Self-inactivating lentiviral vectors with U3 and U5 modifications

Cellular specificity of HIV-1 replication can be controlled by LTR sequences

Two well-established determinants of retroviral tropism are envelope sequences that regulate entry and LTR sequences that can regulate viral expression in a cell-specific manner. Studies with human immunodeficiency virus-1 (HIV-1) have demonstrated that tropism of this virus maps primarily to variable envelope sequences. Studies have demonstrated that T cell and macrophage-specific transcription factor binding motifs exist in the upstream region of the LTR U3; however, the ability of the core enhancer/promoter proximal elements (two NF-kappaB and three Sp1 sites) to function well in macrophages and T cells have led many to conclude that HIV LTR sequences are not primary determinants of HIV tropism. To determine if cellular specificity could be imparted to HIV by the core enhancer elements, the enhancer/promoter proximal region of the HIV LTR was substituted with motifs that control gene expression in a myeloid-specific manner. The enhancer region from equine infectious anemia virus (EIAV) when substituted for the HIV enhancer/promoter proximal region was found to drive expression in a macrophage-specific manner and was responsive to HIV Tat. The addition of a 5' methylation-dependent binding site (MDBP) and a promoter proximal Sp1 motif increased expression without altering cellular specificity. Spacing between the promoter proximal region and the TATA box was also found to influence LTR activity. Infectivity studies using chimeric LTRs within the context of a dual-tropic infectious molecular clone established that these LTRs directed HIV replication and production of infectious virions in macrophages but not primary T cells or T cell lines. This investigation demonstrates that cellular specificity can be imparted onto HIV-1 replication at the level of viral transcription and not entry.

Lentiviral Vector: A Useful Tool for Transduction of Human Liver Endothelial Cells

Endothelial cells play multiple roles in pathophysiologic processes and are increasingly being recognized as target cells of gene therapy. Lentiviral vectors derived from human immunodeficiency virus type 1 have an ability to infect both dividing and nondividing cells and currently receive a great deal of attention as an innovative tool for transduction of target cells. The purpose of the present work was to evaluate the efficacy of a lentiviral vector for transducing human liver endothelial cells (HLECs) in vitro. For the present study, a pseudotyped lentiviral vector encoding a green fluorescent protein (GFP) gene, LtV-GFP, was generated by means of FuGENE 6 method and allowed to infect HLECs. Approximately 95% of HLECs were positive for GFP expression after LtV-GFP infection at a multiplicity of infection of 10. Notably, LtV-GFP transduced HLECs had stable and long term GFP expression, showed gene expression of endothelial markers including CD 34, factor VIII, flt-1, KDR/flk-1 and HGF, and maintained in vitro angiogenic potential in a Matrigel assay to the same extent as primarily cultured HLECs. These findings provide evidence that lentivirus based gene delivery is an efficient tool for transduction of endothelial cells that could be considered for cell and gene therapies and hybrid artificial organs.

Rational development of a HIV-1 gene therapy vector

BACKGROUND

HIV-1 provides an attractive option as the basis for gene transfer vectors due to its ability to stably transduce non-cycling cell populations. In order to fully utilise the promise of HIV-1 as a vector it is important that the effects of viral cis sequence elements on vector function are carefully delineated.

METHODS

In this study we have systematically evaluated the effect of various cis elements from the HIV-1 YU-2 genome that have been implicated as either affecting vector performance, or HIV-1 replication, on the efficiency of vector production (titre and infectivity). As a measure of the relative safety of vectors their propensity to inadvertently transfer the gagpol gene to transduced cells was assessed.

RESULTS

Sequences that were found to increase vector titre were from the 5' end of the gag gene, from the 5' and 3' ends of the env gene, from immediately upstream of the polypurine tract, and the central polypurine tract. The substitution of the HIV-1 RRE with heterologous RNA transport elements, or the deletion of the RRE, resulted in greatly reduced vector titres. RNA analysis suggested that the role of the Rev/RRE system extends beyond simply acting as an RNA nuclear export signal. The relative safety of different vector designs was compared and an optimal construct selected.

