological parameters have on GET additionally hinders GET optimization, resulting in the majority of research being performed using a trial-and-error approach. To explore the current state of knowledge, we conducted a systematic literature review of GET papers in in vitro conditions and performed meta-analyses of the reported GET efficiency. For now, there is no universal GET strategy that would be appropriate for all experimental aims. Apart from the availability of the required electroporation device and electrodes, the choice of an optimal GET approach depends on parameters such as the electroporation medium; type and origin of cells; and the size, concentration, promoter, and type of the NA to be transfected. Equally important are appropriate controls and the measurement or evaluation of the output pulses to allow a fair and unbiased evaluation of the experimental results. Since many experimental electrical and biological parameters can affect GET, it is important that all used parameters are adequately reported to enable the comparison of results, as well as potentially faster and more efficient experiment planning and optimization.

Diseased, differentiated and difficult: Strategies for improved engineering of in vitro neurological systems

The rapidly growing field of cellular engineering is enabling scientists to more effectively create in vitro models of disease and develop specific cell types that can be used to repair damaged tissue. In particular, the engineering of neurons and other components of the nervous system is at the forefront of this field. The methods used to engineer neural cells can be largely divided into systems that undergo directed differentiation through exogenous stimulation (i.e., via small molecules, arguably following developmental pathways) and those that undergo induced differentiation via protein overexpression (i.e., genetically induced and activated; arguably bypassing developmental pathways). Here, we highlight the differences between directed differentiation and induced differentiation strategies, how they can complement one another to generate specific cell phenotypes, and impacts of each strategy on downstream applications. Continued research in this nascent field will lead to the development of improved models of neurological circuits and novel treatments for those living with neurological injury and disease.

Fast-Track and Integration-Free Method of Genome Editing by CRISPR/Cas9 in Murine Pluripotent Stem Cells

The CRISPR/Cas9 system has unprecedentedly revolutionized genome-editing technology, which is being successfully applied virtually in all branches of biological sciences. Although much success has been attained in gene manipulation, still the majority of methods are laborious and non-integration-free, and require prolonged time for the expansion of mutant cell pools/clones, while fewer cells exhibit functional knockout efficiency. To overcome these obstacles, here, we describe an efficient, inexpensive, integration-free, and rapid one-step protocol for CRISPR/Cas9-assisted gene knockout in murine pluripotent stem cells (PSCs). Our protocol has streamlined both the liposome-based transfection system and screening strategy to work more efficiently with small numbers of PSCs (∼2.0 × 10⁴ cells) and to minimize laborious steps of lentiviral packaging, transduction, and single-clone passaging. In our method, around 90% (CI = 95%, 79.5230%-100%) of PSC colonies harbored functional knockout in the context of protein expression. Therefore, the current protocol is technically feasible, time-saving, and highly efficient for genome editing in pluripotent stem cells.

Viral Generation, Packaging, and Transduction on a Digital Microfluidic Platform

Viral-based systems are a popular delivery method for introducing exogenous genetic material into mammalian cells. Unfortunately, the preparation of lentiviruses containing the machinery to edit the cells is labor-intensive, with steps requiring optimization and sensitive handling. To mitigate these challenges, we introduce the first microfluidic method that integrates lentiviral generation, packaging, and transduction. The new method allows the production of viral titers between 10⁶ and 10⁷ (similar to macroscale production) and high transduction efficiency for hard-to-transfect cell lines. We extend the technique for gene editing applications and show how this technique can be used to knock out and knock down estrogen receptor gene─a gene prominently responsible for 70% of breast cancer cases. This new technique is automated with multiplexing capabilities, which have the potential to standardize the methods for viral-based genome engineering.

Methods to Investigate miRNA Function: Focus on Platelet Reactivity

MicroRNAs (miRNAs) are small noncoding RNAs modulating protein production. They are key players in regulation of cell function and are considered as biomarkers in several diseases. The identification of the proteins they regulate, and their impact on cell physiology, may delineate their role as diagnostic or prognostic markers and identify new therapeutic strategies. During the last 3 decades, development of a large panel of techniques has given rise to multiple models dedicated to the study of miRNAs. Since plasma samples are easily accessible, circulating miRNAs can be studied in clinical trials. To quantify miRNAs in numerous plasma samples, the choice of extraction and purification techniques, as well as normalization procedures, are important for comparisons of miRNA levels in populations and over time. Recent advances in bioinformatics provide tools to identify putative miRNAs targets that can then be validated with dedicated assays. In vitro and in vivo approaches aim to functionally validate candidate miRNAs from correlations and to understand their impact on cellular processes. This review describes the advantages and pitfalls of the available techniques for translational research to study miRNAs with a focus on their role in regulating platelet reactivity.

Non-viral reprogramming of human nucleus pulposus cells with FOXF1 via extracellular vesicle delivery: an in vitro and in vivo study

Intervertebral disc (IVD) degeneration is characterized by decreased cellularity and proteoglycan synthesis and increased inflammation, catabolism, and neural/vascular ingrowth. Regenerative methods for IVD degeneration are largely cell-therapy-based or involve viral vectors, which are associated with mutagenesis and undesired immune responses. The present study used bulk electroporation and engineered extracellular vesicles (EVs) to deliver forkhead-box F1 (FOXF1) mRNA to degenerate human nucleus pulposus (NP) cells as a minimally invasive therapeutic strategy for IVD regeneration. Bulk electroporation was used to investigate FOXF1 effects on human NP cells during a 4-week culture in 3D agarose constructs. Engineered EV delivery of FOXF1 into human IVD cells in monolayer was determined, with subsequent in vivo validation in a pilot mouse IVD puncture model. FOXF1 transfection significantly altered gene expression by upregulating healthy NP markers [FOXF1, keratin 19 (KRT19)], decreasing inflammatory cytokines [interleukin (IL)-1β, -6], catabolic enzymes [metalloproteinase 13 (MMP13)] and nerve growth factor (NGF), with significant increases in glycosaminoglycan accumulation in human NP cells. Engineered EVs loaded with FOXF1 demonstrated successful encapsulation of FOXF1 cargo and effective uptake by human NP cells cultured in monolayer. Injection of FOXF1-loaded EVs into the mouse IVD in vivo resulted in a significant upregulation of FOXF1 and Brachyury, compared to controls at 7 d post-injection, with no evidence of cytotoxicity. This is the first study to demonstrate non-viral delivery of FOXF1 and reprogramming of human NP cells in vitro and mouse IVD cells in vivo. This strategy represents a non-addictive approach for treating IVD degeneration and associated back pain.

