Effects of retroviral-mediated tissue plasminogen activator gene transfer and expression on adherence and proliferation of canine endothelial cells seeded onto expanded polytetrafluoroethylene

Gene Therapy for the Extension of Vein Graft Patency: A Review

The mainstay of treatment for long-segment small-vessel chronic occlusive disease not amenable to endovascular intervention remains surgical bypass grafting using autologous vein. The procedure is largely successful and the immediate operative results almost always favorable. However, the lifespan of a given vein graft is highly variable, and less than 50% will remain primarily patent after 5 years. The slow process of graft malfunction is a result of the vein's chronic maladaptive response to the systemic arterial environment, its primary component being the uncontrolled proliferation of vascular smooth muscle cells (SMCs). It has recently been suggested that this response might be attenuated through pre-implantation genetic modification of the vein, so-called gene therapy for the extension of vein graft patency. Gene therapy seems particularly well suited for the prevention or postponement of vein graft failure since: (1) the stimulation of SMC proliferation appears to largely be an early and transient process, matching the kinetics of current gene transfer technology; (2) most veins are relatively normal and free of disease at the time of bypass allowing for effective gene transfer using a variety of systems; and (3) the target tissue is directly accessible during operation because manipulation and irrigation of the vein is part of the normal workflow of the surgical procedure. This review briefly summarizes the current knowledge of the incidence and basic mechanisms of vein graft failure, the vector systems and molecular targets that have been proposed as possible pre-treatments, the results of experimental genetic modification of vein grafts, and the few available clinical studies of gene therapy for vascular proliferative disorders.

The use of antithrombotic therapies in reducing synthetic small-diameter vascular graft thrombosis

BACKGROUND

Thrombosis of synthetic small-diameter bypass grafts remains a major problem. The aim of this article is to review the antithrombotic strategies that have been used in an attempt to reduce graft thrombogenicity.

METHODS

A PubMed/MEDLINE search was performed using the search terms "vascular graft thrombosis," "small-diameter graft thrombosis," "synthetic graft thrombosis" combined with "antithrombotic," "antiplatelet," "anticoagulant," "Dacron," "PTFE," and "polyurethane."

RESULTS

The majority of studies on antithrombotic therapies have used either in vitro models or in vivo animal experiments. Many of the therapies used in these settings do show antithrombotic efficacy against synthetic graft materials. There is however, a distinct lack of human in vivo studies to further delineate the performance and limitations of therapies displaying good antithrombotic characteristics.

CONCLUSION

Very few antithrombotic therapies have translated into clinical use. More human in vivo studies are required to assess the efficacy and safety of such therapies.

Enhancing Endothelial Cell Retention on ePTFE Constructs by siRNA-Mediated SHP-1 Gene Silencing

Polymeric vascular grafts hold great promise for vascular reconstruction, but the lack of endothelial cells renders these grafts susceptible to intimal hyperplasia and restenosis, precluding widespread clinical applications. The purpose of this study is to establish a stable endothelium on expanded polytetrafluoroethylene (ePTFE) membrane by small interfering RNA (siRNA)-induced suppression of the cell adhesion inhibitor SH2 domain-containing protein tyrosine phosphatase-1 (SHP-1). Human umbilical vein endothelial cells (HUVECs) were treated with scrambled siRNA as a control or SHP-1 specific siRNA. Treated cells were seeded onto fibronectin-coated ePTFE scaffolds and exposed to a physiological range of pulsatile fluid shear stresses for 1 h in a variable-width parallel plate flow chamber. Retention of cells was measured and compared between various shear stress levels and between groups treated with scrambled siRNA and SHP-1 specific siRNA. HUVECs seeded on ePTFE membrane exhibited shear stress-dependent retention. Exposure to physiological shear stress (10 dyn/cm2) induced a reduction in the retention of scrambled siRNA treated cells from 100% to 85% at 1 h. Increased shear stress (20 dyn/cm2) further reduced retention of scrambled siRNA treated cells to 55% at 1 h. SHP-1 knockdown mediated by siRNA enhanced endothelial cell retention from approximately 60% to 85% after 1 h of exposure to average shear stresses in the range of 15–30 dyn/cm2. This study demonstrates that siRNA-mediated gene silencing may be an effective strategy for improving the retention of endothelial cells within vascular grafts.

