Lentiviral Vectors For Gene Therapy Research Articles

Correction of osteopetrosis in the neonate oc/oc murine model after lentiviral vector gene therapy and non-genotoxic conditioning

IntroductionAutosomal recessive osteopetrosis (ARO) is a rare genetic disease, characterized by increased bone density due to defective osteoclast function. Most of the cases are due to TCIRG1 gene mutation, leading to severe bone phenotype and death in the first years of life. The standard therapy is the hematopoietic stem cell transplantation (HSCT), but its success is limited by several constraints. Conversely, gene therapy (GT) could minimize the immune-mediated complications of allogeneic HSCT and offer a prompt treatment to these patients.MethodsThe Tcirg1-defective oc/oc mouse model displays a short lifespan and high bone density, closely mirroring the human condition. In this work, we exploited the oc/oc neonate mice to optimize the critical steps for a successful therapy.ResultsFirst, we showed that lentiviral vector GT can revert the osteopetrotic bone phenotype, allowing long-term survival and reducing extramedullary haematopoiesis. Then, we demonstrated that plerixafor-induced mobilization can further increase the high number of HSPCs circulating in peripheral blood, facilitating the collection of adequate numbers of cells for therapeutic purposes. Finally, pre-transplant non-genotoxic conditioning allowed the stable engraftment of HSPCs, albeit at lower level than conventional total body irradiation, and led to long-term survival and correction of bone phenotype, in the absence of acute toxicity.ConclusionThese results will pave the way to the implementation of an effective GT protocol, reducing the transplant-related complication risks in the very young and severely affected ARO patients.

Lentiviral vector gene therapy and CFTR modulators show comparable effectiveness in cystic fibrosis rat airway models.

Mutation-agnostic treatments such as airway gene therapy have the potential to treat any individual with cystic fibrosis (CF), irrespective of their CF transmembrane conductance regulator (CFTR) gene variants. The aim of this study was to employ two CF rat models, Phe508del and CFTR knockout (KO), to assess the comparative effectiveness of CFTR modulators and lentiviral (LV) vector-mediated gene therapy. Cells were isolated from the tracheas of rats and used to establish air-liquid interface (ALI) cultures. Phe508del rat ALIs were treated with the modulator combination, elexacaftor-tezacaftor-ivacaftor (ETI), and separate groups of Phe508del and KO tracheal epithelial cells were treated with LV-CFTR followed by differentiation at ALI. Ussing chamber measurements were performed to assess CFTR function. ETI-treated Phe508del ALI cultures demonstrated CFTR function that was 59% of wild-type level, while gene-addition therapy restored Phe508del to 68% and KO to 47% of wild-type level, respectively. Our findings show that rat Phe508del-CFTR protein can be successfully rescued with ETI treatment, and that CFTR gene-addition therapy provides significant CFTR correction in Phe508del and KO ALI cultures to levels that were comparable to ETI. These findings highlight the potential of an LV vector-based gene therapy for the treatment of CF lung disease.

Pharmacological and pre-clinical safety profile of rSIV.F/HN, a hybrid lentiviral vector for cystic fibrosis gene therapy.

Cystic fibrosis (CF) is caused by mutations in the CF Transmembrane Conductance Regulator (CFTR) gene. CFTR modulators offer significant improvements, but approximately 10% of patients remain nonresponsive or are intolerant. This study provides an analysis of rSIV.F/HN, a lentiviral vector optimized for lung delivery, including CFTR protein expression, functional correction of CFTR defects and genomic integration site analysis in preparation for a first-in-human clinical trial. Air-liquid interface cultures of primary human bronchial epithelial cells (HBEC) from CF patients (F508del/F508del), as well as a CFTR-deficient immortalized human lung epithelial cell line mimicking Class I (CFTR-null) homozygous mutations, were used to assess transduction efficiency. Quantification methods included a novel proximity ligation assay (PLA) for CFTR protein expression. For assessment of CFTR channel activity, Ussing chamber studies were conducted. The safety profile was assessed using integration site analysis and in vitro insertional mutagenesis studies. rSIV.F/HN expressed CFTR and restored CFTR-mediated chloride currents to physiological levels in primary F508del/F508del HBECs as well as in a Class I cells. In contrast, the latter could not be achieved by small-molecule CFTR modulators, underscoring the potential of gene therapy for this mutation class. Combination of rSIV.F/HN-CFTR with the potentiator ivacaftor showed a greater than additive effect. The genomic integration pattern showed no site predominance (frequency of occurrence ≤10%), and a low risk of insertional mutagenesis was observed in an in vitro immortalization assay. The results underscore rSIV.F/HN as a promising gene therapy vector for CF, providing a mutation-agnostic treatment option.

