Organ distribution of gene expression after intravenous infusion of targeted and untargeted lentiviral vectors

Current Status and Prospects of Viral Vector-Based Gene Therapy to Treat Kidney Diseases

Inherited kidney diseases are among the leading causes of chronic kidney disease, reducing the quality of life and resulting in substantial socioeconomic impact. The advent of early genetic testing and the growing understanding of the molecular basis and pathophysiology of these disorders have opened avenues for novel treatment strategies. Viral vector-based gene therapies have evolved from experimental treatments for rare diseases to potent platforms that carry the intrinsic potential to provide a cure with a single application. Several gene therapy products have reached the market, and the numbers are only expected to increase. Still, none target inherited kidney diseases. Gene transfer to the kidney has lagged when compared to other tissue-directed therapies such as hepatic, neuromuscular, and ocular tissues. Systemic delivery of genetic information to tackle kidney disease is challenging. The pharma industry is taking steps to take on kidney disease and to translate the current research into the therapeutic arena. In this review, we provide an overview of the current viral vector-based approaches and their potential. We discuss advances in platforms and injection routes that have been explored to enhance gene delivery toward kidney cells in animal models, and how these can fuel the development of viable gene therapy products for humans.

Biodistribution of lentiviral transduced adipose-derived stem cells for "ex-vivo" regional gene therapy for bone repair

Ex-vivo gene therapy has been shown to be an effective method for treating bone defects in pre-clinical models. As gene therapy is explored as a potential treatment option in humans, an assessment of the safety profile becomes an important next step. The purpose of this study was to evaluate the biodistribution of viral particles at the defect site and various internal organs in a rat femoral defect model after implantation of human ASCs transduced with lentivirus (LV) with two-step transcriptional activation (TSTA) of bone morphogenetic protein-2 (LV-TSTA-BMP-2). Animals were sacrificed at 4-, 14-, 56-, and 84-days post implantation. The defects were treated with either a standard dose (SD) of 5 million cells or a high dose (HD) of 15 million cells to simulate a supratherapeutic dose. Treatment groups included (1) SD LV-TSTA-BMP-2 (2) HD LV-TSTA-BMP-2, (3) SD LV-TSTA-GFP (4) HD LV-TSTA-GFP and (5) SD nontransduced cells. The viral load at the defect site and ten organs was assessed at each timepoint. Histology of all organs, ipsilateral tibia, and femur were evaluated at each timepoint. There were nearly undetectable levels of LV-TSTA-BMP-2 transduced cells at the defect site at 84-days and no pathologic changes in any organ at all timepoints. In conclusion, human ASCs transduced with a lentiviral vector were both safe and effective in treating critical size bone defects in a pre-clinical model. These results suggest that regional gene therapy using lentiviral vector to treat bone defects has the potential to be a safe and effective treatment in humans.

In vivo macrophage engineering reshapes the tumor microenvironment leading to eradication of liver metastases

Liver metastases are associated with poor response to current pharmacological treatments, including immunotherapy. We describe a lentiviral vector (LV) platform to selectively engineer liver macrophages, including Kupffer cells and tumor-associated macrophages (TAMs), to deliver type I interferon (IFNα) to liver metastases. Gene-based IFNα delivery delays the growth of colorectal and pancreatic ductal adenocarcinoma liver metastases in mice. Response to IFNα is associated with TAM immune activation, enhanced MHC-II-restricted antigen presentation and reduced exhaustion of CD8+ T cells. Conversely, increased IL-10 signaling, expansion of Eomes CD4+ T cells, a cell type displaying features of type I regulatory T (Tr1) cells, and CTLA-4 expression are associated with resistance to therapy. Targeting regulatory T cell functions by combinatorial CTLA-4 immune checkpoint blockade and IFNα LV delivery expands tumor-reactive T cells, attaining complete response in most mice. These findings support a promising therapeutic strategy with feasible translation to patients with unmet medical need.

Generation of Stable Cell Lines Expressing Golgi Reassembly Stacking Proteins (GRASPs) by Viral Transduction

Stable cell lines that express a gene of specific interest provide an advantage over transient gene expression by reducing variations in transfection efficiency between experiments, sustaining expression for long-term studies, and controlling expression levels in particular if a clonal population is selected. Transient transfection requires introduction of an exogenous gene into host cells via typically harsh chemicals or conditions that permeabilize the cell membrane, which does not normally integrate into the target cell genome. Here, we describe the method of using retroviral transduction to stably express Golgi proteins fused to a promiscuous biotin ligase (TurboID) in HeLa cells, thus creating cell lines that can be leveraged in studies of the proximome/interactome. We also demonstrate a similar protocol for stable expression of a Golgi protein fused to a fluorescent tag via lentiviral transduction. These methods can be further adapted to establish other cell lines with different sub-cellular markers or fusion tags. Viral transduction is a convenient method to create stable cell lines in cell-based studies.

Incisionless targeted adeno-associated viral vector delivery to the brain by focused ultrasound-mediated intranasal administration

Background

Adeno-associated viral (AAV) vectors are currently the leading platform for gene therapy with the potential to treat a variety of central nervous system (CNS) diseases. There are numerous methods for delivering AAVs to the CNS, such as direct intracranial injection (DI), intranasal delivery (IN), and intravenous injection with focused ultrasound-induced blood–brain barrier disruption (FUS-BBBD). However, non-invasive and efficient delivery of AAVs to the brain with minimal systemic toxicity remain the major challenge. This study aims to investigate the potential of focused ultrasound-mediated intranasal delivery (FUSIN) in AAV delivery to brain.

Methods

Mice were intranasally administered with AAV5 encoding enhanced green fluorescence protein (AAV5-EGFP) followed by FUS sonication in the presence of systemically injected microbubbles. Mouse brains and other major organs were harvested for immunohistological staining, PCR quantification, and in situ hybridization. The AAV delivery outcomes were compared with those of DI, FUS-BBBD, and IN delivery.

Findings

FUSIN achieved safe and efficient delivery of AAV5-EGFP to spatially targeted brain locations, including a superficial brain site (cortex) and a deep brain region (brainstem). FUSIN achieved comparable delivery outcomes as the established DI, and displayed 414.9-fold and 2073.7-fold higher delivery efficiency than FUS-BBBD and IN. FUSIN was associated with minimal biodistribution in peripheral organs, which was comparable to that of DI.

Interpretation

Our results suggest that FUSIN is a promising technique for non-invasive, efficient, safe, and spatially targeted AAV delivery to the brain.

Funding

National Institutes of Health (NIH) grants R01EB027223, R01EB030102, R01MH116981, and UG3MH126861.