Toward Biological Pacing by Cellular Delivery of Hcn2/SkM1

Electronic pacemakers still face major shortcomings that are largely intrinsic to their hardware-based design. Radical improvements can potentially be generated by gene or cell therapy-based biological pacemakers. Our previous work identified adenoviral gene transfer of Hcn2 and SkM1, encoding a "funny current" and skeletal fast sodium current, respectively, as a potent combination to induce short-term biological pacing in dogs with atrioventricular block. To achieve long-term biological pacemaker activity, alternative delivery platforms need to be explored and optimized. The aim of the present study was therefore to investigate the functional delivery of Hcn2/SkM1 via human cardiomyocyte progenitor cells (CPCs). Nucleofection of Hcn2 and SkM1 in CPCs was optimized and gene transfer was determined for Hcn2 and SkM1 in vitro. The modified CPCs were analyzed using patch-clamp for validation and characterization of functional transgene expression. In addition, biophysical properties of Hcn2 and SkM1 were further investigated in lentivirally transduced CPCs by patch-clamp analysis. To compare both modification methods in vivo, CPCs were nucleofected or lentivirally transduced with GFP and injected in the left ventricle of male NOD-SCID mice. After 1 week, hearts were collected and analyzed for GFP expression and cell engraftment. Subsequent functional studies were carried out by computational modeling. Both nucleofection and lentiviral transduction of CPCs resulted in functional gene transfer of Hcn2 and SkM1 channels. However, lentiviral transduction was more efficient than nucleofection-mediated gene transfer and the virally transduced cells survived better in vivo. These data support future use of lentiviral transduction over nucleofection, concerning CPC-based cardiac gene delivery. Detailed patch-clamp studies revealed Hcn2 and Skm1 current kinetics within the range of previously reported values of other cell systems. Finally, computational modeling indicated that CPC-mediated delivery of Hcn2/SkM1 can generate stable pacemaker function in human ventricular myocytes. These modeling studies further illustrated that SkM1 plays an essential role in the final stage of diastolic depolarization, thereby enhancing biological pacemaker functioning delivered by Hcn2. Altogether these studies support further development of CPC-mediated delivery of Hcn2/SkM1 and functional testing in bradycardia models.

Preclinical Toxicity Evaluation of Clinical Grade Placenta-Derived Decidua Stromal Cells

Placenta-derived decidua stromal cells (DSCs) are being investigated as an alternative to other sources of mesenchymal stromal cells (MSCs) for cellular therapy. DSCs are more effective in treating acute inflammatory diseases in human and this is our preclinical safety study of human DSCs in Sprague-Dawley rats and Balb/c mice. Human DSCs were cultured and expanded from fetal membranes obtained from placentas following cesarean section. In rats, 0.5 × 10⁶ cells/kg were injected intravenously (n = 4) or intra-aortal (n = 4). In mice, DSCs were given intravenously at doses ranging from 4–40 × 10⁶ cells/kg (total of n = 120 mice). In vivo tracking of human cells in mice was performed by using transduced DSC with luciferin gene, and in rats by using ¹⁸F-FDG PET. Clotting parameters were determined in vitro and in vivo. All intra-arterially DSC-treated rats had normal motility and behavior and histological examination was normal for liver, spleen kidneys and thigh muscles. Mice treated with DSCs showed no immediate or long-term side effects. None of the mice died or showed acute toxicity or adverse reactions 3 and 30 days after DSC infusion. Murine blood biochemistry profiles related to liver, kidney, heart, and inflammatory indices was not influenced by DSC infusion and complete blood counts were normal. In vivo tracking of infused DSCs detected a signal in the lungs for up to 4 days post infusion. Compared to bone marrow derived MSCs, the DSCs had better viability, smaller size, but stronger clotting in human blood and plasma. Both MSC- and DSC-induced coagulation and complement activation markers, thrombin-anti-thrombin complex (TAT) and C3a, and in vitro clotting parameters were decreased by heparin supplementation. In conclusion, DSCs are safe with almost no side effects even with doses 40 times higher than are used clinically, particularly when supplemented with low-dose heparin.

Episomal Induced Pluripotent Stem Cells: Functional and Potential Therapeutic Applications

The term episomal induced pluripotent stem cells (EiPSCs) refers to somatic cells that are reprogrammed into induced pluripotent stem cells (iPSCs) using non-integrative episomal vector methods. This reprogramming process has a better safety profile compared with integrative methods using viruses. There is a current trend toward using episomal plasmid reprogramming to generate iPSCs because of the improved safety profile. Clinical reports of potential human cell sources that have been successfully reprogrammed into EiPSCs are increasing, but no review or summary has been published. The functional applications of EiPSCs and their potential uses in various conditions have been described, and these may be applicable to clinical scenarios. This review summarizes the current direction of EiPSC research and the properties of these cells with the aim of explaining their potential role in clinical applications and functional restoration.

Nonviral Transfection With Brachyury Reprograms Human Intervertebral Disc Cells to a Pro-Anabolic Anti-Catabolic/Inflammatory Phenotype: A Proof of Concept Study

Intervertebral disc (IVD) degeneration is a major contributor to chronic low back pain and is characterized by decreases in cellularity and proteoglycan synthesis, upregulation of matrix degradation, and increases in pro-inflammatory factors with neurovascular invasion. Current treatments fail to target the underlying pathology or promote tissue repair and approaches such as viral transfection raise safety concerns due to mutagenesis and unwarranted immune responses. To avoid such concerns, nonviral transfection is a viable method of gene delivery into the host cell while bypassing the caveats of viral delivery. Brachyury is expressed in the developing notochord and is associated with an immature healthy nucleus pulposus (NP). We hypothesize that Brachyury can reprogram degenerate NP cells to a healthy pro-anabolic phenotype with increased proteoglycan content and decreased expression of catabolic, inflammatory, and neurovascular markers. NP cells obtained from human autopsy and surgical tissues were transfected with plasmids encoding for Brachyury or an empty vector control via bulk electroporation. Post transfection, cells were seeded in three-dimensional agarose constructs cultured over 4 weeks and analyzed for viability, gene expression, and proteoglycan. Results demonstrated successful transfection of both autopsy and surgical NP cells. We observed long-term Brachyury expression, significant increased expression of NP phenotypic markers FOXF1, KRT19, and chondrogenic marker SOX9 with decreases in inflammatory cytokines IL1-β/IL6, NGF, and MMPs and significant increases in glycosaminoglycan accumulation. These results highlight nonviral transfection with developmental transcription factors, such as Brachyury, as a promising method to reprogram degenerate human disc cells toward a healthy NP phenotype. Clinical significance: This project proposes a novel translational approach for the treatment of intervertebral disc degeneration via direct reprogramming of diseased human patient-derived IVD cells to a healthy phenotype. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:2389-2400, 2019.

