Enhanced prostacyclin synthesis in endothelial cells by retrovirus-mediated transfer of prostaglandin H synthase cDNA

Effect of vectors on human endothelial cell signal transduction: implications for cardiovascular gene therapy

OBJECTIVE

Endothelium is an important target for gene therapy. We have investigated the effect of viral and nonviral vectors on the phenotype and function of endothelial cells (ECs) and developed methods to block any activation caused by these vectors.

METHODS AND RESULTS

Transduction of ECs with viral vectors, including adenovirus, lentiviruses, and Moloney murine leukemia virus, can induce a pro-inflammatory phenotype. This activation was reduced when nonviral vectors were used. We demonstrate that after transduction there is upregulation of dsRNA-triggered antiviral and PI3K/Akt signaling pathway. Blockade of the NFkappaB, PI3-K, or PKR signaling pathways all operated to inhibit partially virally induced activation, and inhibition of both PKR and PI3-K pathways totally blocked EC activation. Furthermore, inhibition of IFN-alpha/beta in addition to PI3-K was effective at preventing EC activation.

CONCLUSIONS

Viral vectors, although efficient at transducing ECs, result in their activation. Blockade of the signaling pathways involved in viral activation may be used to prevent such activation.

Aspirin and salicylate inhibit colon cancer medium- and VEGF-induced endothelial tube formation: correlation with suppression of cyclooxygenase-2 expression

To determine whether aspirin and salicylate suppress colon cancer cell-mediated angiogenesis, we evaluated the effects of aspirin and sodium salicylate on endothelial tube formation on Matrigel. Aspirin and sodium salicylate concentration-dependently inhibited human endothelial cell (EC) tube formation induced by conditioned medium collected from DLD-1, HT-29 or HCT-116 colon cancer cells. Aspirin and sodium salicylate at pharmacological concentrations were equally effective in blocking tube formation. Neutralizing antivascular endothelial growth factor (VEGF) antibodies blocked colon cancer medium-induced tube formation. VEGF receptor 2 but not receptor 1 antibodies inhibited tube formation to a similar extent as anti-VEGF antibodies. These results indicate that VEGF interaction with VEGF receptor 2 is the primary mechanism underlying colon cancer-induced angiogenesis. Aspirin or sodium salicylate inhibited VEGF-induced tube formation in a concentration-dependent manner comparable to that of inhibition of colon cancer medium-induced endothelial tube formation. It has been shown that cyclooxygenase-2 (COX-2) is pivotal in cancer angiogenesis. We found that colon cancer medium-induced COX-2 protein expression in EC and aspirin or sodium salicylate suppressed the cancer-induced COX-2 protein levels at concentrations correlated with those that suppressed endothelial tube formation. Furthermore, aspirin and sodium salicylate inhibited COX-2 expression stimulated by VEGF. These findings indicate that aspirin and other salicylate drugs at pharmacological concentrations inhibit colon cancer-induced angiogenesis which is correlated with COX-2 suppression.

Cyclooxygenase-1 and bicistronic cyclooxygenase-1/prostacyclin synthase gene transfer protect against ischemic cerebral infarction

BACKGROUND

We tested the hypothesis that bicistronic cyclooxygenase-1 (COX-1)/prostacyclin synthase (PGIS) and COX-1 gene transfer reduce cerebral infarct volume by augmenting synthesis of protective prostaglandins.

METHODS AND RESULTS

We infused into lateral ventricle of a rat stroke model recombinant adenoviruses (rAd) containing COX-1 (Adv-COX-1), COX-1 and PGIS (Adv-COX-1/PGIS), or Adv-PGK control vector, and we determined COX-1 and PGIS protein and eicosanoid levels and infarct volume. COX-1 and PGIS proteins were increased in a time-dependent manner. Adv-COX-1/PGIS infusion selectively augmented prostacyclin levels, with reduction of other eicosanoids in ischemic cortex and a significant reduction of infarct volume, even when the rAd was administered 5 hours after ischemia. Infusion of Adv-COX-1 also increased prostacyclin, suppressed leukotriene levels, and achieved a similar degree of cerebral protection. Its neuroprotection was abrogated by treatment with a selective COX-1 inhibitor.

CONCLUSIONS

COX-1/PGIS and COX-1 gene transfer reduce cerebral infarct volume by augmenting prostacyclin and suppressing leukotriene productions. COX-1-based gene transfer has potential for treating ischemic stroke.

