Efficient gene delivery and targeted expression to hepatocytes in vivo by improved lentiviral vectors

MX2 forms nucleoporin-comprising cytoplasmic biomolecular condensates that lure viral capsids

Human myxovirus resistance 2 (MX2) can restrict HIV-1 and herpesviruses at a post-entry step through a process requiring an interaction between MX2 and the viral capsids. The involvement of other host cell factors, however, remains poorly understood. Here, we mapped the proximity interactome of MX2, revealing strong enrichment of phenylalanine-glycine (FG)-rich proteins related to the nuclear pore complex as well as proteins that are part of cytoplasmic ribonucleoprotein granules. MX2 interacted with these proteins to form multiprotein cytoplasmic biomolecular condensates that were essential for its anti-HIV-1 and anti-herpes simplex virus 1 (HSV-1) activity. MX2 condensate formation required the disordered N-terminal region and MX2 dimerization. Incoming HIV-1 and HSV-1 capsids associated with MX2 at these dynamic cytoplasmic biomolecular condensates, preventing nuclear entry of their viral genomes. Thus, MX2 forms cytoplasmic condensates that likely act as nuclear pore decoys, trapping capsids and inducing premature viral genome release to interfere with nuclear targeting of HIV-1 and HSV-1.

Sleeping Beauty mRNA-LNP enables stable rAAV transgene expression in mouse and NHP hepatocytes and improves vector potency

Recombinant adeno-associated virus (rAAV) vector gene delivery systems have demonstrated great promise in clinical trials but continue to face durability and dose-related challenges. Unlike rAAV gene therapy, integrating gene addition approaches can provide curative expression in mitotically active cells and pediatric populations. We explored a novel in vivo delivery approach based on an engineered transposase, Sleeping Beauty (SB100X), delivered as an mRNA within a lipid nanoparticle (LNP), in combination with an rAAV-delivered transposable transgene. This combinatorial approach achieved correction of ornithine transcarbamylase deficiency in the neonatal Spfash mouse model following a single delivery to dividing hepatocytes in the newborn liver. Correction remained stable into adulthood, while a conventional rAAV approach resulted in a return to the disease state. In non-human primates, integration by transposition, mediated by this technology, improved gene expression 10-fold over conventional rAAV-mediated gene transfer while requiring 5-fold less vector. Additionally, integration site analysis confirmed a random profile while specifically targeting TA dinucleotides across the genome. Together, these findings demonstrate that transposable elements can improve rAAV-delivered therapies by lowering the vector dose requirement and associated toxicity while expanding target cell types.

Targeting and delivery of microRNA-targeting antisense oligonucleotides in cardiovascular diseases

Discovered three decades ago, microRNAs (miRNAs) are now recognized as key players in the pathophysiology of multiple human diseases, including those affecting the cardiovascular system. As such, miRNAs have emerged as promising therapeutic targets for preventing the onset and/or progression of several cardiovascular diseases. Anti-miRNA antisense oligonucleotides or "antagomirs" precisely block the activity of specific miRNAs and are therefore a promising therapeutic strategy to repress pathological miRNAs. In this review, we describe advancements in antisense oligonucleotide chemistry that have significantly improved efficacy and safety. Moreover, we summarize recent approaches for the targeted delivery of antagomirs to cardiovascular tissues, highlighting major advantages as well as limitations of viral (i.e., adenovirus, adeno-associated virus, and lentivirus) and non-viral (i.e., liposomes, extracellular vesicles, and polymer nanoparticles) delivery systems. We discuss recent preclinical studies that use targeted antagomir delivery systems to treat three major cardiovascular diseases (atherosclerosis, myocardial infarction, and cardiac hypertrophy, including hypertrophy caused by hypertension), highlighting therapeutic results and discussing challenges that limit clinical applicability.

Implantation of CPT1AM-expressing adipocytes reduces obesity and glucose intolerance in mice

Obesity and its associated metabolic comorbidities are a rising global health and social issue, with novel therapeutic approaches urgently needed. Adipose tissue plays a key role in the regulation of energy balance and adipose tissue-derived mesenchymal stem cells (AT-MSCs) have gained great interest in cell therapy. Carnitine palmitoyltransferase 1A (CPT1A) is the gatekeeper enzyme for mitochondrial fatty acid oxidation. Here, we aimed to generate adipocytes expressing a constitutively active CPT1A form (CPT1AM) that can improve the obese phenotype in mice after their implantation. AT-MSCs were differentiated into mature adipocytes, subjected to lentivirus-mediated expression of CPT1AM or the GFP control, and subcutaneously implanted into mice fed a high-fat diet (HFD). CPT1AM-implanted mice showed lower body weight, hepatic steatosis and serum insulin and cholesterol levels alongside improved glucose tolerance. HFD-induced increases in adipose tissue hypertrophy, fibrosis, inflammation, endoplasmic reticulum stress and apoptosis were reduced in CPT1AM-implanted mice. In addition, the expression of mitochondrial respiratory chain complexes was enhanced in the adipose tissue of CPT1AM-implanted mice. Our results demonstrate that implantation of CPT1AM-expressing AT-MSC-derived adipocytes into HFD-fed mice improves the obese metabolic phenotype, supporting the future clinical use of this ex vivo gene therapy approach.

Gene therapy for liver diseases - progress and challenges

Gene therapy is poised to revolutionize modern medicine, with seemingly unlimited potential for treating and curing genetic disorders. For otherwise incurable indications, including most inherited metabolic liver disorders, gene therapy provides a realistic therapeutic option. In this Review, we discuss gene supplementation and gene editing involving the use of recombinant adeno-associated virus (rAAV) vectors for the treatment of inherited liver diseases, including updates on several ongoing clinical trials that are producing promising results. Clinical testing has been essential in highlighting many key translational challenges associated with this transformative therapy. In particular, the interaction of a patient's immune system with the vector raises issues of safety and the duration of treatment efficacy. Furthermore, several serious adverse events after the administration of high doses of rAAVs suggest greater involvement of innate immune responses and pre-existing hepatic conditions than initially anticipated. Finally, permanent modification of the host genome associated with rAAV genome integration and gene editing raises concerns about the risk of oncogenicity that require careful evaluation. We summarize the main progress, challenges and pathways forward for gene therapy for liver diseases.

Construction of a Chikungunya Virus, Replicon, and Helper Plasmids for Transfection of Mammalian Cells

The genome of Alphaviruses can be modified to produce self-replicating RNAs and virus-like particles, which are useful virological tools. In this work, we generated three plasmids for the transfection of mammalian cells: an infectious clone of Chikungunya virus (CHIKV), one that codes for the structural proteins (helper plasmid), and another one that codes nonstructural proteins (replicon plasmid). All of these plasmids contain a reporter gene (mKate2). The reporter gene in the replicon RNA and the infectious clone are synthesized from subgenomic RNA. Co-transfection with the helper and replicon plasmids has biotechnological/biomedical applications because they allow for the delivery of self-replicating RNA for the transient expression of one or more genes to the target cells.

Maintenance of broad neutralising antibodies and memory B cells 12 months post-infection is predicted by SARS-CoV-2 specific CD4+ T cell responses

Understanding the long-term maintenance of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) immunity is critical for predicting protection against reinfection. In an age- and gender-matched cohort of 24 participants, the association of disease severity and early immune responses on the maintenance of humoral immunity 12 months post-infection is examined. All severely affected participants maintain a stable subset of SARS-CoV-2 receptor-binding domain (RBD)-specific memory B cells (MBCs) and good neutralizing antibody breadth against the majority of the variants of concern, including the Delta variant. Modeling these immune responses against vaccine efficacy data indicate a 45%–76% protection against symptomatic infection (variant dependent). Overall, these findings indicate durable humoral responses in most participants after infection, reasonable protection against reinfection, and implicate baseline antigen-specific CD4+ T cell responses as a predictor of maintenance of antibody neutralization breadth and RBD-specific MBC levels at 12 months post-infection.

