Characterization of retroviral and lentiviral vectors pseudotyped with xenotropic murine leukemia virus-related virus envelope glycoprotein

The development and application of pseudoviruses: assessment of SARS-CoV-2 pseudoviruses

Although most Coronavirus disease (COVID-19) patients can recover fully, the disease remains a significant cause of morbidity and mortality. In addition to the consequences of acute infection, a proportion of the population experiences long-term adverse effects associated with SARS-CoV-2. Therefore, it is still critical to comprehend the virus's characteristics and how it interacts with its host to develop effective drugs and vaccines against COVID-19. SARS-CoV-2 pseudovirus, a replication-deficient recombinant glycoprotein chimeric viral particle, enables investigations of highly pathogenic viruses to be conducted without the constraint of high-level biosafety facilities, considerably advancing virology and being extensively employed in the study of SARS-CoV-2. This review summarizes three methods of establishing SARS-CoV-2 pseudovirus and current knowledge in vaccine development, neutralizing antibody research, and antiviral drug screening, as well as recent progress in virus entry mechanism and susceptible cell screening. We also discuss the potential advantages and disadvantages.

Pseudotyped Viruses for Lyssavirus

Lyssaviruses, which belong to the family Rhabdoviridae, are enveloped and bullet-shaped ssRNA viruses with genetic diversity. All members of Lyssavirus genus are known to infect warm-blooded animals and cause the fatal disease rabies. The rabies virus (RABV) in lyssavirus is the major pathogen to cause fatal rabies. The pseudotyped RABV is constructed to study the biological functions of G protein and evaluation of anti-RABV products including vaccine-induced antisera, rabies immunoglobulins (RIG), neutralizing mAbs, and other antiviral inhibitors. In this chapter, we focus on RABV as a representative and describe the construction of RABV G protein bearing pseudotyped virus and its applications. Other non-RABV lyssaviruses are also included.

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.

A Microfluidic Device to Enhance Viral Transduction Efficiency During Manufacture of Engineered Cellular Therapies

The development and approval of engineered cellular therapies are revolutionizing approaches to treatment of diseases. However, these life-saving therapies require extensive use of inefficient bioprocessing equipment and specialized reagents that can drive up the price of treatment. Integration of new genetic material into the target cells, such as viral transduction, is one of the most costly and labor-intensive steps in the production of cellular therapies. Approaches to reducing the costs associated with gene delivery have been developed using microfluidic devices to increase overall efficiency. However, these microfluidic approaches either require large quantities of virus or pre-concentration of cells with high-titer viral particles. Here, we describe the development of a microfluidic transduction device (MTD) that combines microfluidic spatial confinement with advective flow through a membrane to efficiently colocalize target cells and virus particles. We demonstrate that the MTD can improve the efficiency of lentiviral transduction for both T-cell and hematopoietic stem-cell (HSC) targets by greater than two fold relative to static controls. Furthermore, transduction saturation in the MTD is reached with only half the virus required to reach saturation under static conditions. Moreover, we show that MTD transduction does not adversely affect cell viability or expansion potential.

RNA Virus-Based Episomal Vector with a Fail-Safe Switch Facilitating Efficient Genetic Modification and Differentiation of iPSCs

A gene delivery system that allows efficient and safe stem cell modification is critical for next-generation stem cell therapies. An RNA virus-based episomal vector (REVec) is a gene transfer system developed based on Borna disease virus (BoDV), which facilitates persistent intranuclear RNA transgene delivery without integrating into the host genome. In this study, we analyzed susceptibility of human induced pluripotent stem cell (iPSC) lines from different somatic cell sources to REVec, along with commonly used viral vectors, and demonstrated highly efficient REVec transduction of iPSCs. Using REVec encoding myogenic transcription factor MyoD1, we further demonstrated potential application of the REVec system for inducing differentiation of iPSCs into skeletal muscle cells. Of note, treatment with a small molecule, T-705, completely eliminated REVec in persistently transduced cells. Thus, the REVec system offers a versatile toolbox for stable, integration-free iPSC modification and trans-differentiation, with a unique switch-off mechanism.

