Recent developments in retroviral-mediated gene transduction

Delivering gene therapy for mucopolysaccharide diseases

Mucopolysaccharide diseases are a group of paediatric inherited lysosomal storage diseases that are caused by enzyme deficiencies, leading to a build-up of glycosaminoglycans (GAGs) throughout the body. Patients have severely shortened lifespans with a wide range of symptoms including inflammation, bone and joint, cardiac, respiratory and neurological disease. Current treatment approaches for MPS disorders revolve around two main strategies. Enzyme replacement therapy (ERT) is efficacious in treating somatic symptoms but its effect is limited for neurological functions. Haematopoietic stem cell transplant (HSCT) has the potential to cross the BBB through monocyte trafficking, however delivered enzyme doses limit its use almost exclusively to MPSI Hurler. Gene therapy is an emerging therapeutic strategy for the treatment of MPS disease. In this review, we will discuss the various vectors that are being utilised for gene therapy in MPS as well as some of the most recent gene-editing approaches undergoing pre-clinical and clinical development.

An optimized gene transfection system in WERI-Rb1 cells

The pathogenesis of Rb1 gene inactivation indicates that gene therapy could be a promising treatment for retinoblastoma. An appropriate gene transfer system is the basis for successful gene therapy; however, little attention has been given to an effective gene transfer system for retinoblastoma therapy in previous studies. This study was designed to provide an optimized transgene system for WERI-Rb1 cells (W-RBCs). Green fluorescent protein (GFP) was adopted as a reporter. Four classic viral vectors based on retroviruses, recombinant adeno-associated viruses (rAAV2, rAAV2/1), lentiviruses (LVs) and a novel non-viral vector X-treme HP reagent were adopted for W-RBC gene transfection. The efficacy and cytotoxicity were comprehensively compared among the different vectors through GFP expression and the trypan blue exclusion test. Furthermore, the serum and cell culture status were also optimized for better transfection. Cells transfected by rAAV2/1 expressed more GFP protein and exhibited less staining with trypan blue, compared to the rAAV2 counterpart. However, in comparison to the retroviral group, both the rAAV2/1 and LV groups had considerably less GFP⁺ cells. Interestingly, the X-treme HP presented a similar GFP transfection capacity to the retroviral vector, but with a much lower cytotoxicity. Furthermore, there were more GFP⁺ cells in a suspended condition than that in an adherent culture. Moreover, cells in a serum-positive system expressed more GFP, while cells in a serum-free system showed lower GFP expression and higher cytotoxicity. In conclusion, the retroviral vector and the X-treme HP are effective for W-RBC gene transfection, while the X-treme HP is more preferable due to its lower cytotoxicity. Moreover, the suspended cell culture system is superior to the adherent system, and the serum protects cell viability and facilitates the gene transfection of W-RBCs. This study presents an effective, convenient, and low toxic transfection system for gene delivery in W-RBCs and provides a promising system for further gene therapy of retinoblastoma.

Visualization of targeted transduction by engineered lentiviral vectors

We have reported a method to target lentiviral vectors to specific cell types. This method requires the incorporation of two distinct molecules on the viral vector surface: one is an antibody that renders the targeting specificity for the engineered vector, and the other is a fusogenic protein that allows the engineered vector to enter the target cell. However, the molecular mechanism that controls the targeted infection needs to be defined. In this report, we tracked the individual lentiviral particles by labeling the virus with the GFP-Vpr fusion protein. We were able to visualize the surface-displayed proteins on a single virion as well as antibody-directed targeting to a desired cell type. We also demonstrated the dynamics of virus fusion with endosomes and monitored endosome-associated transport of viruses in target cells. Our results suggest that the fusion between the engineered lentivirus and endosomes takes place at the early endosome level, and that the release of the viral core into the cytosol at the completion of the virus-endosome fusion is correlated with the endosome maturation process. This imaging study sheds some light on the infection mechanism of the engineered lentivirus and can be beneficial to the design of more efficient gene delivery vectors.

