The β-Interferon Scaffold Attachment Region Confers High-Level Transgene Expression and Avoids Extinction by Epigenetic Modifications of Integrated Provirus in Adipose Tissue-Derived Human Mesenchymal Stem Cells

Improved Functionality of Integration-Deficient Lentiviral Vectors (IDLVs) by the Inclusion of IS2 Protein Docks

Integration-deficient lentiviral vectors (IDLVs) have recently generated increasing interest, not only as a tool for transient gene delivery, but also as a technique for detecting off-target cleavage in gene-editing methodologies which rely on customized endonucleases (ENs). Despite their broad potential applications, the efficacy of IDLVs has historically been limited by low transgene expression and by the reduced sensitivity to detect low-frequency off-target events. We have previously reported that the incorporation of the chimeric sequence element IS2 into the long terminal repeat (LTR) of IDLVs increases gene expression levels, while also reducing the episome yield inside transduced cells. Our study demonstrates that the effectiveness of IDLVs relies on the balance between two parameters which can be modulated by the inclusion of IS2 sequences. In the present study, we explore new IDLV configurations harboring several elements based on IS2 modifications engineered to mediate more efficient transgene expression without affecting the targeted cell load. Of all the insulators and configurations analysed, the insertion of the IS2 into the 3′LTR produced the best results. After demonstrating a DAPI-low nuclear gene repositioning of IS2-containing episomes, we determined whether, in addition to a positive effect on transcription, the IS2 could improve the capture of IDLVs on double strand breaks (DSBs). Thus, DSBs were randomly generated, using the etoposide or locus-specific CRISPR-Cas9. Our results show that the IS2 element improved the efficacy of IDLV DSB detection. Altogether, our data indicate that the insertion of IS2 into the LTR of IDLVs improved, not only their transgene expression levels, but also their ability to be inserted into existing DSBs. This could have significant implications for the development of an unbiased detection tool for off-target cleavage sites from different specific nucleases.

Evaluation of the Effects of Human Beta-Interferon Scaffold Attachment Region (IFN-SAR) on Expression of Vascular Endothelial Growth Factor-Fc (VEGF-Fc) Fusion Protein Expression in Chinese Hamster Ovary (CHO) Cells

Background: Recombinant anti-vascular endothelial growth factor (VEGF) monoclonal antibodies and Fc-fusion proteins have been widely used for the effective treatment of retinal neovascular diseases. In this regard, VEGFR-Fc fusions, which act as strong VEGF inhibitors, have been approved for the treatment of age-related macular degeneration (AMD) and diabetic macular edema (DME). Production of monoclonal antibodies and Fc-fusion proteins relies on mammalian host systems such as Chinese hamster ovary (CHO) cells. Application of genomic regulatory elements including scaffold/matrix attachment regions (SAR/MARs) can profoundly affect recombinant protein expression in CHO cells. Methods: To construct the VEGFR-Fc expression vectors, the enhanced green fluorescent protein (EGFP) gene was replaced by the VEGFR-Fc coding sequence in pEGFP-SAR-puro and pEGFP-puro vectors. Recombinant plasmids were transfected to CHO-K1 cells using TurboFect transfection reagent. VEGFR-Fc expression was evaluated in transiently transfected cells as well as stable cell pools and clones using an enzyme-linked immunosorbent assay (ELISA). Results: IFN-SAR showed no significant effect on transient expression of VEGFR-Fc during 72 h of culture. However, a 2.2-fold enhancement in VEGFR-Fc fusion protein titer was observed in IFN-SAR containing stable cell pools. Further evaluation of the VEGFR-Fc expression level in single-cell clones also indicated that clones with the highest VEGFR-Fc expression belonged to the pools transfected with IFN-SAR construct. Conclusion: Our results indicate that the incorporation of IFN-SAR in expression vector can increase the expression of VEGFR-Fc in stable cell pools as well as single-cell clones. In contrast, transient expression of the fusion protein was not affected by IFN-SAR. More studies are needed to investigate the mechanism underlying this effect, including the analysis of mRNA expression and gene copy number in stable cell pools as well as clonal cells.