Effect of harvesting and sorting on beta-1 integrin in canine microvascular cells

BACKGROUND

The goal of seeding prosthetic conduits with endothelial cells (ECs) has focused attention on the role of EC adhesion molecules. Cell preparation techniques may affect adhesion molecule expression and graft seeding.

METHODS

Using fluorescent antibody labeling and flow cytometric analysis, this study examined the effectsof monolayer detachment (scraping vs trypsinization), timing of immunolabeling (pre- vs postdetachment), gene transfection (transfected vs nontransfected), and cell selection (antibiotic vs fluorescence sorting) techniques on beta-1 integrin expression in canine microvascular EC (K9MVEC).

RESULTS

Cell scraping resulted in a significantly higher beta-1 integrin mean fluorescence intensity than did cell trypsinization (P < 0.05). No difference was observed with immunolabeling prior to versus following monolayer harvesting. Gene transfection had no significant effect on beta-1 integrin expression. No advantage was observed between cell selection methods (P > 0.05).

CONCLUSION

This study suggests that the monolayer harvesting technique employed has a significant impact on beta-1 integrin quantification by flow cytometric analysis. Furthermore, microvascular EC expression of beta-1 integrin was not adversely affected by gene transfection.

*NO and oxyradical metabolism in new cell lines of rat brain capillary endothelial cells forming the blood-brain barrier

To investigate the relevance of *NO and oxyradicals in the blood-brain barrier (BBB), differentiated and well-proliferating brain capillary endothelial cells (BCEC) are required. Therefore, rat BCEC (rBCEC) were transfected with immortalizing genes. The resulting lines exhibited endothelial characteristics (factor VIII, angiotensin-converting enzyme, high prostacyclin/thromboxane release rates) and BBB markers (gamma-glutamyl transpeptidase, alkaline phosphatase). The control line rBCEC2 (mock transfected) revealed fibroblastoid morphology, less factor VIII, reduced gamma-glutamyl transpeptidase, weak radical defence, low prostanoid metabolism, and limited proliferation. Lines transfected with immortalizing genes (especially rBCEC4, polyoma virus large T antigen) conserved primary properties: epitheloid morphology, subcultivation with high proliferation rate under pure culture conditions, and powerful defence against reactive oxygen species (Mn-, Cu/Zn-superoxide dismutase, catalase, glutathione peroxidase, glutathione) effectively controlling radical metabolism. Only 100 microM H2O2 overcame this defence and stimulated the formation of eicosanoids similarly as in primary cells. Some BBB markers were expressed to a lower degree; however, cocultivation with astrocytes intensified these markers (e.g., alkaline phosphatase) and paraendothelial tightness, indicating induction of BBB properties. Inducible NO synthase was induced by a cytokine plus lipopolysaccharide mixture in all lines and primary cells, resulting in *NO release. Comparing the cell lines obtained, rBCEC4 are stable immortalized and reveal the best conservation of properties from primary cells, including enzymes producing or decomposing reactive species. These cells can be subcultivated in large amounts and, hence, they are suitable to study the role of radical metabolism in the BBB and in the cerebral microvasculature.

Colocalization of prostacyclin synthase with prostaglandin H synthase-1 (PGHS-1) but not phorbol ester-induced PGHS-2 in cultured endothelial cells

The subcellular colocalization of prostacyclin synthase (PGIS) with prostaglandin H synthase (PGHS) has not been delineated. To test the hypothesis that its colocalization with PGHS is crucial for prostacyclin synthesis, we determined subcellular locations of PGIS, PGHS-1, and PGHS-2 in bovine aortic endothelial cells by immunofluorescent confocal microscopy. PGIS and PGHS-1 were colocalized to nuclear envelope (NE) and endoplasmic reticulum (ER) in resting and adenovirus-infected bovine aortic endothelial cells. PGIS and PGHS-2 were also colocalized to ER in serum-treated or adenovirus-cyclooxygenase-2-infected cells. By contrast, PGIS was not colocalized with PGHS-2 in cells induced with phorbol 12-myristate 13-acetate where PGHS-2 was visualized primarily in vesicle-like structures. The lack of colocalization was accompanied by failed prostacyclin production. Resting ECV304 cells did not produce prostacyclin and had no detectable PGHS-1 and PGIS proteins. Confocal analysis showed abnormal colocalization of PGIS and PGHS-1 to a filamentous structure. Interestingly, the abundant PGIS and PGHS-1 expressed in adenovirus-infected ECV304 cells were colocalized to NE and ER, which synthesized a large quantity of prostacyclin. These findings underscore the importance of colocalization of PGHS and PGIS to ER and NE in prostacyclin synthesis.