Current status on the development of pseudoviruses for enveloped viruses

Emerging and reemerging infectious diseases have a strong negative impact on public health. However, because many of these pathogens must be handled in biosafety level, 3 or 4 containment laboratories, research and development of antivirals or vaccines against these diseases are often impeded. Alternative approaches to address this issue have been vigorously pursued, particularly the use of pseudoviruses in place of wild‐type viruses. As pseudoviruses have been deprived of certain gene sequences of the virulent virus, they can be handled in biosafety level 2 laboratories. Importantly, the envelopes of these viral particles may have similar conformational structures to those of the wild‐type viruses, making it feasible to conduct mechanistic investigation on viral entry and to evaluate potential neutralizing antibodies. However, a variety of challenging issues remain, including the production of a sufficient pseudovirus yield and the inability to produce an appropriate pseudotype of certain viruses. This review discusses current progress in the development of pseudoviruses and dissects the factors that contribute to low viral yields.

The use of RetroNectin in studies requiring in vitro HIV-1 infection of human hematopoietic stem/progenitor cells

Human immunodeficiency virus (HIV) causes damage, directly or indirectly, to the whole hematopoietic system, including CD34⁺ hematopoietic stem/progenitor cells (HSPCs). CXCR4-tropic strains of HIV-1 may affect the function of CD34⁺CXCR4⁺ progenitor cells either by infecting the cells or modifying the dynamics of more differentiated hematopoietic cells. However, CD34⁺ cells are known for their resistance to HIV-1 infection in vitro, which restricts any detailed analysis of the impact of HIV on HSPCs. We report the use of RetroNectin, a recombinant fibronectin fragment used for gene transfer with lentiviral vectors, to overcome the limitation associated with CD34⁺ cell resistance to HIV-1 infection. RetroNectin coating of plates improved in vitro HIV-1 infectivity on human CD34⁺ cells by 10 fold. This resulted in stable HIV-1 infection for 5 weeks in an OP9-DL1 coculture. These results suggest that RetroNectin may be a useful tool for long-term monitoring of in vitro HIV-infected CD34⁺ cells.

Progresses towards safe and efficient gene therapy vectors

The emergence of genetic engineering at the beginning of the 1970′s opened the era of biomedical technologies, which aims to improve human health using genetic manipulation techniques in a clinical context. Gene therapy represents an innovating and appealing strategy for treatment of human diseases, which utilizes vehicles or vectors for delivering therapeutic genes into the patients' body. However, a few past unsuccessful events that negatively marked the beginning of gene therapy resulted in the need for further studies regarding the design and biology of gene therapy vectors, so that this innovating treatment approach can successfully move from bench to bedside. In this paper, we review the major gene delivery vectors and recent improvements made in their design meant to overcome the issues that commonly arise with the use of gene therapy vectors. At the end of the manuscript, we summarized the main advantages and disadvantages of common gene therapy vectors and we discuss possible future directions for potential therapeutic vectors.

Prevention of contamination by xenotropic murine leukemia virus-related virus: susceptibility to alcohol-based disinfectants and environmental stability

Xenotropic murine leukemia virus-related virus (XMRV) represents a novel γ-retrovirus that is capable of infecting human cells and has been classified as a biosafety level 2 (BSL-2) organism. Hence, XMRV represents a potential risk for personnel in laboratories worldwide. Here, we measured the stability of XMRV and its susceptibility to alcohol-based disinfectants. To this end, we exposed an infectious XMRV reporter virus encoding a secretable luciferase to different temperatures, pH values, and disinfectants and infected XMRV-permissive Raji B cells to measure residual viral infectivity. We found that 1 min treatment of XMRV particles at 60°C is sufficient to reduce infectivity by 99.9%. XMRV infectivity was maximal at a neutral pH but was reduced by 86% at pH 4 and 99.9% at pH 10. The common hand and surface disinfectants ethanol and isopropanol as well as the cell fixation reagent paraformaldehyde abrogated XMRV infectivity entirely, as indicated by a reduction of infectivity exceeding 99.99%. Our findings provide evidence of specific means to inactivate XMRV. Their application will help to prevent unintended XMRV contamination of cell cultures in laboratories and minimize the risk for laboratory personnel and health care workers to become infected with this biosafety level 2 organism.