Gene delivery methods and genome editing of human pluripotent stem cells

Induced pluripotent stem cells derived from normal somatic cells could be utilized to study tumorigenesis through overexpression of specific oncogenes, downregulation of tumor suppressors and dysregulation of other factors thought to promote tumorigenesis. Therefore, effective approaches that provide direct modifications of induced pluripotent stem cell genome are extremely needed. Emerging strategies are expected to provide the ability to more effectively introduce diverse genetic alterations, from as small as single-nucleotide modifications to whole gene amplification or deletion, all with a high degree of target specificity. To date, several techniques have been applied in stem cell studies to directly edit cell genome (ZFNs, TALENs or CRISPR/Cas9). In this review, we summarize specific gene delivery strategies that were applied to stem cell studies together with genome editing techniques, which enable a direct modification of endogenous DNA sequences in the context of cancer studies.

Adeno-Associated Virus Vectors and Stem Cells: Friends or Foes?

The infusion of healthy stem cells into a patient-termed "stem-cell therapy"-has shown great promise for the treatment of genetic and non-genetic diseases, including mucopolysaccharidosis type 1, Parkinson's disease, multiple sclerosis, numerous immunodeficiency disorders, and aplastic anemia. Stem cells for cell therapy can be collected from the patient (autologous) or collected from another "healthy" individual (allogeneic). The use of allogenic stem cells is accompanied with the potentially fatal risk that the transplanted donor T cells will reject the patient's cells-a process termed "graft-versus-host disease." Therefore, the use of autologous stem cells is preferred, at least from the immunological perspective. However, an obvious drawback is that inherently as "self," they contain the disease mutation. As such, autologous cells for use in cell therapies often require genetic "correction" (i.e., gene addition or editing) prior to cell infusion and therefore the requirement for some form of nucleic acid delivery, which sets the stage for the AAV controversy discussed herein. Despite being the most clinically applied gene delivery context to date, unlike other more concerning integrating and non-integrating vectors such as retroviruses and adenovirus, those based on adeno-associated virus (AAV) have not been employed in the clinic. Furthermore, published data regarding AAV vector transduction of stem cells are inconsistent in regards to vector transduction efficiency, while the pendulum swings far in the other direction with demonstrations of AAV vector-induced toxicity in undifferentiated cells. The variation present in the literature examining the transduction efficiency of AAV vectors in stem cells may be due to numerous factors, including inconsistencies in stem-cell collection, cell culture, vector preparation, and/or transduction conditions. This review summarizes the controversy surrounding AAV vector transduction of stem cells, hopefully setting the stage for future elucidation and eventual therapeutic applications.

Conditional Manipulation of Gene Function in Human Cells with Optimized Inducible shRNA

The difficulties involved in conditionally perturbing complex gene expression networks represent major challenges toward defining the mechanisms controlling human development, physiology, and disease. We developed an OPTimized inducible KnockDown (OPTiKD) platform that addresses the limitations of previous approaches by allowing streamlined, tightly-controlled, and potent loss-of-function experiments for both single and multiple genes. The method relies on single-step genetic engineering of the AAVS1 genomic safe harbor with an optimized tetracycline-responsive cassette driving one or more inducible short hairpin RNAs (shRNAs). OPTiKD provides homogeneous, dose-responsive, and reversible gene knockdown. When implemented in human pluripotent stem cells (hPSCs), the approach can be then applied to a broad range of hPSC-derived mature cell lineages that include neurons, cardiomyocytes, and hepatocytes. Generation of OPTiKD hPSCs in commonly used culture conditions is simple (plasmid based), rapid (two weeks), and highly efficient (>95%). Overall, this method facilitates the functional annotation of the human genome in health and disease. © 2018 by John Wiley & Sons, Inc.

Bone marrow stem cells to destroy circulating HIV: a hypothetical therapeutic strategy

Human immunodeficiency virus (HIV) still poses enigmatic threats to human life. This virus has mastered in bypassing anti retroviral therapy leading to patients’ death. Circulating viruses are phenomenal for the disease outcome. This hypothesis proposes a therapeutic strategy utilizing receptor-integrated hematopoietic, erythroid and red blood cells. Here, HIV specific receptors trap circulating viruses that enter erythrocyte cytoplasm and form inactive integration complex. This model depicts easy, effective removal of circulating HIV without any adverse effect.

Efficient Nonviral Transfection of Primary Intervertebral Disc Cells by Electroporation for Tissue Engineering Application

Low back pain (LBP) is an increasing global health problem associated with intervertebral disc (IVD) trauma and degeneration. Current treatment options include surgical interventions with partial unsatisfactory outcomes reported such as failure to relieve LBP, nonunions, nerve injuries, or adjacent segment disease. Cell-based therapy and tissue engineered IVD constructs supplemented with transfected disc cells that incorporate factors enhancing matrix synthesis represent an appealing approach to regenerate the IVD. Gene delivery approaches using transient nonviral gene therapy by electroporation are of a high clinical translational value since the incorporated DNA is lost after few cell generations, leaving the host's genome unmodified. Human primary cells isolated from clinically relevant samples were generally found very hard to transfect compared to cell lines. In this study, we present a range of parameters (voltage pulse, number, and duration) from the Neon^® Transfection System for efficient transfection of human and bovine IVD cells. To demonstrate efficiency, these primary cells were exemplarily transfected with the commercially available plasmid pCMV6-AC-GFP tagged with copepod turbo green fluorescent protein. Flow cytometry was subsequently applied to quantify transfection efficiency. Our results showed that two pulses of 1400 V for 20 ms revealed good and reproducible results for both human and bovine IVD cells with efficiencies ≥47%. The presented parameters allow for successful human and bovine IVD cell transfection and provide an opportunity for subsequent regenerative medicine application.

