Lentiviral vectors for gene delivery into cells

In vivo evaluation of an EIAV vector for the systemic genetic delivery of therapeutic antibodies

Lentiviral-based vectors hold great promise as gene delivery vehicles for the treatment of a wide variety of diseases. We have previously reported the development of a nonprimate lentiviral vector system based on the equine infectious anaemia virus (EIAV), which is able to efficiently transduce dividing and nondividing cells both in vitro and in vivo. Here, we report on the application of EIAV vectors for the systemic delivery of an antibody fusion protein designed for the treatment of cancer. The therapeutic potential of a single chain antibody against the tumour-associated antigen, 5T4, fused to immune enhancer moieties has been demonstrated in vitro and here we evaluate the genetic delivery of a 5T4 scFv fused to B7.1 (scFvB7) using an EIAV vector. The kinetics and concentration of protein produced following both intravenous (i.v.) and intramuscular (i.m.) administration was determined in immune competent adult mice. In addition, the immune response to the EIAV vector and the transgene were determined. Here, we show that a single injection of EIAV expressing scFv-B7 can give rise to concentrations of protein in the range of 1-5 microg/ml that persist in the sera for more than 50 days. After a second injection, concentrations of scFv-B7.1 rose as high as 20 microg/ml and levels greater than 2 microg/ml were present in the sera of all mice injected i.v. after 210 days despite the detection of antibodies against both the transgene and viral envelope for the duration of this study. These results demonstrate the potential of EIAV as a gene therapy vector for long-term production of therapeutic recombinant proteins.

Lentiviral transduction of microglial cells

Microglial cells are the resident immune cells of the central nervous system. Their function resembles that of tissue macrophages and, as such, they share many properties with both peripheral macrophages and monocytes. One striking similarity is the difficulty with which these cells can be genetically manipulated via transfection or transduction. We have sought to overcome this challenge and generate stably transduced microglial cell lines. Based on encouraging results from macrophages, we hypothesized that lentiviral vectors might provide a valuable tool in the transduction of microglial cells. Using a lentiviral-based vector system expressing enhanced green fluorescent protein (eGFP) under the control of the murine stem cell virus promoter (MSCV), we found that multiplicities of infection (MOIs) of 1, 10, and 100 transduce >70%, >88%, and >95% of the cells, respectively. From the pool of transduced cells, we established lines of N9 and BV-2 microglial cells with distinct fluorescence intensities. Using real time-polymerase chain reaction (PCR), we correlated the integrated eGFP copy numbers to eGFP fluorescence measured by flow cytometry. When mixed, up to three lines with different eGFP intensities could be separated by flow cytometry and fluorescence microscopy. Neither infection nor transgene expression influenced microglial activation as assessed by nitric oxide (NO) production, cytokine release, and surface antigen expression. Our findings that microglial cells are easily transduced by lentiviral based vectors will facilitate research depending on genetic manipulation and help generate transgenic cell lines. In addition, the availability of microglial cell lines with defined fluorescence properties could replace elaborate staining procedures for microglial identification in co-culture experiments.

Design and in vivo characterization of self-inactivating human and non-human lentiviral expression vectors engineered for streptogramin-adjustable transgene expression

Adjustable transgene expression is considered key for next-generation molecular interventions in gene therapy scenarios, therapeutic reprogramming of clinical cell phenotypes for tissue engineering and sophisticated gene-function analyses in the post-genomic era. We have designed a portfolio of latest generation self-inactivating human (HIV-derived) and non-human (EIAV-based) lentiviral expression vectors engineered for streptogramin-adjustable expression of reporter (AmyS(DeltaS), EYFP, SAMY, SEAP), differentiation-modulating (human C/EBP-alpha) and therapeutic (human VEGF) transgenes in a variety of rodent (CHO-K1, C2C12) and human cell lines (HT-1080, K-562), human and mouse primary cells (NHDF, PBMC, CD4+) as well as chicken embryos. Lentiviral design concepts include (i) binary systems harboring constitutive streptogramin-dependent transactivator (PIT) and PIT-responsive transgene expression units on separate lentivectors; (ii) streptogramin-responsive promoters (P(PIR8)) placed 5' of desired transgenes; (iii) within modified enhancer-free 3'-long terminal repeats; and (iv) bidirectional autoregulated configurations providing streptogramin-responsive transgene expression in a lentiviral one-vector format. Rigorous quantitative analysis revealed HIV-based direct P(PIR)-transgene configurations to provide optimal regulation performance for (i) adjustable expression of intracellular and secreted product proteins, (ii) regulated differential differentiation of muscle precursor cell lines into adipocytes or osteoblasts and (iii) conditional vascularization fine-tuning in chicken embryos. Similar performance could be achieved by engineering streptogramin-responsive transgene expression into an autoregulated one-vector format. Powerful transduction systems equipped with adjustable transcription modulation options are expected to greatly advance sophisticated molecular interventions in clinically and/or biotechnologically relevant primary cells and cell lines.

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.