Murine leukemia virus uses NXF1 for nuclear export of spliced and unspliced viral transcripts

Intron-containing mRNAs are subject to restricted nuclear export in higher eukaryotes. Retroviral replication requires the nucleocytoplasmic transport of both spliced and unspliced RNA transcripts, and RNA export mechanisms of gammaretroviruses are poorly characterized. Here, we report the involvement of the nuclear export receptor NXF1/TAP in the nuclear export of gammaretroviral RNA transcripts. We identified a conserved cis-acting element in the pol gene of gammaretroviruses, including murine leukemia virus (MLV) and xenotropic murine leukemia virus (XMRV), named the CAE (cytoplasmic accumulation element). The CAE enhanced the cytoplasmic accumulation of viral RNA transcripts and the expression of viral proteins without significantly affecting the stability, splicing, or translation efficiency of the transcripts. Insertion of the CAE sequence also facilitated Rev-independent HIV Gag expression. We found that the CAE sequence interacted with NXF1, whereas disruption of NXF1 ablated CAE function. Thus, the CAE sequence mediates the cytoplasmic accumulation of gammaretroviral transcripts in an NXF1-dependent manner. Disruption of NXF1 expression impaired cytoplasmic accumulations of both spliced and unspliced RNA transcripts of XMRV and MLV, resulting in their nuclear retention or degradation. Thus, our results demonstrate that gammaretroviruses use NXF1 for the cytoplasmic accumulation of both spliced and nonspliced viral RNA transcripts.

IMPORTANCE

Murine leukemia virus (MLV) has been studied as one of the classic models of retrovirology. Although unspliced host messenger RNAs are rarely exported from the nucleus, MLV actively exports unspliced viral RNAs to the cytoplasm. Despite extensive studies, how MLV achieves this difficult task has remained a mystery. Here, we have studied the RNA export mechanism of MLV and found that (i) the genome contains a sequence which supports the efficient nuclear export of viral RNAs, (ii) the cellular factor NXF1 is involved in the nuclear export of both spliced and unspliced viral RNAs, and, finally, (iii) depletion of NXF1 results in nuclear retention or degradation of viral RNAs. Our study provides a novel insight into MLV nuclear export.

Library screening and receptor-directed targeting of gammaretroviral vectors

Gene- and cell-based therapies hold great potential for the advancement of the personalized medicine movement. Gene therapy vectors have made dramatic leaps forward since their inception. Retroviral-based vectors were the first to gain clinical attention and still offer the best hope for the long-term correction of many disorders. The fear of nonspecific transduction makes targeting a necessary feature for most clinical applications. However, this remains a difficult feature to optimize, with specificity often coming at the expense of efficiency. The aim of this article is to discuss the various methods employed to retarget retroviral entry. Our focus will lie on the modification of gammaretroviral envelope proteins with an in-depth discussion of the creation and screening of envelope libraries.

Engineering a serum-resistant and thermostable vesicular stomatitis virus G glycoprotein for pseudotyping retroviral and lentiviral vectors