Novel variants in Krueppel like factor 1 that cause persistence of fetal hemoglobin in In(Lu) individuals

Beta-hemoglobinopathies become prominent after birth due to a switch from γ-globin to the mutated β-globin. Haploinsufficiency for the erythroid specific indispensable transcription factor Krueppel-like factor 1 (KLF1) is associated with high persistence of fetal hemoglobin (HPFH). The In(Lu) phenotype, characterized by low to undetectable Lutheran blood group expression is caused by mutations within KLF1 gene. Here we screened a blood donor cohort of 55 Lutheran weak or negative donors for KLF1 variants and evaluated their effect on KLF1 target gene expression. To discriminate between weak and negative Lutheran expression, a flow cytometry (FCM) assay was developed to detect Lu antigen expression. The Lu(a-b-) (negative) donor group, showing a significant decreased CD44 (Indian blood group) expression, also showed increased HbF and HbA2 levels, with one individual expressing HbF as high as 5%. KLF1 exons and promoter sequencing revealed variants in 80% of the Lutheran negative donors. Thirteen different variants plus one high frequency SNP (c.304 T > C) were identified of which 6 were novel. In primary erythroblasts, knockdown of endogenous KLF1 resulted in decreased CD44, Lu and increased HbF expression, while KLF1 over-expressing cells were comparable to wild type (WT). In line with the pleiotropic effects of KLF1 during erythropoiesis, distinct KLF1 mutants expressed in erythroblasts display different abilities to rescue CD44 and Lu expression and/or to affect fetal (HbF) or adult (HbA) hemoglobin expression. With this study we identified novel KLF1 variants to be include into blood group typing analysis. In addition, we provide further insights into the regulation of genes by KLF1.

Jugular Vein Injection of High-Titer Lentiviral Vectors Does Not Transduce the Aorta-Brief Report

Supplemental Digital Content is available in the text.

Objective:

Efficient gene transfer to the vascular wall via intravenous vector injection would be useful for experimental vascular biology and gene therapy. Initial studies of lentiviral vector tropism suggested that intravenously injected vectors do not transduce murine vascular tissue; however, there are also reports of highly efficient aortic transduction after jugular vein injection of high-titer lentiviral vectors. We sought to reproduce these results.

Approach and Results:

We injected high-titer preparations of GFP (green fluorescent protein)-expressing lentiviral vector into jugular veins of 8 mice; 6 mice received vehicle only. Four days later, samples of aorta (thoracic and abdominal), liver, spleen, and other tissues were harvested and processed for quantitative polymerase chain reaction detection of vector DNA and immunohistochemical detection of GFP. Our vector DNA assay did not detect transduction of any of the 16 aortic segments. This finding excludes an aortic transduction efficiency of >0.02 vector copies per cell. In contrast, vector DNA was detected in all 8 spleen and liver extracts (median, 0.8 and 0.1 vector copies per cell, respectively; P<0.001 versus vehicle controls). Quantitative polymerase chain reaction signals from DNA extracted from heart, lung, kidney, skeletal muscle, and femoral artery did not differ from background polymerase chain reaction signals from DNA extracted from tissues of vehicle-injected mice (P≥0.7 for all). Immunohistochemistry revealed GFP in scattered cells in spleen and liver, not in aorta.

Conclusions:

Injection of high-titer lentiviral vectors via the jugular vein transduces cells in the spleen and liver but does not efficiently transduce the aorta.

Electrogenetic cellular insulin release for real-time glycemic control in type 1 diabetic mice

Sophisticated devices for remote-controlled medical interventions require an electrogenetic interface that uses digital electronic input to directly program cellular behavior. We present a cofactor-free bioelectronic interface that directly links wireless-powered electrical stimulation of human cells to either synthetic promoter–driven transgene expression or rapid secretion of constitutively expressed protein therapeutics from vesicular stores. Electrogenetic control was achieved by coupling ectopic expression of the L-type voltage-gated channel CaV1.2 and the inwardly rectifying potassium channel Kir2.1 to the desired output through endogenous calcium signaling. Focusing on type 1 diabetes, we engineered electrosensitive human β cells (Electroβ cells). Wireless electrical stimulation of Electroβ cells inside a custom-built bioelectronic device provided real-time control of vesicular insulin release; insulin levels peaked within 10 minutes. When subcutaneously implanted, this electrotriggered vesicular release system restored normoglycemia in type 1 diabetic mice.

Engineered materials for in vivo delivery of genome-editing machinery

Genome editing technologies, such as CRISPR/Cas9, are promising for treating otherwise incurable genetic diseases. Great progress has been made for ex vivo genome editing; however, major bottlenecks exist in the development of efficient, safe, and targetable in vivo delivery systems, which are needed for the treatment of many diseases. To achieve high efficacy and safety in therapeutic in vivo genome editing, editing activities must be controlled spatially and temporally in the body, which requires novel materials, delivery strategies, and control mechanisms. Thus, there is currently a tremendous opportunity for the biomaterials research community to develop in vivo delivery systems that overcome the problems of low editing efficiency, off-targeting effect, safety, and cell and tissue specificity. In this Review, we summarize delivery approaches and provide perspectives on the challenges and possible solutions, aiming to stimulate further development of engineered materials for in vivo delivery of genome-editing machinery.

A novel mutation in the erythroid transcription factor KLF1 is likely responsible for ameliorating β-thalassemia major

We describe the identification of a novel missense mutation in the second zinc finger of KLF1 in two siblings who, based on their genotype, are predicted to suffer from beta thalassemia major but are, in fact, transfusion‐free and in good health. These individuals, as well as two additional members of the same family also carrying this KLF1 mutation, exhibit high levels of fetal hemoglobin (HbF). KLF1 is an erythroid transcription factor, which plays a critical role in the regulation of the developmental switch between fetal and adult hemoglobin by regulating the expression of a multitude of genes including that of BCL11A. The mutation appears to be the main candidate responsible for the beta thalassemia‐ameliorating effect as this segregates with the observed phenotype and also exogenous expression of the KLF1 mutant protein in human erythroid progenitor cells resulted in the induction of γ‐globin, without, however, affecting BCL11A levels. This report adds to the weight of evidence that heterozygous KLF1 mutations can ameliorate the severity of the β‐thalassemia major phenotype.

An Optimized Lentiviral Vector Efficiently Corrects the Human Sickle Cell Disease Phenotype

Autologous transplantation of hematopoietic stem cells transduced with a lentiviral vector (LV) expressing an anti-sickling HBB variant is a potential treatment for sickle cell disease (SCD). With a clinical trial as our ultimate goal, we generated LV constructs containing an anti-sickling HBB transgene (HBBAS3), a minimal HBB promoter, and different combinations of DNase I hypersensitive sites (HSs) from the locus control region (LCR). Hematopoietic stem progenitor cells (HSPCs) from SCD patients were transduced with LVs containing either HS2 and HS3 (β-AS3) or HS2, HS3, and HS4 (β-AS3 HS4). The inclusion of the HS4 element drastically reduced vector titer and infectivity in HSPCs, with negligible improvement of transgene expression. Conversely, the LV containing only HS2 and HS3 was able to efficiently transduce SCD bone marrow and Plerixafor-mobilized HSPCs, with anti-sickling HBB representing up to ∼60% of the total HBB-like chains. The expression of the anti-sickling HBB and the reduced incorporation of the β^S-chain in hemoglobin tetramers allowed up to 50% reduction in the frequency of RBC sickling under hypoxic conditions. Together, these results demonstrate the ability of a high-titer LV to express elevated levels of a potent anti-sickling HBB transgene ameliorating the SCD cell phenotype.