Secondary failure of lentiviral vector gene therapy in a cerebral adrenoleukodystrophy patient with an ABCD1 whole-gene deletion

A nine-year boy with adrenoleukodystrophy due to an ABCD1 whole gene deletion was diagnosed with the active cerebral adrenoleukodystrophy characterized by demyelination and gadolinium enhancement on brain MRI. He underwent hemopoietic cell transplant (HCT) with autologous CD34+ cells transduced with an ABCD1-expressing lentiviral vector (eli-cel, elivaldogene autotemcel) as part of the ALD-104 clinical trial. Fifty days after HCT, the patient’s MRI showed gadolinium resolution; whole blood vector copy number (VCN) was 0.666 copies/mL. Six months following HCT, an MRI showed re-emergence of gadolinium enhancement; VCN had decreased to 0.029 copies/mL. Polyclonal antibodies to the ABCD1 gene product were detectable 9 months after transplant showing reactivity to peroxisomes, suggesting an immune response, however, no antibody binding to human CD34+ cells could be shown. The patient underwent a successful allogeneic HCT 12 months after gene therapy with resultant gadolinium resolution, cerebral disease stabilization, and the disappearance of antibodies. The coincident VCN loss and appearance of antibody to the ABCD1 gene product is of interest, and we postulate that it is related to the patient’s whole ABCD1 gene deletion. We suggest close monitoring of loss of gene therapy efficacy due to immune response in patients with full deletions who are considering gene therapy.

P046 Lenticlair™-ON: An extension trial examining long-term safety and efficacy outcomes associated with an inhaled F/HN-pseudotyped lentiviral vector for CF gene therapy in people with cystic fibrosis

P046 Lenticlair™-ON: An extension trial examining long-term safety and efficacy outcomes associated with an inhaled F/HN-pseudotyped lentiviral vector for CF gene therapy in people with cystic fibrosis

P045 Lenticlair™ 1: A phase 1/2 trial evaluating the safety, tolerability and efficacy of an inhaled F/HN-pseudotyped lentiviral vector for CF gene therapy in people with CF ineligible for CFTR modulators

P045 Lenticlair™ 1: A phase 1/2 trial evaluating the safety, tolerability and efficacy of an inhaled F/HN-pseudotyped lentiviral vector for CF gene therapy in people with CF ineligible for CFTR modulators

A novel high-titer, bifunctional lentiviral vector for autologous hematopoietic stem cell gene therapy of sickle cell disease

A major limitation of gene therapy for sickle cell disease (SCD) is the availability and access to a potentially curative one-time treatment, due to high treatment costs. We have developed a high-titer bifunctional lentiviral vector (LVV) in a vector backbone that has reduced size, high vector yields, and efficient gene transfer to human CD34+ hematopoietic stem and progenitor cells (HSPC). This LVV contains locus control region cores expressing an anti-sickling βAS3-globin gene and two microRNA adapted short hairpin RNA simultaneously targeting BCL11A and ZNF410 transcripts to maximally induce fetal hemoglobin (HbF) expression. This LVV induces high levels of anti-sickling hemoglobins (HbAAS3 + HbF), while concurrently reducing sickle hemoglobin (HbS). The reduction in HbS and increased anti-sickling hemoglobin impedes deoxygenated HbS polymerization and red blood cell sickling at low vector copy per cell in transduced SCD patient CD34+ cells differentiated into erythrocytes. The dual alterations in red cell hemoglobins ameliorated the SCD phenotype in the SCD Berkeley mouse model in vivo. With high titer and enhanced transduction of HSPC at low multiplicity of infection, this LVV will increase the number of patient doses of vector from production lots to reduce costs and help improve accessibility to gene therapy for SCD.

Microglia cells treated with synthetic vasoactive intestinal peptide or transduced with LentiVIP protect neuronal cells against degeneration.