Efficient Transformation of Primary Human Mesenchymal Stromal Cells by Adenovirus Early Region 1 Oncogenes

Previous observations that human amniotic fluid cells (AFC) can be transformed by human adenovirus type 5 (HAdV-5) E1A/E1B oncogenes prompted us to identify the target cells in the AFC population that are susceptible to transformation. Our results demonstrate that one cell type corresponding to mesenchymal stem/stroma cells (hMSCs) can be reproducibly transformed by HAdV-5 E1A/E1B oncogenes as efficiently as primary rodent cultures. HAdV-5 E1-transformed hMSCs exhibit all properties commonly associated with a high grade of oncogenic transformation, including enhanced cell proliferation, anchorage-independent growth, increased growth rate, and high telomerase activity as well as numerical and structural chromosomal aberrations. These data confirm previous work showing that HAdV preferentially transforms cells of mesenchymal origin in rodents. More importantly, they demonstrate for the first time that human cells with stem cell characteristics can be completely transformed by HAdV oncogenes in tissue culture with high efficiency. Our findings strongly support the hypothesis that undifferentiated progenitor cells or cells with stem cell-like properties are highly susceptible targets for HAdV-mediated cell transformation and suggest that virus-associated tumors in humans may originate, at least in part, from infections of these cell types. We expect that primary hMSCs will replace the primary rodent cultures in HAdV viral transformation studies and are confident that these investigations will continue to uncover general principles of viral oncogenesis that can be extended to human DNA tumor viruses as well.

IMPORTANCE

It is generally believed that transformation of primary human cells with HAdV-5 E1 oncogenes is very inefficient. However, a few cell lines have been successfully transformed with HAdV-5 E1A and E1B, indicating that there is a certain cell type which is susceptible to HAdV-mediated transformation. Interestingly, all those cell lines have been derived from human embryonic tissue, albeit the exact cell type is not known yet. We show for the first time the successful transformation of primary human mesenchymal stromal cells (hMSCs) by HAdV-5 E1A and E1B. Further, we show upon HAdV-5 E1A and E1B expression that these primary progenitor cells exhibit features of tumor cells and can no longer be differentiated into the adipogenic, chondrogenic, or osteogenic lineage. Hence, primary hMSCs represent a robust and novel model system to elucidate the underlying molecular mechanisms of adenovirus-mediated transformation of multipotent human progenitor cells.

The role of semaphorin 4D in tumor development and angiogenesis in human breast cancer

Background

Semaphorin 4D (Sema4D) is highly expressed in certain types of tumors and functions in the regulation of tumor angiogenesis and growth. However, it is still not clear regarding the roles of Sema4D in breast cancer. This study was designed to explore the effects of Sema4D on proliferation, cell cycle progression, apoptosis, invasion, migration, tumor growth, and angiogenesis in breast cancer.

Materials and methods

The expression level of Sema4D was investigated in MCF10A, 184A1, HCC1937, MDA-MB-468, MDA-MB-231, Hs578T, BT474, MCF-7, and T47D breast cancer cell lines by Western blotting analysis. Sema4D downregulation or overexpression was established by infection with lentiviruses-encoding Sema4D short hairpin RNA (shRNA) or Sema4D. To evaluate the effects of Sema4D on cell proliferation, cell cycle progression, apoptosis, invasion, and migration of MDA-MB-231 and MDA-MB-468 cells, methods including MTT assay, flow cytometry, wound healing assay, and transwell experiments were applied. BALB/c nude mice were injected with MDA-MB-231 cells, which were respectively infected with lentiviruses-encoding Sema4D, Sema4D shRNA, and GFP, followed by tumor angiogenesis assay.

Results

Sema4D was expressed at higher levels in breast cancer cell lines compared with the normal human breast epithelial cell lines, especially in MDA-MB-231 and MDA-MB-468 cells. Cell proliferation ability was remarkably inhibited in Sema4D downregulated condition, whereas the proportions of cells in the G0/G1 phase and apoptosis increased in MDA-MB-231 and MDA-MB-468 cells. In addition, the invasion and migration abilities of these cells were obviously reduced. Xenograft growth as well as angiogenesis was inhibited when infected with lentiviruses-encoding Sema4D shRNA in vivo.

Conclusion

Downregulation of Sema4D had notable influence on cell proliferation ability, invasion, migration, and apoptosis of both MDA-MB-231 and MDA-MB-468 cells. Furthermore, infection with lentiviruses-encoding Sema4D shRNA obviously inhibited tumor growth and angiogenesis in BALB/c nude mice. Our results showed that Sema4D may represent a novel therapeutic target for human breast cancer.

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.

The role of semaphorin 4D as a potential biomarker for antiangiogenic therapy in colorectal cancer

Background

Semaphorin 4D (Sema4D) belongs to the class IV semaphorins, and accumulating evidence has indicated that its elevated level may be one strategy by which tumors evade current anti-angiogenic therapies. The biological roles of Sema4D in colorectal cancer (CRC), however, remain largely undefined. This study was designed to investigate the effects of Sema4D on tumor angiogenesis and growth in CRC, especially in different vascular endothelial growth factor (VEGF) backgrounds.

Methods

The expression of Sema4D in human CRC was evaluated by immunohistochemical analysis of tumors and their matching normal control tissues. The expression level of Sema4D and VEGF was investigated in different CRC cell lines. To evaluate the contributions of Sema4D to tumor-induced angiogenesis, two CRC cell lines with opposite VEGF backgrounds were infected with lentiviruses expressing Sema4D or Sema4D short hairpin RNA, followed by in vitro migration and in vivo tumor angiogenic assays.

Results

Immunohistochemical analysis of human CRC revealed high levels of Sema4D in a cell surface pattern. In all, 84.85% of CRC samples analyzed exhibited moderate to strong Sema4D expression. The positive ratios of Sema4D staining for well, moderately, and poorly differentiated cancers were 71.43%, 96.67%, and 77.27%, respectively. Sema4D is highly expressed in five different CRC cell lines, while VEGF expression level varies among these cell lines. HCT-116 showed the lowest VEGF level, while Caco-2 showed the maximum VEGF level. In vitro migration results show that regardless of cell type and VEGF background, Sema4D showed an enhanced in vitro proangiogenic effect to induce the migration of human umbilical vein endothelial cells. Finally, in vivo tumor angiogenic assays demonstrated that Sema4D alone can elicit a significant angiogenic response to promote tumor growth independently of VEGF.