Tissue engineering of the vascular system: from capillaries to larger blood vessels

Tissue engineering is a novel approach to the repair of wounded tissues. Application of this technology to the vascular system is important because of the fundamental nutritional role of the vasculature. This perspective is currently being applied to the first tissue-engineered organ: the skin. Knowledge of capillary constitution and factors inducing their formation has led to attempts to induce their formation in reconstructed skin. Such vascular conduits grown in vitro could also benefit the nutrition of tissues and organs in vivo. The paper reviews recent progress in the in-vitro development of vascularised skin and tissue-engineered blood vessels. It points out the necessity of obtaining pure and well-characterised cultures of the different cell populations that are the basic building blocks of the reconstructions. The importance of an adequate cell-culture environment (nutrients and bi- or tri-dimensional scaffolds for cells) for success in elaborating a reconstructed living tissue able to replace the original is emphasised. Engineered tissues can serve not only as tissue replacements but also as in-vitro models for research in organ physiology and physiopathology. These tissues are also attractive vehicles for gene therapy, one of the more promising new methods of disease treatment.

Upregulation of prostacyclin synthesis-related gene expression by shear stress in vascular endothelial cells

Prostacyclin (prostaglandin I2, PGI2) has a variety of functions, including inhibition of smooth muscle cell proliferation, vasodilation, and antiplatelet aggregation. PGI2 production in endothelial cells has been reported to increase biphasically after shear loading, but the underlying mechanism is not well understood. To clarify the mechanism for the second phase of PGI2 upregulation, we examined the gene expression of the enzymes involved in PGI2 production in human umbilical vein endothelial cells (HUVECs) after shear-stress (24 dyne/cm2) loading. The production of 6-keto-PGF1alpha, a stable metabolite of PGI2, increased time-dependently under shear stress. The arachidonic acid liberation from membrane phospholipids in HUVECs after 12 hours of shear loading was increased significantly compared with the static condition. No change was observed for cytosolic phospholipase A2 expression, as detected by reverse transcription-polymerase chain reaction and Western blotting. Cyclooxygenase (COX)-1 mRNA increased after 1 hour of shear loading, and the increase lasted for 12 hours, the longest time tested, whereas COX-2 mRNA increased after 1 hour of shear loading and peaked at 6 hours. An increase of COX-1 expression was detected at 12 hours of shear loading by Western blotting. No expression of COX-2 was detected in the static control, but induced expression was observed at 6 hours after shear loading. PGI2 synthase was also found to be upregulated. These results suggest that the elevated PGI2 production by shear stress is mediated by increased arachidonic acid release and a combination of increased expression of COXs and PGI2 synthase.

Retroviral gene transfer: effects on endothelial cell phenotype

BACKGROUND

Endothelial cells (EC) are an attractive target for somatic cell gene therapy, both for the treatment of cardiovascular disease and for the systemic delivery of recombinant gene products directly into the circulation. Recent evidence, however, suggests that viral transduction may induce unfavorable changes in EC phenotype. We examined the proliferative capacity and cell adhesion molecule (CAM) profile of EC after retroviral gene transfer (GT), employing a clinically relevant ex vivo GT protocol.

METHODS

Human umbilical vein EC (HUVEC, N = 14 isolates) were exposed to supernatants containing the MFG.nlsLACZ vector, which codes for a nuclear localized beta-galactosidase. Control HUVEC were exposed to empty virus (CRIP) or no virus (NT). Efficiency of GT was quantitated by direct counting of beta-galactosidase-stained cells on a grid. Proliferation was quantitated by a 1-week assay of viable cell counts. Expression of EC activation molecules (Class II major histocompatibility antigen [MHC II], E-selectin, intercellular adhesion molecule-1 [ICAM-1], and vascular cell adhesion molecule-1 [VCAM-1]) was examined using fluorescent cytometry (FACS) at rest and after cytokine stimulation.