Sustained Expression of Negative Regulators of Myelination Protects Schwann Cells from Dysmyelination in a Charcot-Marie-Tooth 1B Mouse Model

Schwann cell differentiation and myelination in the PNS are the result of fine-tuning of positive and negative transcriptional regulators. As myelination starts, negative regulators are downregulated, whereas positive ones are upregulated. Fully differentiated Schwann cells maintain an extraordinary plasticity and can transdifferentiate into "repair" Schwann cells after nerve injury. Reactivation of negative regulators of myelination is essential to generate repair Schwann cells. Negative regulators have also been implicated in demyelinating neuropathies, although their role in disease remains elusive. Here, we used a mouse model of Charcot-Marie-Tooth neuropathy type 1B (CMT1B), the P0S63del mouse characterized by ER stress and the activation of the unfolded protein response, to show that adult Schwann cells are in a partial differentiation state because they overexpress transcription factors that are normally expressed only before myelination. We provide evidence that two of these factors, Sox2 and Id2, act as negative regulators of myelination in vivo However, their sustained expression in neuropathy is protective because ablation of Sox2 or/and Id2 from S63del mice of both sexes results in worsening of the dysmyelinating phenotype. This is accompanied by increased levels of mutant P0 expression and exacerbation of ER stress, suggesting that limited differentiation may represent a novel adaptive mechanism through which Schwann cells counter the toxic effect of a mutant terminal differentiation protein.SIGNIFICANCE STATEMENT In many neuropathies, Schwann cells express high levels of early differentiation genes, but the significance of these altered expression remained unclear. Because many of these factors may act as negative regulators of myelination, it was suggested that their misexpression could contribute to dysmyelination. Here, we show that the transcription factors Sox2 and Id2 act as negative regulators of myelination in vivo, but that their sustained expression in Charcot-Marie-Tooth type 1B (CMT1B) represents an adaptive response activated by the Schwann cells to reduce mutant protein toxicity and prevent demyelination.

Enhanced protection of C57 BL/6 vs Balb/c mice to melanoma liver metastasis is mediated by NK cells

The B16F10 murine melanoma cell line displays a low expression of MHC class I molecules favoring immune evasion and metastases in immunocompetent C57 BL/6 wild-type mice. Here, we generated metastases to the liver, an organ that is skewed towards immune tolerance, by intrasplenic injection of B16F10 cells in syngeneic C57 BL/6 compared to allogeneic Balb/c mice. Surprisingly, Balb/c mice, which usually display a pronounced M2 macrophage and Th2 T cell polarization, were ∼3 times more susceptible to metastasis than C57 BL/6 mice, despite a much higher M1 and Th1 T cell immune response. The anti-metastatic advantage of C57 BL/6 mice could be attributed to a more potent NK-cell mediated cytotoxicity against B16F10 cells. Our findings highlight the role of NK cells in innate anti-tumor immunity in the context of the liver – particularly against highly aggressive MHC I-deficient cancer cells. Moreover, the B16F10 model of melanoma liver metastasis is suited for developing novel therapies targeting innate NK cell related immunity in liver metastases and liver cancer.

Aberrant Rac1-cofilin signaling mediates defects in dendritic spines, synaptic function, and sensory perception in fragile X syndrome

Fragile X syndrome (FXS) is the most common inherited cause of intellectual disabilities and a leading cause of autism. FXS is caused by a trinucleotide expansion in the gene FMR1 on the X chromosome. The neuroanatomical hallmark of FXS is an overabundance of immature dendritic spines, a factor thought to underlie synaptic dysfunction and impaired cognition. We showed that aberrantly increased activity of the Rho GTPase Rac1 inhibited the actin-depolymerizing factor cofilin, a major determinant of dendritic spine structure, and caused disease-associated spine abnormalities in the somatosensory cortex of FXS model mice. Increased cofilin phosphorylation and actin polymerization coincided with abnormal dendritic spines and impaired synaptic maturation. Viral delivery of a constitutively active cofilin mutant (cofilinS3A) into the somatosensory cortex of Fmr1-deficient mice rescued the immature dendritic spine phenotype and increased spine density. Inhibition of the Rac1 effector PAK1 with a small-molecule inhibitor rescued cofilin signaling in FXS mice, indicating a causal relationship between PAK1 and cofilin signaling. PAK1 inhibition rescued synaptic signaling (specifically the synaptic ratio of NMDA/AMPA in layer V pyramidal neurons) and improved sensory processing in FXS mice. These findings suggest a causal relationship between increased Rac1-cofilin signaling, synaptic defects, and impaired sensory processing in FXS and uncover a previously unappreciated role for impaired Rac1-cofilin signaling in the aberrant spine morphology and spine density associated with FXS.

Cellular GFP Toxicity and Immunogenicity: Potential Confounders in in Vivo Cell Tracking Experiments

Green Fluorescent protein (GFP), used as a cellular tag, provides researchers with a valuable method of measuring gene expression and cell tracking. However, there is evidence to suggest that the immunogenicity and cytotoxicity of GFP potentially confounds the interpretation of in vivo experimental data. Studies have shown that GFP expression can deteriorate over time as GFP tagged cells are prone to death. Therefore, the cells that were originally marked with GFP do not survive and cannot be accurately traced over time. This review will present current evidence for the immunogenicity and cytotoxicity of GFP in in vivo studies by characterizing these responses.

Preferential association with ClC-3 permits sorting of ClC-4 into endosomal compartments

ClC-4 is an intracellular Cl^-/H⁺ exchanger that is highly expressed in the brain and whose dysfunction has been linked to intellectual disability and epilepsy. Here we studied the subcellular localization of human ClC-4 in heterologous expression systems. ClC-4 is retained in the endoplasmic reticulum (ER) upon overexpression in HEK293T cells. Co-expression with distinct ClC-3 splice variants targets ClC-4 to late endosome/lysosomes (ClC-3a and ClC-3b) or recycling endosome (ClC-3c). When expressed in cultured astrocytes, ClC-4 sorted to endocytic compartments in WT cells but was retained in the ER in Clcn3^-/- cells. To understand the virtual absence of ER-localized ClC-4 in WT astrocytes, we performed association studies by high-resolution clear native gel electrophoresis. Although other CLC channels and transporters form stable dimers, ClC-4 was mostly observed as monomer, with ClC-3-ClC-4 heterodimers being more stable than ClC-4 homodimers. We conclude that unique oligomerization properties of ClC-4 permit regulated targeting of ClC-4 to various endosomal compartment systems via expression of different ClC-3 splice variants.

Tumor targeting by lentiviral vectors combined with magnetic nanoparticles in mice

Nanomaterials conjugated or complexed with biological moieties such as antibodies, polymers or peptides appear to be suitable not only for drug delivery but also for specific cancer treatment. Here, biocompatible iron oxide magnetic nanoparticles (MNPs) with or without a silica shell coupled with lentiviral vectors (LVs) are proposed as a combined therapeutic approach to specifically target gene expression in a cancer mouse model. Initially, four different MNPs were synthesized and their physical properties were characterized to establish and discriminate their behaviors. MNPs and LVs strictly interacted and transduced cells in vitro as well as in vivo, with no toxicity or inflammatory responses. By injecting LV-MNPs complexes intravenously, green fluorescent protein (GFP) resulted in a sustained long-term expression. Furthermore, by applying a magnetic field on the abdomen of intravenous injected mice, GFP positive cells increased in livers and spleens. In liver, LV-MNPs were able to target both hepatocytes and non-parenchymal cells, while in a mouse model with a grafted tumor, intra-tumor LV-MNPs injection and magnetic plaque application next to the tumor demonstrated the efficient uptake of LV-MNPs complexes with high number of transduced cells and iron accumulation in the tumor site. More important, LV-MNPs with the application of the magnetic plaque spread in all the tumor parenchyma and dissemination through the body was prevented confirming the efficient uptake of LV-MNPs complexes in the tumor. Thus, these LV-MNPs complexes could be used as multifunctional and efficient tools to selectively induce transgene expression in solid tumor for therapeutic purposes.