Vesicular stomatitis virus G glycoprotein (VSV-G) is the most widely used envelope protein for retroviral and lentiviral vector pseudotyping; however, serum inactivation of VSV-G pseudotyped vectors is a significant challenge for in vivo gene delivery. To address this problem, we conducted directed evolution of VSV-G to increase its resistance to human serum neutralization. After six selection cycles, numerous common mutations were present. Based on their location within VSV-G, we analyzed whether substitutions in several surface exposed residues could endow viral vectors with higher resistance to serum. S162T, T230N, and T368A mutations enhanced serum resistance, and additionally K66T, T368A, and E380K substitutions increased the thermostability of VSV-G pseudotyped retroviral vectors, an advantageous byproduct of the selection strategy. Analysis of a number of combined mutants revealed that VSV-G harboring T230N + T368A or K66T + S162T + T230N + T368A mutations exhibited both higher in vitro resistance to human serum and higher thermostability, as well as enhanced resistance to rabbit and mouse serum. Finally, lentiviral vectors pseudotyped with these variants were more resistant to human serum in a murine model. These serum-resistant and thermostable VSV-G variants may aid the application of retroviral and lentiviral vectors to gene therapy.

Utilization of replication-competent XMRV reporter-viruses reveals severe viral restriction in primary human cells

The gammaretrovirus termed xenotropic murine leukemia virus-related virus (XMRV) was described to be isolated from prostate cancer tissue biopsies and from blood of patients suffering from chronic fatigue syndrome. However, many studies failed to detect XMRV and to verify these disease associations. Data suggesting the contamination of specimens in particular by PCR-based methods and recent reports demonstrating XMRV generation via recombination of two murine leukemia virus precursors raised serious doubts about XMRV being a genuine human pathogen. To elucidate cell tropism of XMRV, we generated replication competent XMRV reporter viruses encoding a green fluorescent protein or a secretable luciferase as tools to analyze virus infection of human cell lines or primary human cells. Transfection of proviral DNAs into LNCaP prostate cancer cells resulted in readily detectably reporter gene expression and production of progeny virus. Inoculation of known XMRV susceptible target cells revealed that these virions were infectious and expressed the reporter gene, allowing for a fast and highly sensitive quantification of XMRV infection. Both reporter viruses were capable of establishing a spreading infection in LNCaP and Raji B cells and could be easily passaged. However, after inoculation of primary human blood cells such as CD4 T cells, macrophages or dendritic cells, infection rates were very low, and a spreading infection was never established. In line with these results we found that supernatants derived from these XMRV infected primary cell types did not contain infectious virus. Thus, although XMRV efficiently replicated in some human cell lines, all tested primary cells were largely refractory to XMRV infection and did not support viral spread. Our results provide further evidence that XMRV is not a human pathogen.

Phylogenetic and biological analysis of a laboratory-generated gammaretrovirus xenotropic murine leukemia virus-related virus (XMRV)

A xenotropic murine leukemia virus-related virus (XMRV) has been reported to be an emerging pathogen associated with prostate cancer (PC) and chronic fatigue syndrome (CFS). However, recent studies have demonstrated that XMRV is a laboratory-derived virus resulting from genetic recombination between two mouse viral genomes during serial xenograft tissue transplantation. This study describes a phylogenetic analysis that compared XMRV with the ecotropic murine leukemia viruses (E-MLV), xenotropic MLV (X-MLV), and other retroviruses, including HTLV-1 and HIV-1. We found that sequences corresponding to three XMRV structural proteins (Env, Gag, and Pol) exhibited high degrees of homology with X-MLV (>91 %) and E-MLV (67-96 %), but not HTLV-1 (13-16 %) or HIV-1 (10-15 %), indicating that XMRV was derived from X-MLV and/or E-MLV. We then compared the infectivity of XMRV and E-MLV for human and murine lymphocytes, respectively. Results showed that human PBMCs were not susceptible to XMRV infection, suggesting that XMRV exhibits host cell tropism similar to E-MLV that only infects murine PBMCs. These data suggest that it is unlikely that this laboratory-generated retrovirus could cause disease in humans.

