A triploblast origin for Myxozoa?

Gene transfer to urethral strictures in rabbits: a preliminary report

OBJECTIVE

To assess the rationale for virus-mediated gene transfer into the urethra in vivo and in vitro, using a rabbit model, as this is an attractive approach to prevent recurrence after the endoscopic management of urethral strictures.

MATERIALS AND METHODS

Primary cultures of rabbit urethral stromal cells were infected with adenoviral and retroviral solutions carrying a nucleus-targeted beta-galactosidase (beta-Gal) reporter gene (respectively 109 and 107 plaque-forming units/mL). In addition, to mimic the human clinical situation, a model was developed of thermally induced stricture in rabbit urethra which produced fibrotic stenosis within 15 days. Using a prototype channelled balloon catheter, these strictures were endoscopically dilated and then instilled with the beta-Gal adenoviral or retroviral constructs.

RESULTS

The application of recombinant adenovirus and retrovirus harbouring a nucleus-targeted beta-Gal reporter gene to cultured rabbit urethral stromal cells resulted in a high transduction efficiency of up to 90% and 96%, respectively. Five days after infection, histochemical and immunohistochemical staining of the strictured urethrae showed a 3% rate of transfection targeted to stromal cells within the fibrosis, confirmed by polymerase chain reaction (PCR) analysis. Adjacent and distal spread of the virus was excluded by histochemistry, immunohistochemistry and PCR.

CONCLUSION

These results represent the first report of endoscopic adenovirus and retrovirus-mediated gene transfer to the urethra. Although at a low rate, transduction reached stromal cells transmurally within the induced strictures and was site-specific.

Gene therapy-directed osteogenesis: BMP-7-transduced human fibroblasts form bone in vivo

An ex vivo gene therapy strategy was used to achieve localized skeletal regeneration in vivo. When an adenovirus vector engineered to express bone morphogenetic protein 7 transduced human gingival fibroblasts or rat dermal fibroblasts, these nonosteogenic tissues formed bone and supported the development of hematopoietic tissue when transplanted into immunocompromised mice. Transduced gingival fibroblasts formed marrow-containing ossicles in 100% of transplants after 1-2 weeks in vivo (n = 30). Immunostaining with murine and human-specific antisera raised against osteonectin and in situ hybridization of human-specific Alu genomic sequence demonstrated that the newly formed bone organ was a chimera of both the human donor and the mouse recipient cells. In experiments of greater clinical relevance, AdCMVBMP-7-transduced dermal fibroblasts repaired critical size skeletal defects in rat calvariae (n = 6). The results of this study suggest a bifunctional role of BMP-7-transduced fibroblasts. The transduced, nonosteogenic cells not only secreted biologically active BMP-7 in vitro and in vivo, but also differentiated into bone-forming cells in vivo. This model exploits the use of an easily biopsied, self-regenerating tissue such as gingiva or skin and suggests that local regeneration of tissues by ex vivo gene therapy may not require that autogenous cells be cultured from the tissue that is to be regenerated.

Molecular engineering of matrix-targeted retroviral vectors incorporating a surveillance function inherent in von Willebrand factor

A major obstacle that limits the potential of human gene therapy is the inefficiency of gene delivery to appropriate sites in vivo. Previous studies demonstrated that the physiological surveillance function performed by von Willebrand factor (vWF) could be incorporated into retroviral vectors by molecular engineering of the MuLV ecotropic envelope (Env) protein. To advance the application of vWF targeting technology beyond laboratory animals, we prepared an extensive series of Env proteins bearing modified vWF-derived matrix-binding sequences and assembled these chimeric proteins into targeted vectors that are capable of transducing human cells. Initially, a dual envelope configuration was utilized, which required coexpression of a wild-type amphotropic Env. Subsequently, streamlined "escort" Env proteins were constructed wherein the inoperative receptor-binding domain of the targeting partner was replaced by the vWF-derived collagen-binding motif. Ultimately, an optimal construct was developed that exhibited properties of both extracellular matrix (ECM)-targeting and near wild-type amphotropic infectivity, and could be arrayed as a single envelope on a retroviral particle. On intraarterial instillation, enhanced focal transduction of neointimal cells (approximately 20%) was demonstrated in a rat model of balloon angioplasty. Moreover, transduction of tumor foci (approximately 1-3%) was detected after portal vein infusion of a matrix-targeted vector in a nude mouse model of liver metastasis. We conclude that the unique properties of these targeted injectable retroviral vectors would be suitable for improving therapeutic gene delivery in numerous clinical applications, including vascular restenosis, laser and other surgical procedures, orthopedic injuries, wound healing, ischemia, arthritis, inflammatory disease, and metastatic cancer.

Gene therapy for head and neck cancer

OBJECTIVES/HYPOTHESIS

New treatment methods are needed for head and neck cancer to improve survival without increasing morbidity. Gene therapy is a potential method of improving patient outcome. Progress in gene therapy for cancer is reviewed with emphasis on the limitations of vector technology and treatment strategies. Given the current technological vector limitations in transmitting the therapeutic genes, treatments that require the fewest number of cells to be altered by the new gene are optimal. Therefore an immune-based gene therapy strategy was selected in which the tumors were transfected with the gene for an alloantigen, human leukocyte antigen (HLA)-B7, a class I major histocompatibility complex (MHC). This would restore an antigen presentation mechanism in the tumor to induce an antitumor response. This gene therapy strategy was tested in patients with advanced, unresectable head and neck cancer.

STUDY DESIGN

Prospective trial.

METHODS

Twenty patients with advanced head and neck cancer who had failed conventional therapy and did not express HLA-B7 were treated with gene therapy using a lipid vector by direct intratumoral injection. The gene therapy product contained the HLA-B7 gene and the beta2-microglobulin gene, which permits complete expression of the class I MHC at the cell surface. Patients were assessed for any adverse effects, for changes in tumor size, for time to disease progression, and for survival. Biopsy specimens were assessed for pathological response, HLA-B7 expression, apoptosis, cellular proliferation, CD-8 cells, granzyme, and p53 status.

RESULTS

There were no adverse effects from the gene therapy. At 16 weeks after beginning gene therapy, four patients had a partial response and two patients had stable disease. Two of the tumors completely responded clinically, but tumor was still seen on pathological examination. The time to disease progression in the responding patients was 20 to 80 weeks. The median survival in patients who completed gene therapy was 54 weeks, compared with 21 weeks in patients whose tumors progressed after the first cycle of treatment. One patient survived for 106 weeks without any additional therapy. HLA-B7 was demonstrated in the treated tumors, and increased apoptosis was seen in the responding tumors.