STATEMENT OF SIGNIFICANCE

Our study describes a novel approach of combining magnetic properties of nanomaterials with gene therapy. Magnetic nanoparticles (MNPs) coated with or without a silica shell coupled with lentiviral vectors (LVs) were used as vehicle to target biological active molecules in a mouse cancer model. After in situ injection, the presence of MNP under the magnetic field improve the vector distribution in the tumor mass and after systemic administration, the application of the magnetic field favor targeting of specific organs for LV transduction and specifically can direct LV in specific cells (or avoiding them). Thus, our findings suggest that LV-MNPs complexes could be used as multifunctional and efficient tools to selectively induce transgene expression in solid tumor for therapeutic purposes.

Toward Personalized Gene Therapy: Characterizing the Host Genetic Control of Lentiviral-Vector-Mediated Hepatic Gene Delivery

The success of lentiviral vectors in curing fatal genetic and acquired diseases has opened a new era in human gene therapy. However, variability in the efficacy and safety of this therapeutic approach has been reported in human patients. Consequently, lentiviral-vector-based gene therapy is limited to incurable human diseases, with little understanding of the underlying causes of adverse effects and poor efficacy. To assess the role that host genetic variation has on efficacy of gene therapy, we characterized lentiviral-vector gene therapy within a set of 12 collaborative cross mouse strains. Lentiviral vectors carrying the firefly luciferase cDNA under the control of a liver-specific promoter were administered to female mice, with total-body and hepatic luciferase expression periodically monitored through 41 weeks post-vector administration. Vector copy number per diploid genome in mouse liver and spleen was determined at the end of this study. We identified major strain-specific contributions to overall success of transduction, vector biodistribution, maximum luciferase expression, and the kinetics of luciferase expression throughout the study. Our results highlight the importance of genetic variation on gene-therapeutic efficacy; provide new models with which to more rigorously assess gene therapy approaches; and suggest that redesigning preclinical studies of gene-therapy methodologies might be appropriate.

"Marker of Self" CD47 on lentiviral vectors decreases macrophage-mediated clearance and increases delivery to SIRPA-expressing lung carcinoma tumors

Lentiviruses infect many cell types and are now widely used for gene delivery in vitro, but in vivo uptake of these foreign vectors by macrophages is a limitation. Lentivectors are produced here from packaging cells that overexpress "Marker of Self" CD47, which inhibits macrophage uptake of cells when prophagocytic factors are also displayed. Single particle analyses show "hCD47-Lenti" display properly oriented human-CD47 for interactions with the macrophage's inhibitory receptor SIRPA. Macrophages derived from human and NOD/SCID/Il2rg-/- (NSG) mice show a SIRPA-dependent decrease in transduction, i.e., transgene expression, by hCD47-Lenti compared to control Lenti. Consistent with known "Self" signaling pathways, macrophage transduction by control Lenti is decreased by drug inhibition of Myosin-II to the same levels as hCD47-Lenti. In contrast, human lung carcinoma cells express SIRPA and use it to enhance transduction by hCD47-Lenti- as illustrated by more efficient gene deletion using CRISPR/Cas9. Intravenous injection of hCD47-Lenti into NSG mice shows hCD47 prolongs circulation, unless a blocking anti-SIRPA is preinjected. In vivo transduction of spleen and liver macrophages also decreases for hCD47-Lenti while transduction of lung carcinoma xenografts increases. hCD47 could be useful when macrophage uptake is limiting on other viral vectors that are emerging in cancer treatments (e.g., Measles glycoprotein-pseudotyped lentivectors) and also in targeting various SIRPA-expressing tumors such as glioblastomas.

A multiplexed miRNA and transgene expression platform for simultaneous repression and expression of protein coding sequences

Knockdown of single or multiple gene targets by RNA interference (RNAi) is necessary to overcome escape mutants or isoform redundancy. It is also necessary to use multiple RNAi reagents to knockdown multiple targets. It is also desirable to express a transgene or positive regulatory elements and inhibit a target gene in a coordinated fashion. This study reports a flexible multiplexed RNAi and transgene platform using endogenous intronic primary microRNAs (pri-miRNAs) as a scaffold located in the green fluorescent protein (GFP) as a model for any functional transgene. The multiplexed intronic miRNA - GFP transgene platform was designed to co-express multiple small RNAs within the polycistronic cluster from a Pol II promoter at more moderate levels to reduce potential vector toxicity. The native intronic miRNAs are co-transcribed with a precursor GFP mRNA as a single transcript and presumably cleaved out of the precursor-(pre) mRNA by the RNA splicing machinery, spliceosome. The spliced intron with miRNA hairpins will be further processed into mature miRNAs or small interfering RNAs (siRNAs) capable of triggering RNAi effects, while the ligated exons become a mature messenger RNA for the translation of the functional GFP protein. Data show that this approach led to robust RNAi-mediated silencing of multiple Renilla Luciferase (R-Luc)-tagged target genes and coordinated expression of functional GFP from a single transcript in transiently transfected HeLa cells. The results demonstrated that this design facilitates the coordinated expression of all mature miRNAs either as individual miRNAs or as multiple miRNAs and the associated protein. The data suggest that, it is possible to simultaneously deliver multiple negative (miRNA or shRNA) and positive (transgene) regulatory elements. Because many cellular processes require simultaneous repression and activation of downstream pathways, this approach offers a platform technology to achieve that dual manipulation efficiently. In conclusion, the current platform technology offers a miRNA/shRNA scaffold for the expression of combinations of native or synthetic intronic miRNAs as singletons or polycistrons for combinatorial multiplexed RNAi silencing or RNA-based gene therapy applications.

v-SNARE transmembrane domains function as catalysts for vesicle fusion

Vesicle fusion is mediated by an assembly of SNARE proteins between opposing membranes, but it is unknown whether transmembrane domains (TMDs) of SNARE proteins serve mechanistic functions that go beyond passive anchoring of the force-generating SNAREpin to the fusing membranes. Here, we show that conformational flexibility of synaptobrevin-2 TMD is essential for efficient Ca(2+)-triggered exocytosis and actively promotes membrane fusion as well as fusion pore expansion. Specifically, the introduction of helix-stabilizing leucine residues within the TMD region spanning the vesicle's outer leaflet strongly impairs exocytosis and decelerates fusion pore dilation. In contrast, increasing the number of helix-destabilizing, ß-branched valine or isoleucine residues within the TMD restores normal secretion but accelerates fusion pore expansion beyond the rate found for the wildtype protein. These observations provide evidence that the synaptobrevin-2 TMD catalyzes the fusion process by its structural flexibility, actively setting the pace of fusion pore expansion.