CONCLUSIONS

Based on our results we have constructed a vector that is both more efficient, and has better safety characteristics, than the widely used pHR' HIV-1 vector construct.

Genetically modified NT2N human neuronal cells mediate long-term gene expression as CNS grafts in vivo and improve functional cognitive outcome following experimental traumatic brain injury

Human Ntera-2 (NT2) cells can be differentiated in vitro into well-characterized populations of NT2N neurons that engraft and mature when transplanted into the adult CNS of rodents and humans. They have shown promise as treatments for neurologic disease, trauma, and ischemic stroke. Although these features suggest that NT2N neurons would be an excellent platform for ex vivo gene therapy in the CNS, stable gene expression has been surprisingly difficult to achieve in these cells. In this report we demonstrate stable, efficient, and nontoxic gene transfer into undifferentiated NT2 cells using a pseudotyped lentiviral vector encoding the human elongation factor 1-alpha promoter and the reporter gene eGFP. Expression of eGFP was maintained when the NT2 cells were differentiated into NT2N neurons after treatment with retinoic acid. When transplanted into the striatum of adult nude mice, transduced NT2N neurons survived, engrafted, and continued to express the reporter gene for long-term time points in vivo. Furthermore, transplantation of NT2N neurons genetically modified to express nerve growth factor significantly attenuated cognitive dysfunction following traumatic brain injury in mice. These results demonstrate that defined populations of genetically modified human NT2N neurons are a practical and effective platform for stable ex vivo gene delivery into the CNS.

Efficient large-scale production and concentration of HIV-1-based lentiviral vectors for use in vivo

The aim of this study was to develop an efficient method for packaging and concentrating lentiviral vectors that consistently yields high-titer virus on a scale suitable for in vivo applications. Transient cotransfection of 293T packaging cells with DNA plasmids encoding lentiviral vector components was optimized using SuperFect, an activated dendrimer-based transfection reagent. The use of SuperFect allowed reproducible and efficient production of high-titer lentiviral vector at concentrations greater than 1 x 10(7) transducing units per ml (TU/ml) and required less than one-third of the total amount of DNA used in traditional calcium phosphate transfection methods. Viral titers were further increased using a novel concentration protocol that yielded an average final titer of 1.4 x 10(10) TU/ml. Lentiviruses produced using these methods exhibited efficient transduction of central nervous system and peripheral tissues in vivo. The method is reproducible and can be scaled up to facilitate the use of these vectors in animal studies.

Gene therapy of apolipoprotein E-deficient mice using a novel macrophage-specific retroviral vector

The use of retroviral gene transfer into hematopoietic stem cells for human gene therapy has been hampered by the absence of retroviral vectors that can generate long-lasting, lineage-specific gene expression. We developed self-inactivating retroviral vectors that incorporate gene-regulatory elements from the macrophage-restricted human CD68 gene. Through the transplantation of transduced murine hematopoietic stem cells (HSCs), we show that a vector incorporating a 342-base pair (bp) fragment of 5' flanking sequence from the CD68 gene, in addition to the CD68 first intron, was able to direct macrophage-specific expression of an enhanced green fluorescent protein (EGFP) reporter gene in inflammatory cell exudates and lymphoid organs in vivo. Levels of EGFP expression generated by this vector were greater than those generated by a standard Moloney murine leukemia retroviral vector, and they were stable for at least a year after transplantation of transduced HSCs. To evaluate the ability of this vector to generate therapeutically useful levels of gene expression, we transplanted apolipoprotein E (ApoE)-deficient HSCs transduced with a virus encoding ApoE into ApoE-deficient mice. Macrophages from these mice expressed levels of ApoE that were comparable to those from wild-type mice, and vector-driven expression of ApoE in macrophages was sufficient to reverse both hypercholesterolemia and atherosclerotic lesion development. The future application of this retroviral vector should provide a powerful tool to further elucidate macrophage function and for human gene therapy.