CONCLUSION

Significant advances have been made in the field of gene therapy for cancer. Alloantigen gene therapy has had efficacy in the treatment of cancer and can induce tumor responses in head and neck tumors. Alloantigen gene therapy has significant potential as an adjunctive treatment of head and neck cancer.

Efficient gene transfer and expression of biologically active glial cell line-derived neurotrophic factor in rat motoneurons transduced wit lentiviral vectors

Several studies have shown the ability of human immunodeficiency virus type 1 (HIV1)-based lentiviral vectors to infect nondividing brain and retinal neurons with high efficiency and long-term expression of the transduced gene. We show that purified embryonic motoneurons can be efficiently (>95%) transduced in culture using an HIV1-based lentiviral vector encoding LacZ. Expression of beta-galactosidase was observed for at least 9 days in these conditions. Furthermore, motoneurons transduced with a lentiviral vector expressing glial cell line-derived neurotrophic factor survived in the absence of additional trophic support, showing that the overexpressed protein was biologically active. Our results demonstrate the potential of lentiviral vectors in studying the biological effects of proteins expressed in motoneurons and in the development of future gene therapy for motoneuron diseases.

Emerging concepts in the management of the malignant haematological disorders

A comprehensive review of novel cytoreductive agents is presented. Such novel agents may be found among chemical compounds directed against specific molecular targets (cytostatics) or within the biological substances selectively aimed at the malignant clone (immunotherapy). It is stated that the purposes of immunotherapy in general are to generate a T-lymphocytic response against the tumour cells, e.g., graft versus leukaemia (GvL) effect, natural killer T-cell cytolysis, antibody-dependent cytolysis etc.; or to reprogramme the immune system of the tumour-bearing host by DNA and/or RNA manipulation with subsequent interference with the signalling pathway in the tumour cells. Some immunotherapeutic modalities are shortly described: donor T-lymphocyte infusion and GvL effect, polyclonal antibodies, monoclonal antibodies, vaccines, gene replacement therapy, suicide gene therapy, antisense oligonucleotides, alterations of DNA-RNA transcript factors and malignant antigenic drive etc. Most likely, a sequence of different treatment modalities will be used in the future comprising an initial debulking by means of standard chemotherapy and/or irradiation followed by target unspecific immunotherapy (polyclonal immunoglobulins, GvL effect etc.) and finally target specific elimination of residual tumour, probably with repeated use of the minimum effective pharmacologic dose (MEPD) of the agents used. In contrast, the current use of high-dose myeloablative chemotherapy with the use of maximum tolerable dose (MTD) and associated severe organ toxicity, and high rates of secondary malignancies will probably be substituted in the future. An effective supportive treatment will be highly necessary, especially related to prevention and treatment of infections.

Photochemical transfection: a new technology for light-induced, site-directed gene delivery

The development of methods for specific delivery of therapeutic genes into target tissues is an important issue for the further progress of in vivo gene therapy. In this article we report on a novel technology, named photochemical transfection, to use light to direct a precise delivery of therapeutic genes to a desired location. The technology makes use of photosensitizing compounds that localize mainly in the membranes of endosomes and lysosomes. On illumination these membrane structures will be destroyed, releasing endocytosed DNA into the cell cytosol. Using a green fluorescent protein gene as a model we show that illumination of photosensitizer-treated cells induces a substantial increase in the efficiency of transfection by DNA-poly-L-lysine complexes. Thus, in a human melanoma cell line the light treatment can increase the transfection efficiency more than 20-fold, reaching transfection levels of about 50% of the surviving cells. In this article various parameters of importance for the use of this technology are examined, and the potential use of the technology in gene therapy is discussed.

Targeting retrovirus to cancer cells expressing a mutant EGF receptor by insertion of a single chain antibody variable domain in the envelope glycoprotein receptor binding lobe

We have investigated targeting of retroviral vectors to a mutant EGF receptor (EGFRvIII) that is expressed in cancers of the brain, breast, lung and ovary, but is not found in any normal tissues. An expression plasmid was made in which a single chain Fv antibody specific for EGFRvIII was inserted at a novel position within a disulphide-bonded surface loop near the native receptor binding site of the Moloney leukemia virus ecotropic envelope glycoprotein. This fusion protein was expressed and incorporated into retroviral particles as efficiently as normal envelope glycoprotein. Retroviral vectors made with the fusion protein were able to bind peptide antigen and EGFRvIII expressed on the surface of human glioblastoma cells. The retroviral vectors had normal levels of infectivity on mouse cells, showing that the envelope glycoprotein tolerated a large insertion at this site, but did not show significant infectivity to human cells expressing EGFRvIII. Thus we were able to redirect retrovirus binding to this tumour-specific target without perturbing the normal function of the ecotropic envelope glycoprotein, but this was not sufficient to mediate infectivity via this receptor.

Gene therapy and metabolic engineering

Gene therapy involves the introduction of normal, healthy genes into cells to correct the underlying cause of a wide variety of inherited and acquired diseases. Future progress in developing effective clinical protocols involving gene therapy for the treatment of cellular dysfunction associated with disease may incorporate metabolic engineering. Metabolic engineering can be applied to gene therapy for the successful identification of disease genes; elucidation of disease pathways; development of safe and efficient gene-delivery systems; and regulation and control of gene expression. Cystic fibrosis, cancer, and diabetes are reviewed as examples of diseases where gene therapy approaches are being studied.

Gene therapy for autoimmune disease

Autoantigen-specific CD4(+) T lymphocytes have been implicated in the pathogenesis of autoimmune diseases. Tissue-specific homing properties of autoantigen-specific CD4(+) T cells suggested that these cells might be ideal vehicles for delivery of retroviral-encoded regulatory proteins in a site-specific manner as a therapy for autoimmune diseases. Application of retroviral transduction of autoantigen-reactive CD4(+) T cells in gene therapy of autoimmunity must include systems capable of targeting these rare populations of antigen-activated T cells. Studies discussed below suggest that retroviral transduction of autoantigen-specific murine CD4(+) T cells may provide a method to target and isolate nontransformed autoantigen-specific murine CD4(+) T cells and provide a rational approach to gene therapy in animal models of autoimmunity.