Gene Therapy Applications of Viral Vectors

Viral vectors have frequently been applied in gene therapy with the final goal of treating various diseases in the areas of neurology, neurodegeneration, metabolic disease, and cancer. Vectors have been engineered based on AAV, adenoviruses, alphaviruses, herpes simplex viruses, lentiviruses, and retroviruses. Some vectors are suitable for short-term episomal transgene expression, whereas others are integrated into the host cell genome to provide long-term expression. Additionally, hybrid vectors with favorable features from different viruses have been developed. Therapeutic genes of choice have typically been toxic genes such as thymidine kinase, pro-apoptotic genes like Bax, and immunostimulatory genes (for instance, interleukin-12). A large number of animal studies have demonstrated proof of concept of viral gene therapy. Many types of viral vectors have been employed in more than 700 clinical trials that have been carried out or are currently in progress.

Human Lipoaspirate as Autologous Injectable Active Scaffold for One-Step Repair of Cartilage Defects

Research on mesenchymal stem cells from adipose tissue shows promising results for cell-based therapy in cartilage lesions. In these studies, cells have been isolated, expanded, and differentiated in vitro before transplantation into the damaged cartilage or onto materials used as scaffolds to deliver cells to the impaired area. The present study employed in vitro assays to investigate the potential of intra-articular injection of micro-fragmented lipoaspirate as a one-step repair strategy; it aimed to determine whether adipose tissue can act as a scaffold for cells naturally present at their anatomical site. Cultured clusters of lipoaspirate showed a spontaneous outgrowth of cells with a mesenchymal phenotype and with multilineage differentiation potential. Transduction of lipoaspirate clusters by lentiviral vectors expressing GFP evidenced the propensity of the outgrown cells to repopulate fragments of damaged cartilage. On the basis of the results, which showed an induction of proliferation and ECM production of human primary chondrocytes, it was hypothesized that lipoaspirate may play a paracrine role. Moreover, the structure of a floating culture of lipoaspirate, treated for 3 weeks with chondrogenic growth factors, changed: tissue with a high fat component was replaced by a tissue with a lower fat component and connective tissue rich in GAG and in collagen type I, increasing the mechanical strength of the tissue. From these promising in vitro results, it may be speculated that an injectable autologous biologically active scaffold (lipoaspirate), employed intra-articularly, may 1) become a fibrous tissue that provides mechanical support for the load on the damaged cartilage; 2) induce host chondrocytes to proliferate and produce ECM; and 3) provide cells at the site of injury, which could regenerate or repair the damaged or missing cartilage.

Truncated RAF kinases drive resistance to MET inhibition in MET-addicted cancer cells

Constitutively active receptor tyrosine kinases (RTKs) are known oncogenic drivers and provide valuable therapeutic targets in many cancer types. However, clinical efficacy of RTK inhibitors is limited by intrinsic and acquired resistance. To identify genes conferring resistance to inhibition of the MET RTK, we conducted a forward genetics screen in the GTL-16 gastric cancer cell line, carrying MET amplification and exquisitely sensitive to MET inhibition. Cells were transduced with three different retroviral cDNA expression libraries and selected for growth in the presence of the MET inhibitor PHA-665752. Selected cells displayed robust and reproducible enrichment of library-derived cDNAs encoding truncated forms of RAF1 and BRAF proteins, whose silencing reversed the resistant phenotype. Transduction of naïve GTL-16 cells with truncated, but not full length, RAF1 and BRAF conferred in vitro and in vivo resistance to MET inhibitors, which could be reversed by MEK inhibition. Induction of resistance by truncated RAFs was confirmed in other MET-addicted cell lines, and further extended to EGFR-addicted cells. These data show that truncated RAF1 and BRAF proteins, recently described as products of genomic rearrangements in gastric cancer and other malignancies, have the ability to render neoplastic cells resistant to RTK-targeted therapy.

Evaluation of cytotoxicity and DNA damage response with analysis of intracellular ATM signaling pathways

Maintenance of genome integrity by preventing and overcoming DNA damage is critical for cell survival. Deficiency or aberrancy in the DNA damage response, for example, through ataxia telangiectasia mutated (ATM) signaling, lead to pathophysiological perturbations in organs throughout the body. Therefore, control of DNA damage is of major interest for development of therapeutic agents. Such efforts will greatly benefit from convenient and simple diagnostic and/or drug development tools to demonstrate whether ATM and related genes have been activated and to then determine whether these have been returned to normal levels of activity because pathway members sense and also repair DNA damage. To overcome difficulties in analyzing differences in multitudinous ATM pathway members following DNA damage, we measured ATM promoter activity with a fluorescent td-Tomato reporter gene to interrogate the global effects of ATM signaling pathways. In cultured HuH-7 cell line derived from human hepatocellular carcinoma, cis-platinum, acetaminophen, or hydrogen peroxide caused DNA strand breaks and ATM pathway activation as shown by γH2AX expression, which in turn, led to rapid and sustained increases in ATM promoter activity. This assay of ATM promoter activity identified biological agents capable of controlling cellular DNA damage in toxin-treated HuH-7 cells and in mice after onset of drug-induced acute liver failure. Therefore, the proposed assay of ATM promoter activity in HuH-7 cells was appropriately informative for treating DNA damage. High-throughput screens using ATM promoter activation will be helpful for therapeutic development in DNA damage-associated abnormal ATM signaling in various cell types and organs.

EphrinB2 controls vessel pruning through STAT1-JNK3 signalling

Angiogenesis produces primitive vascular networks that need pruning to yield hierarchically organized and functional vessels. Despite the critical importance of vessel pruning to vessel patterning and function, the mechanisms regulating this process are not clear. Here we show that EphrinB2, a well-known player in angiogenesis, is an essential regulator of endothelial cell death and vessel pruning. This regulation depends upon phosphotyrosine-EphrinB2 signaling repressing JNK3 activity via STAT1. JNK3 activation causes endothelial cell death. In the absence of JNK3, hyaloid vessel physiological pruning is impaired, associated with abnormal persistence of hyaloid vessels, defective retinal vasculature and microphthalmia. This syndrome closely resembles human persistent hyperplastic primary vitreus (PHPV), attributed to failed involution of hyaloid vessels. Our results provide evidence that EphrinB2/STAT1/JNK3 signaling is essential for vessel pruning, and that defects in this pathway may contribute to PHPV.

Shedding of clinical-grade lentiviral vectors is not detected in a gene therapy setting

Gene therapy using viral vectors that stably integrate into ex vivo cultured cells holds great promises for the treatment of monogenic diseases as well as cancer. However, carry-over of infectious vector particles has been described to occur upon ex vivo transduction of target cells. This, in turn, may lead to inadvertent spreading of viral particles to off-target cells in vivo, raising concerns for potential adverse effects, such as toxicity of ectopic transgene expression, immunogenicity from in vivo transduced antigen-presenting cells and, possibly, gene transfer to germline cells. Here, we have investigated factors influencing the extent of lentiviral vector (LV) shedding upon ex vivo transduction of human hematopoietic stem and progenitor cells. Our results indicate that, although vector carry-over is detectable when using laboratory-grade vector stocks, the use of clinical-grade vector stocks strongly decreases the extent of inadvertent transduction of secondary targets, likely because of the higher degree of purification. These data provide supportive evidence for the safe use of the LV platform in clinical settings.