Moloney murine leukemia virus decay mediated by retroviral reverse transcriptase degradation of genomic RNA

Retroviral vectors are powerful tools for the introduction of transgenes into mammalian cells and for long-term gene expression. However, their application is often limited by a rapid loss of bioactivity: retroviruses spontaneously loose activity at 37 degrees C, with a half-life of 4 to 9 h depending on the retrovirus type. We sought to determine which components of the retrovirus are responsible for this loss in bioactivity and to obtain a quantitative characterization of their stability. To this end, we focused on RNA and viral proteins, two major components that we hypothesized may undergo degradation and negatively influence viral infectivity. Reverse transcription PCR (RT-PCR) targeting RNA encoding portions of the viral genome clearly demonstrated time-dependent degradation of RNA which correlated with the loss in viral bioactivity. Circular dichroism spectroscopy, SDS-PAGE and two-dimensional SDS-PAGE analyses of viral proteins did not show any change in secondary structure or evidence of proteolysis. The mechanism underlying the degradation of viral RNA was investigated by site-directed mutagenesis of proteins encoded by the viral genome. Reverse transcriptase and protease mutants exhibited enhanced RNA stability in comparison to wild type recombinant virus, suggesting that the degradation of RNA, and the corresponding virus loss of activity, is mediated by the reverse transcriptase enzyme.

Novel vectors forin vivogene delivery to vascular tissue

Although some success has been achieved with gene delivery in animal models of vascular disorders, the results from some clinical trials have been less promising, possibly due, in part, to the use of suboptimal vectors for in vivo gene transfer. Non-viral vectors have a very low transfection efficiency so are largely unsuitable for most in vivo applications, and the relatively broad tropism of many of the commonly used viral vectors can limit efficient gene delivery specifically to target vascular tissues. However, characterisation of novel virus serotypes and advances in techniques that enable vectors to be targeted to the required tissue have led to progress in the development of novel vectors that could be utilised for gene delivery for vascular disorders.

Common co-lipids, in synergy, impart high gene transfer properties to transfection-incompetent cationic lipids

Efficacious cationic transfection lipids usually need either DOPE or cholesterol as co-lipid to deliver DNA inside the cell cytoplasm in non-viral gene delivery. If both of these co-lipids fail in imparting gene transfer properties, the cationic lipids are usually considered to be transfection inefficient. Herein, using both the reporter gene assay in CHO, COS-1 and HepG2 cells and the whole cell histochemical X-gal staining assay in representative CHO cells, we demonstrate that common co-lipids DOPE, Cholesterol and DOPC, when act in synergy, are capable of imparting improved gene transfer properties to a novel series of cationic lipids (1-5). Contrastingly, lipids 1-5 became essentially transfection-incompetent when used in combination with each of the pure co-lipid components alone.

High-yield retroviral production using a temperature-modulated two-stage operation

For clinical trials, large amounts of high-titer retroviral supernatants are required. However, retroviral concentration is relatively low compared with other viral vectors. Moreover, less than half of retroviral vectors suspended in a collected supernatant are infectious because of their short half-lives. In this study, a culture medium of ecotropic retrovirus-producing GP + E86/LNCX cells in tissue culture dishes was circulated through a reservoir, which was arranged with an incubator or ice-bath stage. Titers determined from the retroviral supernatant circulated through an ice-cold reservoir increased for a week from the beginning of retroviral production, while the titers from static production with circulation through the 37 degrees C reservoir reached a plateau after 3 days of retroviral production. After 5 days, 10 times more infectious retroviruses were obtained by circulating and keeping the majority of supernatant longer in the cold reservoir than in the production vessel at 37 degrees C in comparison with the number collected from the static tissue culture dish without circulating the culture medium. Furthermore, the concentration of transduction inhibitors in the supernatant was decreased along with the retardation of retroviral decay at low temperature. The two-stage operation developed in this study should be easily applied to large-scale bioreactors for mass production of high-titer retroviral supernatants.

Endothelium-Targeted Gene and Cell-Based Therapies for Cardiovascular Disease

Most common cardiovascular diseases are accompanied by endothelial dysfunction. Because of its predominant role in the pathogenesis of cardiovascular disease, the vascular endothelium is an attractive therapeutic target. The identification of promoter sequences capable of rendering endothelial-specific transgene expression together with the recent development of vectors with enhanced tropism for endothelium may offer opportunities for the design of new strategies for modulation of endothelial function. Such strategies may be useful in the treatment of chronic diseases such as hypertension, atherosclerosis, and ischemic artery disease, as well as in acute myocardial infarction and during open heart surgery for prevention of ischemia and reperfusion (I/R)-induced injury. The recent identification of putative endothelial progenitor cells in peripheral blood may allow the design of autologous cell-based strategies for neovascularization of ischemic tissues and for the repair of injured blood vessels and bioengineering of vascular prosthesis. "Proof-of-concept" for some of these strategies has been established in animal models of cardiovascular disease. However the successful translation of these novel strategies into clinical application will require further developments in vector and delivery technologies. Further characterization of the processes involved in mobilization, migration, homing, and incorporation of endothelial progenitor cells into the target tissues is necessary, and the optimal conditions for therapeutic application of these cells need to be defined and standardized.