Hepatocyte-targeted in vivo gene expression by intravenous injection of plasmid DNA complexed with synthetic multi-functional gene delivery system

To achieve hepatocyte-targeted in vivo gene expression, a carrier that controls both the tissue and intracellular distribution of DNA was designed and synthesized. A cationic polymer, poly(L-ornithine) (pOrn), was modified first with galactose, then with a fusigenic peptide (mHA2) to obtain Gal-pOrn-mHA2. When applied with Gal-pOrn-mHA2 to asialoglycoprotein receptor-positive cells, fluorescein-labeled DNA showed a diffuse profile, suggesting the release of DNA from endosomes and/or lysosomes by the carrier. Then the biodistribution and gene expression after intravenous injection of DNA complexes (10 microg DNA per mouse) were examined. After injection of [32P]DNA/Gal-pOrn-mHA2, about 60% of the radioactivity was recovered in the liver, mostly in parenchymal cells. A large amount (81 ng/g tissue) of transgene product (luciferase) was detected in the liver of mice injected with DNA/Gal-pOm-mHA2, which was 280-fold greater than that obtained with DNA/DOTMA:Chol liposomes (50 microg DNA). Prior administration of galactosylated albumin reduced the gene expression to 1/100, indicating the asialoglycoprotein receptor-mediated gene transfer in liver parenchymal cells, ie hepatocytes. The luciferase activity in hepatocytes contributed more than 95% of the total activity in all the tissues examined. Thus, hepatocyte-targeted in vivo gene expression was achieved by the intravenous injection of DNA complex with the multifunctional gene carrier.

Identification of regions in the Moloney murine leukemia virus SU protein that tolerate the insertion of an integrin-binding peptide

Targeting of retroviral vectors to specific cells has been attempted through engineering of the surface (SU) protein of the murine leukemia viruses (MuLVs), but in many cases this has adversely affected protein function and targeted delivery has been difficult to achieve. In this study, we have inserted a 15-mer peptide that binds specifically to the alpha(v)beta(3) integrin into the Moloney MuLV SU protein, including regions that are surface exposed in the crystal structure of the ecotropic receptor-binding domain. We have concentrated in particular on the variable regions VRA, VRB, and VRC, which are responsible for the use of distinct cellular receptors by different MuLV subtypes and therefore may be more likely to accommodate a heterologous binding moiety. Despite these considerations, only 8 of 26 insertion sites were tolerated, including two separate regions in VRA, a cluster of sites in VRC, and previously identified sites at the N-terminus of the protein and in the proline-rich region immediately downstream of the receptor-binding domain. When expressed on retroviral vector particles, all of the viable proteins retained the ability to bind to and transduce murine cells, although the VRC mutants and an insertion in VRA gave reduced binding and titer. Finally, although all of the viable chimeras could bind to alpha(v)beta(3) in a solid-phase binding assay, we were unable to demonstrate expanded tropism for alpha(v)beta(3)-expressing human cells. This study highlights the difficulty of engineering the Moloney MuLV SU protein, even when structural information is available, and provides guidelines for the insertion of peptide ligands into the SU protein.

Intravenous injection of naked DNA encoding secreted flt3 ligand dramatically increases the number of dendritic cells and natural killer cells in vivo

The trace number of dendritic cells (DCs) present in tissues has limited the study of DC biology and development of clinical applications utilizing DCs. Here we show that hydrodynamics-based gene delivery of naked DNA encoding secreted human flt3 ligand (hFLex) can dramatically increase the number of functional DCs and natural killer (NK) cells. After a single injection of the hFLex gene, hFLex levels in mouse serum reached approximately 40 microg/ml and remained above 1 microg/ml for 5-6 days. Sustained levels of serum hFLex correlated with significant increases in the size of the lymphoid organs and in the proportion of dendritic cells and NK cells in both lymph nodes and spleen. The increase in DC and NK cell numbers started from day 5, and reached peak levels between day 8 and day 12. The levels then returned to normal on day 20. These DCs and NK cells were functional as evidenced by mixed leukocyte reactions and lysis of YAC-1 cells, respectively. These results suggest that delivery of the hFLex gene provides a simple, efficient, and inexpensive way of increasing DC and NK cell populations in vivo, and may have broad applications in the further study of DC and NK cell biology and in the development of immunotherapy strategies.

Antisense therapeutics in chronic myeloid leukaemia: the promise, the progress and the problems

DNA sequences which are complementary or 'antisense' to a target mRNA can inhibit expression of that mRNA's protein product. Antisense therapeutics has therefore received attention for inhibiting oncogenes in haematological malignancy, in particular in chronic myeloid leukaemia. However, it is now becoming clear that antisense therapeutics is considerably more problematic than was naively initially assumed. In this article, some of these difficulties are discussed, together with the achievements in CML so far. Considerable further research is required in order to define an optimal antisense therapeutics strategy for clinical use.

Progress and potential for gene-based medicines

During the past decade researchers have explored the potential of gene-based medicines to extend current treatments employing chemical entities and proteins. However, progress has been slower than was originally predicted due to our limited knowledge of the genetic components of major diseases, the complexity of developing active biological agents as therapies, and the stringent and time-consuming tests necessary to ensure safety prior to introduction of these novel modalities in the clinic. In spite of the present technology challenges and clinical setbacks in gene therapy it is anticipated that gene-based medicines will find their niche in disease prevention and management strategies in the coming decade, extending the repertoire of medicines available to satisfy key unmet medical needs. Additionally, progress in xenotransplantation research is creating the opportunity to use gene-modified porcine organs for human transplantation. This innovative approach aims to address the current insufficiency of human donor organs for clinical transplantation.

Decreased binding to proteins and cells of polymeric gene delivery vectors surface modified with a multivalent hydrophilic polymer and retargeting through attachment of transferrin

Binding of serum proteins to polyelectrolyte gene delivery complexes is thought to be an important factor limiting bloodstream circulation and restricting access to target tissues. Protein binding can also inhibit transfection activity in vitro. In this study a multivalent reactive hydrophilic polymer has been used to inhibit protein binding. This polymer is based on poly-[N-(2-hydroxypropyl)methacrylamide] (pHPMA) bearing pendent oligopeptide (Gly-Phe-Leu-Gly) side chains terminated in reactive 4-nitrophenoxy groups (8.6 mol%). The polymer reacts with the primary amino groups of poly(L-lysine) (pLL) and produces a hydrophilic coating on the surface of pLL.DNA complexes (as measured by fluorescamine). The resulting pHPMA-coated complexes show a decreased surface charge (from +14 mV for pLL.DNA complexes to -25 mV for pHPMA-modified complexes) as measured by zeta potential analysis. The pHPMA-coated complexes also show a slightly increased average diameter (approximately 90 nm compared with 60 nm for pLL. DNA complexes) as viewed by atomic force and transmission electron microscopy and around 100 nm as viewed by photon correlation spectroscopy. They are completely resistant to protein interaction, as determined by turbidometry and SDS-polyacrylamide gel electrophoresis analysis of complexes isolated from plasma, and show significantly decreased nonspecific uptake into cells in vitro. Spare reactive ester groups can be used to conjugate targeting ligands (e.g. transferrin) on to the surface of the complex to provide a means of tissue-specific targeting and transfection. The properties of these complexes therefore make them promising candidates for targeted gene delivery, both in vitro and potentially in vivo.