Systemic gene transfer of binding immunoglobulin protein (BiP) prevents disease progression in murine collagen-induced arthritis

Summary Recombinant human binding immunoglobulin protein (BiP) has previously demonstrated anti-inflammatory properties in multiple models of inflammatory arthritis. We investigated whether these immunoregulatory properties could be exploited using gene therapy techniques. A single intraperitoneal injection of lentiviral vector containing the murine BiP (Lenti-mBiP) or green fluorescent protein (Lenti-GFP) transgene was administered in low- or high-dose studies during early arthritis. Disease activity was assessed by visual scoring, histology, serum cytokine and antibody production measured by cell enzyme-linked immunosorbent assay (ELISA) and ELISA, respectively. Lentiviral vector treatment caused significant induction of interferon (IFN)-γ responses regardless of the transgene; however, further specific effects were directly attributable to the BiP transgene. In both studies Lenti-mBiP suppressed clinical arthritis significantly. Histological examination showed that low-dose Lenti-mBiP suppressed inflammatory cell infiltration, cartilage destruction and significantly reduced pathogenic anti-type II collagen (CII) antibodies. Lenti-mBiP treatment caused significant up-regulation of soluble cytotoxic T lymphocyte antigen-4 (sCTLA-4) serum levels and down-regulation of interleukin (IL)-17A production in response to CII cell restimulation. In-vitro studies confirmed that Lenti-mBiP spleen cells could significantly suppress the release of IL-17A from CII primed responder cells following CII restimulation in vitro, and this suppression was associated with increased IL-10 production. Neutralization of CTLA-4 in further co-culture experiments demonstrated inverse regulation of IL-17A production. In conclusion, these data demonstrate proof of principle for the therapeutic potential of systemic lentiviral vector delivery of the BiP transgene leading to immunoregulation of arthritis by induction of soluble CTLA-4 and suppression of IL-17A production.

Endogenous antiviral microRNAs determine permissiveness for hepatitis B virus replication in cultured human fetal and adult hepatocytes

Superior cell culture models for hepatitis B virus (HBV) will help advance insights into host-virus interactions. To identify mechanisms regulating HBV replication, this study used cultured human HepG2 cells and adult or fetal hepatocytes transduced with adenoviral vector to express HBV upstream of green fluorescent protein. The vector efficiently transduced all cell types. In HepG2 cells, replicative viral intermediates, nucleocapsid-associated HBcAg, and HBsAg were expressed. However, in fetal or adult hepatocytes, pregenomic HBV RNA and viral RNAs were expressed, but nucleocapsid-associated HBcAg in cells or HBsAg in culture medium were absent, indicating interruptions in viral replication due to possible microRNA-related interference. MicroRNA profiling demonstrated that a large number of microRNAs with antiviral potential were differentially expressed in hepatocytes after culture. In transfection assays using HepG2 cells, candidate antiviral microRNAs, e.g., hsa-miR-24 or hsa-miR-638 decreased the levels of HBV transcripts or HBV gene products. Since candidate microRNAs could have targeted interferon response genes as an alternative explanation interferon signaling was examined. However, HBV replication in cultured hepatocytes was not restored despite successful inhibition of JAK1/2-STAT signaling by the inhibitor, ruxolitinib. Therefore, HBV was unable to complete replication in cultured hepatocytes due to expression of multiple antiviral microRNAs. This mechanism should help understand restrictions in HBV replication for developing HBV models in cultured cells while providing frameworks for pathophysiological studies of HBV replication in subsets of hepatocytes or stem/progenitor cells during hepatitis.

Gene therapy for hemophilia

Hemophilia is an X-linked inherited bleeding disorder consisting of two classifications, hemophilia A and hemophilia B, depending on the underlying mutation. Although the disease is currently treatable with intravenous delivery of replacement recombinant clotting factor, this approach represents a significant cost both monetarily and in terms of quality of life. Gene therapy is an attractive alternative approach to the treatment of hemophilia that would ideally provide life-long correction of clotting activity with a single injection. In this review, we will discuss the multitude of approaches that have been explored for the treatment of both hemophilia A and B, including both in vivo and ex vivo approaches with viral and nonviral delivery vectors.

In vitro rescue of FGA deletion by lentiviral transduction of an afibrinogenemic patient's hepatocytes

BACKGROUND

Congenital afibrinogenemia is a rare inherited autosomal recessive disorder in which a mutation in one of three genes coding for the fibrinogen polypeptide chains Aα, Bβ and γ results in the absence of a functional coagulation protein. A patient with congenital afibrinogenemia, resulting from an FGA homozygous gene deletion, underwent an orthotopic liver transplant that resulted in complete restoration of normal hemostasis. The patient's explanted liver provided a unique opportunity to further investigate a potential novel treatment modality.

OBJECTIVE

To explore a targeted gene therapy approach for patients with congenital afibrinogenemia.

METHODS AND RESULTS

At the time of transplant, the patient's FGA-deficient hepatocytes were isolated and transduced with lentiviral vectors encoding the human fibrinogen Aα-chain. FGA-transduced hepatocytes produced fully functional fibrinogen in vitro.

CONCLUSIONS

Orthotopic liver transplantation is a possible rescue treatment for failure of on-demand fibrinogen replacement therapy. In addition, we provide evidence that hepatocytes homozygous for a large FGA deletion can be genetically modified to restore Aα-chain protein expression and secrete a functional fibrinogen hexamer.

Disappearance of GFP-positive hepatocytes transplanted into the liver of syngeneic wild-type rats pretreated with retrorsine

Background and Aim

Green fluorescent protein (GFP) is a widely used molecular tag to trace transplanted cells in rodent liver injury models. The differing results from various previously reported studies using GFP could be attributed to the immunogenicity of GFP.

Methods

Hepatocytes were obtained from GFP-expressing transgenic (Tg) Lewis rats and were transplanted into the livers of wild-type Lewis rats after they had undergone a partial hepatectomy. The proliferation of endogenous hepatocytes in recipient rats was inhibited by pretreatment with retrorsine to enhance the proliferation of the transplanted hepatocytes. Transplantation of wild-type hepatocytes into GFP-Tg rat liver was also performed for comparison.

Results

All biopsy specimens taken seven days after transplantation showed engraftment of transplanted hepatocytes, with the numbers of transplanted hepatocytes increasing until day 14. GFP-positive hepatocytes in wild-type rat livers were decreased by day 28 and could not be detected on day 42, whereas the number of wild-type hepatocytes steadily increased in GFP-Tg rat liver. Histological examination showed degenerative change of GFP-positive hepatocytes and the accumulation of infiltrating cells on day 28. PCR analysis for the GFP transgene suggested that transplanted hepatocytes were eliminated rather than being retained along with the loss of GFP expression. Both modification of the immunological response using tacrolimus and bone marrow transplantation prolonged the survival of GFP-positive hepatocytes. In contrast, host immunization with GFP-positive hepatocytes led to complete loss of GFP-positive hepatocytes by day 14.

Conclusion

GFP-positive hepatocytes isolated from GFP-Tg Lewis rats did not survive long term in the livers of retrorsine-pretreated wild-type Lewis rats. The mechanism underlying this phenomenon most likely involves an immunological reaction against GFP. The influence of GFP immunogenicity on cell transplantation models should be considered in planning in vivo experiments using GFP and in interpreting their results.

Correction of methylmalonic aciduria in vivo using a codon-optimized lentiviral vector

Methylmalonic aciduria is a rare disorder of organic acid metabolism with limited therapeutic options, resulting in high morbidity and mortality. Positive results from combined liver/kidney transplantation suggest, however, that metabolic sink therapy may be efficacious. Gene therapy offers a more accessible approach for the treatment of methylmalonic aciduria than organ transplantation. Accordingly, we have evaluated a lentiviral vector-mediated gene transfer approach in an in vivo mouse model of methylmalonic aciduria. A mouse model of methylmalonic aciduria (Mut(-/-)MUT(h2)) was injected intravenously at 8 weeks of age with a lentiviral vector that expressed a codon-optimized human methylmalonyl coenzyme A mutase transgene, HIV-1SDmEF1αmurSigHutMCM. Untreated Mut(-/-)MUT(h2) and normal mice were used as controls. HIV-1SDmEF1αmurSigHutMCM-treated mice achieved near-normal weight for age, and Western blot analysis demonstrated significant methylmalonyl coenzyme A enzyme expression in their livers. Normalization of liver methylmalonyl coenzyme A enzyme activity in the treated group was associated with a reduction in plasma and urine methylmalonic acid levels, and a reduction in the hepatic methylmalonic acid concentration. Administration of the HIV-1SDmEF1αmurSigHutMCM vector provided significant, although incomplete, biochemical correction of methylmalonic aciduria in a mouse model, suggesting that gene therapy is a potential treatment for this disorder.