A common pathological hallmark of neurodegenerative disorders is neuronal cell death, accompanied by neuroinflammation and oxidative stress. The vasoactive intestinal peptide (VIP) is a pleiotropic peptide that combines neuroprotective and immunomodulatory actions. The gene therapy field shows long-term promise for treating a wide range of neurodegenerative diseases (ND). In this study, we aimed to investigate the in vitro efficacy of transduction of microglia using lentiviral gene therapy vectors encoding VIP (LentiVIP). Additionally, we tested the protective effects of the secretome derived from LentiVIP-infected "immortalized human" microglia HMC3 cells, and cells treated with Synthetic VIP (SynVIP), against toxin-induced neurodegeneration. First, LentiVIP, which stably expresses VIP, was generated and purified. VIP secretion in microglial conditioned media (MG CM) for LentiVIP-infected HMC3 microglia cells was confirmed. Microglia cells were activated with lipopolysaccharide, and groups were formed as follows: 1) Control, 2) SynVIP-treated, or 3) LentiVIP-transduced. These MG CM were applied on an in vitro neurodegenerative model formed by differentiated (d)-SH-SY5Y cells. Then, cell survival analysis and apoptotic nuclear staining, besides measurement of oxidative/inflammatory parameters in CM of cells were performed. Activated MG CM reduced survival rates of both control and toxin-applied (d)-SH-SY5Y cells, whereas LentiVIP-infected MG CM and SynVIP-treated ones exhibited better survival rates. These findings were supported by apoptotic nuclear evaluations of (d)-SH-SY5Y cells, alongside oxidative/inflammatory parameters in their CM. LentiVIP seems worthy of further studies for the treatment of ND because of the potential of gene therapy to treat diseases effectively with a single injection.

Gene Therapy Expressing Platelet-Derived Factor VIII for Correction of Hemophilia Α with a History of Inhibitors

Introduction: Platelet targeted gene therapy with human factor VIII has established hemostasis in murine and canine models with severe hemophilia A withouteliciting inhibitory antibodies. Here-in we describe feasibility, safety and efficacy of the first subject treated on a first-in-human phase 1 trial that targets factor FVIII synthesis and storage within platelet α-granules for delivery at the site of vascular injury for hemophilia A (NCT03818763). Method: Eligible are severe hemophilia A patients ≥18 years with a history of inhibitors to factor VIII (≥0.6 Bethesda Units [BU]/ml). Following mobilization, autologous CD 34+ cells (≥6 x 10 6/kg) are collected and transduced with a lentiviral vector encoding the ITGA2B gene promoter for ectopic expression of human B-domain-deleted factor VIII within the megakaryocyte lineage. The transduced cells are infused after reduced intensity cytoreduction with fludarabine (120 mg/m 2) and melphalan (120 mg/m 2) followed by a washout period of ≥24 hours. The primary endpoints of feasibility and safety are defined as: 1) feasibility of the cell manufacturing procedure by the availability of ≥4 x 10 6/kg transduced clinical grade CD34+cells, cell viability ≥70% and undetectable microbial contamination and 2) safety defined as hematopoietic recovery ≤28 days of infusion and absence of ≥ grade 3 toxicity (CTCAE version 5.0). Outcome: Subject 1 is a 29-year-old male with severe hemophilia A who developed inhibitors to factor VIII (2.6 BU/ml) in his first year of life. Immune tolerance to factor VIII had been established with a non-detectable inhibitor titer at enrollment. Hemostatic prophylaxis was maintained with emicizumab weekly and recombinant factor VIII for breakthrough bleeding. His annualized bleeding rate was 16 in the 12-month period preceding infusion. The cell product was the result of 1 day of collection yielding 6.73 x 10 6 /kg total viable CD34+ cells post-transduction and vector copy number by qPCR of 1.16 copies/cell. Megakaryocyte factor VIII:C levels were 0.00 mU/10 6 before transduction and 101.32 mU/10 6 after transduction. The cell product satisfied release criteria. Neutrophil recovery (≥0.5 x 10 9/L) and platelet transfusion independence (≥50 x 10 9/L) was achieved 15 days post-infusion and sustained for >12 months. The duration of hospitalization was 21 days with no re-admissions. There was no breakthrough bleeding during collection and hospitalization. During and post-infusion there was no unexpected toxicity ≥ grade 1. He has not required immune suppression. Emicizumab was discontinued 3.6 months post-infusion after demonstration of whole blood vector copy number at 1 and 3-months. There has been no spontaneous bleeding or a need for “on demand” factor VIII after discontinuing emicizumab. Secondary outcomes are summarized in Table 1. No replication competent lentivirus was detected through month 12 post-infusion. Integration site analysis was carried out, and none of the samples tested through 12 months contained cell clones which exceeded 20% relative abundance. Transduced cells were highly polyclonal. Integration site analysis showed no enrichment of integration near cancer-associated genes in the cell product nor in whole blood cell lineages post-infusion. Conclusion: We report feasibility, safety and efficacy in the first subject with severe hemophilia A and a history of inhibitors who received lentiviral vector gene therapy directed to induce megakaryocytes to synthesize and store factor VIII within platelets. These findings extend the potential to treat severe hemophilia A patients who are not eligible for valoctcogene roxaoarvovec (AAV5-hFVIII-SQ).