Identification of synthetic endothelial cell-specific promoters by use of a high-throughput screen

Transcriptional targeting is a desirable property for many gene transfer applications. Because endothelial cells line most blood vessels, they are attractive candidates for the introduction of therapeutic gene products. As a proof-of-concept study, we attempted to identify a synthetic, endothelial cell-specific promoter by use of a high-throughput screen involving self-inactivating (SIN) human immunodeficiency virus type 1 (HIV-1)-based vectors. Select duplex oligodeoxynucleotides recognized by transcription factors and located 5' of endothelial cell-specific mRNA transcripts were randomly ligated and cloned upstream of a minimal ICAM-2 promoter driving enhanced green fluorescent protein (eGFP) in a SIN HIV-1-based vector. Vesicular stomatitis virus G protein-pseudotyped particles were prepared from a library of >10(6) vector recombinants and used to transduce an endothelial cell line. The highest eGFP expressers were repeatedly sorted, and the synthetic promoters were recovered and retested by a luciferase reporter. Several promoters were active and specific to endothelial cells of varied species, with high selectivity indexes and inducibility under hypoxia-mimetic conditions. One in particular was then introduced back into a SIN HIV-1-based vector to confirm its endothelial cell activity and specificity. This study suggests that SIN vectors may be used in a high-throughput manner to identify tissue-specific promoters of high activity, with potential applications for both transcriptional targeting and gene transfer.

Therapeutic potential of decoy oligonucleotides strategy in cardiovascular diseases

Recent progress in molecular biology has provided several new techniques to inhibit target gene expression. In particular, the application of DNA technology, such as an antisense strategy, to regulate the transcription of disease-related genes in vivo has important therapeutic potential. Recently, transfer of cis-element double-stranded oligonucleotides (ODN) (= decoy) has been reported as a new powerful tool in a new class of antigene strategies for gene therapy. Transfer of the double-stranded ODN corresponding to the cis-sequence will result in attenuation of the authentic cis-trans interaction, leading to removal of trans-factors from the endogenous cis-elements with subsequent modulation of gene expression.

Lentiviral Vectors Efficiently Transduce Quiescent Mature 3T3-L1 Adipocytes

Obesity is associated with many serious afflictions such as cardiovascular disease, cancer, and diabetes. One of the main cellular systems used to study the underlying physiological and biological processes is the 3T3-L1 preadipocyte differentiation model. However, studies on 3T3-L1 adipocytes are hampered by the fact that genetic modification of mature adipocytes is notoriously difficult. In this report, we evaluated the use of lentivirus-mediated gene transfer into 3T3-L1 mature adipocytes. We demonstrate that quiescent, fully differentiated 3T3-L1 adipocytes as well as 3T3-L1 preadipocytes can be efficiently transduced with HIV-1-derived lentiviral vectors. Upon transduction using LV-PGK-GFP lentiviral vector at 100 ng p24 per 10(5) cells, more than 95% of the 3T3-L1 adipocytes in the culture expressed the GFP reporter gene. There were no overt signs of toxicity or cytopathogenicity in the cultures. Furthermore, modification of undifferentiated preadipocytes did not affect their capacity to differentiate. In addition, insulin-induced glucose uptake was not affected by the procedure. In contrast, adenoviral-mediated gene transfer into 3T3-L1 adipocytes is associated with marked cytopathogenicity. From these data, we conclude that lentiviral vectors are the gene-transfer system of choice for genetic modification of mature adipocytes. The availability of an efficient vector system may stimulate the use of adipose tissue as a target for gene therapy in obesity and other disorders.

Comparison of serum sensitivities of pseudotype retroviruses produced from newly established packaging cell lines of human and feline origins

To apply retrovirus vectors for in vivo gene therapy in cats, it is necessary to develop vector systems that are not inactivated by cat serum. In this study, the retrovirus packaging cell lines 2SC-1 and AHCeB7 were newly established from human embryonic kidney (HEK) 293 and feline fibroblastic AH927 cells, respectively. Then the sensitivities of pseudotype viruses released from these cell lines to fresh sera from humans and cats were compared. Pseudotype viruses from the 2SC-1 cells were inactivated efficiently by cat serum but not by human serum. Pseudotype viruses from the AHCeB7 cells were also inactivated efficiently by human serum, however they were rather resistant to cat serum. When the xenoantigenicity of the cell lines was examined by flow cytometry, AH927 cells reacted with human serum, however, HEK293 cells did not react with cat serum. These results suggested that pseudotype viruses from 2SC-1 cells were inactivated by the fresh cat serum in an antibody-independent manner. Chelating experiments revealed that certain temperature-sensitive factor(s) other than complements might be involved in the inactivation. The usage of feline cells as packaging cells is suitable for in vivo gene therapy in cats.

A future for transgenic livestock

The techniques that are used to generate transgenic livestock are inefficient and expensive. This, coupled with the fact that most agriculturally relevant traits are complex and controlled by more than one gene, has restricted the use of transgenic technology. New methods for modifying the genome will underpin a resurgence of research using transgenic livestock. This will not only increase our understanding of basic biology in commercial species, but might also lead to the generation of animals that are more resistant to infectious disease.

Target discovery

Target discovery, which involves the identification and early validation of disease-modifying targets, is an essential first step in the drug discovery pipeline. Indeed, the drive to determine protein function has been stimulated, both in industry and academia, by the completion of the human genome project. In this article, we critically examine the strategies and methodologies used for both the identification and validation of disease-relevant proteins. In particular, we will examine the likely impact of recent technological advances, including genomics, proteomics, small interfering RNA and mouse knockout models, and conclude by speculating on future trends.