Changes in Myonuclear Number During Postnatal Growth -Implications for AAV Gene Therapy for Muscular Dystrophy

Adult skeletal muscle is a relatively stable tissue, as the multinucleated muscle fibres contain post-mitotic myonuclei. During early postnatal life, muscle growth occurs by the addition of skeletal muscle stem cells (satellite cells) or their progeny to growing muscle fibres. In Duchenne muscular dystrophy, which we shall use as an example of muscular dystrophies, the muscle fibres lack dystrophin and undergo necrosis. Satellite-cell mediated regeneration occurs, to repair and replace the necrotic muscle fibres, but as the regenerated muscle fibres still lack dystrophin, they undergo further cycles of degeneration and regeneration.AAV gene therapy is a promising approach for treating Duchenne muscular dystrophy. But for a single dose of, for example, AAV coding for dystrophin, to be effective, the treated myonuclei must persist, produce sufficient dystrophin and a sufficient number of nuclei must be targeted. This latter point is crucial as AAV vector remains episomal and does not replicate in dividing cells. Here, we describe and compare the growth of skeletal muscle in rodents and in humans and discuss the evidence that myofibre necrosis and regeneration leads to the loss of viral genomes within skeletal muscle. In addition, muscle growth is expected to lead to the dilution of the transduced nuclei especially in case of very early intervention, but it is not clear if growth could result in insufficient dystrophin to prevent muscle fibre breakdown. This should be the focus of future studies.

Gene therapy research for kidney diseases

A resurgence in the development of newer gene therapy systems has led to recent successes in the treatment of B cell cancers, retinal degeneration and neuromuscular atrophy. Gene therapy offers the ability to treat the patient at the root cause of their malady by restoring normal gene function and arresting the pathological progression of their genetic disease. The current standard of care for most genetic diseases is based upon the symptomatic treatment with polypharmacy while minimizing any potential adverse effects attributed to the off-target and drug-drug interactions on the target or other organs. In the kidney, however, the development of gene therapy modifications to specific renal cells has lagged far behind those in other organ systems. Some positive strides in the past few years provide continued enthusiasm to invest the time and effort in the development of new gene therapy vectors for medical intervention to treat kidney diseases. This mini-review will systematically describe the pros and cons of the most commonly tested gene therapy vector systems derived from adenovirus, retrovirus, and adeno-associated virus and provide insight about their potential utility as a therapy for various types of genetic diseases in the kidney.

Reg3g overexpression promotes β cell regeneration and induces immune tolerance in nonobese-diabetic mouse model

The regenerating islet-derived gene was first isolated in regenerated pancreas tissues, greatly contributing to β cell regeneration. It is an anti-inflammatory in response to cellular stress. This encouraged us to investigate the exact role of a novel member of Reg family, regenerating islet-derived gene γ, in type 1 diabetes of nonobese-diabetic mice. For this, Reg3g gene was overexpressed in pancreatic islets, and conferred beneficial effects on β cell regeneration through activating the Janus kinase 2/signal transducer and activator of transcription 3/nuclear factor κB signaling pathway. Lentiviral vector-encoding regenerating islet-derived gene γ treatment also decreased lymphocyte infiltrates of the intra-islet and peri-islet by inducing both differentiation of regulatory T cell and immature dendritic cells of tolerogenic properties, which attenuated autoimmunity. This treatment further contributed to rebalanced levels of type 1/2 helper T cell cytokines and elevated α1-antitrypsin levels in the serum. These results were not observed in phosphate-buffered saline-treated mice or in lentivirus-control mice. We have shown, for the first time, to our knowledge, that regenerating islet-derived gene γ promotes β cell regeneration and preserves β cells from autoimmunity damage by increasing regulatory T cell differentiation and inducing tolerated dendritic cells. This regenerating islet-derived gene γ infusion could probably be developed into an optimal gene therapy for the prevention and reversal of type 1 diabetes.

Gene therapy for the nervous system: challenges and new strategies

Current clinical treatments for central nervous system (CNS) diseases, such as Parkinson's disease and glioblastoma do not halt disease progression and have significant treatment morbidities. Gene therapy has the potential to "permanently" correct disease by bringing in a normal gene to correct a mutant gene deficiency, knocking down mRNA of mutant alleles, and inducing cell-death in cancer cells using transgenes encoding apoptosis-inducing proteins. Promising results in clinical trials of eye disease (Leber's congenital aumorosis) and Parkinson's disease have shown that gene-based neurotherapeutics have great potential. The recent development of genome editing technology, such as zinc finger nucleases, TALENS, and CRISPR, has made the ultimate goal of gene correction a step closer. This review summarizes the challenges faced by gene-based neurotherapeutics and the current and recent strategies designed to overcome these barriers. We have chosen the following challenges to focus on in this review: (1) delivery vehicles (both virus and nonviral), (2) use of promoters for vector-mediated gene expression in CNS, and (3) delivery across the blood-brain barrier. The final section (4) focuses on promising pre-clinical/clinical studies of neurotherapeutics.

Ablation of nectin4 binding compromises CD46 usage by a hybrid vesicular stomatitis virus/measles virus

Measles virus (MV) immunosuppression is due to infection of SLAM-positive immune cells, whereas respiratory shedding and virus transmission are due to infection of nectin4-positive airway epithelial cells. The vaccine lineage MV strain Edmonston (MV-Edm) acquired an additional tropism for CD46 which is the basis of its oncolytic specificity. VSVFH is a vesicular stomatitis virus (VSV) encoding the MV-Edm F and H entry proteins in place of G. The virus spreads faster than MV-Edm and is highly fusogenic and a potent oncolytic. To determine whether ablating nectin4 tropism from VSVFH might prevent shedding, increasing its safety profile as an oncolytic, or might have any effect on CD46 binding, we generated VSVFH viruses with H mutations that disrupt attachment to SLAM and/or nectin4. Disruption of nectin4 binding reduced release of VSVFH from the basolateral side of differentiated airway epithelia composed of Calu-3 cells. However, because nectin4 and CD46 have substantially overlapping receptor binding surfaces on H, disruption of nectin4 binding compromised CD46 binding and greatly diminished the oncolytic potency of these viruses on human cancer cells. Thus, our results support continued preclinical development of VSVFH without ablation of nectin4 binding.

A new dual-promoter system for cardiomyocyte-specific conditional induction of apoptosis

Apoptosis is a key determinant of major pathological processes, including chronic cardiac failure. We developed and tested in vitro a novel system to induce cardiomyocyte-specific apoptosis by virus-mediated delivery of a conditional transgene. The entire system was packaged in a lentiviral vector. We used the cardiomyocyte-specific Na⁺-Ca²⁺ exchange promoter to control the transcription of the reverse tetracycline transactivator, while the transgene expression was driven by the tetracycline-responsive element. The proapoptotic transgene of choice was the short isoform of the apoptosis-inducing factor, known to quickly induce the caspase-independent apoptosis when overexpressed in cells. Transduction of cardiomyocyte cells with this vector caused a tetracycline-regulated induction of apoptosis, which was not observed in noncardiac cells. Therefore, our system proved a valuable molecular tool for inducing controlled apoptosis in selected cells. Furthermore, the vector we developed is suitable for “lentivirus transgenesis,” an interesting strategy recently proposed for the genetic manipulation of animals other than mice, including large mammals.

Optimizing patient derived mesenchymal stem cells as virus carriers for a phase I clinical trial in ovarian cancer

Background

Mesenchymal stem cells (MSC) can serve as carriers to deliver oncolytic measles virus (MV) to ovarian tumors. In preparation for a clinical trial to use MSC as MV carriers, we obtained cells from ovarian cancer patients and evaluated feasibility and safety of this approach.