Generation of a Stable Transgenic Swine Model Expressing a Porcine Histone 2B-eGFP Fusion Protein for Cell Tracking and Chromosome Dynamics Studies

Transgenic pigs have become an attractive research model in the field of translational research, regenerative medicine, and stem cell therapy due to their anatomic, genetic and physiological similarities with humans. The development of fluorescent proteins as molecular tags has allowed investigators to track cell migration and engraftment levels after transplantation. Here we describe the development of two transgenic pig models via SCNT expressing a fusion protein composed of eGFP and porcine Histone 2B (pH2B). This fusion protein is targeted to the nucleosomes resulting a nuclear/chromatin eGFP signal. The first model (I) was generated via random insertion of pH2B-eGFP driven by the CAG promoter (chicken beta actin promoter and rabbit Globin poly A; pCAG-pH2B-eGFP) and protected by human interferon-β matrix attachment regions (MARs). Despite the consistent, high, and ubiquitous expression of the fusion protein pH2B-eGFP in all tissues analyzed, two independently generated Model I transgenic lines developed neurodegenerative symptoms including Wallerian degeneration between 3–5 months of age, requiring euthanasia. A second transgenic model (II) was developed via CRISPR-Cas9 mediated homology-directed repair (HDR) of IRES-pH2B-eGFP into the endogenous β-actin (ACTB) locus. Model II transgenic animals showed ubiquitous expression of pH2B-eGFP on all tissues analyzed. Unlike the pCAG-pH2B-eGFP/MAR line, all Model II animals were healthy and multiple pregnancies have been established with progeny showing the expected Mendelian ratio for the transmission of the pH2B-eGFP. Expression of pH2B-eGFP was used to examine the timing of the maternal to zygotic transition after IVF, and to examine chromosome segregation of SCNT embryos. To our knowledge this is the first viable transgenic pig model with chromatin-associated eGFP allowing both cell tracking and the study of chromatin dynamics in a large animal model.

An Optimized GD2-Targeting Retroviral Cassette for More Potent and Safer Cellular Therapy of Neuroblastoma and Other Cancers

Neuroblastoma is the commonest extra cranial solid cancer of childhood. Despite escalation of treatment regimens, a significant minority of patients die of their disease. Disialoganglioside (GD2) is consistently expressed at high-levels in neuroblastoma tumors, which have been targeted with some success using therapeutic monoclonal antibodies. GD2 is also expressed in a range of other cancer but with the exception of some peripheral nerves is largely absent from non-transformed tissues. Chimeric Antigen Receptors (CARs) are artificial type I proteins which graft the specificity of a monoclonal antibody onto a T-cell. Clinical data with early CAR designs directed against GD2 have shown some promise in Neuroblastoma. Here, we describe a GD2-targeting CAR retroviral cassette, which has been optimized for CAR T-cell persistence, efficacy and safety.

Sus scrofa matrix attachment region enhances expression of the PiggyBac system transfected into HEK293T cells

OBJECTIVES

To determine the effects of the Sus scrofa matrix attachment region (SusMAR) on transgene expression in HEK293T cells.

RESULTS

Three expression vectors with the MAR at different sites in the PiggyBac (PB) transposon vector backbone were compared: two MARs flanking the β-galactosidase (β-gal) expression cassette, and one at the upstream or downstream site. Bos taurus MAR (BosMAR) and a β-gal expression cassette without MARs were the positive and negative controls, respectively. Compared to the control, β-gal activity of all SusMAR and BosMAR vectors was significantly improved in the presence of PB transposase (PBase). However, only the downstream SusMAR and upstream BosMAR vectors showed increased expression in the absence of PBase. Expression was significantly increased in all vectors with the PBase group compared to those without the PBase group. Gene copy numbers were not increased compared to the negative control.

CONCLUSIONS

SusMAR enhanced recombinant gene expression levels and stability in HEK293T cells, was not increase transgene copy number. These results could facilitate the development of vectors for stable production of therapeutic proteins.