Lentiviral vectors: basic to translational

More than two decades have passed since genetically modified HIV was used for gene delivery. Through continuous improvements these early marker gene-carrying HIVs have evolved into safer and more effective lentiviral vectors. Lentiviral vectors offer several attractive properties as gene-delivery vehicles, including: (i) sustained gene delivery through stable vector integration into host genome; (ii) the capability of infecting both dividing and non-dividing cells; (iii) broad tissue tropisms, including important gene- and cell-therapy-target cell types; (iv) no expression of viral proteins after vector transduction; (v) the ability to deliver complex genetic elements, such as polycistronic or intron-containing sequences; (vi) potentially safer integration site profile; and (vii) a relatively easy system for vector manipulation and production. Accordingly, lentivector technologies now have widespread use in basic biology and translational studies for stable transgene overexpression, persistent gene silencing, immunization, in vivo imaging, generating transgenic animals, induction of pluripotent cells, stem cell modification and lineage tracking, or site-directed gene editing. Moreover, in the present high-throughput '-omics' era, the commercial availability of premade lentiviral vectors, which are engineered to express or silence genome-wide genes, accelerates the rapid expansion of this vector technology. In the present review, we assess the advances in lentiviral vector technology, including basic lentivirology, vector designs for improved efficiency and biosafety, protocols for vector production and infection, targeted gene delivery, advanced lentiviral applications and issues associated with the vector system.

Transgene-free disease-specific induced pluripotent stem cells from patients with type 1 and type 2 diabetes

The induced pluripotent stem cell (iPSC) technology enables derivation of patient-specific pluripotent stem cells from adult somatic cells without using an embryonic cell source. Redifferentiation of iPSCs from diabetic patients into pancreatic islets will allow patient-specific disease modeling and autologous cell replacement therapy for failing islets. To date, diabetes-specific iPSCs have been generated from patients with type 1 diabetes using integrating retroviral vectors. However, vector integration into the host genome could compromise the biosafety and differentiation propensities of derived iPSCs. Although various integration-free reprogramming systems have been described, their utility to reprogram somatic cells from patients remains largely undetermined. Here, we used nonintegrating Sendai viral vectors to reprogram cells from patients with type 1 and type 2 diabetes (T2D). Sendai vector infection led to reproducible generation of genomic modification-free iPSCs (SV-iPSCs) from patients with diabetes, including an 85-year-old individual with T2D. SV-iPSCs lost the Sendai viral genome and antigens within 8-12 passages while maintaining pluripotency. Genome-wide transcriptome analysis of SV-iPSCs revealed induction of endogenous pluripotency genes and downregulation of genes involved in the oxidative stress response and the INK4/ARF pathways, including p16(INK4a), p15(INK4b), and p21(CIP1). SV-iPSCs and iPSCs made with integrating lentiviral vectors demonstrated remarkable similarities in global gene expression profiles. Thus, the Sendai vector system facilitates reliable reprogramming of patient cells into transgene-free iPSCs, providing a pluripotent platform for personalized diagnostic and therapeutic approaches for diabetes and diabetes-associated complications.

Membrane fusion and cell entry of XMRV are pH-independent and modulated by the envelope glycoprotein's cytoplasmic tail

Xenotropic murine leukemia virus-related virus (XMRV) is a gammaretrovirus that was originally identified from human prostate cancer patients and subsequently linked to chronic fatigue syndrome. Recent studies showed that XMRV is a recombinant mouse retrovirus; hence, its association with human diseases has become questionable. Here, we demonstrated that XMRV envelope (Env)-mediated pseudoviral infection is not blocked by lysosomotropic agents and cellular protease inhibitors, suggesting that XMRV entry is not pH-dependent. The full length XMRV Env was unable to induce syncytia formation and cell-cell fusion, even in cells overexpressing the viral receptor, XPR1. However, truncation of the C-terminal 21 or 33 amino acid residues in the cytoplasmic tail (CT) of XMRV Env induced substantial membrane fusion, not only in the permissive 293 cells but also in the nonpermissive CHO cells that lack a functional XPR1 receptor. The increased fusion activities of these truncations correlated with their enhanced SU shedding into culture media, suggesting conformational changes in the ectodomain of XMRV Env. Noticeably, further truncation of the CT of XMRV Env proximal to the membrane-spanning domain severely impaired the Env fusogenicity, as well as dramatically decreased the Env incorporations into MoMLV oncoretroviral and HIV-1 lentiviral vectors resulting in greatly reduced viral transductions. Collectively, our studies reveal that XMRV entry does not require a low pH or low pH-dependent host proteases, and that the cytoplasmic tail of XMRV Env critically modulates membrane fusion and cell entry. Our data also imply that additional cellular factors besides XPR1 are likely to be involved in XMRV entry.