Conclusion

Targeting Sema4D might serve as a parallel option for antiangiogenic therapy for CRC, particularly when traditional anti-VEGF therapies fail or tumors develop resistance to strategies targeting a single angiogenic signaling pathway.

Beyond the mouse monopoly: studying the male germ line in domestic animal models

Spermatogonial stem cells (SSCs) are the foundation of spermatogenesis and essential to maintain the continuous production of spermatozoa after the onset of puberty in the male. The study of the male germ line is important for understanding the process of spermatogenesis, unravelling mechanisms of stemness maintenance, cell differentiation, and cell-to-cell interactions. The transplantation of SSCs can contribute to the preservation of the genome of valuable individuals in assisted reproduction programs. In addition to the importance of SSCs for male fertility, their study has recently stimulated interest in the generation of genetically modified animals because manipulations of the male germ line at the SSC stage will be maintained in the long term and transmitted to the offspring. Studies performed mainly in the mouse model have laid the groundwork for facilitating advancements in the field of male germ line biology, but more progress is needed in nonrodent species in order to translate the technology to the agricultural and biomedical fields. The lack of reliable markers for isolating germ cells from testicular somatic cells and the lack of knowledge of the requirements for germ cell maintenance have precluded their long-term maintenance in domestic animals. Nevertheless, some progress has been made. In this review, we will focus on the state of the art in the isolation, characterization, culture, and manipulation of SSCs and the use of germ cell transplantation in domestic animals.

High-Efficient Transfection of Human Embryonic Stem Cells by Single-Cell Plating and Starvation

Nowadays, the low efficiency of small interfering RNA (siRNA) or plasmid DNA (pDNA) transfection is a critical issue in genetic manipulation of human embryonic stem (hES) cells. Development of an efficient transfection method for delivery of siRNAs and plasmids into hES cells becomes more and more imperative. In this study, we tried to modify the traditional transfection protocol by introducing two crucial processes, single-cell plating and starvation, to increase the transfection efficiency in hES cells. Furthermore, we comparatively examined the transfection efficiency of some commercially available siRNA or pDNA transfection reagents in hES cells. Our results showed that the new developed method markedly enhanced the transfection efficiency without influencing the proliferation and pluripotency of hES cells. Lipofectamine RNAiMAX exhibited much higher siRNA transfection efficiency than the other reagents, and FuGENE HD was identified as the best suitable reagent for efficient pDNA transfection of hES cells among the tested reagents.

Direct Induction of Hemogenic Endothelium and Blood by Overexpression of Transcription Factors in Human Pluripotent Stem Cells

During development, hematopoietic cells arise from a specialized subset of endothelial cells, hemogenic endothelium (HE). Modeling HE development in vitro is essential for mechanistic studies of the endothelial-hematopoietic transition and hematopoietic specification. Here, we describe a method for the efficient induction of HE from human pluripotent stem cells (hPSCs) by way of overexpression of different sets of transcription factors. The combination of ETV2 and GATA1 or GATA2 TFs is used to induce HE with pan-myeloid potential, while a combination of GATA2 and TAL1 transcription factors allows for the production of HE with erythroid and megakaryocytic potential. The addition of LMO2 to GATA2 and TAL1 combination substantially accelerates differentiation and increases erythroid and megakaryocytic cells production. This method provides an efficient and rapid means of HE induction from hPSCs and allows for the observation of the endothelial-hematopoietic transition in a culture dish. The protocol includes hPSCs transduction procedures and post-transduction analysis of HE and blood progenitors.

Generation of primitive neural stem cells from human fibroblasts using a defined set of factors

In mice, leukemia inhibitory factor (LIF)-dependent primitive neural stem cells (NSCs) have a higher neurogenic potential than bFGF-dependent definitive NSCs. Therefore, expandable primitive NSCs are required for research and for the development of therapeutic strategies for neurological diseases. There is a dearth of suitable techniques for the generation of human long-term expandable primitive NSCs. Here, we have described a method for the conversion of human fibroblasts to LIF-dependent primitive NSCs using a strategy based on techniques for the generation of induced pluripotent stem cells (iPSCs). These LIF-dependent induced NSCs (LD-iNSCs) can be expanded for >100 passages. Long-term cultured LD-iNSCs demonstrated multipotent neural differentiation potential and could generate motor neurons and dopaminergic neurons, as well as astrocytes and oligodendrocytes, indicating a high level of plasticity. Furthermore, LD-iNSCs easily reverted to human iPSCs, indicating that LD-iNSCs are in an intermediate iPSC state. This method may facilitate the generation of patient-specific human neurons for studies and treatment of neurodegenerative diseases.

Summary: A novel method for the generation of self-renewable, multipotent and neural lineage-restricted LIF-dependent induced primitive neural stem cells (LD-iNSCs) from human fibroblasts with the potential to facilitate human neuronal studies.

Evaluating Electroporation and Lipofectamine Approaches for Transient and Stable Transgene Expressions in Human Fibroblasts and Embryonic Stem Cells

Objective

Genetic modification of human embryonic stem cells (hESCs) is critical for their extensive use as a fundamental tool for cell therapy and basic research. Despite the fact that various methods such as lipofection and electroporation have been applied to transfer the gene of interest (GOI) into the target cell line, however, there are few re- ports that compare all parameters, which influence transfection efficiency. In this study, we examine all parameters that affect the efficiency of electroporation and lipofection for transient and long-term gene expression in three different cell lines to introduce the best method and determinant factor.

Materials and Methods

In this experimental study, both electroporation and lipofection approaches were employed for genetic modification. pCAG-EGFP was applied for tran- sient expression of green fluorescent protein in two genetically different hESC lines, Roy- an H5 (XX) and Royan H6 (XY), as well as human foreskin fibroblasts (hFF). For long-term EGFP expression VASA and OLIG2 promoters (germ cell and motoneuron specific genes, respectively), were isolated and subsequently cloned into a pBluMAR5 plasmid backbone to drive EGFP expression. Flow cytometry analysis was performed two days after trans- fection to determine transient expression efficiency. Differentiation of drug resistant hESC colonies toward primordial germ cells (PGCs) was conducted to confirm stable integration of the transgene.