Advances in lentiviral vector design for gene-modification of hematopoietic stem cells

Lentiviral vectors are more efficient at transducing quiescent hematopoietic stem cells than murine retroviral vectors. This characteristic is due to multiple karyophilic components of the lentiviral vector pre-integration complex. Lentiviral vectors are also able to carry more complex payloads than murine retroviral vectors, making it possible to deliver expression cassettes that direct either constitutive or targeted expression in various hematopoietic stem cell progeny.

RNA 3' readthrough of oncoretrovirus and lentivirus: implications for vector safety and efficacy

The expression of reporter genes driven by the same human elongation factor 1alpha (EF1alpha) promoter in murine leukemia virus (MLV)- and human immunodeficiency virus type 1 (HIV-1)-based vectors was studied in either transfected or virally transduced cells. The HIV-1 vectors consistently expressed 3 to 10 times higher activity than the MLV vectors at both the RNA and protein levels. The difference was not attributable to transcriptional interference, alternative enhancer/silencer, or differential EF1alpha intron splicing. Based on nuclear run-on assays, both vectors exhibited similar EF1alpha transcriptional activity. The reduced RNA levels of MLV vectors could not be explained by the decrease in RNA half-lives. Southern analysis of proviral DNA indicated that both HIV-1 and MLV vectors efficiently propagated the EF1alpha intron in the transduced cells. To decipher the discrepancy in transgene expression between MLV and HIV-1 vectors, the role of RNA 3'-end processing was examined using a sensitive Cre/lox reporter assay. The results showed that MLV vectors, but not HIV-1 vectors, displayed high frequencies of readthrough of the 3' polyadenylation signal. Interestingly, the polyadenylation signal of a self-inactivating (SIN) HIV-1 vector was as leaky as that of the MLV vectors, suggesting a potential risk of oncogene activation by the lentiviral SIN vectors. Together, our results suggest that an efficient polyadenylation signal would improve both the efficacy and the safety of these vectors.

Comparison of gene transfer efficiencies and gene expression levels achieved with equine infectious anemia virus- and human immunodeficiency virus type 1-derived lentivirus vectors

This report compares gene transfer efficiencies as well as durations and levels of gene expression for human immunodeficiency virus (HIV) and equine infectious anemia virus (EIAV) lentiviral vectors in a variety of human cell types in vitro. EIAV and HIV vectors transduced equivalent numbers of proliferating and G1/S- and G2/M-arrested cells, and both had very low efficiencies of transduction into G0-arrested cells. Analysis of the levels of both the enhanced green fluorescent protein (EGFP) and mRNA demonstrated that the HIV-transduced cells expressed greater levels of EGFP protein and RNA than the EIAV-transduced cells. Measurements of vector-derived EGFP RNA half-lives were fourfold higher with the HIV vector than with the EIAV vector. Long-term culture of EIAV-transduced human cells showed a significant decrease in the number of cells expressing the transgene; however, no corresponding loss was found in EIAV-transduced equine cells. In contrast, only a moderate decrease in the number of transgene-expressing cells was seen with the HIV vectors. Taken together, these results demonstrate that the EIAV vectors transduced human cells with efficiencies similar to those of the HIV vectors. However, our data indicate that transgene expression from EIAV vectors is limited by the instability of vector-derived RNA transcripts and silencing of the EIAV vectors over time.

Characterization of mitotic neurons derived from adult rat hypothalamus and brain stem