Human mesenchymal stem cells resolve airway inflammation, hyperreactivity, and histopathology in a mouse model of occupational asthma

Occupational asthma (OA) is characterized by allergic airway inflammation and hyperresponsiveness, leading to progressive airway remodeling and a concomitant decline in lung function. The management of OA remains suboptimal in clinical practice. Thus, establishing effective therapies might overcome the natural history of the disease. We evaluated the ability of human adipose-tissue-derived mesenchymal stem cells (hASCs), either unmodified or engineered to secrete the IL-33 decoy receptor sST2, to attenuate the inflammatory and respiratory symptoms in a previously validated mouse model of OA to ammonium persulfate (AP). Twenty-four hours after a dermal AP sensitization and intranasal challenge regimen, the animals received intravenously 1 × 10(6) cells (either hASCs or hASCs overexpressing sST2) or saline and were analyzed at 1, 3, and 6 days after treatment. The infused hASCs induced an anti-inflammatory and restorative program upon reaching the AP-injured, asthmatic lungs, leading to early reduction of neutrophilic inflammation and total IgE production, preserved alveolar architecture with nearly absent lymphoplasmacytic infiltrates, negligible smooth muscle hyperplasia/hypertrophy in the peribronchiolar areas, and baseline airway hyperreactivity (AHR) to methacholine. Local sST2 overexpression barely increased the substantial efficacy displayed by unmodified hASCs. Thus, hASCs may represent a viable multiaction therapeutic capable to adequately respond to the AP-injured lung environment by resolving inflammation, tissue remodeling, and bronchial hyperresponsiveness typical of OA.

Human mesenchymal stem cells overexpressing the IL-33 antagonist soluble IL-1 receptor-like-1 attenuate endotoxin-induced acute lung injury

Acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) are characterized by pulmonary edema attributable to alveolar epithelial-interstitial-endothelial injury, associated with profound inflammation and respiratory dysfunction. The IL-33/IL-1 receptor-like-1 (ST2) axis plays a key role in the development of immune-inflammatory responses in the lung. Cell-based therapy has been recently proposed as an effective alternative for the treatment of ALI and ARDS. Here, we engineered human adipose tissue-derived mesenchymal stem cells (hASCs) overexpressing soluble IL-1 receptor-like-1 (sST2), a decoy receptor for IL-33, in order to enhance their immunoregulatory and anti-inflammatory properties when applied in a murine ALI model. We administered both hASCs and hASC-sST2 systemically at 6 hours after intranasal LPS instillation, when pathological changes had already occurred. Bioluminescence imaging, immunohistochemistry, and focused transcriptional profiling confirmed the increased presence of hASCs in the injured lungs and the activation of an immunoregulatory program (CXCR-4, tumor necrosis factor-stimulated gene 6 protein, and indoleamine 2,3-dioxygenase up-regulation) in these cells, 48 hours after endotoxin challenge. A comparative evaluation of hASCs and the actions of hASC-sST2 revealed that local sST2 overproduction by hASC-sST2 further prevented IL-33, Toll-like receptor-4, IL-1β, and IFN-γ induction, but increased IL-10 expression in the injured lungs. This synergy caused a substantial decrease in lung airspace inflammation and vascular leakage, characterized by significant reductions in protein content, differential neutrophil counts, and proinflammatory cytokine (TNF-α, IL-6, and macrophage inflammatory protein 2) concentrations in bronchoalveolar lavage fluid. In addition, hASC-sST2-treated ALI lungs showed preserved alveolar architecture, an absence of apoptosis, and minimal inflammatory cell infiltration. These results suggest that hASCs genetically engineered to produce sST2 could become a promising therapeutic strategy for ALI/ARDS management.

Engraftment of genetically modified human amniotic fluid-derived progenitor cells to produce coagulation factor IX after in utero transplantation in mice

Human amniotic fluid derived progenitor cells (hAFPCs) may be multipotent and can be considered a potential tool in the field of cell therapy for haemophilia B. Their capacity to express human coagulation factor IX (hFIX) after transduction and their fate after in utero transplantation is unknown. hAFPCs isolated from second trimester pregnancies were assessed for their phenotypic markers, multilineage capacity, and expression of hFIX after transduction. Their engraftment potential was analysed in a mouse model after in utero transplantation at embryonic day 12.5. Immunohistochemistry, fluorescence in situ, ELISA and PCR were used to assess post-transplant chimeras. hAFPCs expressed several pluripotent markers, including NANOG, SOX2, SSEA4 and TRA-1-60, and could differentiate into adipocytes and osteocytes. In vitro, after transduction with hFIX and EGFP cDNAs, constitutive hFIX protein expression and clotting activity were found. Engraftment was achieved in various foetal tissues after in utero transplantation. Safe engraftment without oncogenesis was confirmed, with low donor cell levels, but persistent engraftment, into different organs (liver, heart and lung) through to 12 weeks of age. Transgenic expression of circulating hFIX was detected in recipient mice for up to 12 weeks. hAFPCs can be engrafted long-term in immunocompetent mice after in utero transplantation. Thus, cell transplantation approaches using genetically engineered hAFPCs may prove valuable for the prenatal treatment for haemophilia B.