Results

Transient and stable expression suggested a variable potential for different cell lines against transfection. Analysis of parameters that influenced gene transformation ef- ficiency revealed that the vector concentrations from 20-60 μg and the density of the sub- jected cells (5×10⁵and 1×10⁶cells) were not as effective as the genetic background and voltage rate. The present data indicated that in contrast to the circular form, the linearized vector generated more distinctive drug resistant colonies.

Conclusion

Electroporation was an efficient tool for genetic engineering of hESCs compared to the chemical method. The genetic background of the subjected cell line for transfection seemed to be a fundamental factor in each gene delivery method. For each cell line, optimum voltage rate should be calculated as it has been shown to play a crucial role in cell death and rate of gene delivery.

Dual gene expression in embryoid bodies derived from human induced pluripotent stem cells using episomal vectors

Transcription factors are essential for the differentiation of human induced pluripotent stem cells (iPS) into specialized cell types. Embryoid body (EB) formation promotes the differentiation of iPS cells. We sought to establish an efficient method of transfection and rotary culture to generate EBs that stably express two genes. The pMetLuc2-Reporter vector was transfected using FuGENE HD (FuGENE), Lipofectamine LTX (LTX), X-tremeGENE, or TransIT-2020 transfection reagents. The media was analyzed using a Metridia luciferase (MetLuc) assay. Transfections were performed on cells adherent to plates/dishes (adherent method) or suspended in the media (suspension method). The 201B7 cells transfected with episomal vectors were selected using G418 (200 μg/mL) or hygromycin B (300 μg/mL). Rotary culture was performed at 2.5 or 9.9 rpm. Efficiency of EB formation was compared among plates and dishes. Cell density was compared at 1.6×10(3),×10(4), and×10(5) cells/mL. The suspended method of transfection using the FuGENE HD reagent was the most efficient. The expression of pEBMulti/Met-Hyg was detected 11 days posttransfection. Double transformants were selected 6 days posttransfection with pEBNK/EGFP-Neo and pEBNK/Cherry-Hyg. Both EGFP and CherryPicker were expressed in all of the surviving cells. EBs were formed most efficiently from cells cultured at a density of 1.6×10(5) cells/mL in six-well plates or 6 cm dishes. The selected cells formed EBs. FuGENE-mediated transfection of plasmids using the suspension method was effective in transforming iPS cells. Furthermore, the episomal vectors enabled us to perform a stable double transfection of EB-forming iPS cells.

Spatial and Temporal Control of Cavitation Allows High In Vitro Transfection Efficiency in the Absence of Transfection Reagents or Contrast Agents

Sonoporation using low-frequency high-pressure ultrasound (US) is a non-viral approach for in vitro and in vivo gene delivery. In this study, we developed a new sonoporation device designed for spatial and temporal control of ultrasound cavitation. The regulation system incorporated in the device allowed a real-time control of the cavitation level during sonoporation. This device was evaluated for the in vitro transfection efficiency of a plasmid coding for Green Fluorescent Protein (pEGFP-C1) in adherent and non-adherent cell lines. The transfection efficiency of the device was compared to those observed with lipofection and nucleofection methods. In both adherent and non-adherent cell lines, the sonoporation device allowed high rate of transfection of pEGFP-C1 (40–80%), as determined by flow cytometry analysis of GFP expression, along with a low rate of mortality assessed by propidium iodide staining. The transfection efficiency and toxicity of sonoporation on the non-adherent cell lines Jurkat and K562 were similar to those of nucleofection, while these two cell lines were resistant to transfection by lipofection. Moreover, sonoporation was used to produce three stably transfected human lymphoma and leukemia lines. Significant transfection efficiency was also observed in two fresh samples of human acute myeloid leukemia cells. In conclusion, we developed a user-friendly and cost-effective ultrasound device, well adapted for routine in vitro high-yield transfection experiments and which does not require the use of any transfection reagent or gas micro-bubbles.

Gene delivery in tissue engineering and regenerative medicine

As a promising strategy to aid or replace tissue/organ transplantation, gene delivery has been used for regenerative medicine applications to create or restore normal function at the cell and tissue levels. Gene delivery has been successfully performed ex vivo and in vivo in these applications. Excellent proliferation capabilities and differentiation potentials render certain cells as excellent candidates for ex vivo gene delivery for regenerative medicine applications, which is why multipotent and pluripotent cells have been intensely studied in this vein. In this review, gene delivery is discussed in detail, along with its applications to tissue engineering and regenerative medicine. A definition of a stem cell is compared to a definition of a stem property, and both provide the foundation for an in-depth look at gene delivery investigations from a germ lineage angle.

Efficient biotechnological approach for lentiviral transduction of induced pluripotent stem cells

Induced pluripotent stem (iPS) cells are generated from differentiated adult somatic cells by reprogramming them. Unlimited self-renewal, and the potential to differentiate into any cell type, make iPS cells very promising candidates for basic and clinical research. Furthermore, iPS cells can be genetically manipulated for use as therapeutic tools. DNA can be introduced into iPS cells, using lentiviral vectors, which represent a helpful choice for efficient transduction and stable integration of transgenes. In this study, we compare two methods of lentiviral transduction of iPS cells, namely, the suspension method and the hanging drop method. In contrast to the conventional suspension method, in the hanging drop method, embryoid body (EB) formation and transduction occur concurrently. The iPS cells were cultured to form EBs, and then transduced with lentiviruses, using the conventional suspension method and the hanging drop method, to express miR-128 and green fluorescent protein (GFP). The number of transduced cells were assessed by fluorescent microscopy and flow cytometry. MTT assay and real-time PCR were performed to determine the cell viability and transgene expression, respectively. Morphologically, GFP+ cells were more detectable in the hanging drop method, and this finding was quantified by flow cytometric analysis. According to the results of the MTT assay, cell viability was considerably higher in the hanging drop method, and real-time PCR represented a higher relative expression of miR-128 in the iPS cells introduced with lentiviruses in drops. Altogether, it seems that lentiviral transduction of challenging iPS cells using the hanging drop method offers a suitable and sufficient strategy in their gene transfer, with less toxicity than the conventional suspension method.