Development and application of a high-throughput microneutralization assay: lack of xenotropic murine leukemia virus-related virus and/or murine leukemia virus detection in blood donors

BACKGROUND

Xenotropic murine leukemia virus (MLV)-related virus (XMRV) and other related MLVs have been described with chronic fatigue syndrome and certain types of prostate cancer. In addition, prevalence rates as high as 7% have been reported in blood donors, raising the risk of transfusion-related transmission. Several laboratories have utilized microneutralization assays as a surrogate marker for detection of anti-MLV serologic responses--with up to 25% of prostate cancer patients reported to harbor neutralizing antibody responses.

STUDY DESIGN AND METHODS

We developed a high-throughput microneutralization assay for research studies on blood donors using retroviral vectors pseudotyped with XMRV-specific envelopes. Infection with these pseudotypes was neutralized by sera from both macaques and mice challenged with XMRV, but not preimmune serum. A total of 354 plasma samples from blood donors in the Reno/Tahoe area were screened for neutralization.

RESULTS

A total of 6.5% of donor samples gave moderate neutralization of XMRV, but not control pseudotypes. However, further testing by Western blot revealed no evidence of antibodies against MLVs in any of these samples. Furthermore, no evidence of infectious virus or viral nucleic acid was observed.

CONCLUSION

A microneutralization assay was developed for detection of XMRV and can be applied in a high-throughput format for large-scale studies. Although a proportion of blood donors demonstrated the ability to block XMRV envelope-mediated infection, we found no evidence that this inhibition was mediated by specific antibodies elicited by exposure to XMRV or MLV. It is likely that this moderate neutralization is mediated through another, nonspecific mechanism.

Long-term infection and vertical transmission of a gammaretrovirus in a foreign host species

Increasing evidence has indicated natural transspecies transmission of gammaretroviruses; however, viral-host interactions after initial xeno-exposure remain poorly understood. Potential association of xenotropic murine leukemia virus-related virus (XMRV) in patients with prostate cancer and chronic fatigue syndrome has attracted broad interests in this topic. Although recent studies have indicated that XMRV is unlikely a human pathogen, further understanding of XMRV xenoinfection would allow in vivo modeling of the initial steps of gammaretroviral interspecies transmission, evolution and dissemination in a new host population. In this study, we monitored the long-term consequences of XMRV infection and its possible vertical transmission in a permissive foreign host, wild-derived Mus pahari mice. One year post-infection, XMRV-infected mice showed no notable pathological changes, while proviral DNA was detected in three out of eight mice. XMRV-infected mice remained seropositive throughout the study although the levels of gp70 Env- and p30 capsid-specific antibodies gradually decreased. When vertical XMRV transmission was assessed, no viremia, humoral immune responses nor endogenization were observed in nine offspring from infected mothers, yet one offspring was found PCR-positive for XMRV-specific sequences. Amplified viral sequences from the offspring showed several mutations, including one amino acid deletion in the receptor binding domain of Env SU. Our results therefore demonstrate long-term asymptomatic infection, low incidence of vertical transmission and limited evolution of XMRV upon transspecies infection of a permissive new host, Mus pahari.

Highly efficient concentration of lenti- and retroviral vector preparations by membrane adsorbers and ultrafiltration

BACKGROUND

Lentiviral vectors (LVs) can efficiently transduce a broad spectrum of cells and tissues, including dividing and non-dividing cells. So far the most widely used method for concentration of lentiviral particles is ultracentrifugation (UC).An important feature of vectors derived from lentiviruses and prototypic gamma-retroviruses is that the host range can be altered by pseudotypisation. The most commonly used envelope protein for pseudotyping is the glycoprotein of the Vesicular Stomatitis Virus (VSV.G), which is also essential for successful concentration using UC.