Engraftment potential of adipose tissue-derived human mesenchymal stem cells after transplantation in the fetal rabbit

Due to their favorable intrinsic features, including engraftment, differentiation, and immunomodulatory potential, adult mesenchymal stem cells (MSCs) have been proposed for therapeutic in utero intervention. Further improvement of such attributes for particular diseases might merely be achieved by ex vivo MSC genetic engineering previous to transplantation. Here, we evaluated for the first time the feasibility, biodistribution, long-term engraftment, and transgenic enhanced green fluorescent protein (EGFP) expression of genetically engineered human adipose tissue-derived MSCs (EGFP(+)-ASCs) after intra-amniotic xenotransplantation at E17 of gestation into our validated pregnant rabbit model. Overall, the procedure was safe (86.4% survival rate; absence of anatomical defects). Stable, low-level engraftment of EGFP(+)-ASCs was confirmed by assessing the presence of the pWT-EGFP lentiviral provirus in the young transplanted rabbit tissues. Accordingly, similar frequencies of provirus-positive animals were found at both 8 weeks (60%) and 16 weeks (66.7%) after in utero intervention. The presence of EGFP(+)-ASCs was more frequent in respiratory epithelia (lung and trachea), according to the route of administration. However, we were unable to detect EGFP expression, neither by real-time polymerase chain reaction nor by immunohistochemistry, in the provirus-positive tissues, suggesting EGFP transgene silencing mediated by epigenetic events. Moreover, we noticed lack of both host cellular immune responses against xenogeneic ASCs and humoral immune responses against transgenic EGFP. Therefore, the fetal microchimerism achieved by the EGFP(+)-ASCs in the young rabbit hosts indicates induction of donor-specific tolerance after fetal rabbit xenotransplantation, which should boost postnatal transplantation for the early treatment/prevention of many devastating congenital disorders.

Fetal liver-derived mesenchymal stem cell engraftment after allogeneic in utero transplantation into rabbits

Prenatal transplantation of genetically engineered mesenchymal stem cells (MSCs) might benefit prevention or treatment of early-onset genetic disorders due to the cells' intrinsic regenerative potential plus the acquired advantage from therapeutic transgene expression. However, a thorough assessment of the safety, accessibility, and behavior of these MSCs in the fetal environment using appropriate animal models is required before we can advance toward a clinical application. We have recently shown that fetal rabbit liver MSCs (fl-MSCs) have superior growth rate, clonogenic capability, and in vitro adherence and differentiation abilities compared with adult rabbit bone marrow MSCs. In this follow-up study, we report safe and widespread distribution of recombinant pSF-EGFP retrovirus-transduced fl-MSCs (EGFP(+)-fl-MSCs) in neonatal rabbit tissues at 10 days after fetal allogeneic transplantation through both intrahepatic and intra-amniotic administration. Conversely, a more restricted biodistribution pattern according to the route of administration was apparent in the young rabbits intervened at 16 weeks after fetal EGFP(+)-fl-MSC transplantation. Furthermore, the presence of these cells in the recipients' tissues, tracked with the reporter provirus, was inversely related to the developmental stage of the fetuses at the time of intervention. Long-term engraftment was confirmed both by fluorescence in situ hybridization analysis on touch tissue imprints using a chromosome Y-specific BAC probe, and by immunohistochemical localization of EGFP expression. Finally, there was no evidence of immune responses against the transplanted EGFP(+)-fl-MSCs or the EGFP transgenic product in the treated young rabbits. Thus, cell transplantation approaches using genetically engineered fetal MSCs may prove particularly valuable to frontier medical treatments for congenital birth defects in perinatology.