Embryonic or neonatal rat neurons retain plasticity and are readily grown in tissue culture, but neurons of the adult brain were thought to be terminally differentiated and therefore difficult to culture. Recent studies, however, suggest that it may be possible to culture differentiated neurons from the hippocampus of adult rats. We modified these procedures to grow differentiated neurons from adult rat hypothalamus and brain stem. At day 7 in tissue culture and beyond, the predominant cell types in hypothalamic and brain stem cultures had a stellate morphology and could be subdivided into two distinct groups, one of which stained with antibodies to the immature neuron marker alpha-internexin, while the other stained with the astrocyte marker GFAP. The alpha-internexin positive cells were mitotic and grew to form a characteristic two-dimensional cellular network. These alpha-internexin positive cells coimmunostained for the neuronal markers MAP2, type III beta-tubulin, and tau, and also bound tetanus toxin, but were negative for the oligodendrocyte marker GalC and also for the neurofilament triplet proteins NF-L, NF-M, and NF-H, markers of more mature neurons. Patch-clamp analysis of these alpha-internexin positive cells revealed small Ca(2+) currents with a peak current of -0.5 +/- 0.1 pA/pF at a membrane potential of -20 mV (n = 5) and half-maximal activation at -30 mV (n = 5). Na(+) currents with a peak current density of -154.5 +/- 49.8 pA/pF at a membrane potential of -15 mV (n = 5) were also present. We also show that these cells can be frozen and regrown in tissue culture and that they can be efficiently infected by viral vectors. These cells therefore have the immunological and electrophysiological properties of immature mitotic neurons and should be useful in a variety of future studies of neuronal differentiation and function.

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

Safe and efficient genetic modification of liver cells could enable new therapies for a variety of hepatic and systemic diseases. Lentiviral vectors are promising tools for in vivo gene delivery. Previous data suggested that recruitment into the cell cycle was required for transduction of hepatocytes in vivo. We developed an improved vector design that enhanced nuclear translocation in target cells and significantly improved gene transfer performance. Using the new vector and a panel of internal promoters, we showed that rat hepatocytes were transduced ex vivo to high frequency without requirement for proliferation. On intravenous administration of vector into adult severe combined immunodeficient (SCID) mice, we found high levels (up to 30%) of transduction of parenchymal and nonparenchymal cells of the liver, integration of the vector genome in liver DNA and stable expression of the marker green fluorescent protein (GFP)-encoding gene without signs of toxicity. Coadministration of vectors and 5'-bromo-2'-deoxyuridine in vivo proved that cell cycling was not required for efficient transduction of hepatocytes. In addition to the liver, the spleen and the bone marrow were transduced effectively by systemic delivery of vector. GFP expression was observed in all these organs when driven by the cytomegalovirus promoter and by the phosphoglycerate kinase gene promoter. Using the promoter of the albumin gene, we could restrict expression to hepatocytes. By a single vector injection into the bloodstream of SCID mice, we achieved therapeutic-range levels of the human clotting factor IX, stable in the plasma for up to 1 year (the longest time tested), indicating the potential efficacy of improved lentiviral vectors for the gene therapy of hemophilias and other diseases.

Targeting transgene expression to antigen-presenting cells derived from lentivirus-transduced engrafting human hematopoietic stem/progenitor cells

Hematopoietic stem cells (HSCs) represent an important target for the treatment of various blood disorders. As the source of critical cells within the immune system, genetic modification of HSCs can also be used to modulate immune responses. The effectiveness of HSC-mediated gene therapy largely depends on efficient gene delivery into long-term repopulating progenitors and targeted transgene expression in an appropriate progeny of the transduced pluripotent HSCs. Self-inactivating (SIN) lentiviral vectors have been demonstrated to be capable of transducing mitotically inactive cells, including HSCs, and accommodating a nonviral promoter to control the transgene expression in transduced cells. In this study, we constructed 2 SIN lentiviral vectors, EF.GFP and DR.GFP, to express the green fluorescent protein (GFP) gene controlled solely by the promoter of either a housekeeping gene EF-1alpha or the human HLA-DRalpha gene, which is selectively expressed in antigen-presenting cells (APCs). We demonstrated that both vectors efficiently transduced human pluripotent CD34+ cells capable of engrafting nonobese diabetic/severe combined immunodeficiency (NOD/SCID) mice. When the EF.GFP vector was used, constitutive high-level GFP expression was obtained in all the human HSC progeny detectable in NOD/SCID mice and in subsequent in vitro differentiation assays, indicating that engrafting human HSCs have been transduced. In contrast, the DR.GFP vector mediated transgene expression specifically in human HLA-DR+ cells and highly in differentiated dendritic cells (DCs), which are critical in regulating immunity. Furthermore, human DCs derived from transduced and engrafted human cells potently stimulated allogeneic T-cell proliferation. This study demonstrated successful targeting of transgene expression to APCs/DCs after stable gene transduction of pluripotent HSCs.