Methods

MSC from adipose tissues of healthy donors (hMSC) and nine ovarian cancer patients (ovMSC) were characterized for susceptibility to virus infection and tumor homing abilities.

Results

Adipose tissue (range 0.16-3.96 grams) from newly diagnosed and recurrent ovarian cancer patients yielded about 7.41×10⁶ cells at passage 1 (range 4–9 days). Phenotype and doubling times of MSC were similar between ovarian patients and healthy controls. The time to harvest of 3.0×10⁸ cells (clinical dose) could be achieved by day 14 (range, 9–17 days). Two of nine samples tested had an abnormal karyotype represented by trisomy 20. Despite receiving up to 1.6×10⁹ MSC/kg, no tumors were seen in SCID beige mice and MSC did not promote the growth of SKOV3 human ovarian cancer cells in mice. The ovMSC migrated towards primary ovarian cancer samples in chemotaxis assays and to ovarian tumors in athymic mice. Using non-invasive SPECT-CT imaging, we saw rapid co-localization, within 5–8 minutes of intraperitoneal administration of MV infected MSC to the ovarian tumors. Importantly, MSC can be pre-infected with MV, stored in liquid nitrogen and thawed on the day of infusion into mice without loss of activity. MV infected MSC, but not virus alone, significantly prolonged the survival of measles immune ovarian cancer bearing animals.

Conclusions

These studies confirmed the feasibility of using patient derived MSC as carriers for oncolytic MV therapy. We propose an approach where MSC from ovarian cancer patients will be expanded, frozen and validated to ensure compliance with the release criteria. On the treatment day, the cells will be thawed, washed, mixed with virus, briefly centrifuged and incubated for 2 hours with virus prior to infusion of the virus/MSC cocktail into patients.

PolyIC GE11 polyplex inhibits EGFR-overexpressing tumors

Phage display has identified the dodecapeptide YHWYGYTPQNVI (GE11) as a ligand that binds to the epidermal growth factor receptor (EGFR) but does not activate the receptor. Here, we compare the EGFR binding affinities of GE11, EGF, and their polyethyleneimine-polyethyleneglycol (PEI-PEG) conjugates. We found that although GE11 by itself does not exhibit measurable affinity to the EGFR, tethering it to PEI-PEG increases its affinity markedly, and complex formation with polyinosine/cytosine (polyIC) further enhances the affinity to the submicromolar range. PolyIC/PPGE11 has a similar strong antitumor effect against EGFR overexpressing tumors in vitro and in vivo, as polyIC/polyethyleneimine-polyetheleneglycol-EGF (polyIC/PP-EGF). Absence of EGFR activation, as previously shown by us and easier production of GE11 and GE11 conjugates, confer polyIC/PPGE11 a significant advantage over similar EGF-based polyplexes as a potential therapy of EGFR overexpressing tumors.

Disconnecting the yin and yang relation of epidermal growth factor receptor (EGFR)-mediated delivery: a fully synthetic, EGFR-targeted gene transfer system avoiding receptor activation

The epidermal growth factor receptor (EGFR) is upregulated within a high percentage of solid tumors and hence is an attractive target for tumor-targeted therapies including gene therapy. The natural EGFR ligand epidermal growth factor (EGF) has been used for this purpose, despite the risk of mitogenic effects due to EGFR activation. We have developed a fully synthetic, EGFR-targeted gene delivery system based on PEGylated linear polyethylenimine (LPEI), allowing evaluation of different EGFR-binding peptides in terms of transfection efficiency and EGFR activation. Peptide sequences directly derived from the human EGF molecule enhanced transfection efficiency with concomitant EGFR activation. Only the EGFR-binding peptide GE11, which has been identified by phage display technique, showed specific enhancement of transfection on EGFR-overexpressing tumor cells including glioblastoma and hepatoma, but without EGFR activation. EGFR targeting led to high levels of cell association of fluorescently labeled polyplexes after only 30 min of incubation. EGF pretreatment of cells induced enhanced cellular internalization of all polyplex types tested, pointing at generally enhanced macropinocytosis. EGF polyplexes diminished cell surface expression of EGFR for up to 4 hr, whereas GE11 polyplexes did not. In a clinically relevant orthotopic prostate cancer model, intratumorally injected GE11 polyplexes were superior in inducing transgene expression when compared with untargeted polyplexes.

Targeted gene therapy for the treatment of heart failure

Chronic heart failure is one of the leading causes of morbidity and mortality in Western countries and is a major financial burden to the health care system. Pharmacologic treatment and implanting devices are the predominant therapeutic approaches. They improve survival and have offered significant improvement in patient quality of life, but they fall short of producing an authentic remedy. Cardiac gene therapy, the introduction of genetic material to the heart, offers great promise in filling this void. In-depth knowledge of the underlying mechanisms of heart failure is, obviously, a prerequisite to achieve this aim. Extensive research in the past decades, supported by numerous methodological breakthroughs, such as transgenic animal model development, has led to a better understanding of the cardiovascular diseases and, inadvertently, to the identification of several candidate genes. Of the genes that can be targeted for gene transfer, calcium cycling proteins are prominent, as abnormalities in calcium handling are key determinants of heart failure. A major impediment, however, has been the development of a safe, yet efficient, delivery system. Nonviral vectors have been used extensively in clinical trials, but they fail to produce significant gene expression. Viral vectors, especially adenoviral, on the other hand, can produce high levels of expression, at the expense of safety. Adeno-associated viral vectors have emerged in recent years as promising myocardial gene delivery vehicles. They can sustain gene expression at a therapeutic level and maintain it over extended periods of time, even for years, and, most important, without a safety risk.

Tumor-specific imaging through progression elevated gene-3 promoter-driven gene expression

Molecular-genetic imaging is advancing from a valuable preclinical tool to guiding patient management. The strategy involves pairing an imaging reporter gene with a complementary imaging agent in a system that can be used to measure gene expression, protein interaction or track gene-tagged cells in vivo. Tissue-specific promoters can be used to delineate gene expression in certain tissues, particularly when coupled with an appropriate amplification mechanism. Here we show that the progression elevated gene-3 promoter (PEG-Prom), derived from a rodent gene mediating the malignant phenotype, can be used to drive imaging reporters selectively to enable detection of micrometastatic disease in murine models of human melanoma and breast cancer using bioluminescence and radionuclide-based molecular imaging techniques. Because of its strong promoter, tumor specificity and capacity for clinical translation, PEG-Prom-driven gene expression may represent a practical, new system for facilitating cancer imaging and therapy.

Viral vectors: from virology to transgene expression

In the late 1970s, it was predicted that gene therapy would be applied to humans within a decade. However, despite some success, gene therapy has still not become a routine practise in medicine. In this review, we will examine the problems, both experimental and clinical, associated with the use of viral material for transgenic insertion. We shall also discuss the development of viral vectors involving the most important vector types derived from retroviruses, adenoviruses, herpes simplex viruses and adeno-associated viruses.