RESULTS

GT was reproducibly efficient (mean 57%, range 40-77%) using sequential viral exposures without selection. NT, CRIP, and LACZ-transduced HUVEC exhibited identical FACS profiles for E-selectin, ICAM-1, VCAM-1, and MHC II at rest, consistent with a nonactivated state. Upregulation of expression by cytokine was quantitatively similar for all groups. Growth rates were likewise not different between groups.

CONCLUSIONS

Retroviral vectors may be employed to achieve high percentages of transduced EC for ex vivo GT without the use of selection. Transduced EC generated in this fashion are not activated, demonstrate an unaltered pattern of inducible CAM expression, and exhibit normal cell growth. The effects of GT on target cell phenotype are likely to be both vector and protocol specific and should be carefully assessed in each case prior to in vivo applications.

A completely biological tissue-engineered human blood vessel

Mechanically challenged tissue-engineered organs, such as blood vessels, traditionally relied on synthetic or modified biological materials for structural support. In this report, we present a novel approach to tissue-engineered blood vessel (TEBV) production that is based exclusively on the use of cultured human cells, i.e., without any synthetic or exogenous biomaterials. Human vascular smooth muscle cells (SMC) cultured with ascorbic acid produced a cohesive cellular sheet. This sheet was placed around a tubular support to produce the media of the vessel. A similar sheet of human fibroblasts was wrapped around the media to provide the adventitia. After maturation, the tubular support was removed and endothelial cells were seeded in the lumen. This TEBV featured a well-defined, three-layered organization and numerous extracellular matrix proteins, including elastin. In this environment, SMC reexpressed desmin, a differentiation marker known to be lost under standard culture conditions. The endothelium expressed von Willebrand factor, incorporated acetylated LDL, produced PGI2, and strongly inhibited platelet adhesion in vitro. The complete vessel had a burst strength over 2000 mmHg. This is the first completely biological TEBV to display a burst strength comparable to that of human vessels. Short-term grafting experiment in a canine model demonstrated good handling and suturability characteristics. Taken together, these results suggest that this novel technique can produce completely biological vessels fulfilling the fundamental requirements for grafting: high burst strength, positive surgical handling, and a functional endothelium.

Endothelial cell-specific expression of tumor necrosis factor-alpha from the KDR or E-selectin promoters following retroviral delivery

The tumor vasculature offers a target for anti-cancer gene therapy which has the advantages both of good accessibility to systemically delivered therapy and comparative homogeneity across solid tumor types. We aimed to develop retroviruses carrying endothelial-specific promoters for the delivery of genes to proliferating endothelial cells in vitro and to tumor endothelial cells in vivo. This paper reports the generation of such retroviral vectors and the level of expression of murine tumor necrosis factor-alpha (mTNF-alpha) cDNA following infection into endothelial cells and stromal fibroblasts. Retroviral vectors carrying mTNF-alpha have been generated whose expression is controlled either by the retroviral long terminal repeat or by 5' proximal promoter sequences from the endothelial-specific kinase insert domain receptor (KDR)/VEGF receptor and E-Selectin promoters within the context of a self-inactivating (SIN) vector backbone. Both KDR and E-Selectin have been shown to be upregulated on tumor endothelium. A putative polyadenylation sequence AAATAAA within the E-Selectin promoter was mutated to permit faithful transmission of retroviral vectors carrying this promoter. We demonstrate a 10- to 11-fold increase in mTNF-alpha expression from promoter elements within sEND endothelioma cells as compared to NIH-3T3 fibroblasts. Suggestions for further improvements in vector design are discussed.

Retroviral mediated gene transduction alters integrin expression on vascular endothelial cells

Genetically recombinant endothelial cells (rEC) may improve the patency of small diameter vascular grafts by preventing thrombosis or limiting neointimal hyperplasia. Previous work has shown that rEC have reduced adhesion to vascular bypass grafts in vivo. Poor adhesion may be due to altered adhesion (integrin) receptors. This study evaluated the expression of the alpha 5 beta 1 (fibronectin), alpha 2 beta 1 (collagen IV), and alpha v beta 3 (vitronectin) integrin subunits on rEC. Human umbilical vein EC or canine jugular vein EC were transduced with neoR, neoR and human tPA or hygromycin resistance genes using retroviral vectors. Naive EC and EC exposed to empty viral particles (mEC) were controls. Naive EC, mEC, and all rEC's were evaluated for alpha and beta subunits for each integrin receptor studied using immunoblotting. Blotting for alpha 2, alpha 5, and alpha v exhibited expression of the alpha integrin subunits in all cells. The beta 1 and beta 3 subunits were present in mEC and nEC but were absent or truncated in all rEC. The decreased adhesion of rEC's to synthetic vascular grafts may be accounted for by their altered beta 1 and beta 3 integrin subunit expression. The beta subunit is critical for organization of the cytoskeleton and cellular signal transduction. Diminished beta subunit expression in rEC is neither vector specific nor related to retroviral exposure alone. Alteration of beta integrin expression may be to associated with the over-expression of phosphotransferase genes such as neoR or hygromycin B used as selectable markers in gene transfer protocols.