Improved safety and titre of murine leukaemia virus (MLV)-based retroviral vectors

Many retroviral vectors based on murine leukaemia virus (MLV) contain the first 420 nucleotides of the gag gene, as this was reported to increase vector titre by increasing the efficiency of RNA packaging. In this study, deletion of this gag sequence from its original location did not decrease the titre of two retroviral vectors, pBabe puro and MFG-S-. The two vectors could be improved by replacing the gag sequence with a CTE from Mason-Pfizer monkey virus (MPMV). This substitution improved vector titre, while eliminating a region of homology between vector and packaging constructs. Gene Therapy (2000) 7, 300-305.

Genomic integration and gene expression by a modified adenoviral vector

A replication-deficient recombinant adenovirus encoding luciferase was constructed using 5' and 3' long terminal repeat (LTR) sequences of the Moloney murine leukemia virus. Gene expression was observed in cultured cells in vitro and in submandibular gland, cortex, and caudate nucleus for as long as three months in vivo. The vector integrated randomly into the genome of both dividing and nondividing cells as determined by fluorescence in situ hybridization (FISH) (10-15% of cells in vitro and 5% in rat spleen in vivo), gene walking, Southern hybridization, and polymerase chain reaction (PCR), in the absence of transcomplementing reverse transcriptase or integrase activity. The new vector combines the high titer and versatility of adenoviral vectors with the long-term gene expression and integration of retroviral vectors.

DeltahGHR, a novel biosafe cell surface-labeling molecule for analysis and selection of genetically transduced human cells

We describe a new selectable marker for retroviral transduction and selection of human and murine cells. The molecule expressed on the cell surface of the transduced population is a truncated version of human growth hormone receptor (deltahGHR), capable of ligand (hGH) binding, but devoid of the domains involved in signal triggering. We demonstrate that the engineered molecule is stably expressed in the target cells as an inert protein unable to trigger proliferation or to rescue the cells from apoptosis after ligand binding. This new marker will probably have a wide application spectrum, since hGHR in the human adult is highly expressed only in liver cells, and lower levels have been reported in certain lymphocyte cell populations. The deltahGHR label has high biosafety potential, as it belongs to a well-characterized hormonal system that is nonessential in adults, and there is extensive clinical experience with hGH administration in humans. This record allows us to hypothesize the lack of relevant clinical consequences resulting from massive transgene expression caused by successful replacement of a large tissue with genetically transduced cells. We take advantage of the differential binding properties of several monoclonal antibodies (MAbs) in describing a cell rescue method in which the antibody used to select deltahGHR-transduced cells is eluted by competition with hGH or, alternatively biotinylated hGH is used to capture tagged cells. In the latter system, the final purified population would be recovered free of attached antibodies in hGH (a substance approved for human use)-containing medium, providing additional biosafety relative to currently existing methods that rely on the use of murine MAb to rescue genetically labeled cells.

Genetically modified CD34+ cells as cellular vehicles for gene delivery into areas of angiogenesis in a rhesus model

To develop a cellular vehicle able to reach systemically disseminated areas of angiogenesis, we sought to exploit the natural tropism of circulating endothelial progenitor cells (EPCs). Primate CD34+ EPCs were genetically modified with high efficiency and minimal toxicity using a non-replicative herpes virus vector. These EPCs localized in a skin autograft model of angiogenesis in rhesus monkeys, and sustained the expression of a reporter gene for several weeks while circulating in the blood. In animals infused with autologous CD34+ EPCs transduced with a thymidine kinase-encoding herpes virus, skin autografts and subcutaneous Matrigel pellets impregnated with vascular growth factors underwent necrosis or accelerated regression after administration of ganciclovir. Importantly, the whole intervention was perfectly well tolerated. The accessibility, easy manipulation, lack of immunogenicity of the autologous CD34+ cell vehicles, and tropism for areas of angiogenesis render autologous CD34+ circulating endothelial progenitors as ideal candidates for exploration of their use as cellular vehicles when systemic gene delivery to those areas is required. Gene Therapy (2000) 7, 43-52.

Synthetic DNA delivery systems

The ability to safely and efficiently transfer foreign DNA into cells is a fundamental goal in biotechnology. Toward this end, rapid advances have recently been made in our understanding of mechanisms for DNA stability and transport within cells. Current synthetic DNA delivery systems are versatile and safe, but substantially less efficient than viruses. Indeed, most current systems address only one of the obstacles to DNA delivery by enhancing DNA uptake. In fact, the effectiveness of gene expression is also dependent on several additional factors, including the release of intracellular DNA, stability of DNA in the cytoplasm, unpackaging of the DNA-vector complex, and the targeting of DNA to the nucleus. Delivery systems of the future must fully accommodate all these processes to effectively shepherd DNA across the plasma membrane, through the hostile intracellular environment, and into the nucleus.

Tumor cell viability in clear cell sarcoma requires DNA binding activity of the EWS/ATF1 fusion protein

Chimeric proteins resulting from characteristic chromosomal translocations are believed to play a key role in the development of neoplasia. The consistent chromosomal translocation t(12;22) found in Clear Cell sarcoma (CCS) fuses the genes for Ewing's sarcoma protein (EWS) and activating transcription factor 1 (ATF1). Contribution of the chimeric EWS/ATF1 protein to maintenance of the tumor phenotype was investigated using intracellular expression of an inhibitory anti-ATF1 single chain antibody fragment (scFv4). Transfection of scFv4 into a cell line (SU-CCS-1) derived from CCS resulted in a 90% reduction in cyclic AMP response element-driven reporter activity. The delivery of scFv4 into SU-CCS-1 cells by a Moloney sarcoma retroviral vector (SRalpha-Fv4) significantly reduced viability and induced apoptosis as measured by terminal deoxynucleotidetransferase-mediated dUTP-biotin nick end labeling and flow cytometry. Conversely, scFv4 had no effect on viability of HeLa cells. The level of EWS/ATF1 expression was found to be significantly higher in primary tumor tissue than in SU-CCS-1 cells or in 293T cells following introduction of an EWS/ATF1 expression vector. These studies demonstrate a direct role for the EWS/ATF1 fusion protein in maintaining tumor cell viability of Clear Cell sarcoma and indicate that intracellular antibodies may be used to achieve a phenotypic knockout of tumor-related proteins as a method to explore their function.