Lentiviral vectors transduce proliferating dendritic cell precursors leading to persistent antigen presentation and immunization

Lentiviral vectors (LVs) are tools for in vivo gene delivery, to correct genetic defects or to deliver antigens for vaccination. It was reported that systemic injection of LVs in mice transduced cells in liver and spleen. Here we describe the reasons for, and consequences of, persistent gene expression in spleen. After 5 days of intravenous injection, a green fluorescence protein (GFP)-expressing LV was detected in lymphocytes, macrophages and all subsets of dendritic cells (DCs) in spleen. In the case of macrophages and DCs, the percentage of transduced cells increased between 5 and 30 days after injection. We used bromodeoxyuridine (BrdU) incorporation to show that the macrophages were largely nondividing, whereas the transduced DCs arose from dividing precursor cells and could be detected in spleen 2 months after injection. Expression of ovalbumin (OVA) in the LV reduced the number of transduced DCs in spleen after 30 days. However, the remaining transduced cells stimulated proliferation and activation of OVA-specific CD8(+) T cells transferred 2 months after LV injection. The mice also maintained cytolytic activity against OVA-pulsed targets. These results show that LVs transduce DC precursors, which maintain transduced DCs in spleen for at least 2 months, leading to prolonged antigen presentation and effective T-cell memory.

Measles virus for cancer therapy

Measles virus offers an ideal platform from which to build a new generation of safe, effective oncolytic viruses. Occasional so-called spontaneous tumor regressions have occurred during natural measles infections, but common tumors do not express SLAM, the wild-type MV receptor, and are therefore not susceptible to the virus. Serendipitously, attenuated vaccine strains of measles virus have adapted to use CD46, a regulator of complement activation that is expressed in higher abundance on human tumor cells than on their nontransformed counterparts. For this reason, attenuated measles viruses are potent and selective oncolytic agents showing impressive antitumor activity in mouse xenograft models. The viruses can be engineered to enhance their tumor specificity, increase their antitumor potency, and facilitate noninvasive in vivo monitoring of their spread. A major impediment to the successful deployment of oncolytic measles viruses as anticancer agents is the high prevalence of preexisting anti-measles immunity, which impedes bloodstream delivery and curtails intratumoral virus spread. It is hoped that these problems can be addressed by delivering the virus inside measles-infected cell carriers and/or by concomitant administration of immunosuppressive drugs. From a safety perspective, population immunity provides an excellent defense against measles spread from patient to carers and, in 50 years of human experience, reversion of attenuated measles to a wild-type pathogenic phenotype has not been observed. Clinical trials testing oncolytic measles viruses as an experimental cancer therapy are currently underway.

Lentiviruses in cancer immunotherapy

Lentiviral vectors have emerged as promising tools for cancer immunotherapy owing to their capacity to transduce a wide range of different cell types, including dendritic cells (DCs), the key regulators of immunity. Ex vivo transduced DCs proved to be potent inducers of strong antigen-specific T-cell responses, both in vitro and in vivo. Moreover, lentiviral vectors have been successfully applied for antigen-specific immunization, offering the advantage that the same lentivirus can be used for all patients resulting in an ‘off-the-shelf’ therapeutic. This review provides an update on the state-of-the-art induction of tumor-specific immune responses in vivo upon direct administration of tumor-associated antigen-encoding lentiviruses. Focusing on the cell types transduced, the results of current studies and the explanation for the potency of lentiviral vectors are discussed.

Engineering targeted viral vectors for gene therapy

Translating knowledge of genetic disease mechanisms into gene therapies has been slow with limited clinical success. One major reason is that the transfer vectors, which are most often of viral origin, are not targeted sufficiently towards the cells of interest.

To achieve successful delivery of genetic material, transductional targeting is often essential to enter the target cell and to avoid side effects from the transduction of non-target cells.

Many techniques to target viral vectors to specific cells have been developed. They can be divided into three types: systems that use adaptor proteins from other viruses (pseudotyping); systems that use adaptors to couple the targeting ligand to the vector; and systems that genetically incorporate the targeting moiety into the viral genome.

Whereas systems involving adaptor proteins are highly useful in preclinical evaluations, systems that make use of genetically incorporated targeting ligands are advantageous for clinical applications.

Combinations of several targeting principles (including ablation of natural tropism, pseudotyping and adaptors) and novel combinations (such as the adeno-associated virus (AAV) genome in a phage vector) allow systemic vector application.

An initial clinical study with a targeted retrovirus showed feasibility to transfer laboratory success to patient application, underlining that there are no principal regulatory barriers for targeted vectors.

Systemic vector applications will be facilitated by enabling the vector to move beyond the vascular endothelium at specific sites, using transcytosis or cellular vehicles. The application of existing targeting techniques to new viral vector serotypes and new vector classes is extending the therapeutic capabilities further.

Obstacles to systemic application of vectors are found in the blood as immune reactions against the vector and as binding of blood proteins to the vector. Some targeting approaches might have the potential to circumvent these obstacles.

To preclinically evaluate new targeting strategies, several models that reflect the human situation to varying degrees are available. The use of primary cells, tissue-slice systems and transgenic animals seems to be especially promising.

Imaging technologies provide the ability to monitor the vector in vivo in real time without sacrificing the animal model. These techniques facilitate vector targeting and biodistribution studies.

A key challenge in gene therapy is vector targeting to specific cells, while avoiding effects on other tissues. Several strategies have been developed recently to enable targeting of the main viral vectors, moving them a step closer to clinical use.

To achieve therapeutic success, transfer vehicles for gene therapy must be capable of transducing target cells while avoiding impact on non-target cells. Despite the high transduction efficiency of viral vectors, their tropism frequently does not match the therapeutic need. In the past, this lack of appropriate targeting allowed only partial exploitation of the great potential of gene therapy. Substantial progress in modifying viral vectors using diverse techniques now allows targeting to many cell types in vitro. Although important challenges remain for in vivo applications, the first clinical trials with targeted vectors have already begun to take place.

G-CSF-lentivirus administration in rats provided sustained elevated neutrophil counts and subsequent EPO-lentivirus administration increased hematocrits

BACKGROUND

Towards gene therapy treatment of patients with neutropenia, characterized by neutrophil counts < 500 cells/microl, we investigated the ability of lentivirus vectors to provide sustained granulocyte colony-stimulating factor (G-CSF) delivery and to permit transgene expression from a second virus administration in a preclinical rat model.

METHODS

Rats were injected intramuscularly (IM) with 24 x 10(6) and 9 x 10(6) infectious units (IU) of a VSV-G-pseudotyped self-inactivating (SIN) lentivirus encoding rat G-CSF cDNA and containing cPPT and PRE elements. To determine the effectiveness of a second virus administration treated rats and a naïve rat received erythropoietin (EPO)-lentivirus IM. Rats were monitored for neutrophil and red blood cell production. Lentivirus antibodies were assayed by virus-neutralizing assay and ELISA.