Injection of Propidium Iodide into HeLa Cells Using a Silicon Nanoinjection Lance Array

Delivering foreign molecules into human cells is a wide and ongoing area of research. Gene therapy, or delivering nucleic acids into cells via nonviral or viral pathways, is an especially promising area for pharmaceutics. All gene therapy methods have their respective advantages and disadvantages, including limited delivery efficiency and low viability. We present an electromechanical method for delivering foreign molecules into human cells. Nanoinjection, or delivering molecules into cells using a solid lance, has proven to be highly efficient while maintaining high viability levels. This paper describes an array of solid silicon microlances that was tested to determine efficiency and viability when nanoinjecting tens of thousands of HeLa cells simultaneously. Propidium iodide (PI), a dye that fluoresces when bound to nucleic acids and does not fluoresce when unbound, was delivered into cells using the lance array. Results show that the lance array delivers PI into up to 78% of a nanoinjected HeLa cell culture, while maintaining 78–91% viability. With these results, we submit the nanoinjection method using a silicon lance array as another promising particle delivery method for mammalian culture cells.

Simplified prototyping of perfusable polystyrene microfluidics

Cell culture in microfluidic systems has primarily been conducted in devices comprised of polydimethylsiloxane (PDMS) or other elastomers. As polystyrene (PS) is the most characterized and commonly used substrate material for cell culture, microfluidic cell culture would ideally be conducted in PS-based microsystems that also enable tight control of perfusion and hydrodynamic conditions, which are especially important for culture of vascular cell types. Here, we report a simple method to prototype perfusable PS microfluidics for endothelial cell culture under flow that can be fabricated using standard lithography and wet laboratory equipment to enable stable perfusion at shear stresses up to 300 dyn/cm(2) and pumping pressures up to 26 kPa for at least 100 h. This technique can also be extended to fabricate perfusable hybrid PS-PDMS microfluidics of which one application is for increased efficiency of viral transduction in non-adherent suspension cells by leveraging the high surface area to volume ratio of microfluidics and adhesion molecules that are optimized for PS substrates. These biologically compatible microfluidic devices can be made more accessible to biological-based laboratories through the outsourcing of lithography to various available microfluidic foundries.

Non-integrating gamma-retroviral vectors as a versatile tool for transient zinc-finger nuclease delivery

Designer nucleases, like zinc-finger nucleases (ZFNs), represent valuable tools for targeted genome editing. Here, we took advantage of the gamma-retroviral life cycle and produced vectors to transfer ZFNs in the form of protein, mRNA and episomal DNA. Transfer efficacy and ZFN activity were assessed in quantitative proof-of-concept experiments in a human cell line and in mouse embryonic stem cells. We demonstrate that retrovirus-mediated protein transfer (RPT), retrovirus-mediated mRNA transfer (RMT), and retrovirus-mediated episome transfer (RET) represent powerful methodologies for transient protein delivery or protein expression. Furthermore, we describe complementary strategies to augment ZFN activity after gamma-retroviral transduction, including serial transduction, proteasome inhibition, and hypothermia. Depending on vector dose and target cell type, gene disruption frequencies of up to 15% were achieved with RPT and RMT, and >50% gene knockout after RET. In summary, non-integrating gamma-retroviral vectors represent a versatile tool to transiently deliver ZFNs to human and mouse cells.

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.

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.

Gene delivery techniques for adult stem cell-based regenerative therapy

Over the past decade, stem cells have been considered to be a promising resource to cure and regenerate damaged or diseased tissues with research extending from basic studies to clinical application. Furthermore, genetically modified stem cells have the potential to reduce tumorigenic risks and achieve safe tissue formation. Recent advances in genetic modification of stem cells have rendered these cells more accessible and stable. The successful genetic modification of stem cells relies heavily on designing vector systems, either viral or nonviral vectors, which can efficiently deliver therapeutic genes to the cells with minimum toxicity. Currently, viral vectors showing high transfection efficiencies still raise safety issues, whereas safer nonviral vectors exhibit extremely poor transfection in stem cells. Here, we attempt to review and discuss the main factors raising concern in previous reports, and devise strategies to solve the issues in gene delivery systems for successful stem cell-targeting regenerative therapy.

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.

Optimization of transfection methods for Huh-7 and Vero cells: A comparative study

Availability of an efficient transfection protocol is the first determinant in success of gene transferring studies in mammalian cells which is accomplished experimentally for every single cell type. Herein, we provide data of a comparative study on optimization of transfection condition by electroporation and chemical methods for Huh-7 and Vero cells. Different cell confluencies, DNA/reagent ratios and total transfection volumes were optimized for two chemical reagents including jetPEI™ and Lipofectamine™ 2000. Besides, the effects of electric field strength and pulse length were investigated to improve electroporation efficiency. Transfection of cells by pEGFP-N1 vector and tracking the expression of GFP by FACS and Fluorescence Microscopy analysis were the employed methods to evaluate transfection efficiencies. Optimized electroporation protocols yielded 63.73 ± 2.36 and 73.9 ± 1.6% of transfection in Huh-7 and Vero cells respectively, while maximum achieved level of transfection by jetPEI™ was 14.2 ± 0.69 and 28 ± 1.11% Huh-7 and Vero cells, respectively. Post transfectional chilling of the cells did not improve electrotransfection efficiency of Huh-7 cells. Compared to chemical based reagents, electroporation showed superior levels of transfection in both cell lines. The presented protocols should satisfy most of the experimental applications requiring high transfection efficiencies of these two cell lines.

Microfluidic approaches for gene delivery and gene therapy

Recent advances in microfluidics have created new and exciting prospects for gene delivery and therapy. The micro-scaled environment within microfluidic systems enables precise control and optimization of multiple processes and techniques used in gene transfection and the production of gene and drug transporters. Traditional non-viral gene transfection methods, such as electroporation, microinjection and optical gene transfection, are improved from the use of innovative microfluidic systems. Additionally, microfluidic systems have also made the production of many viral and non-viral vectors controlled, automated, and reproducible. In summary, the development and application of microfluidic systems are producing increased efficiency in gene delivery and promise improved gene therapy results.