In vivo cell type-specific gene delivery with retroviral vectors that display single chain antibodies

Cell type-specific gene delivery will be essential for in vivo gene therapy. Our laboratory has previously developed retroviral vector particles, derived from spleen necrosis virus, SNV, which display the antigen-binding site of an antibody on the viral surface. Such particles infected only human cells in vitro, which expressed a receptor recognized by the antibody. To test cell type-specific gene delivery in vivo, a mouse model system has been developed. Antibiotic resistant human target and non-target cells were injected into the peritoneum of SCID mice. Subsequently, a vector solution containing 106 infectious particles, which display scAs against the human her2neu cell surface protein, was injected. Cells were recovered from the peritoneum, subjected to antibiotic selection, and tested for the expression of a lacZ gene transduced by the retroviral vector. We found that human target cells, which express her2neu, were infected in vivo. However, neither human cells that do not express her2neu, nor normal mouse cells were infected by such viral particles. These data give proof of principle that retroviral vector-mediated, cell type-specific gene delivery can be obtained in vivo.

A radical demise. Toxins and trauma share common pathways in hair cell death

The pathologic similarities noted after ototoxic and/or traumatic injury to the cochlea as well as the key features of the cochlea that make it susceptible to reactive oxygen species (ROS) damage are reviewed. Recent evidence linking ROS to cochlear damage associated with both ototoxins and/or trauma are presented. Mechanisms of generation of ROS in the cochlea and how these metabolites damage the cochlea and impair function are also reviewed. Finally, examples of novel therapeutic strategies to prevent and reverse hearing loss due to noise and/or ototoxins are presented to illustrate the clinical relevance of these new findings.

Cellular immune responses of healthy individuals to intradermal administration of an E1-E3- adenovirus gene transfer vector

In animals, Ad-mediated gene transfer initiates anti-Ad host immune responses that vary, depending on vector design, dose, host, and transgene. To begin to understand whether the anti-Ad vector responses in humans simulate those in animals, Ad(GV)CD.10, an E1-E3- Ad5 vector encoding the E. coli cytosine deaminase gene, was administered by the intradermal route to six normal individuals (8 x 10(7) to 8 x 10(9) particle units, each dose administered to two sites; n = 2 per group). No adverse events were observed. Polymerase chain reaction/Southern analysis demonstrated vector genome in the skin through 28 days in all individuals except one of two at the lowest dose. Local induration, independent of vector dose and baseline systemic anti-Ad5 neutralizing antibodies, developed in all subjects (6 to 17 mm, peak by day 3). Biopsies revealed a mild to moderate T cell (CD3+, CD4+, CD8+), B cell, and macrophage infiltrate at day 3, all decreased by day 28. Langerhans cells accumulated primarily in the papillary dermis. The day 3 cellular response was dose independent. On day 28, CD4+ and CD8+ T lymphocytes and macrophages showed dose dependency. There was minimal systemic Ad5-specific lymphocyte proliferation induced by Ad vector administration in three individuals studied, and no Ad5-specific cytotoxic T lymphocytes (evaluated in two subjects) could be detected. Thus, intradermal administration of an E1-E3- Ad vector to normal subjects induces mild/moderate local cellular responses, even in Ad-immunized individuals. These observations provide a baseline to determine if these human anti-Ad vector host responses can be circumvented by using "stealth" vectors and/or immunosuppression.

Hematologic recovery in mice transplanted with bone marrow stem cells expressing anti-human immunodeficiency virus genes

We have used a mouse bone marrow transplantation (BMT) model to study the safety of retrovirus-mediated transfer of anti-HIV genes (RevM10 and HIV-1 pol antisense) into hematopoietic stem/progenitor cells (HSPCs). In particular, we have monitored the hematologic recovery post-BMT and transgene expression in myeloid and lymphoid lineages, and analyzed tissue sections for evidence of any transgene-related pathological condition. Expression of anti-HIV genes had no effect on kinetics of hematologic recovery post-BMT. The average time to reach 20% of normal cell counts was 15-17 days for white blood cells and 12-14 days for platelets, and the average time to reach complete recovery was 42-56 days for leukocytes and 104-161 days for platelets. Hematocrit levels were not significantly affected by irradiation and transplantation procedures. Donor chimerism was uniformly > or =90% in all transplanted animals. At 4-5 weeks post-BMT transgene expression was detected in peripheral blood leukocytes in 100% of the animals and ranged from 4.5 to 44.7%. In a majority of the animals the percentage of transgene-expressing cells in circulation decreased over time but remained detectable for the length of the study (>6 months). Expression was detected in all analyzed cell lineages (RBCs, platelets, monocytes, granulocytes, and T and B cells). Relative counts of various leukocytes (Mac1+ monocytes, Gr1+ granulocytes, CD3+ T cells, and B220+ B cells) were normal. There were no treatment-related histopathological changes in a wide range of tissues examined. In addition, there were no treatment effects on differential leukocyte counts, and morphology of peripheral blood and bone marrow brush smears. In summary, transfer and expression of the RevM10 and the HIV-1 antisense genes into hematopoietic stem/progenitor cells in vivo appears safe. We propose that the mouse bone marrow transplantation model could be used to evaluate some safety aspects of HSPC-based gene therapies.