RESULTS

High and low dose virus administration increased neutrophil counts to 5660 +/- 930 cells/microl (mean +/- SD) and 4010 +/- 850 cells/microl, respectively, that were sustained for > 17 months and were significantly higher than controls counts of 1890 +/- 570 cells/microl (p< or =0.0002). Rats treated with EPO-virus produced significantly increased hematocrits (HCT) (63.1 +/- 4.3% vs. 46.0 +/- 3.2%, p < 0.0001) without effect on G-CSF-virus-mediated neutrophil production. Antivirus antibodies were not detectable at serum dilutions > or =1:10 by virus neutralization or ELISA. Lymphocytes and platelets were not significantly different between control and treated animals (p > 0.1). Only genomic DNA from muscle at injection sites was positive for provirus suggesting lack of virus spread.

CONCLUSIONS

G-CSF-lentivirus administered IM provided elevated, sustained neutrophil counts that were unchanged by subsequent EPO-lentivirus administration. Significantly increased hematocrits were obtained following EPO-lentivirus delivery. These data support the treatment of patients with severe chronic neutropenia by dosed lentivirus delivery IM.

Bioluminescence imaging of systemic tumor targeting using a prostate-specific lentiviral vector

Developments in vector design using tissue-specific and tumor-specific promoters have led to significant improvements in tumor-targeting strategies. These developments combined with the ability to monitor gene expression by molecular imaging have facilitated the detection and prolonged monitoring of disease progression in small-animal models. Bioluminescence imaging offers a convenient and sensitive platform for monitoring gene expression patterns in preclinical models of gene therapy. Targeting a specific subset of cells/tissues via systemic delivery of vectors would be highly beneficial in gene therapy protocols. Using a two-step transcriptional amplification (TSTA)-based lentiviral vector (LV-TSTA), we demonstrate specific targeting of prostate tumors in vivo after systemic administration of lentivirus. Four days after intravenous administration of LV-TSTA into adult severe combined immunodeficient (SCID) mice (n=5) carrying subcutaneous prostate tumors, we found significant levels of transduction at the tumor site when compared with other organs (p<0.05). Gene expression was sustained in the tumor for up to 3 weeks (7.3x10(4)+/-2x10(4) photons/ sec/cm2/steradian (p/sec/cm2/sr) on day 4 and 7.0x10(4)+/-4x10(4) p/sec/cm2/sr on day 21). Low levels of transduction were also observed in the spleen and liver (5.0x10(2)+/-1.7x10(2) p/sec/cm2/sr). The results from this study support the use of TSTA-based lentiviral vectors for prostate tumor targeting after systemic delivery. Noninvasive imaging using such vectors should be useful for monitoring long-term gene expression in gene therapy applications.

Prolonged adherence of human immunodeficiency virus-derived vector particles to hematopoietic target cells leads to secondary transduction in vitro and in vivo

Human immunodeficiency virus type 1-derived lentivirus vectors bearing the vesicular stomatitis virus G (VSV-G) envelope glycoprotein demonstrate a wide host range and can stably transduce quiescent hematopoietic stem cells. In light of concerns about biosafety and potential germ line transmission, they have been used predominantly for ex vivo strategies, thought to ensure the removal of excess surface-bound particles and prevent in vivo dissemination. Studies presented here instead reveal prolonged particle adherence after ex vivo exposure, despite serial wash procedures, with subsequent transduction of secondary target cells in direct and transwell cocultures. We explored the critical parameters affecting particle retention and transfer and show that attachment to the cell surface selectively protects virus particles from serum complement-mediated inactivation. Moreover, studies with nonmyeloablated murine recipients show that transplantation of vector-exposed, washed hematopoietic cells results in systemic dissemination of functional VSV-G/lentivector particles. We demonstrate genetic marking by inadvertent transfer of vector particles and prolonged expression of transgene product in recipient tissues. Our findings have implications for biosafety, vector design, and cell biology research.

Lentiviral gene delivery to CNS by spinal intrathecal administration to neonatal mice

BACKGROUND

Direct injection of lentivectors into the central nervous system (CNS) mostly results in localized parenchymal transgene expression. Intrathecal gene delivery into the spinal canal may produce a wider dissemination of the transgene and allow diffusion of secreted transgenic proteins throughout the cerebrospinal fluid (CSF). Herein, we analyze the distribution and expression of LacZ and SEAP transgenes following the intrathecal delivery of lentivectors into the spinal canal.

METHODS

Four weeks after intrathecal injection into the spinal canal of newborn mice, the expression of the LacZ gene was assessed by histochemical staining and by in situ polymer chain reaction (PCR). Following the spinal infusion of a lentivector carrying the SEAP gene, levels of enzymatically active SEAP were measured in the CSF, blood serum, and in brain extracts.

RESULTS

Intrathecal spinal canal delivery of lentivectors to newborn mice resulted in patchy, widely scattered areas of beta-gal expression mostly in the meninges. The transduction of the meningeal cells was confirmed by in situ PCR. Following the spinal infusion of a lentivector carrying the SEAP gene, sustained presence of the reporter protein was detected in the CSF, as well as in blood serum, and brain extracts.

CONCLUSIONS

These findings indicate that intrathecal injections of lentivectors can provide significant levels of transgene expression in the meninges. Unlike intracerebral injections of lentivectors, intrathecal gene delivery through the spinal canal appears to produce a wider diffusion of the transgene. This approach is less invasive and may be useful to address those neurological diseases that benefit from the ectopic expression of soluble factors impermeable to the blood-brain barrier.

Targeted retroviral vectors displaying a cleavage site-engineered hemagglutinin (HA) through HA-protease interactions

We report here a targeting method that exploits the expression pattern of cell surface proteases to induce gene delivery to specific tissues. We describe retroviral vectors harboring modified surface glycoproteins derived from an avian influenza virus hemagglutinin (HA) for which the cell entry properties, dependent on HA cleavage by producer cells, were conditionally blocked at a postbinding step by insertion of matrix metalloproteinase (MMP) substrates. We demonstrate that such vectors induce gene transfer, both in vitro and in mice harboring human tumor xenografts, only through contact with target cells expressing MMPs that cleave the substrate introduced into the recombinant HA. This selective gene transfer in MMP-rich cells was specifically inhibited by 1,10-phenanthroline, a broad-range MMP inhibitor. Importantly, such MMP-activatable vectors selectively transduced MMP-rich cells in heterogeneous populations containing MMP-rich and MMP-poor cells. These vectors will allow useful gene transfer applications into target cells exhibiting specific protease activities.

Real-time quantitative PCR for the design of lentiviral vector analytical assays

From the recent and emerging concerns for approving lentiviral vector-mediated gene transfer in human clinical applications, several analytical methods have been applied in preclinical models to address the lentiviral vector load in batches, cells or tissues. This review points out the oldest generation methods (blots, RT activity, standard PCR) as well as a full description of the newest real-time quantitative PCR (qPCR) applications. Combinations of primer and probe sequences, which have worked in the lentiviral amplification context, have been included in the effort to dress an exhaustive list. Also, great variations have been observed from interlaboratory results, we have tempted to compare between them the different analytical methods that have been used to consider (i) the titration of lentiviral vector batches, (ii) the absence of the susceptible emerging replicative lentiviruses or (iii) the lentiviral vector biodistribution in the organism.