Exploring nutrient supplementation and bioprocess optimization to improve the production of lentiviral vectors in serum-free medium suspension cultures.

The use of lentiviral vectors (LV) in gene therapy has been growing in recent years. To meet the increasing clinical demand, LV production platforms will benefit from improved productivity and scalability to enable cost-effective manufacture of LV-based therapies. Here we report the adaptation of 293T cells to serum-free suspension cultures and the improvement of LV yields through transfection parameters optimization, process intensification and medium supplementation with nutrient boosters. Cells were sequentially adapted to different serum-free culture media, transfection parameters were optimized and the two best-performing conditions were selected to explore process intensification by increasing cell density at the time of transfection. LV production at higher cell densities increased volumetric titers up to 12-fold and lipid supplementation was the most efficient metabolic optimization strategy further enhancing LV productivity by 3-fold. Furthermore, cell concentration was identified and validated as an important source of transfection variability impairing cellular uptake of DNA polyplexes, impacting transfection efficiency and reducing LV titers down to 6-fold. This work contributes to improving LV-based gene therapy by establishing new scalable manufacturing platforms and providing key metabolic insights, unveiling important bioreaction parameters to improve vector yields.

Partial correction of immunodeficiency by lentiviral vector gene therapy in mouse models carrying Rag1 hypomorphic mutations.

Recombination activating genes (RAG) 1 and 2 defects are the most frequent form of severe combined immunodeficiency (SCID). Patients with residual RAG activity have a spectrum of clinical manifestations ranging from Omenn syndrome to delayed-onset combined immunodeficiency, often associated with granulomas and/or autoimmunity (CID-G/AI). Lentiviral vector (LV) gene therapy (GT) has been proposed as an alternative treatment to the standard hematopoietic stem cell transplant and a clinical trial for RAG1 SCID patients recently started. However, GT in patients with hypomorphic RAG mutations poses additional risks, because of the residual endogenous RAG1 expression and the general state of immune dysregulation and associated inflammation. In this study, we assessed the efficacy of GT in 2 hypomorphic Rag1 murine models (Rag1F971L/F971L and Rag1R972Q/R972Q), exploiting the same LV used in the clinical trial encoding RAG1 under control of the MND promoter. Starting 6 weeks after transplant, GT-treated mice showed a decrease in proportion of myeloid cells and a concomitant increase of B, T and total white blood cells. However, counts remained lower than in mice transplanted with WT Lin- cells. At euthanasia, we observed a general redistribution of immune subsets in tissues, with the appearance of mature recirculating B cells in the bone marrow. In the thymus, we demonstrated correction of the block at double negative stage, with a modest improvement in the cortical/medullary ratio. Analysis of antigenspecific IgM and IgG serum levels after in vivo challenge showed an amelioration of antibody responses, suggesting that the partial immune correction could confer a clinical benefit. Notably, no overt signs of autoimmunity were detected, with B-cell activating factor decreasing to normal levels and autoantibodies remaining stable after GT. On the other hand, thymic enlargement was frequently observed, although not due to vector integration and insertional mutagenesis. In conclusion, our work shows that GT could partially alleviate the combined immunodeficiency of hypomorphic RAG1 patients and that extensive efficacy and safety studies with alternative models are required before commencing RAG gene therapy in thesehighly complex patients.

Development and Validation of a Liquid Chromatography-Tandem Mass Spectrometry Method for Sensitive Analysis of Residual Protein Tat Bh1-101 in Lentiviral Vectors for Gene Therapy.