Helper plasmids for production of HIV-1-derived vectors

Vectors derived from human immunodeficiency virus type 1 (HIV-1) appear an attractive option for many gene therapy applications. This is due to their ability to transduce noncycling cell populations and to integrate their genome into the host cell chromosome, resulting in the stable genetic modification of the transduced cell. These properties have permitted the direct in vivo transduction of several tissues, including the central nervous system, retina, and liver. However, the pathogenic nature of HIV-1 has raised considerable concerns about the safety of such vector systems. To help address these concerns, we have expressed each of the primary transcriptional units encoding trans functions relevant for vector production in individual plasmid constructs. The gag-pol gene sequence was codon-optimized for expression in mammalian cells resulting in high level Rev/Rev-response element (RRE)-independent expression. Codon optimization of gag-pol also reduces sequence homology with vectors containing gag gene sequences, which results in reduced transfer of biologically active gag-pol sequences to transduced cells. Furthermore, the vif reading frame overlapping the 3' end of the pol coding sequence is destroyed by codon optimization. We have also shown that the Gag and Gag-Pol polyproteins can be efficiently expressed from separate transcriptional units. This has enabled the removal of a cis-acting viral element, the gag-pol translational frameshift sequence, from the vector/packaging system and prevents detectable transfer of biologically active sequences equivalent to the gag-pol gene to transduced cells.

A new-generation stable inducible packaging cell line for lentiviral vectors

We have successfully generated and characterized a stable packaging cell line for HIV-1-based vectors. To allow safe production of vector, a minimal packaging construct carrying only the coding sequences of the HIV-1 gag-pol, tat, and rev genes was stably introduced into 293G cells under the control of a Tet(o) minimal promoter. 293G cells express the chimeric Tet(R)/VP16 trans-activator and contain a tetracycline-regulated vesicular stomatitis virus protein G (VSV-G) envelope gene. When the cells were grown in the presence of tetracycline the expression of both HIV-1-derived and VSV-derived packaging functions was suppressed. On induction, approximately 50 ng/ml/24 hr of Gag p24 equivalent of vector was obtained. After introduction of the transfer vector by serial infection, vector could be collected for several days with a transduction efficiency similar or superior to that of vector produced by transient transfection both for dividing and growth-arrested cells. The vector could be effectively concentrated to titers reaching 10(9) transducing units/ml and allowed for efficient delivery and stable expression of a GFP transgene in the mouse brain. The packaging cell line and all vector producer clones described here were shown to be free from replication-competent recombinants, and from recombinants between packaging and vector constructs that transfer the viral gag-pol genes. The packaging cell line and the assays developed will advance lentiviral vectors toward the stringent requirements of clinical applications.

Enhanced transgene expression in cord blood CD34(+)-derived hematopoietic cells, including developing T cells and NOD/SCID mouse repopulating cells, following transduction with modified trip lentiviral vectors

The recent development of lentivirus-derived vectors is an important breakthrough in gene transfer technology because these vectors allow transduction of nondividing cells such as hematopoietic stem cells (HSC), due to an active nuclear import of reverse-transcribed vector DNA. We recently demonstrated that addition of the central DNA flap of HIV-1 to an HIV-derived lentiviral vector strikingly increases transduction of CD34(+) cells. We now describe improvements of the transduction protocol designed to preserve HSC properties and two modifications of the previously described TRIP-CMV vector. First, deletion of the enhancer/promoter of the 3' LTR in the TRIP-CMV vector resulted in a safer vector (TRIPDeltaU3-CMV) with conserved transduction efficiency and increased EGFP transgene expression. Second, the original internal CMV promoter was replaced with the promoter for the ubiquitously expressed elongation factor 1alpha (EF1alpha). This promoter substitution resulted in a significantly more homogeneous expression of the EGFP transgene in all hematopoietic cell types, including CD34(+)-derived T lymphocytes, in which the CMV promoter was inactive, and NOD/SCID mouse repopulating cells. We thus present here an HIV-derived lentiviral vector, TRIPDeltaU3-EF1alpha, which can very efficiently transduce human cord blood HSC and results in high long-term transgene expression in CD34(+)-derived T, B, NK, and myeloid hematopoietic cells.