VP22 does not significantly enhance enzyme prodrug cancer gene therapy as a part of a VP22-HSVTk-GFP triple fusion construct

BACKGROUND

VP22 is a herpes simplex virus type 1 (HSV-1) tegument protein that has been suggested to spread from cell to cell, alone or as a part of fusion proteins. Creating controversy, some reports indicate that VP22 cannot facilitate significant intercellular spreading. To study the capacity of VP22 to cause spreading and enhance thymidine kinase/ganciclovir cancer gene therapy, we constructed a novel triple fusion protein containing VP22, HSV thymidine kinase and green fluorescent protein (VP22-Tk-GFP). This fusion protein has three functional domains in the same polypeptide, thus making it possible to reliably compare the causality between transduction rate and cell killing efficiency in vitro and in vivo.

METHODS

VP22-Tk-GFP was cloned into lenti- and adenoviral vectors and used for expression studies, analyses for VP22-mediated protein spreading, and to study the effect of VP22 to thymidine kinase/ganciclovir-mediated cytotoxicity. The function of VP22-Tk-GFP was also investigated in vivo.

RESULTS

The triple fusion protein was expressed correctly in vitro, but intercellular trafficking was not observed in any of the studied cell lines. However, under certain conditions, VP22-Tk-GFP sensitized cells more efficiently to ganciclovir than Tk-GFP. In vivo there was a trend for increased inhibition of tumor growth with VP22-Tk-GFP when ganciclovir was present, but the difference with Tk-GFP was not statistically significant.

CONCLUSIONS

Based on our results, VP22 fusion proteins do not seem to traffic intercellularly at detectable levels in most tumor cell types. Even though VP22 enhanced cytotoxicity in one cell line in vitro, the effect in vivo was modest. Therefore, our results do not support the utility of VP22 as an enhancer of enzyme prodrug cancer gene therapy.

Efficient Tet-Dependent Expression of Human Factor IX in Vivo by a New Self-Regulating Lentiviral Vector

Regulation of gene expression represents a long-sought goal of gene therapy. However, most viral vectors pose constraints on the incorporation of drug-dependent transcriptional regulatory systems. Here, by optimizing the design of self-regulating lentiviral vectors based on the tetracycline system, we have been able to overcome the limitations of previously reported constructs and to reach both robust expression and efficient regulation from a single vector. The improved performance allows us to report for the first time effective long-term in vivo regulation of a human clotting Factor IX (hF.IX) transgene upon systemic administration of a single vector to SCID mice. We showed that hF.IX expression in the plasma could be expressed to therapeutically significant concentrations, adjusted to different set levels by varying the tetracycline dose, rapidly turned off and on, and completely recovered after each treatment cycle. The new vector design was versatile, as it successfully incorporated a tissue-specific promoter that selectively targeted regulated expression to hepatocytes. Robust transgene expression in the systemic circulation coupled to the ability to switch off and even adjust the expression level may open the way to safer gene-based delivery of therapeutics.

Newborn liver gene transfer by an HIV-2-based lentiviral vector

Newborn gene therapy, because it can prevent the damage caused by the onset of a disease, deserves specific attention. To evaluate gene transfer in tissues of newborn mice, we used a human immunodeficiency virus (HIV)-2 based lentiviral vector pseudotyped with vesicular stomatitis virus G glycoprotein expressing the green fluorescent protein reporter gene under the control of the cytomegalovirus promoter. We found that very low doses of HIV-2 could infect and be expressed in newborn mice. Under these conditions, the virus was preferentially expressed in the liver and hepatocytes were the predominant target. The treatment was not toxic, the infected liver cells proliferated and the transduced gene was stably expressed. Adult mice could be infected by HIV-2, but the vector was detected in the liver only utilizing the sensitive method of polymerase chain reaction coupled with Southern blot. Direct comparison between newborn and adult recipients demonstrated a much greater efficiency of liver transduction in the newborn mouse. These results indicate that the combination of early intervention and low multiplicity of infection may be a strategy for preferentially and efficiently targeting newborn liver for gene therapy applications.

Transduction of human glial and neuronal tumor cells with different lentivirus vector pseudotypes

Lentiviral vectors have proven to be valuable tools for in vitro and in vivo gene delivery because they can transduce dividing and non-dividing cells efficiently, and mediate long-term gene expression. Pseudotyping of lentiviral vectors with envelope proteins other than VSV-G has resulted in enhanced transduction of certain cell types and tissues. In order to improve lentiviral vector-based gene therapy for peripheral neuroectodermal and brain tumors, we compared the efficiency of eight different lentivirus pseudotypes in transducing neuronal and glial tumor cell lines. Here, lentiviral vectors pseudotyped with the envelopes from human foamy virus, rabies, Mokola or amphotropic murine leukemia virus displayed the highest transduction efficiency in neuroblastomas, whereas pseudotyping with the lymphocytic choriomeningitis virus glycoprotein from strain Armstrong 53b resulted in the highest transduction efficiency in gliomas.

Optimized large-scale production of high titer lentivirus vector pseudotypes

The goal of the present study was to develop an efficient transient transfection method for large-scale production of high titer lentivirus vector stocks of eight different pseudotypes. The envelope genes used for this purpose were those from VSV-G, Mokola, Rabies, MLV-Ampho, MLV-10A1, LCMV-WE, and LCMV-Arm53b. All envelopes were cloned into phCMV, which yielded lentivirus vector titers one, two, or three orders of magnitude higher than the original plasmids for the Rabies, MLV-10A1, and MLV-Ampho envelopes, respectively. When these newly constructed envelope expression plasmids were used for packaging, treatment with sodium butyrate resulted in almost five-fold increase in titers for some of the pseudotypes, had no effect for others (VSV-G and Rabies), and negatively impacted titers for the LCMV-derived pseudotypes. Production of vectors in serum-free media yielded titers only slightly lower than those obtained in the presence of serum. The efficiency of concentrating vector supernatants by ultracentrifugation or ultrafiltration was compared, with higher recovery efficiencies for the latter method, but the highest titers for most pseudotypes were obtained by ultracentrifugation. The best conditions for each individual pseudotype yielded lentivirus vector stocks with titers above 1 x 10(9) tu/mL for most pseudotypes, and higher than 1 x 10(10) tu/mL for VSV-G.

Systemic administration of naked DNA with targeting specificity to mammalian kidneys

A major challenge for gene therapy is to be able to deliver efficiently the gene of interest to specific cell types. Here we describe a safe and simple effective naked DNA gene delivery method, via inferior vena cava (IVC) injection, to the recipient's kidneys. It was further demonstrated that gene expression was concentrated in the proximal tubular epithelial cells of the cortico-medullary region of the kidney. Confocal microscopy analyses demonstrated the presence of the exogenous DNA in the renal cell membrane 10 min postgene delivery. However, it was only by 30 min that the presence of the exogenous DNA could be detected in the cell cytoplasm and in the nuclei of the renal cells. Stable expression of the beta-galactosidase gene could be detected for up to 35 days and no toxicity or any adverse pathological effect associated with the delivery method could be observed. Importantly, this IVC gene delivery method could promote the targeting of genes to carcinoma established in the kidney of SCID mice. These results provide the first evidence to support that stable gene expression could be achieved in the renal cells of kidney and the established carcinoma in the kidneys following in vivo gene delivery with naked DNA and could therefore provide the potential to design protocols for the gene therapy of the kidney diseases.