Prostacyclin and nitric oxide-related gene transfer in preventing arterial thrombosis and restenosis

Prostacyclin (PGI2) and nitric oxide (NO) are potent vascular mediators, playing key roles in protecting arterial wall from injury-induced lesions. The key enzyme that catalyzes PGI2 biosynthesis is cyclooxygenase (COX). COX-1 undergoes auto-inactivation, which severely limits PGI2 synthesis. Overexpression of COX-1 in cultured endothelial cells by COX-1 gene transfer was accompanied by a higher capacity for and sustained synthesis of PGI2. Adenovirus-mediated COX-1 gene transfer to angioplasty damaged carotid arteries in pigs augmented PGI2 synthesis and prevents thrombus formation. Transfer of endothelial NO synthase (eNOS) into angioplasty injured, carotid arteries was reported to suppress intimal hyperplasia in rats. Transfer of PGI2 and NO synthetic enzymes restores the vasoprotective properties and represents an exciting new strategy for treating arterial thrombotic disorders.

Endothelial function in different organs

The endothelial lining represents an organ of 1.5 kg in an adult which is distributed throughout the body and serves multifunctional purposes. It regulates vascular growth processes and adaptations and controls the delicate equilibrium between coagulation-hemostasis and fibrinolysis. The endothelium is not only a simple diffusion barrier between the intravascular and extravascular space of blood and lymph vessels thus regulating permeability (ie, the fluid, metabolite and catabolite exchange), but synthetizes, releases, converts, activates and/or inactivates various vasoactive hormones. Thus, it regulates vascular tone and organ blood supply as well as lymphatic flow and expression of surface receptors for the activation of leukocytes eg, during inflammation. In different organs it has additional, organ specific functions (eg, cerebral endothelial lining/blood brain barrier, endothelium mediated changes in renal, splenic and hepatic function and in skeletal muscle perfusion) by generating various autacoids such as nitric oxide, prostaglandins, endothelins, hyperpolarizing factors, and so on. These autacoids are not only vasoactive compounds but also modulate the activation of transcription factors. The endothelial autacoids exert an important role in vascular homeostasis (eg, by direct inhibition of atherogenesis and by inhibition of proatherogenic genes).

Role of endothelium in thrombosis and hemostasis

Vascular endothelium is strategically located at the interface between tissue and blood. It is pivotal for protecting against vascular injury and maintaining blood fluidity. Normal endothelium releases prostacyclin and nitric oxide, potent inhibitors of platelet and monocyte activation and vasodilators. Their syntheses are governed by isoforms of enzymes. Normal endothelial surface expresses ecto-adenosine diphosphatase, which degrades adenosine diphosphate and inhibits platelet aggregation; thrombomodulin, which serves as a binding site for thrombin to activate protein C; and heparin-like molecules, which serve as a cofactor for antithrombin III. Normal endothelium secretes tissue plasminogen activator, which activates the fibrinolysis system. Endothelium produces and secretes von Willebrand factor, which mediates platelet adhesion and shear-stress-induced aggregation. Injury to endothelium is accompanied by loss of protective molecules and expression of adhesive molecules, procoagulant activities, and mitogenic factors, leading to development of thrombosis, smooth muscle cell migration, and proliferation and atherosclerosis.

Prevention of arterial thrombosis by adenovirus-mediated transfer of cyclooxygenase gene

BACKGROUND

Prostacyclin is an important vasoprotective molecule. It inhibits platelet aggregation, monocyte interaction with endothelium, and smooth muscle cell lipid accumulation. Vascular cyclooxygenase-1 (COX-1) is the rate-limiting step in prostacyclin synthesis. The objective of this study was to determine whether adenovirus-mediated transfer of COX-1 could restore COX-1 activity, augment prostacyclin synthesis, and prevent thrombus formation in a porcine carotid angioplasty model.