The future of hypertension therapy: sense, antisense, or nonsense?

Hypertension is a debilitating disease with significant socioeconomic and emotional impact. Despite recent success in the development of traditional pharmacotherapy for the management of hypertension, the incidence of this disease is on the rise and has reached epidemic proportions by all estimates. This has led many to conclude that traditional pharmacotherapy has reached an intellectual plateau, and novel approaches for the treatment and control of hypertension must be explored. We have begun to investigate the possibility of treating and/or curing hypertension by using genetic means. In this review, we will provide evidence in favor of targeting of the renin-angiotensin system by antisense gene therapy as an effective strategy for the lifelong prevention of hypertension in the spontaneously hypertensive rat model. In addition, we will discuss the properties of an ideal vector for the systemic delivery of genes and the potential experimental hurdles that must be overcome to take this innovative approach to the next level of evaluation.

Use of intron-disrupted polyadenylation sites to enhance expression and safety of retroviral vectors

Normal mRNA polyadenylation signals are composed of an AAUAAA motif and G/U box spaced 20 to 30 bp apart. If this spacing is increased further, then polyadenylation is disrupted. Previously it has been demonstrated that insertion of an intron will similarly disrupt this signal even though such introns are removed during a nuclear splicing reaction (X. Liu and J. Mertz, Nucleic Acids Res. 21:5256-5263, 1993). This observation has led to the suggestion that polyadenylation site selection is undertaken prior to intron excision. We now present results that both support and extend these observations and in doing so create a novel class of retroviral expression vector with improved qualities. We found that when an intron-disrupted polyadenylation signal is inserted within a retroviral expression vector, such a signal, although reformed in the producer cell, remains benign until transduction, where it is then preferentially used. Thus, we demonstrate that upon transduction these vectors now produce a majority of shortened subgenomic species and as a consequence have a reduced tendency for subsequent mobilization from transduced cells. In addition, we demonstrate that the use of this internal signal leads to enhanced expression from such vectors and that this is achieved without any loss in titer. Therefore, split polyadenylation signals confer enhanced performance and improved safety upon retroviral expression vectors into which they are inserted. Such split signals may prove useful for the future optimization of retroviral vectors in gene therapy.

Lentivirus and foamy virus vectors: novel gene therapy tools

The aim of gene therapy is to modify the genetic material of living cells to achieve therapeutic benefit. Gene therapy involves the insertion of a functional gene into a cell, to replace an absent or defective gene, or to fight an infectious agent or a tumour. At present, a wide variety of somatic tissues are being explored for the introduction of foreign genes with a view towards treatment. A prime requirement for successful gene therapy is the sustained expression of the therapeutic gene without any adverse effect on the recipient. A highly desirable vector would be generated at high titres, integrate into target cells (including non-dividing cells) and have little or no associated immune reactions. Lentiviruses have the ability to infect dividing and non-dividing cells and, therefore, constitute ideal candidates for development of vectors for gene therapy. This review presents a description of available lentiviral vectors, including vector design, applications to disease treatment and safety considerations. In addition, general aspects of the biology of lentiviruses with relevance to vector development will be discussed. Recent investigations have revealed that foamy viruses, another group of retroviruses, are also capable of infecting non-dividing cells. Thus, foamy virus vectors are actively being developed in parallel to lentivirus vectors. This review will also include various aspects of the biology of foamy viruses with relevance to vector development.