Efficient gene transfer and long-term expression in neurons using a recombinant adenovirus with a neuron-specific promoter

Adenoviruses are highly efficient vectors for gene transfer into brain cells. Restricting transgene expression to specific cell types and maintaining long-term expression are major goals for gene therapy in the central nervous system. We targeted gene expression to neurons by constructing an adenoviral vector that expressed the E. coli LacZ reporter gene under the control of the rat neuron-specific enolase promoter (Ad-NSE). Expression from Ad-NSE was compared with that from an adenoviral vector encoding the same reporter gene under the control of the Rous sarcoma virus LTR promoter (Ad-RSV). Both recombinant adenoviruses were injected stereotactically into rat hippocampus, cerebellum and striatum. Anatomical and immunohistochemical analyses of the Ad-NSE-stained cells showed that neurons were preferentially transduced. More neurons were stained in the hippocampus following infection with Ad-NSE than with Ad-RSV. Cytotoxicity from Ad-NSE was lower than from Ad-RSV. beta-Galactosidase gene expression after Ad-NSE infection remained stable for 3(1/2) months, and was detectable for 6 months. Thus, the NSE-adenoviral vector can be used to transfer potentially therapeutic genes into neuronal cells. The use of a cell-specific promoter also resulted in high in vivo efficiency and long-term transgene expression.

Temporal, spatial, and cell type-specific control of Cre-mediated DNA recombination in transgenic mice

We have developed a universal system for temporal, spatial, and cell type-specific control of gene expression in mice that (1) integrates the advantages of tetracycline-controlled gene expression and Cre-recombinase-loxP site-mediated gene inactivation, and (2) simplifies schemes of animal crosses by combination of two control elements in a single transgene. Two transgenic strains were generated in which the cell type-specific control was provided by either the retinoblastoma gene promoter or the whey acidic protein promoter. Both promoters drive the expression of the reverse tetracycline-controlled transactivator (rtTA). Placed in cis configuration to the rtTA transcription unit, the rtTA-inducible promoter directs expression of Cre recombinase. In both strains crossed with cActXstopXLacZ reporter mice, which have a loxP-stop of transcription/translation-loxP-LacZ cassette driven by chicken beta-actin promoter, Cre-loxP-mediated DNA recombination leading to LacZ expression was accurately regulated in a temporal, spatial, and cell type-specific manner. This approach can be applied to establishment of analogous mouse strains with virtually any promoter as systems to control gene regulation in a variety of cell types.

A genetically engineered spleen necrosis virus-derived retroviral vector that displays the HIV type 1 glycoprotein 120 envelope peptide

We reported that SNV-derived retroviral vectors, which display single-chain antibodies on the viral surface, enable cell type-specific gene delivery into various human cells. In particular, the SNV cell type-specific gene delivery vector system appears to be well suited to transduce genes into cells of the human hematopoietic system (Jiang et al., J. Virol. 72:10148-10156, 1998). Here, we report the construction of SNV vector particles that display the complete gp120 surface unit of the envelope protein of human immunodeficiency virus type 1 (HIV-1) on the viral surface. The complete gp120-coding region of a T cell-tropic HIV-1 strain (LAI/BRU) was fused to a short peptide spacer coding region [(Gly4Ser)3] linking it to the SNV TM-coding region. The corresponding protein was expressed as a single 145-kDa peptide as expected. This peptide was nontoxic and could be stably expressed in dog D17 SNV-derived packaging cells. Particles harvested from stable packaging lines infected CD4+ human hematopoietic cells with titers exceeding 10(5) CFU/ml supernatant tissue culture medium. Titers in other, CD4- cell lines expressing various coreceptors of HIV-1 were 100-fold lower than titers obtained in CD4+ cells. Specificity of infection was demonstrated by antibody inhibition assays or by preincubating cells with SDF-1alpha, the ligand, which binds to the CXCR4 coreceptor, to which this gp120 binds. Our data indicate that binding of the HIV-1 gp120 to either CD4 or CXCR4 is sufficient to enable infection of human cells with SNV vector particles. We constructed retroviral vector particles that display chimeric HIV-1-SU-SNV-TM proteins plus wild-type SNV envelope on the viral surface. Such particles allowed efficient infection of CD4-positive human T lymphocytes, and, at a lower efficiency, also cells expressing CXCR4 without CD4. These data coincide with our earlier hypothesis that the chimeric envelope is required only to bind the vector particle to a cell surface receptor of the target cell, while membrane fusion is mediated by wild-type Env, which alone is not sufficient to enable infection of human cells.

Targeted gene transfer system using a streptavidin-transforming growth factor-alpha chimeric protein

The previously reported streptavidin-TGFalpha chimeric protein-based delivery system (Ohno and Meruelo, DNA Cell Biol. 15:401-406, 1996) could efficiently transfer protein molecules into A431 cells via the epidermal growth factor (EGF) receptor. We have modified this delivery system for the transfer of DNA. For this purpose, we have linked the chimeric protein ST-TGFalpha to DNA through biotinylated polylysine molecules. We show with this system, in the presence of the endosome-destabilizing reagent chloroquine, an average of 50-fold increase in reporter gene expression in comparison with polylysine DNA complexes alone. This gene expression is specific for EGF receptor-expressing cells and is blocked by EGF-binding molecules. These results suggest that the ST-TGFalpha biotinylated polylysine system could be used to deliver DNA to targeted cells.

Strategies for targeting therapeutic gene delivery

A major goal for gene therapy is to obtain targeted vectors that transfer genes efficiently to specific cell types. In theory, this can be achieved by targeting entry of the vector or by building gene expression cassettes that restrict gene expression to certain cell types. This review summarizes recent strategies to alter vector tropism for targeted gene delivery.

Ultrasonographically guided direct gene transfer in utero: successful induction of beta-galactosidase in a rabbit model

OBJECTIVE

We sought to determine whether the transfer of enzyme-encoding genes in utero can be detected after birth.

STUDY DESIGN

An adenoviral vector carrying the gene for beta-galactosidase was injected under ultrasonographic guidance into the livers of 4 rabbit fetuses per litter (3 litters total) at 27 days' gestation. On delivery of the pups 2 to 3 days later, the livers were analyzed for beta-galactosidase activity by using 5-bromo-4-chloro-3-indolyl-beta-D -galactopyranoside (X-gal) staining. Polymerase chain reaction was also performed on liver extracts as an additional independent measure of successful vector delivery.

RESULTS

Successful targeting of the livers of fetal rabbits was demonstrated by beta-galactosidase activity in the nuclei of liver serosal cells, parenchymal hepatocytes, or columnar cells of the gallbladder in 7 (58%) of 12 injected pups and by polymerase chain reaction in liver extracts from 10 (83%) of 12 injected pups.

CONCLUSIONS

These results suggest that vectors that carry genes for specific enzymes can be delivered to fetal organs in utero and that expression of the enzyme can be detected after delivery.