Lentiviral (LV) vector-based gene therapy is gaining popularity for treating a wide range of diseases. Various LV vectors are being developed for transducing cells in cellular gene therapy at St. Jude. Some LV vectors are produced using stable 293T packaging cell lines, which includes gag-pol-rev-tat and virus-glycoprotein. Transactivating factor (transactivator of transcription [Tat]) is a regulatory protein that drastically increases the efficiency of lentiviral transcription. Residual analysis of Tat is critical for gene vector quality and safety. In this work, we developed a highly sensitive liquid chromatography-tandem mass spectrometry method for analysis of residual Tat in Lentivirus as an alternative to enzyme-linked immunosorbent assay. Residual Tat in LV can be accurately quantified with high specificity with a limit of detection of 0.3 ng/mL.

HIV Preintegration Transcription and Host Antagonism.

Retrovirus integration is an obligatory step for the viral life cycle, but large amounts of unintegrated DNA (uDNA) accumulate during retroviral infection. For simple retroviruses, in the absence of integration, viral genomes are epigenetically silenced in host cells. For complex retroviruses such as HIV, preintegration transcription has been found to occur at low levels from a large population of uDNA even in the presence of host epigenetic silencing mechanisms. HIV preintegration transcription has been suggested to be a normal early process of HIV infection that leads to the syntheses of all three classes of viral transcripts: multiply-spliced, singly-spliced, and unspliced genomic RNA; only viral early proteins such as Nef are selectively translated at low levels in blood CD4 T cells and macrophages, the primary targets of HIV. The initiation and persistence of HIV preintegration transcription have been suggested to rely on viral accessory proteins, particularly virion Vpr and de novo Tat generated from uDNA; both proteins have been shown to antagonize host epigenetic silencing of uDNA. In addition, stimulation of latently infected resting T cells and macrophages with cytokines, PKC activator, or histone deacetylase inhibitors has been found to greatly upregulate preintegration transcription, leading to low-level viral production or even replication from uDNA. Functionally, Nef synthesized from preintegration transcription is biologically active in modulating host immune functions, lowering the threshold of T cell activation, and downregulating surface CD4, CXCR4/CCR5, and HMC receptors. The early Tat activity from preintegration transcription antagonizes repressive minichromatin assembled onto uDNA. The study of HIV preintegration transcription is important to understanding virus-host interaction and antagonism, viral persistence, and the mechanism of integrase drug resistance. The application of unintegrated lentiviral vectors for gene therapy also offers a safety advantage for minimizing retroviral vector-mediated insertional mutagenesis.

Toward lentiviral vectors for antiangiogenic ocular gene therapy

Toward lentiviral vectors for antiangiogenic ocular gene therapy

CD90-targeted lentiviral vectors for HSC gene therapy

Hematopoietic stem cell (HSC) gene therapy is currently performed on CD34+ hematopoietic stem and progenitor cells containing less than 1% true HSCs and requiring a highly specialized infrastructure for cell manufacturing and transplantation. We have previously identified the CD34+CD90+ subset to be exclusively responsible for short- and long-term engraftment. However, purification and enrichment of this subset is laborious and expensive. HSC-specific delivery agents for the direct modification of rare HSCs are currently lacking. Here, we developed novel targeted viral vectors to specifically transduce CD90-expressing HSCs. Anti-CD90 single chain variable fragments (scFvs) were engineered onto measles- and VSV-G-pseudotyped lentiviral vectors that were knocked out for native targeting. We further developed a custom hydrodynamic titration methodology to assess the loading of surface-engineered capsids, measure antigen recognition of the scFv, and predict the performance on cells. Engineered vectors formed with minimal impairment in the functional titer, maintained their ability to fuse with the target cells, and showed highly specific recognition of CD90 on cells exvivo. Most important, targeted vectors selectively transduced human HSCs with secondary colony-forming potential. Our novel HSC-targeted viral vectors have the potential to significantly enhance the feasibility of exvivo gene therapy and pave the way for future invivo applications.