On the disulfide-linker strategy for designing efficacious cationic transfection lipids: an unexpected transfection profile

Herein, employing a previously reported disulfide-linker strategy, we have designed and synthesized a novel cationic lipid 2 with a disulfide-linker and its non-disulfide control analog lipid 1. The relative efficacies of lipids 1 and 2 in transfecting CHO, COS-1 and MCF-7 cells were measured using both reporter gene and whole cell histochemical staining assays. In stark contrast to the expectation based on the disulfide-linker strategy, the control non-disulfide cationic lipid 1 showed phenomenally superior in vitro transfection efficacies to its essentially transfection incompetent disulfide counterpart lipid 2. Results in DNase I protection experiments and the electrophoretic gel patterns in the presence of glutathione, taken together, are consistent with the notion that the success of the disulfide-linker strategy may depend more critically on the DNase I sensitivity of the lipoplexes than on the efficient DNA release induced by intracellular glutathione pool.

Single additional methylene group in the head-group region imparts high gene transfer efficacy to a transfection-incompetent cationic lipid

In combination with equimolar 1,2-dioleoyl-L-alpha-glycero-3-phosphatidyl ethanolamine, a novel cholesterol-based cationic lipid with beta-alanine head-group (2) has been demonstrated to be strikingly more efficacious (10-24-fold) in transfecting CHO, COS-1 and HepG2 cells than its glycine analog (1) containing just one less methylene unit in its head-group region. Syntheses, characterizations and in vitro transfection biology of lipids 1 and 2 are described. Present findings demonstrate that even truly minor structural alterations, such as inclusion of just one additional methylene functionality in the polar head-group region, can convert an essentially transfection-incompetent cholesterol-based cationic amphiphile to a remarkably efficient cationic transfection lipid.

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.

Highly efficient, large volume flow electroporation

Electroporation is widely used to transfect and load cells with various molecules. Traditional electroporation using a static mode is typically restricted to volumes less than 1 mL, which limits its use in clinical and industrial bioprocessing applications. Here we report efficient, large volume transfection results by using a scalable-volume electroporation system. Suspended (Jurkat) and adherent cells (10T1/2 and Huh-7) were tested. A large macromolecule, FITC-conjugated dextran (MW=500 kD) was used to measure cell uptake, while a plasmid carrying the gene coding for enhanced green fluorescence protein (eGFP) was used to quantitate the flow electrotransfection efficiency as determined by flow cytometry. The flow electroloading efficiency of FITC-dextran was >90%, while the cell viability was highly maintained (>90%). High flow electrotransfection efficiency (up to 75%) and cell viability (up to 90%) were obtained with processing volumes ranging from 1.5 to 50 mL. No significant difference of electrotransfection efficiency was observed between flow and static electrotransfection. When 50 mL of cell volume was processed and samples collected at different time points during electroporation, the transgene expression and cell viability results were identical. We also demonstrated that DNA plasmid containing EBNA1-OriP elements from Epstein-Barr virus were more efficient in transgene expression than standard plasmid without the elements (at least 500 too 1000-fold increase in expression level). Finally, to examine the feasibility of utilizing flow electrotransfected cells as a gene delivery vehicle, 10T1/2 cells were transfected with a DNA plasmid containing the gene coding for mIL12. mIL12 transfected cells were injected subcutaneously into mice, and produced functional mIL12, as demonstrated by anti-angiogenic activity. This is the first demonstration of efficient, large volume, flow electroporation and the in vivo efficacy of flow electrotransfected cells. This technology may be useful for clinical gene therapy and large-scale bioprocesses.