Gene therapy for osteoinduction

One application of gene therapy that holds great promise is the stimulation of bone formation. Gene therapy offers several potential advantages over other methods of osteoinduction and current research suggests that it may be a feasible treatment option for the orthopedic surgeon in the near future. This article reviews the basic concepts and strategies of gene therapy and evaluates the current research using gene therapy to induce bone formation and enhance healing.

Ribozymes and the anti-gene therapy: how a catalytic RNA can be used to inhibit gene function

Ribozymes are RNA molecules that possess the dual properties of RNA sequence-specific recognition and site-specific cleavage of other RNA molecules. These properties provide powerful tools for studies requiring gene inhibition, when the DNA sequence is known. The use of these molecules goes beyond basic research, with a potential impact in therapeutical practice in medicine in the near future. In this review, we briefly describe the progress towards developing this class of molecules and its applications for the control of gene expression.

In vivo protein transduction: delivery of a biologically active protein into the mouse

Delivery of therapeutic proteins into tissues and across the blood-brain barrier is severely limited by the size and biochemical properties of the proteins. Here it is shown that intraperitoneal injection of the 120-kilodalton beta-galactosidase protein, fused to the protein transduction domain from the human immunodeficiency virus TAT protein, results in delivery of the biologically active fusion protein to all tissues in mice, including the brain. These results open new possibilities for direct delivery of proteins into patients in the context of protein therapy, as well as for epigenetic experimentation with model organisms.

Neuron-restrictive silencer elements mediate neuron specificity of adenoviral gene expression

Neuron-restrictive silencer elements (NRSEs) were used to target the gene expression of adenoviral vectors specifically to neuron cells in the central nervous system. By generating adenoviral constructs in which NRSE sequences were placed upstream from the ubiquitous phosphoglycerate kinase promoter, the specificity of expression of a luciferase reporter gene was tested in both cell lines and primary cultures. Whereas transgene expression was negligible in nonneuronal cells following infection with an adenovirus containing 12 NRSEs, neuronal cells strongly expressed luciferase when infected with the same adenovirus. The NRSEs restricted expression of the luciferase gene to neuronal cells in vivo when adenoviruses were injected both intramuscularly into mice and intracerebrally into rats. This NRSE strategy may avoid side effects resulting from the ectopic expression of therapeutic genes in the treatment of neurological diseases. In particular, it may allow the direct transfection of motor neurons without promoting transgene expression within inoculated muscles or the secretion of transgene products into the bloodstream.

Future prospects in prostate cancer

BACKGROUND

Prostate cancer has displayed an increase in incidence unparalleled by any other tumor in the last two decades, with a steady, more gradual increase in mortality rate. Current curative strategies are focused on the detection and treatment of early-stage (T1-2 N0 M0), clinically significant tumors.

METHODS

To this aim, refinement of surgical approaches, with appropriate adjuvant therapies, will ensure more complete cancer control, while minimizing associated morbidity. New delivery systems for radiotherapy, as well as other energy sources, are evolving, while a number of promising pharmacological agents, including angiogenesis inhibitors and drugs which alter signal transduction pathways, are currently under investigation. Early detection is also being facilitated by a more widespread implementation of screening programs. Advances in tumor markers, and imaging and biopsy techniques, will allow more accurate preoperative staging. These, coupled with improvements in prognostic markers, aid the physician and patient alike in deciding on the suitability of treatment options with better estimation of outcome. Perhaps the most exciting developments in prostate cancer will come from knowledge of the molecular mechanisms underlying carcinogenesis. The potential for the development of diagnostic and therapeutic tools is immense. The efficacy of treatment can be studied at a molecular level, and strategies for preventing or slowing the development of malignancy can be formulated. RESULTS AND CONCLUSIONS Application of this knowledge in the form of gene and cellular therapy and in the development of novel systemic agents is beginning to enter the realm of clinical practice, and it may be in this field that means for cure and prevention of prostate cancer will eventually be found.

Metabolic engineering with recombinant adenoviruses

Fuel homeostasis in mammals is accomplished by the interplay between tissues and organs with distinct metabolic roles. These regulatory mechanisms are disrupted in obesity and diabetes, leading to a renewed emphasis on discovery of molecular and pharmacologic methods for reversing metabolic disorders. In this chapter, we review the use of recombinant adenoviral vectors as tools for delivering metabolic regulatory genes to cells in culture and to tissues of intact animals. Included are studies on the use of these vectors for gaining insights into the biochemical mechanisms that regulate glucose-stimulated insulin secretion from pancreatic islet beta-cells. We also highlight their use for understanding the function of newly discovered genes that regulate glycogen metabolism in liver and other tissues, and for evaluating "candidate" genes such as glucose-6-phosphatase, which may contribute to development of metabolic dysfunction in pancreatic islets and liver. Finally, we discuss the use of adenoviral and related vectors for causing chronic increases in the levels of circulating hormones. These examples serve to highlight the power of viral gene transfer vectors as tools for understanding metabolic regulatory mechanisms.

Transcription map and expression of bovine herpesvirus-1 glycoprotein D in early region 4 of bovine adenovirus-3

Early region 4 (E4) of bovine adenovirus type 3 (BAV-3) was analyzed by Northern blotting, RT-PCR analysis, cDNA sequencing, and S1 nuclease protection assays. The transcriptional map of the E4 region of BAV-3 has marked dissimilarities from those of mouse adenovirus-1, ovine adenovirus-287, and human adenovirus-2, for which the transcriptional maps have been constructed. The E4 region of BAV-3, located between 98.6 and 89.8 MU transcribes seven distinct classes of bovine adenovirus type 3 mRNA. The seven mRNA species formed by the removal of one to three introns share both the 3' end and a short 5' leader (25 nucleotides). The E4 mRNAs can encode at least five unique polypeptides, namely, 143R1, 69R, 143R2, 268R, and 219R. Isolation of a replication-competent recombinant "BAV404" containing 1.9-kb insertion [glycoprotein (gD) of bovine herpesvirus 1, under the control of a SV40 early promoter and poly(A)] in the region between E4 and the right ITR suggested that this region is nonessential for BAV-3 replication. Expression of gD by BAV404 recombinant virus was confirmed by immunoprecipitation with gD-specific monoclonal antibodies. Analysis of the kinetics of protein expression indicated that gD is expressed at both early and late times postinfection. These results suggest that: (a) E4 produces seven 5'-3' coterminal mRNAs and (b) the right terminal region of BAV-3 can be used for the expression of vaccine antigens.

Purification of plasmid DNA using selective precipitation by compaction agents

A scaleable method for the liquid-phase separation of plasmid DNA from RNA.