Novel lentiviral vectors for gene therapy of sickle cell disease combining gene addition and gene silencing strategies

Sickle cell disease (SCD) is due to a mutation in the β-globin gene causing production of the toxic sickle hemoglobin (HbS; α2βS 2). Transplantation of autologous hematopoietic stem and progenitor cells (HSPCs) transduced with lentiviral vectors (LVs) expressing an anti-sickling β-globin (βAS) is a promising treatment; however, it is only partially effective, and patients still present elevated HbS levels. Here, we developed a bifunctional LV expressing βAS3-globin and an artificial microRNA (amiRNA) specifically downregulating βS-globin expression with the aim of reducing HbS levels and favoring βAS3 incorporation into Hb tetramers. Efficient transduction of SCD HSPCs by the bifunctional LV led to a substantial decrease of βS-globin transcripts in HSPC-derived erythroid cells, a significant reduction of HbS+ red cells, and effective correction of thesickling phenotype, outperforming βAS gene addition and BCL11A gene silencing strategies. The bifunctional LV showed a standard integration profile, and neither HSPC viability, engraftment, and multilineage differentiation nor the erythroid transcriptome and miRNAome were affected by the treatment, confirming the safety of this therapeutic strategy. In conclusion, the combination of gene addition and gene silencing strategies can improve the efficacy of current LV-based therapeutic approaches without increasing the mutagenic vector load, thus representing a novel treatment for SCD.

Improved Lentiviral In Vivo Gene Therapy for Chronic Granulomatous Disease

Background: Chronic granulomatous disease (CGD) is a congenital immunodeficiency characterized by severe life-threatening infections. CGD patients lack reactive oxygen species (ROS) in phagocytic leukocytes and often develop widespread tissue granulomas. The current treatment for CGD is lifelong antibiotic prophylaxis or hematopoietic stem cell transplantation (HSCT). However, most patients cannot find matched donors, and HSCT is known to have increased risk in CGD patients. Gene therapy has become a promising treatment for CGD. At present, "ex vivo" HSC gene therapy is the widely applied strategy. "In vivo" gene therapy is based on direct delivery of gene therapy vectors into patients, which could overcome the difficulties in HSCT. Methods: We have developed an in vivo CGD gene therapy strategy by intravenous (iv) injection of lentiviral vectors (LVs) carrying an universal EF1a promoter or a myeloid-specific miR223 promoter driving the expression of CYBB (cytochrome B-245 beta chain, or p91-phox) in X-CGD mice (X-CGD; B6.129S-Cybbtm1Din/J). Each mouse received 1x109 transduction units (TU) of LV-CYBB via iv injection after non-myeloablative conditioning. A second injection of 1x109 TU of LV-CYBB after re-conditioning was given 12 weeks later. Results: We developed a chemotherapy conditioning regimen to improve gene delivery efficiency by using busulfan, cyclophosphamide and dexamethasone. The X-CGD mice received two iv injections of LVs, and the expression and function of the LV-CYBB gene were analyzed by intracellular gp91-phox staining and DHR123 assay 4 weeks after each injection. Based on flow cytometry, we detected gp91-phox positive cells in the blood as the following, EF1a: 1.14-5.18% and 5.27-14.36%, and miR223: 1.65-5.17% and 4.59-17.89% after the first and the second injections, respectively, as compared with the WT mice: 79.9-87.6%. Functional analyses of ROS showed the following, EF1a: 1.93-5.2% and 2.39-18.51%, miR223: 2.65-6.67% and 3.75-19.8%, after the first and the second injections respectively, as compared with WT: 72.6-85.31% (Figure A). The LV vector copy number (VCN) in the peripheral blood mononuclear cells was detected by qPCR as the following, EF1a: 1.11-2.32% and 1.35-9.32%, and miR223: 1.01-2.39% and 2.71-8.51% after the first and the second injections, respectively. These results indicated that iv LV injection effectively delivered and expressed the LV-CYBB gene in vivo, and repeated injection of the LVs could increase the gene transfer efficiency in the CGD mice. Importantly, after the second injection, we found no antibody response to the LV particle-associated protein p24. However, after 3-12 months, markedly reduced VCN was found in the blood of the treated mice, suggesting exhaustion of the transgenes in the somatic cells. To improve the gene delivery into HSCs, we treated the mice with AMD3100 to mobilize HSCs into peripheral blood. The mice were treated with chemo-conditioning and AMD3100 prior to LV ivinjection. After four weeks, the gp91-phox positive HSCs of total Sca1+ HSCs in blood with or without (+/-) AMD3100 treatment were examined by flow cytometry, and the results showed the following, EF1a: (-) 9.52-15.43%, (+) 16.1-29.4%, and miR223: (-) 4.49-10.35% and (+) 7.06-16.84%. To confirm stem cell gene transfer, we transplanted the bone marrow cells from the LV-CYBB-treated CGD mice into untreated CGD mice. The VCN in blood was examined before (donor mice) and 4 weeks after (recipient mice) the HSCT, and the results showed the following, EF1a: before 4.49% (in the donor) and after 1.05-2.57% (in the recipients), and miR223: before 4.91% (in the donor) and after 1.04-2.69% (in the recipients) (Figure B). This transplantation study confirmed that the AMD3100 treatment effectively increased iv LV gene delivery into HSCs. Conclusion: We have developed an improved LV iv gene delivery strategy by applying chemo-conditioning and AMD3100 mobilization prior to the injection of the LVs into CGD mice. This in vivo LV gene therapy strategy could potentially be translated into future CGD gene therapy applications. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