Enhanced transgene expression in primitive hematopoietic progenitor cells and embryonic stem cells efficiently transduced by optimized retroviral hybrid vectors

Oncoretroviral vectors have been successfully used in gene therapy trials, yet low transduction rates and loss of transgene expression are still major obstacles for their application. To overcome these problems we modified the widely used Moloney murine leukemia virus-derived retroviral vector pMX by replacing the 3'LTR with the spleen focus-forming virus LTR and inserting the woodchuck hepatitis B virus post-translational regulatory element. To compare requirements crucial for efficient transgene expression, we generated the hybrid retroviral vectors pMOWS and pOWS that harbor the complete murine embryonic stem cell virus (MESV)-leader sequence or a shortened MESV-leader not comprising primer binding site (PBS) and splice donor (SD). Applying these retroviral vectors significantly augmented transgene expression in hematopoietic cell lines and progenitor cells. For transduction of murine embryonic stem (ES) cells the retroviral vector pMOWS that harbors the MESV-PBS and -SD was superior resulting in 65% green fluorescent protein (GFP) expressing ES cells. Surprisingly, in murine and human primitive hematopoietic progenitor cells (HPC), the highest efficiency of up to 66% GFP expressing cells was achieved with pOWS, a retroviral vector that retains the negative regulatory element coinciding with the MoMuLV-PBS. In summary our hybrid retroviral vectors facilitate significantly improved transgene expression in multipotent cells and thus possess great potential for reconstituting genes in primary cells of disease models, as well as for gene therapy.

Gene therapy: promises and problems

Gene therapy can be broadly defined as the transfer of genetic material to cure a disease or at least to improve the clinical status of a patient. One of the basic concepts of gene therapy is to transform viruses into genetic shuttles, which will deliver the gene of interest into the target cells. Based on the nature of the viral genome, these gene therapy vectors can be divided into RNA and DNA viral vectors. The majority of RNA virus-based vectors have been derived from simple retroviruses like murine leukemia virus. A major shortcoming of these vectors is that they are not able to transduce nondividing cells. This problem may be overcome by the use of novel retroviral vectors derived from lentiviruses, such as human immunodeficiency virus (HIV). The most commonly used DNA virus vectors are based on adenoviruses and adeno-associated viruses. Although the available vector systems are able to deliver genes in vivo into cells, the ideal delivery vehicle has not been found. Thus, the present viral vectors should be used only with great caution in human beings and further progress in vector development is necessary.

High-efficiency gene transfer into nontransformed cells: utility for studying gene regulation and analysis of potential therapeutic targets

The elucidation of the signalling pathways involved in inflammatory diseases, such as rheumatoid arthritis, could provide long sought after targets for therapeutic intervention. Gene regulation is complex and varies depending on the cell type, as well as the signal eliciting gene activation. However, cells from certain lineages, such as macrophages, are specialised to degrade exogenous material and consequently do not easily transfect. Methods for high-efficiency gene transfer into primary cells of various lineages and disease states are desirable, as they remove the uncertainties associated with using transformed cell lines. Significant research has been undertaken into the development of nonviral and viral vectors for basic research, and as vehicles for gene therapy. We briefly review the current methods of gene delivery and the difficulties associated with each system. Adenoviruses have been used extensively to examine the role of various cytokines and signal transduction molecules in the pathogenesis of rheumatoid arthritis. This review will focus on the involvement of different signalling molecules in the production of tumour necrosis factor alpha by macrophages and in rheumatoid synovium. While the NF-kappaB pathway has proven to be a major mediator of tumour necrosis factor alpha production, it is not exclusive and work evaluating the involvement of other pathways is ongoing.

Multigene lentiviral vectors based on differential splicing and translational control

Lentiviral vectors, so far, have been optimized for the expression of a single open reading frame. Certain practical applications of gene therapy will, however, require expression of multiple genes. The goal of this study was to explore the feasibility of directing expression of two marker genes from a lentiviral vector. We designed two types of multigene lentiviral vectors. First, we used a strategy based on the natural splicing signals of HIV-1, by which multiple mRNAs are generated from a single transcriptional unit. A second strategy was construction of a polycistronic mRNA using a translational cis-acting element, the encephalomyocarditis virus internal ribosome entry site (IRES). Our studies show that the inclusion of multiple genes in lentiviral vectors does not result in reduction in virus titers or in the loss of ability to infect nondividing cells. We introduced mutations in tat and/or rev to test whether splicing modulates the relative levels of expression of reporter genes. We also developed a truncated version of tat, which is devoid of the apoptosis-associated domain. Inclusion of this tat mutant in a lentiviral vector resulted in the generation of virus with titers similar to those of lentivirus vectors expressing wild-type tat.