Parasites in cultured and feral fish

Parasites, causing little apparent damage in feral fish populations, may become causative agents of diseases of great importance in farmed fish, leading to pathological changes, decrease of fitness or reduction of the market value of fish. Despite considerable progress in fish parasitology in the last decades, major gaps still exist in the knowledge of taxonomy, biology, epizootiology and control of fish parasites, including such 'evergreens' as the ciliate Ichthyophthirius multifiliis, a causative agent of white spot disease, or proliferative kidney disease (PKD), one of the most economically damaging diseases in the rainbow trout industry which causative agent remain enigmatic. Besides long-recognized parasites, other potentially severe pathogens have appeared quite recently such as amphizoic amoebae, causative agents of amoebic gill disease (AGD), the monogenean Gyrodactylus salaris which has destroyed salmon populations in Norway, or sea lice, in particular Lepeophtheirus salmonis that endanger marine salmonids in some areas. Recent spreading of some parasites throughout the world (e.g. the cestode Bothriocephalus acheilognathi) has been facilitated through insufficient veterinary control during import of fish. Control of many important parasitic diseases is still far from being satisfactory and further research is needed. Use of chemotherapy has limitations and new effective, but environmentally safe drugs should be developed. A very promising area of future research seems to be studies on immunity in parasitic infections, use of molecular technology in diagnostics and development of new vaccines against the most pathogenic parasites.

An advanced generation of adenoviral vectors selectively enhances gene transfer for ovarian cancer gene therapy approaches

OBJECTIVE

We hypothesized that incorporation of an integrin binding Arg-Gly-Asp (RGD)-containing peptide to the HI loop of the adenovirus fiber knob would allow enhanced, coxsackie-adenovirus receptor-independent gene transfer by modified Ad vector in the context of ovarian cancer.

METHODS

Ovarian cancer cell lines, primary ovarian cancer cells, primary tumor explants, and mesothelial tissue were transfected with luciferase encoding adenovirus (AdCMVLuc) or a genetically modified adenovirus (Ad5lucRGD) which contained an RGD motif within the HI loop of the knob. The luciferase activity was measured and the transduction efficiencies of both viruses were compared.

RESULTS

In all established ovarian cell lines and primary tumor cell samples there was dramatically augmented gene transfer observed with the Ad5lucRGD compared to AdCMVLuc. The enhanced gene transfer in ovarian cancer cell lines ranged from 2.5- to 471.6-fold, in ascites samples from 26.1- to 64.0-fold, and in tumor explants from 1.6- to 11.1-fold. Although gene transfer to normal mesothelial tissue was slightly augmented by RGD retargeting, the level of gene transfer was much lower than that seen in ovarian cancer cells.

CONCLUSION

This study demonstrates that genetically altered adenoviruses with modified tropism are capable of more efficient gene transfer in the context of ovarian cancer. The higher level of transfer with respect to peritoneal mesothelium can be exploited to enhance the therapeutic index of interventions using adenoviral vectors. Studies are warranted, therefore, to determine the in vivo utility of this targeted vector approach in the context of gene therapeutic strategies for cancer of the ovary.

New prospects for human stem-cell therapy in the nervous system

It would be of enormous benefit if human neural tissue could be generated in vitro as this would allow screening for neuroactive compounds, and provide a source of tissue for testing cellular and gene therapies for CNS disorders. It is now well established that pluripotent embryonic stem cells (ES cells) from the mouse can be propagated in culture and differentiated into a range of tissues, including neuronal and glial cells. In other studies, more-restricted neural stem cells have been isolated from both the developing and adult rodent brain. Current reports now describe similar pluripotent and neural stem cells cultured from human embryos. While the exact nature of these cells continues to be explored, they can be grown for extended periods of time while retaining the capacity for neuronal and glial differentiation. In some cases, they have been shown to integrate into the developing or damaged adult brain. This article reviews their biology, with a focus on the possible links between ES-cell and neural stem-cell technologies, and the strategies used to isolate and expand defined cell populations.

Intracellular accumulation of secreted proteoglycans inhibits cationic lipid-mediated gene transfer. Co-transfer of glycosaminoglycans to the nucleus

Molecules secreted by potential target cells may interfere with cationic lipid-mediated gene transfer. This has been studied using human lung fibroblasts and human epidermoid lung cancer cells. Secreted cell medium components caused a substantial decrease both in the uptake of cationic lipid-DNA complexes (2-4-fold) and in reporter gene expression (100-1000-fold). Metabolic labeling of the cell medium showed that especially [35S]sulfate-labeled macromolecules competed with DNA for binding to the cationic lipid. Release of DNA from the cationic lipid by cell medium components was demonstrated by an ethidium bromide intercalation assay. In the presence of the cationic lipid, the secreted macromolecules were internalized by the cells. By enzymatic digestions, it was shown that the competing macromolecules consist of chondroitin/dermatan sulfate and heparan sulfate proteoglycans and that the effects on transfection were mediated by the polyanionic glycosaminoglycan portion of the proteoglycan. Accordingly, pretreatment of cell medium with the polycationic peptide protamine sulfate abrogated the inhibitory effects on gene transfer. Fluorescence microscopy studies revealed that heparan sulfate, internalized as a complex with cationic lipids, accumulated in the cell nuclei. These results support the view that the lack of specificity of this type of gene transfer vehicle is a major hindrance to efficient and safe in vivo administration.

Cancer gene and immunotherapy: recent developments

Gene and immunotherapeutic approaches to treat human malignant tumors are reviewed. Special attention is given to the different strategies of cancer gene therapy and to recent aspects of cytokine-supported tumor immunotherapy or tumor-specific vaccination. The limitations of these therapy approaches are critically discussed especially with respect to immune escape mechanisms.

Efficient retrovirus-mediated transfer of cell-cycle control genes to transformed cells

The use of gene therapy continues to be a promising, yet elusive, alternative for the treatment of cancer. The origins of cancer must be well understood so that the therapeutic gene can be chosen with the highest chance of successful tumor regression. The gene delivery system must be tailored for optimum transfer of the therapeutic gene to the target tissue. In order to accomplish this, we study models of G1 cell-cycle control in both normal and transformed cells in order to understand the reasons for uncontrolled cellular proliferation. We then use this information to choose the gene to be delivered to the cells. We have chosen to study p16, p21, p53 and pRb gene transfer using the pCL-retrovirus. Described here are some general concepts and specific results of our work that indicate continued hope for the development of genetically based cancer treatments.