Targeted therapy by gene transfer of a monovalent antibody fragment against the Met oncogenic receptor

Due to the key role played in critical sub-populations, Met is considered a relevant therapeutic target for glioblastoma multiforme and lung cancers. The anti-Met DN30 antibody, engineered to a monovalent Fab (Mv-DN30), proved to be a potent antagonist, inducing physical removal of Met receptor from the cell surface. In this study, we designed a gene therapy approach, challenging Mv-DN30 in preclinical models of Met-driven human glioblastoma and lung carcinoma. Mv-DN30 was delivered by a Tet-inducible-bidirectional lentiviral vector. Gene therapy solved the limitations dictated by the short half-life of the low molecular weight form of the antibody. In vitro, upon doxycycline induction, the transgene: (1) drove synthesis and secretion of the correctly assembled Mv-DN30; (2) triggered the displacement of Met receptor from the surface of target cancer cells; (3) suppressed the Met-mediated invasive growth phenotype. Induction of transgene expression in cancer cells-transplanted either subcutaneously or orthotopically in nude mice-resulted in inhibition of tumor growth. Direct Mv-DN30 gene transfer in nude mice, intra-tumor or systemic, was followed by a therapeutic response. These results provide proof of concept for a gene transfer immunotherapy strategy by a Fab fragment and encourage clinical studies targeting Met-driven cancers with Mv-DN30.

KEY MESSAGE

Gene transfer allows the continuous in vivo production of therapeutic Fab fragments. Mv-DN30 is an excellent tool for the treatment of Met-driven cancers. Mv-DN30 gene therapy represents an innovative route for Met targeting.

Efficient liver gene transfer with foamy virus vectors

Background

Liver gene transfer offers hope for the correction of genetic and acquired disorders. Efficient gene transfer in large animals can be obtained with hydrodynamic gene transfer (HGT), a method that can achieve sufficient levels of gene delivery.

Material/Methods

To test the relative efficiency between plasmid versus foamy virus (FV) vector-based liver gene transfer efficiency, we applied HGT in 4 juvenile pigs, using the same plasmid backbone, either naked or coated as a FV vector particle. Gene transfer efficiency and persistence of expression was assayed by PCR and real-time PCR, respectively, at 1 week and at 1 month after the infusions.

Results

HGT was tolerated well and no adverse reactions were observed. Plasmid injections resulted in no detectable DNA sequences at 1 week. At the 1 month time point, 2/15 liver sections analyzed were positive for the presence of plasmid DNA. When FV vectors were infused under identical conditions, 18/28 (64.3%) of the liver samples were positive for the presence of vector sequences, and the expression levels reached 29.7 and 15.6% of the endogenous GAPDH levels in the injected and the adjacent liver lobes.

Conclusions

Our results indicate that medium-term therapeutic levels of gene expression can be obtained with FV vectors, an effect that can be attributed to the potential of the HGT procedure and to the natural affinity of FV vectors for hepatocytes.

SIRT1 regulates the neurogenic potential of neural precursors in the adult subventricular zone and hippocampus

Within the two neurogenic niches of the adult mammalian brain, i.e., the subventricular zone lining the lateral ventricle and the subgranular zone of the hippocampus, there exist distinct populations of proliferating neural precursor cells that differentiate to generate new neurons. Numerous studies have suggested that epigenetic regulation by histone-modifying proteins is important in guiding precursor differentiation during development; however, the role of these proteins in regulating neural precursor activity in the adult neurogenic niches remains poorly understood. Here we examine the role of an NAD(+) -dependent histone deacetylase, SIRT1, in modulating the neurogenic potential of neural precursors in the neurogenic niches of the adult mouse brain. We show that SIRT1 is expressed by proliferating adult subventricular zone and hippocampal neural precursors, although its transcript and protein levels are dramatically reduced during neural precursor differentiation. Utilizing a lentiviral-mediated delivery strategy, we demonstrate that abrogation of SIRT1 signaling by RNAi does not affect neural precursor numbers or their proliferation. However, SIRT1 knock down results in a significant increase in neuronal production in both the subventricular zone and the hippocampus. In contrast, enhancing SIRT1 signaling either through lentiviral-mediated SIRT1 overexpression or through use of the SIRT1 chemical activator Resveratrol prevents adult neural precursors from differentiating into neurons. Importantly, knock down of SIRT1 in hippocampal precursors in vivo, either through RNAi or through genetic ablation, promotes their neurogenic potential. These findings highlight SIRT1 signaling as a negative regulator of neuronal differentiation of adult subventricular zone and hippocampal neural precursors. © 2013 Wiley Periodicals, Inc.

Intravenous delivery of HIV-based lentiviral vectors preferentially transduces F4/80+ and Ly-6C+ cells in spleen, important target cells in autoimmune arthritis

Antigen presenting cells (APCs) play an important role in arthritis and APC specific gene therapeutic targeting will enable intracellular modulation of cell activity. Viral mediated overexpression is a potent approach to achieve adequate transgene expression levels and lentivirus (LV) is useful for sustained expression in target cells. Therefore, we studied the feasibility of lentiviral mediated targeting of APCs in experimental arthritis. Third generation VSV-G pseudotyped self-inactivating (SIN)-LV were injected intravenously and spleen cells were analyzed with flow cytometry for green fluorescent protein (GFP) transgene expression and cell surface markers. Collagen-induced arthritis (CIA) was induced by immunization with bovine collagen type II in complete Freund's adjuvant. Effect on inflammation was monitored macroscopically and T-cell subsets in spleen were analyzed by flow cytometry. Synovium from arthritic knee joints were analyzed for proinflammatory cytokine expression. Lentiviruses injected via the tail vein preferentially infected the spleen and transduction peaks at day 10. A dose escalating study showed that 8% of all spleen cells were targeted and further analysis showed that predominantly Ly6C+ and F4/80+ cells in spleen were targeted by the LV. To study the feasibility of blocking TAK1-dependent pathways by this approach, a catalytically inactive mutant of TAK1 (TAK1-K63W) was overexpressed during CIA. LV-TAK1-K63W significantly reduced incidence and arthritis severity macroscopically. Further histological analysis showed a significant decrease in bone erosion in LV-TAK1-K63W treated animals. Moreover, systemic Th17 levels were decreased by LV-TAK1-K63W treatment in addition to diminished IL-6 and KC production in inflamed synovium. In conclusion, systemically delivered LV efficiently targets monocytes and macrophages in spleen that are involved in autoimmune arthritis. Moreover, this study confirms efficacy of TAK1 targeting in arthritis. This approach may provide a valuable tool in targeting splenic APCs, to unravel their role in autoimmune arthritis and to identify and validate APC specific therapeutic targets.

Lentiviral vector-based insertional mutagenesis identifies genes associated with liver cancer

Transposons and γ-retroviruses have been efficiently used as insertional mutagens in different tissues to identify molecular culprits of cancer. However, these systems are characterized by recurring integrations that accumulate in tumor cells and that hamper the identification of early cancer-driving events among bystander and progression-related events. We developed an insertional mutagenesis platform based on lentiviral vectors (LVVs) by which we could efficiently induce hepatocellular carcinoma (HCC) in three different mouse models. By virtue of the LVV's replication-deficient nature and broad genome-wide integration pattern, LVV-based insertional mutagenesis allowed identification of four previously unknown liver cancer-associated genes from a limited number of integrations. We validated the oncogenic potential of all the identified genes in vivo, with different levels of penetrance. The newly identified genes are likely to play a role in human cancer because they are upregulated, amplified and/or deleted in human HCCs and can predict clinical outcomes of patients.