Sustained elevation of neutrophils in rats induced by lentivirus-mediated G-CSF delivery

BACKGROUND

Patients with severe chronic and cyclic neutropenia, characterized by neutrophil numbers <500 cells/microl, are treated daily with recombinant granulocyte colony-stimulating factor (G-CSF). As an alternative delivery approach we investigated the ability of lentivirus vectors to provide sustained G-CSF expression.

METHODS

Fischer rats were injected intramuscularly (IM) with vesicular stomatitis virus G (VSV-G)-pseudotyped lentivirus pRRL-CMV-G-CSF-SIN that encoded rat G-CSF cDNA regulated by the human cytomegalovirus (CMV) promoter and incorporated a self-inactivating (SIN) construct in the 3' long terminal repeat (LTR). Control rats received normal saline or lentivirus encoding the enhanced green fluorescent protein (eGFP). Rats were serially monitored for blood cell production and tissues assayed for provirus distribution.

RESULTS

Rats receiving a single IM injection of lentivirus exhibited elevated neutrophil counts for 14 months. Virus administration of 6 x 10(7) infectious units induced sustained levels of neutrophil production having a mean +/- standard deviation (SD) of 5650 +/- 900 cells/microl and rats that received a 10-fold lower dose of virus showed mean neutrophil counts of 3340 +/- 740 cells/microl. These were significantly higher than the mean of control animals receiving saline or control lentivirus (1,760 +/- 540 cells/microl, P < 0.0001). White blood cell (WBC) counts were significantly elevated in treated over control animals (P < 0.0001). Hematocrits (P > 0.3), lymphocytes (P > 0.2) and platelets (P > 0.1) were not significantly different between control and treated animals. Genomic DNA from muscle at the injection sites was positive for provirus, whereas lung, spleen, liver, kidney and non-injected muscle samples were all negative, suggesting lack of virus spread.

CONCLUSIONS

These studies indicate that lentivirus vectors administered IM provide sustained, therapeutic levels of neutrophils and suggest this approach to treat patients with severe and cyclic neutropenia.

Kupffer Cells and Not Liver Sinusoidal Endothelial Cells Prevent Lentiviral Transduction of Hepatocytes

Lentiviral vectors can stably transduce dividing and nondividing cells in vivo and are best suited to long-term correction of inherited liver diseases. Intraportal administration of lentiviral vectors expressing green fluorescent protein (Lenti-GFP) in mice resulted in a higher transduction of nonparenchymal cells than hepatocytes (7.32 +/- 3.66% vs 0.22 +/- 0.08%, respectively). Therefore, various treatments were explored to increase lentiviral transduction of hepatocytes. Lenti-GFP was injected into the common bile duct, which led to transduction of biliary epithelium and hepatocytes at low efficiency. Transient removal of the sinusoidal endothelial cell layer by cyclophosphamide to increase accessibility to hepatocytes did not improve hepatocyte transduction (0.42 +/- 0.36%). Inhibition of Kupffer cell function by gadolinium chloride led to a significant decrease in GFP-positive nonparenchymal cells (2.15 +/- 3.14%) and a sevenfold increase in GFP-positive hepatocytes compared to nonpretreated mice (1.48 +/- 2.01%). These findings suggest that sinusoidal endothelial cells do not significantly limit lentiviral transduction of hepatocytes, while Kupffer cells sequester lentiviral particles thereby preventing hepatocyte transduction. Therefore, the use of agents that inhibit Kupffer cell function may be important for lentiviral vector treatment of liver disease.

Targeted retroviral transduction of c-kit+ hematopoietic cells using novel ligand display technology

Gene therapy for a wide variety of disorders would be greatly enhanced by the development of vectors that could be targeted for gene delivery to specific populations of cells. We describe here high-efficiency targeted transduction based on a novel targeting strategy that exploits the ability of retroviruses to incorporate host cell proteins into the surface of the viral particle as they bud through the plasma membrane. Ecotropic retroviral particles produced in cells engineered to express the membrane-bound form of stem cell factor (mbSCF) transduce both human cell lines and primary cells with high efficiency in a strictly c-kit (SCF receptor)-dependent fashion. The availability of efficient targeted vectors provides a platform for the development of a new generation of therapies using in vivo gene delivery. (Blood. 2004;104: 2697-2703)

Gene transfer vector biodistribution: pivotal safety studies in clinical gene therapy development

Techniques allowing for gene transfer vectors biodistribution investigation, in the frame of preclinical gene therapy development, are exposed. Emphasis is given on validation and test performance assessment. In the second part, specific gene vector distribution properties are reviewed (adenovirus, AAV, plasmid, retroviruses, herpes-derived vectors, germline transmission risks). The rationale for biodistribution by quantitative PCR, animal study and result interpretation is discussed. The importance and pivotal role of biodistribution study in gene transfer medicine development is shown through the determination of target organs for toxicity, germline transmission assessment and determination of risks of shedding and spreading of vectors in the gene transfer recipient and the environment.

Lentiviral vectors

Vectors based on lentiviruses have reached a state of development such that clinical studies using these agents as gene delivery vehicles have now begun. They have particular advantages for certain in vitro and in vivo applications especially the unique capability of integrating genetic material into the genome of non-dividing cells. Their rapid progress into clinical use reflects in part the huge body of knowledge which has accumulated about HIV in the last 20 years. Despite this, many aspects of viral assembly on which the success of these vectors depends are rather poorly understood. Sufficient is known however to be able to produce a safe and reproducible high titre vector preparation for effective transduction of growth-arrested tissues such as neural tissue, muscle and liver.

Reduction of natural adenovirus tropism to mouse liver by fiber-shaft exchange in combination with both CAR- and alphav integrin-binding ablation

The primary receptor, the coxsackievirus and adenovirus receptor (CAR), and the secondary receptor, alphav integrins, are the tropism determinants of adenovirus (Ad) type 5. Inhibition of the interaction of both the fiber with CAR and the penton base with the alphav integrin appears to be crucial to the development of targeted Ad vectors, which specifically transduce a given cell population. In this study, we developed Ad vectors with ablation of both CAR and alphav integrin binding by mutating the fiber knob and the RGD motif of the penton base. We also replaced the fiber shaft domain with that derived from Ad type 35. High transduction efficiency in the mouse liver was suppressed approximately 130- to 270-fold by intravenous administration of the double-mutant Ad vectors, which mutated two domains each of the fiber knob and shaft and the RGD motif of the penton base compared with those of conventional Ad vectors (type 5). Most significantly, the triple-mutant Ad vector containing the fiber knob with ablation of CAR binding ability, the fiber shaft of Ad type 35, and the penton base with a deletion of the RGD motif mediated a >30,000-fold lower level of mouse liver transduction than the conventional Ad vectors. This triple-mutant Ad vector also mediated reduced transduction in other organs (the spleen, kidney, heart, and lung). Viral DNA analysis showed that systemically delivered triple-mutant Ad vector was primarily taken up by liver nonparenchymal cells and that most viral DNAs were easily degraded, resulting in little gene expression in the liver. These results suggest that the fiber knob, fiber shaft, and RGD motif of the penton base each plays an important role in Ad vector-mediated transduction to the mouse liver and that the triple-mutant Ad vector exhibits little tropism to any organs and appears to be a fundamental vector for targeted Ad vectors.