In vivo lentiviral vector gene therapy to cure hereditary tyrosinemia type 1 and prevent development of precancerous and cancerous lesions

Conventional therapy for hereditary tyrosinemia type-1 (HT1) with 2-(2-nitro-4-trifluoromethylbenzoyl)−1,3-cyclohexanedione (NTBC) delays and in some cases fails to prevent disease progression to liver fibrosis, liver failure, and activation of tumorigenic pathways. Here we demonstrate cure of HT1 by direct, in vivo administration of a therapeutic lentiviral vector targeting the expression of a human fumarylacetoacetate hydrolase (FAH) transgene in the porcine model of HT1. This therapy is well tolerated and provides stable long-term expression of FAH in pigs with HT1. Genomic integration displays a benign profile, with subsequent fibrosis and tumorigenicity gene expression patterns similar to wild-type animals as compared to NTBC-treated or diseased untreated animals. Indeed, the phenotypic and genomic data following in vivo lentiviral vector administration demonstrate comparative superiority over other therapies including ex vivo cell therapy and therefore support clinical application of this approach.

Lentiviral Vectors for Ocular Gene Therapy.

This review offers the basics of lentiviral vector technologies, their advantages and pitfalls, and an overview of their use in the field of ophthalmology. First, the description of the global challenges encountered to develop safe and efficient lentiviral recombinant vectors for clinical application is provided. The risks and the measures taken to minimize secondary effects as well as new strategies using these vectors are also discussed. This review then focuses on lentiviral vectors specifically designed for ocular therapy and goes over preclinical and clinical studies describing their safety and efficacy. A therapeutic approach using lentiviral vector-mediated gene therapy is currently being developed for many ocular diseases, e.g., aged-related macular degeneration, retinopathy of prematurity, inherited retinal dystrophies (Leber congenital amaurosis type 2, Stargardt disease, Usher syndrome), glaucoma, and corneal fibrosis or engraftment rejection. In summary, this review shows how lentiviral vectors offer an interesting alternative for gene therapy in all ocular compartments.

Characterization of an immune-evading doxycycline-inducible lentiviral vector for gene therapy in the spinal cord

Gene therapy is a powerful approach to promote spinal cord regeneration. For a clinical application it is important to restrict therapeutic gene expression to the appropriate time window to limit unwanted side effects. The doxycycline (dox)-inducible system is a widely used regulatable gene expression platform, however, this system depends on a bacterial-derived immunogenic transactivator. The foreign origin of this transactivator prevents reliable regulation of therapeutic gene expression and currently limits clinical translation. The glycine-alanine repeat (GAR) of Epstein-Barr virus nuclear antigen-1 protein inhibits its presentation to cytotoxic T cells, allowing virus-infected cells to evade the host immune system. We developed a chimeric transactivator (GARrtTA) and show that GARrtTA has an immune-evading advantage over “classical” rtTA in vivo. Direct comparison of lentiviral vectors expressing rtTA and GARrtTA in the rat spinal cord shows that the GARrtTA system is inducible for 6 doxycycline-cycles over a 47 week period, whereas with the rtTA-based system luciferase reporter expression declines during the 3rd cycle and is no longer re-inducible, indicating that GARrtTA provides an immune-advantage over rtTA. Immunohistochemistry revealed that GARrtTA expressing cells in the spinal cord appear healthier and survive better than rtTA expressing cells. Characterization of the immune response shows that expression of GARrtTA, in contrast to rtTA, does not recruit cytotoxic T-cells to the transduced spinal cord. This study demonstrates that fusion of the GAR domain to rtTA results in a functional doxycycline-inducible transactivator with a clear immune-advantage over the classical rtTA in vivo.