METHODS AND RESULTS

Human COX-1 cDNA driven by a cytomegalovirus promoter was constructed into a replication-defective adenovirus 5 vector by homologous recombination. Recombinant adenovirus without a foreign gene (Ad-RR) and buffer were included as controls. Recombinant Ad-LacZ was used for marking the transfected cells in vivo. In the in vitro experiments, cultured human endothelial cells (ECs) and porcine arterial smooth muscle cells (SMCs) were incubated with Ad-COX-1 for 2 hours and 6-keto-PGF(1 alpha) level and the transgene expression were determined 72 hours after infection. In the in vivo experiments, recombinant adenoviruses were directly instilled into angioplasty-injured porcine carotid arteries for 30 minutes. Cyclic flow changes were monitored for 10 days and thrombus formation was examined histologically thereafter. Transgene expression and prostaglandin I2 (PGI2) synthesis by the injured arteries were determined. Cultured ECs infected with Ad-COX-1 produced a fivefold to eightfold increase in PGI2, and the transgene expression in cultured porcine SMCs was demonstrated by Northern analysis. Direct administration of Ad-COX-1 at a dose of 3 x 10(10) pfu completely inhibited carotid cyclic flow changes and thrombus formation accompanied by a fourfold increase in PGI2 synthesis by the injured arteries 10 days after infection, whereas Ad-COX-1 at a lower dose, 5 x 10(9) pfu, had no antithrombotic effects when compared with Ad-RR vector and buffer controls.

CONCLUSIONS

Adenovirus-mediated transfer of COX-1 to angioplasty-injured carotid arteries was efficacious in augmenting PGI2 synthesis and was associated with an inhibition of thrombosis when a relatively high titer of adenovirus was instilled.

Control of coronary blood flow by autacoids

Coronary flow and thus myocardial perfusion is regulated by myogenic, metabolic, humoral and neuro-hormonal factors which closely interact with local autacoids released from the endothelial lining of the coronary bed. In a number of disease states an impaired synthesis and release of autacoids decisively limit the overall capacity of coronary regulation and adaptation of myocardial perfusion to increased metabolic demands. The important factors for these control mechanisms are analyzed and reviewed in this article.

Cardiovascular gene transfer

The cardiovascular system is a promising site for gene delivery because of its large surface area and direct contact with the blood stream. Gene transfer into vascular cells by adenoviral and retroviral vectors or liposomes has been demonstrated in several cell types and animal models. These methods have been somewhat successful; however, many improvements must be made before use in humans is possible. Some of these vectors exhibit toxicity and mediate variable expression of the transferred gene. New generations of viral vectors, new lipid formulations, other gene transfer methods, and more effective delivery methods must be developed to combat these problems.

Molecular regulation and augmentation of prostacyclin biosynthesis

Prostacyclin is a major vasoprotective molecule. It has multiple physiological functions. Its synthesis is determined by several enzymes of which cyclooxygenase (COX) plays a key role. Two isoforms of COX have been identified. Their expression and regulation are controlled by different mechanisms. COX-1 is constitutively expressed and physiologically important. PGI2 synthesis can be augmented by virus-mediated transfer COX-1 gene. This strategy may be useful for therapy of vascular thrombosis and tissue ischemia.

Gene therapy to restore prostacyclin presence to injured endothelium

These preliminary studies demonstrate the feasibility of restoration of prostacyclin synthesis in mechanically-injured porcine carotid arteries following angioplasty. Our initial data suggest the possibility of inhibiting thrombus development by adenovirus-CMV-PGHS-1 therapy in the initial 10 days following angioplasty.

Gene therapy for vascular diseases

Gene transfer by virus- and liposome-mediated vectors has potential for treating genetic diseases, cancer, and cardiovascular diseases. In this article, we discuss the general principle and techniques for gene transfer and the specific issues facing therapy for vascular diseases. We also propose a strategy for using virus-mediated gene transfer to restore the vasoprotective function of the vascular wall, thereby preventing vascular thrombosis. Experimental data from ongoing work in our laboratories are presented to illustrate the importance of this approach in vascular gene transfer therapy.