Rev-independent expression of synthetic gag-pol genes of human immunodeficiency virus type 1 and simian immunodeficiency virus: implications for the safety of lentiviral vectors

The safety of lentiviral vectors for clinical applications is still a major concern. The gag-pol expression plasmids and the lentiviral vectors used in previous studies contain homologous regions, which constitute a risk for recombination events. Synthetic gag-pol genes of human immunodeficiency virus type 1 (HIV-1) and simian immunodeficiency virus (SIV) were therefore constructed, in which the codon usage was optimized for expression in human cells without altering the amino acid sequences. The synthetic gag-pol genes allowed efficient expression of these genes in the absence of Rev and the 5' untranslated leader region. Both the HIV-1 and the SIV synthetic gag-pol expression plasmids could mediate transduction of an SIV vector into nondividing human cells with titers of about 10(6) transducing units/ml. Similar titers were obtained with a four-plasmid vector-packaging system based on HIV-1. Using a biological assay, homologous recombination events between the synthetic gag-pol expression plasmids and an SIV vector were undetectable and in comparison with a previously used gag-pol expression plasmid at least approximately 100-fold less frequent. By eliminating regions of homology and sequences involved in packaging, synthetic gag-pol genes should improve the safety profile of lentiviral vectors.

Prospects for gene therapy for inherited cardiomyopathies

Over the last few years the genes responsible for a number of genetic diseases of the cardiovascular system have been identified. These have included X-linked and autosomal dominant dilated cardiomyopathy, and hypertrophic cardiomyopathy. Genetic heterogeneity has been described in both of these diseases but a commonality of function has been apparent: defects in cytoskeletal proteins cause dilated cardiomyopathy and mutations in sarcomeric proteins cause hypertrophic cardiomyopathy. This led us to develop a 'final common pathway' hypothesis as a framework for selecting candidate genes for mutation screening in families with these diseases. The characterization of gene mutations has led to the development of therapies specifically targeting the defective protein or the pathway in which it is involved. These have included the use of pharmaceutical agents to replace or to antagonize the mutated protein, and replacement of the defective gene with a functional one (gene therapy). While early studies using gene therapy vectors were promising, translating studies in animals to viable therapeutic options for humans has remained problematic. There have been many publications describing the use of vectors to transduce target cells for the correction of gene defects, including recombinant retroviruses, adenoviruses, and adeno-associated viruses, as well as non-viral vectors. In this review we will discuss the identification of gene defects associated with cardiomyopathies, and the potential of gene therapy for the treatment of these diseases, as well as addressing some concerns related to the use of adenovirus-based vectors, a virus known to be an etiologic agent of acquired dilated cardiomyopathy.

Lentiviral vectors: excellent tools for experimental gene transfer and promising candidates for gene therapy

Lentiviral vectors are tools for gene transfer derived from lentiviruses. From their first application to now they have been strongly developed in design, in biosafety and in their ability of transgene expression into target cells. Primate and non-primate derived lentiviral vectors are now available and with both types of systems a lot of studies tuned to improve their performances in a large number of tissues are ongoing. Here we review the state of the art of lentiviral vector systems discussing their potential for gene therapy.

Gene therapy in the CNS

Gene therapy for neurological disorder is currently an experimental concept. The goals for clinical utilization are the relief of symptoms, slowing of disease progression, and correction of genetic abnormalities. Experimental studies are realizing these goals in the development of gene therapies in animal models. Discoveries of the molecular basis of neurological disease and advances in gene transfer systems have allowed focal and global delivery of therapeutic genes for a wide variety of CNS disorders. Limitations are still apparent, such as stability and regulation of transgene expression, and safety of both vector and expressed transgene. In addition, the brain adds several challenges not seen in peripheral gene therapy paradigms, such as post-mitotic cells, heterogeneity of cell types and circuits, and limited access. Moreover, it is likely that several modes of gene delivery will be necessary for successful gene therapies of the CNS. Collaborative efforts between clinicians and basic researchers will likely yield effective gene therapy in the CNS.