RESULTS

Here, we describe a purification method that is based on membrane adsorbers (MAs). Viral particles are efficiently retained by the anionic exchange MAs and can be eluted with a high-salt buffer. Buffer exchange and concentration is then performed by utilizing ultrafiltration (UF) units of distinct molecular weight cut off (MWCO). With this combined approach similar biological titers as UC can be achieved (2 to 5×10⁹ infectious particles (IP)/ml). Lentiviral particles from small starting volumes (e.g. 40 ml) as well as large volumes (up to 1,000 ml) cell culture supernatant (SN) can be purified. Apart from LVs, vectors derived from oncoretroviruses can be efficiently concentrated as well. Importantly, the use of the system is not confined to VSV.G pseudotyped lenti- and retroviral particles and other pseudotypes can also be purified.

CONCLUSIONS

Taken together the method presented here offers an efficient alternative for the concentration of lenti- as well as retroviral vectors with different pseudotypes that needs no expensive equipment, is easy to handle and can be used to purify large quantities of viral vectors within a short time.

Gene therapy for lysosomal storage disorders

INTRODUCTION

Lysosomal storage disorders (LSDs) encompass more than 50 distinct diseases, caused by defects in various aspects of lysosomal function. Neurodegeneration and/or dysmyelination are the hallmark of roughly 70% of LSDs. Gene therapy represents a promising approach for the treatment of CNS manifestations in LSDs, as it has the potential to provide a permanent source of the deficient enzyme, either by direct injection of vectors or by transplantation of gene-corrected cells. In this latter approach, the biology of neural stem/progenitor cells and hematopoietic cells might be exploited.

AREAS COVERED

Based on an extensive literature search up until March 2011, the author reviews and discusses the progress, the crucial aspects and the major challenges towards the development of novel gene therapy strategies aimed to target the CNS, with particular attention to direct intracerebral gene delivery and transplantation of neural stem/progenitor cells.

EXPERT OPINION

The implementation of viral vector delivery systems with specific tropism, regulated transgene expression, low immunogenicity and low genotoxic risk and the improvement in isolation and manipulation of relevant cell types to be transplanted, are fundamental challenges to the field. Also, combinatorial strategies might be required to achieve full correction in LSDs with neurological involvement.

Early events in retrovirus XMRV infection of the wild-derived mouse Mus pahari

A novel gammaretrovirus, xenotropic murine leukemia virus-related virus (XMRV), has been identified in patients with prostate cancer and in patients with chronic fatigue syndromes. Standard Mus musculus laboratory mice lack a functional XPR1 receptor for XMRV and are therefore not a suitable model for the virus. In contrast, Gairdner's shrew-mice (Mus pahari) do express functional XPR1. To determine whether Mus pahari could serve as a model for XMRV, primary Mus pahari fibroblasts and mice were infected with cell-free XMRV. Infection of cells in vitro resulted in XMRV Gag expression and the production of XMRV virions. After intraperitoneal injection of XMRV into Mus pahari mice, XMRV proviral DNA could be detected in spleen, blood, and brain. Intravenous administration of a green fluorescent protein (GFP) vector pseudotyped with XMRV produced GFP(+) CD4(+) T cells and CD19(+) B cells. Mice mounted adaptive immune responses against XMRV, as evidenced by the production of neutralizing and Env- and Gag-specific antibodies. Prominent G-to-A hypermutations were also found in viral genomes isolated from the spleen, suggesting intracellular restriction of XMRV infection by APOBEC3 in vivo. These data demonstrate infection of Mus pahari by XMRV, potential cell tropism of the virus, and immunological and intracellular restriction of virus infection in vivo. These data support the use of Mus pahari as a model for XMRV pathogenesis and as a platform for vaccine and drug development against this potential human pathogen.