Improved lentiviral gene transfer into human embryonic stem cells grown in co-culture with murine feeder and stroma cells

Genetic modification of human embryonic stem cells (hESCs) using biophysical DNA transfection methods are hampered by the very low single cell survival rate and cloning efficiency of hESCs. Lentiviral gene transfer strategies are widely used to genetically modify hESCs but limited transduction efficiencies in the presence of feeder or stroma cells present problems, particularly if vesicular stomatitis virus glycoprotein (VSV-G) pseudotyped viral particles are applied. Here, we investigated whether the recently described semen derived enhancer of virus infection (SEVI) and alternative viral envelope proteins derived from either Gibbon ape leukaemia virus (GALV) or feline leukaemia virus (RD114) are applicable for transducing hESCs during co-culture with feeder or stroma cells. Our first set of experiments demonstrates that SEVI has no toxic effect on murine or hESCs and that exposure to SEVI does not interfere with the pluripotency-associated phenotype. Focusing on hESCs, we were able to further demonstrate that SEVI increases the transduction efficiencies of GALV and RD114 pseudotyped lentiviral vectors. More importantly, aiming at targeted differentiation of hESCs into functional somatic cell types, GALV pseudotyped lentiviral particles could efficiently and exclusively transduce hESCs grown in co-culture with OP9-GFP stroma cells (which were often used to induce differentiation into haematopoietic derivatives).

Pipette tip with integrated electrodes for gene electrotransfer of cells in suspension: a feasibility study in CHO cells

Background

Gene electrotransfer is a non-viral gene delivery method that requires successful electroporation for DNA delivery into the cells. Changing the direction of the electric field during the pulse application improves the efficacy of gene delivery. In our study, we tested a pipette tip with integrated electrodes that enables changing the direction of the electric field for electroporation of cell suspension for gene electrotransfer.

Materials and methods

A new pipette tip consists of four cylindrical rod electrodes that allow the application of electric pulses in different electric field directions. The experiments were performed on cell suspension of CHO cells in phosphate buffer. Plasmid DNA encoding for green fluorescent protein (GFP) was used and the efficiency of gene electrotransfer was determined by counting cells expressing GFP 24 h after the experiment.

Results

Experimental results showed that the percentage of cells expressing GFP increased when the electric field orientation was changed during the application. The GFP expression was almost two times higher when the pulses were applied in orthogonal directions in comparison with single direction, while cell viability was not significantly affected.

Conclusions

We can conclude that results obtained with the described pipette tip are comparable to previously published results on gene electrotransfer using similar electrode geometry and electric pulse parameters. The tested pipette tip, however, allows work with small volumes/samples and requires less cell manipulation.

Design of "smart" probes for optical imaging of apoptosis

Apoptosis is a mode of programmed cell death in multicellular organisms and plays a central role in controlling embryonic development, growth and differentiation and monitoring the induction of tumor cell death through anticancer therapy. Since the most effective chemotherapeutics rely on apoptosis, imaging apoptotic processes can be an invaluable tool to monitor therapeutic intervention and discover new drugs modulating apoptosis. The most attractive target for developing specific apoptosis imaging probes is caspases, crucial mediators of apoptosis. Up to now, various optical imaging strategies for apoptosis have been developed as an easy and economical modality. However, current optical applications are limited by poor sensitivity and specificity. A subset of molecular imaging contrast agents known as "activatable" or "smart" molecular probes allow for very high signal-to-background ratios compared to conventional targeted contrast agents and open up the possibility of imaging intracellular targets. In this review, we will discuss the unique design strategies and applications of activatable probes recently developed for fluorescence and bioluminescence imaging of caspase activity.

Efficient recombinase-mediated cassette exchange at the AAVS1 locus in human embryonic stem cells using baculoviral vectors

Insertion of a transgene into a defined genomic locus in human embryonic stem cells (hESCs) is crucial in preventing random integration-induced insertional mutagenesis, and can possibly enable persistent transgene expression during hESC expansion and in their differentiated progenies. Here, we employed homologous recombination in hESCs to introduce heterospecific loxP sites into the AAVS1 locus, a site with an open chromatin structure that allows averting transgene silencing phenomena. We then performed Cre recombinase mediated cassette exchange using baculoviral vectors to insert a transgene into the modified AAVS1 locus. Targeting efficiency in the master hESC line with the loxP-docking sites was up to 100%. Expression of the inserted transgene lasted for at least 20 passages during hESC expansion and was retained in differentiated cells derived from the genetically modified hESCs. Thus, this study demonstrates the feasibility of genetic manipulation at the AAVS1 locus with homologous recombination and using viral transduction in hESCs to facilitate recombinase-mediated cassette exchange. The method developed will be useful for repeated gene targeting at a defined locus of the hESC genome.

Non-invasive imaging of human embryonic stem cells

Human embryonic stem cells (hESCs) hold tremendous therapeutic potential in a variety of diseases. Over the last decade, non-invasive imaging techniques have proven to be of great value in tracking transplanted hESCs. This review article will briefly summarize the various techniques used for non-invasive imaging of hESCs, which include magnetic resonance imaging (MRI), bioluminescence imaging (BLI), fluorescence, single-photon emission computed tomography (SPECT), positron emission tomography (PET), and multimodality approaches. Although the focus of this review article is primarily on hESCs, the labeling/tracking strategies described here can be readily applied to other (stem) cell types as well. Non-invasive imaging can provide convenient means to monitor hESC survival, proliferation, function, as well as overgrowth (such as teratoma formation), which could not be readily investigated previously. The requirement for hESC tracking techniques depends on the clinical scenario and each imaging technique will have its own niche in preclinical/clinical research. Continued evolvement of non-invasive imaging techniques will undoubtedly contribute to significant advances in understanding stem cell biology and mechanisms of action.

Genetic recombination pathways and their application for genome modification of human embryonic stem cells

Human embryonic stem cells are pluripotent cells derived from early human embryo and retain a potential to differentiate into all adult cell types. They provide vast opportunities in cell replacement therapies and are expected to become significant tools in drug discovery as well as in the studies of cellular and developmental functions of human genes. The progress in applying different types of DNA recombination reactions for genome modification in a variety of eukaryotic cell types has provided means to utilize recombination-based strategies also in human embryonic stem cells. Homologous recombination-based methods, particularly those utilizing extended homologous regions and those employing zinc finger nucleases to boost genomic integration, have shown their usefulness in efficient genome modification. Site-specific recombination systems are potent genome modifiers, and they can be used to integrate DNA into loci that contain an appropriate recombination signal sequence, either naturally occurring or suitably pre-engineered. Non-homologous recombination can be used to generate random integrations in genomes relatively effortlessly, albeit with a moderate efficiency and precision. DNA transposition-based strategies offer substantially more efficient random strategies and provide means to generate single-copy insertions, thus potentiating the generation of genome-wide insertion libraries applicable in genetic screens.