Priming of hepatocytes enhances in vivo liver transduction with lentiviral vectors in adult mice

Lentiviral vectors are promising tools for liver disease gene therapy, because they can achieve protracted expression of transgenes in hepatocytes. However, the question as to whether cell division is required for optimal hepatocyte transduction has still not been completely answered. Liver gene-transfer efficiency after in vivo administration of recombinant lentiviral vectors carrying a green fluorescent protein reporter gene under the control of a liver-specific promoter in mice that were either hepatectomized or treated with cholic acid or phenobarbital was compared. Phenobarbital is known as a weak inducer of hepatocyte proliferation, whereas cholic acid has no direct effect on the cell cycle. This study shows that cholic acid is able to prime hepatocytes without mitosis induction. Both phenobarbital and cholic acid significantly increased hepatocyte transduction six- to ninefold, although cholic acid did not modify the mitotic index or cell-cycle entry. However, the effect of either compound was weaker than that observed after partial hepatectomy. In no cases was there a correlation between the expression of cell-cycle marker and transduction efficiency. We conclude that priming of hepatocytes should be considered a clinically applicable strategy to enhance in vivo liver gene therapy with lentiviral vectors.

A TLR and non-TLR mediated innate response to lentiviruses restricts hepatocyte entry and can be ameliorated by pharmacological blockade

Lentiviral vector (LV)-mediated gene transfer is a promising method of gene therapy. We previously reported that systemic injection of HIV-based LV triggers a transient inflammatory response. Here, we carried out studies to better characterize this response, and to develop a strategy to overcome the adverse effects of interferon (IFN) on LV-mediated gene transfer. We profiled gene expression in the liver after LV administration using deep-sequencing (RNA-seq), and identified several innate response pathways. We examined the response to LV in MyD88-TRIF knockout mice, which are incapable of toll-like receptor (TLR) signaling. Unexpectedly, the IFN response to LV was not reduced in the liver indicating that a non-TLR pathway can recognize LV in this organ. Indeed, blocking reverse transcription with azidothymidine (AZT) reduced the IFN response only in the liver, suggesting that proviral DNA can be a trigger. To block the inflammatory response, we pretreated mice with a short course of dexamethasone (Dex). At 4 hours post-treatment, all the IFN-induced genes were normalized. By blocking the inflammatory response, hepatocyte transduction was dramatically increased, which in turn doubled the level of human factor IX (FIX) produced by a hepatocyte-specific LV. Our studies uncover new insights into LV-induced immune responses in the liver, and provide a means to increase the safety and efficiency of LV-mediated gene transfer.

Phoenix rising: gene therapy makes a comeback

Despite the first application of gene therapy in 1990, gene therapy has until recently failed to meet the huge expectations set forth by researchers, clinicians, and patients, thus dampening enthusiasm for an imminent cure for many life-threatening genetic diseases. Nonetheless, in recent years we have witnessed a strong comeback for gene therapy, with clinical successes in young and adult subjects suffering from inherited forms of blindness or from X-linked severe combined immunodeficiency disease. In this review, various gene therapy vectors progressing into clinical development and pivotal advances in gene therapy trials will be discussed.

Gene therapy by targeted adenovirus-mediated knockdown of pulmonary endothelial Tph1 attenuates hypoxia-induced pulmonary hypertension

Serotonin is produced by pulmonary arterial endothelial cells (PAEC) via tryptophan hydroxylase-1 (Tph1). Pathologically, serotonin acts on underlying pulmonary arterial cells, contributing to vascular remodeling associated with pulmonary arterial hypertension (PAH). The effects of hypoxia on PAEC-Tph1 activity are unknown. We investigated the potential of a gene therapy approach to PAH using selective inhibition of PAEC-Tph1 in vivo in a hypoxic model of PAH. We exposed cultured bovine pulmonary arterial smooth muscle cells (bPASMCs) to conditioned media from human PAECs (hPAECs) before and after hypoxic exposure. Serotonin levels were increased in hypoxic PAEC media. Conditioned media evoked bPASMC proliferation, which was greater with hypoxic PAEC media, via a serotonin-dependent mechanism. In vivo, adenoviral vectors targeted to PAECs (utilizing bispecific antibody to angiotensin-converting enzyme (ACE) as the selective targeting system) were used to deliver small hairpin Tph1 RNA sequences in rats. Hypoxic rats developed PAH and increased lung Tph1. PAEC-Tph1 expression and development of PAH were attenuated by our PAEC-Tph1 gene knockdown strategy. These results demonstrate that hypoxia induces Tph1 activity and selective knockdown of PAEC-Tph1 attenuates hypoxia-induced PAH in rats. Further investigation of pulmonary endothelial-specific Tph1 inhibition via gene interventions is warranted.

Lentiviral vector integration in the human genome induces alternative splicing and generates aberrant transcripts

Retroviral vectors integrate in genes and regulatory elements and may cause transcriptional deregulation of gene expression in target cells. Integration into transcribed genes also has the potential to deregulate gene expression at the posttranscriptional level by interfering with splicing and polyadenylation of primary transcripts. To examine the impact of retroviral vector integration on transcript splicing, we transduced primary human cells or cultured cells with HIV-derived vectors carrying a reporter gene or a human β-globin gene under the control of a reduced-size locus-control region (LCR). Cells were randomly cloned and integration sites were determined in individual clones. We identified aberrantly spliced, chimeric transcripts in more than half of the targeted genes in all cell types. Chimeric transcripts were generated through the use of constitutive and cryptic splice sites in the HIV 5ι long terminal repeat and gag gene as well as in the β-globin gene and LCR. Compared with constitutively spliced transcripts, most aberrant transcripts accumulated at a low level, at least in part as a consequence of nonsense-mediated mRNA degradation. A limited set of cryptic splice sites caused the majority of aberrant splicing events, providing a strategy for recoding lentiviral vector backbones and transgenes to reduce their potential posttranscriptional genotoxicity.

Preclinical safety and efficacy of human CD34(+) cells transduced with lentiviral vector for the treatment of Wiskott-Aldrich syndrome

Gene therapy with ex vivo-transduced hematopoietic stem/progenitor cells may represent a valid therapeutic option for monogenic immunohematological disorders such as Wiskott-Aldrich syndrome (WAS), a primary immunodeficiency associated with thrombocytopenia. We evaluated the preclinical safety and efficacy of human CD34⁺ cells transduced with lentiviral vectors (LV) encoding WAS protein (WASp). We first set up and validated a transduction protocol for CD34⁺ cells derived from bone marrow (BM) or mobilized peripheral blood (MPB) using a clinical grade, highly purified LV. Robust transduction of progenitor cells was obtained in normal donors and WAS patients' cells, without evidence of toxicity. To study biodistribution of human cells and exclude vector release in vivo, LV-transduced CD34⁺ cells were transplanted in immunodeficient mice, showing a normal engraftment and differentiation ability towards transduced lymphoid and myeloid cells in hematopoietic tissues. Vector mobilization to host cells and transmission to germline cells of the LV were excluded by different molecular assays. Analysis of vector integrations showed polyclonal integration patterns in vitro and in human engrafted cells in vivo. In summary, this work establishes the preclinical safety and efficacy of human CD34⁺ cells gene therapy for the treatment of WAS.