Efficient Retroviral Vector Targeting of Carcinoembryonic Antigen-Positive Tumors

Many gene therapy approaches require specific, efficient gene delivery to cells in vivo. To target colorectal tumors we fused a single-chain variable fragment (scFv) directed against carcinoembryonic antigen (CEA) to the amphotropic murine leukemia virus envelope. A proline-rich hinge and matrix metalloprotease (MMP) cleavage site linked the two proteins. Following attachment to CEA, MMP cleavage of the envelope at the cell surface removed the scFv and proline-rich hinge, allowing transduction. This allowed selective targeting of CEA-positive cells in vivo after injection of producer cells at the site of the tumor, with up to 10% of cells within a CEA-positive tumor xenograft becoming transduced. Intraperitoneal injection of amphotropic producer cells resulted in transduction of cells in spleen, liver, and kidney, which was not detected when CEA-targeted producer cells were used. These results demonstrate the feasibility of using targeted retroviral vectors for in vivo gene delivery to tumors. Furthermore, the lack of transduction of host cells eliminates the risk of insertional mutagenesis leading to transformation of host hematopoietic cells.

Targeting retroviral and lentiviral vectors

Retroviral vectors capable of efficient in vivo gene delivery to specific target cell types or to specific locations of disease pathology would greatly facilitate many gene therapy applications. The surface glycoproteins of membrane-enveloped viruses stand among the choice candidates to control the target cell receptor recognition and host range of retroviral vectors onto which they are incorporated. This can be achieved in many ways, such as the exchange of glycoprotein by pseudotyping, their biochemical modifications, their conjugation with virus-cell bridging agents or their structural modifications. Understanding the fundamental properties of the viral glycoproteins and the molecular mechanism of virus entry into cells has been instrumental in the functional alteration of their tropism. Here we briefly review the current state of our understanding of the structure and function of viral envelope glycoproteins and we discuss the emerging targeting strategies based on retroviral and lentiviral vector systems.

Optimized lentiviral vector production and purification procedure prevents immune response after transduction of mouse brain

HIV-derived lentiviral vectors are efficient vehicula to deliver genes into the brain and hold great promise for future gene therapy of neurodegenerative disorders. However, administration of the current vector preparations in mouse brain was found to induce a systemic immune response to vector proteins and a modest inflammation in the brain. Moreover, serum antibodies from vector-treated animals were capable of partially neutralizing lentiviral vector-mediated transduction in cell culture. To avoid this unexpected immune reaction, we have optimized new vector production and purification protocols. Purification by sucrose gradient ultracentrifugation abolished the immune response, but vector titers also decreased substantially. Lentiviral vector production in the absence of serum in the cell culture medium equally reduced immunogenicity without affecting transduction efficiency. These results have important implications for future clinical use of lentiviral vectors, and for the use of lentiviral vectors to create animal models for neurodegenerative diseases that have an important neuroinflammatory component.

Characterization of in vitro and in vivo gene transfer properties of adenovirus serotype 35 vector

We have recently developed a replication-defective, recombinant adenovirus (Ad) vector composed of the whole Ad serotype 35 (Ad35), a member of subgroup B. We describe herein the in vitro and in vivo gene transfer properties of Ad35 vector in comparison with Ad serotype 5 (Ad5) and the Ad5F35 vector, which is a fiber-substituted Ad5 vector containing Ad35 fiber proteins. In vitro, Ad35 vector efficiently transduced not only human CAR-positive cells but also CAR-negative cells. Following intravenous administration into mice, both Ad5 and Ad35 vectors were rapidly cleared from the bloodstream with a half-life of approximately 3 min. Ad5 vector-mediated transgene expression predominantly occurred in liver parenchymal cells, although the Ad5 vector was delivered to both liver parenchymal and nonparenchymal cells. In contrast, Ad35 vector was efficiently taken up by liver nonparenchymal cells and mediated transduction efficiency in the liver on a level 4 log orders lower than the Ad5 vector. These findings demonstrate that Ad35 vector is an attractive vehicle for gene transfer into human cells, while the biodistribution profile of Ad35 vector in mice is much different from that of the Ad5 vector.

Treatment of canine cyclic neutropenia by lentivirus-mediated G-CSF delivery

Cyclic neutropenia is a rare disease that occurs both in humans and gray collie dogs and is characterized by recurrent severe neutropenia leading to bacterial infections and shortened life expectancy. Daily injections of recombinant granulocyte colony-stimulating factor (rG-CSF) are effective in shortening the period of severe neutropenia and reducing infections. After demonstrating that rG-CSF induced elevated neutrophil production in an affected dog, cytokine administration was stopped and 109 infectious units (IUs) of a lentivirus pseudotyped with vesicular stomatitis virus G protein (VSV-G) encoding canine G-CSF cDNA was administered intramuscularly. Serial blood cell counts showed elevated neutrophil production for longer than 17 months. Although neutrophil counts continued to cycle, the range at nadirs was from 3710 to 5300 cells/microL, well above the nadirs before lentivirus administration. After the injection of lentivirus, mean neutrophil counts +/- SD were 12 460 +/- 4240 cells/microL, significantly increased over both pretreatment values of 3040 +/- 2540 cells/microL(P <.0001) and neutrophil counts during G-CSF administration of 10 290 +/- 4860 cells/microL(P <.007). The changes in blood counts from lentivirus injection were associated with absence of clinical signs of infection and fever. The gray collie continued to gain weight and was no longer housed in a pathogen-free environment. Genomic DNA from muscle at injection sites was positive for provirus, whereas gonad, lung, spleen, heart, liver, kidney, leukocytes, and noninjected muscle samples were all negative for provirus. Thus, intramuscular administration of lentivirus encoding G-CSF provided sustained therapeutic levels of neutrophils, suggesting this approach may be applied for long-term treatment of patients with cyclic and other neutropenias.

Vectors for the treatment of autoimmune disease

Gene therapy has been applied in a variety of experimental models of autoimmunity with some success. In this article, we outline recent developments in gene therapy vectors, discuss advantages and disadvantages of each, and highlight their recent applications in autoimmune models. We also consider progress in vector targeting and components for regulating transgene expression, which will both improve gene therapy safety and empower gene therapy to fullfil its potential as a therapeutic modality. In conclusion, we consider candidate vectors that satisfy requirements for application in the principal therapeutic strategies in which gene therapy will be applied to autoimmune conditions.