A HUVEC line with a stable expression of the VEGF121 gene to achieve complete endothelialization of blood conduits

The purpose of this investigation was to establish monoclonal cell lines of HUVEC with the stable expression of the VEGF(121) gene. Such cells are likely to better adhere to the luminal surface of stents or grafts and to promote a complete endothelialization. The eukaryotic expression vector PCD(2)-VEGF(121) was transfected into cell lines of HUVEC mediated by lipofect AMINE. The positive clones were obtained by the screening of G(418). The transcription and expression of the VEGF gene were investigated by RT-PCR and immunocytochemistry, respectively. The experiment of Miles was applied for the assay of the biological activity of the protein of the VEGF produced by the HUVEC lines with transfected PCD(2)-VEGF(121). The growth curve was made for comparison with that of non-transfected HUVEC line cells. The positive clone cells from which transcripted the mRNA of VEGF(121) gene were obtained by RT-PCR. The positive results of the immunocytochemistry were found and the high biological activity of VEGF in the media was detected in the positive clone cells only. The time to achieve the multiplication of the positive clone cells by a factor of 2 was shorter than that of the non-transfected HUVEC line calculated from the growth curve. The HUVEC line of monoclonal cells with the stable expression of VEGF(121) gene has been established successfully and can be employed on the luminal surfaces of foreign blood conduits.

The adhesive properties of endothelial cells on endovascular stent coated by substrates of poly-l-lysine and fibronectin

Optimizing endothelial cell growth and adhesion on the surface of metallic stents implanted in the vascular system is a fundamental issue in understanding and improving their long-term biocompatibility. The ability of the endothelial cell to attach and adhere to the luminal stent surface as well as the capacity to withstand the significant shear stress associated with blood flow are important determinants. The adhesive characteristics of human umbilical vein endothelial cellsectin (HUVEC) on stent surfaces coated with either Poly-L-Lysine (PLL) or fibron (FN) were compared with uncoated controls. Increasing concentrations of PLL and FN were measured using a micropipette aspiration system. The adhesivenamic properties of HUVECs under static flow conditions were compared to a dy environment on endovascular stents using a parallel-plate-flow chamber. A scanning electron microscope picture was used to measure the number and the adhesive cell ratio as well as the percentage of surface coverage of stent by endothelial cells. The adhesive forces of HUVECs on foreign surfaces coated with PLL and FN were higher compared to uncoated surfaces, and were dependent on incr ing concentrations. These coatings resulted in significant increase of the adhesive force of HUVECs. The influence of substrates on the adhesion of the endothelial cell monolayer under static or dynamic flow conditions was highly significant compared with controls (p<0.01). No significant differences were observed between PLL and FN substrates. Both PLL and FN coated surfaces can significantly increase the adhesion and growth of HUVECs on metallic stent surfaces.

Endograft technology: a delivery vehicle for intravascular gene therapy

PURPOSE

The purpose of this study was to determine whether vascular smooth muscle cells (SMCs) suffused into a bilayered stent graft retain and express a retrovirally transduced gene for 7 months in vivo.

METHODS

SMCs harvested from dog jugular vein were retrovirally transduced to introduce genes for tissue plasminogen activator (t-PA) and beta-galactosidase. These cells were then suffused into a novel dual-layered Dacron graft and cultured for 36 to 48 hours. The grafts were mounted on a Palmaz stent and balloon- expanded in the infrarenal aorta of the SMC donor dogs (n = 6). Grafts were recovered at 1, 2, 3, 4, 5, and 7 months. A control endograft suffused with SMCs transduced with only the beta-galactosidase gene was placed in the dogs with grafts recovered at 2, 3, and 4 months. t-PA antigen concentration and expression were analyzed with an enzyme-linked immunosorbent assay.

RESULTS

Retained engineered SMCs (blue nuclei) were identified in the explanted grafts, neointima, and underlying aorta with X-gal staining. The t-PA antigen concentration and t-PA activity from the SMCs recovered from the grafts remained elevated for the duration of the experiment (7 months) at levels significantly higher (3.7 +/- 0.2 ng/mL per 10(5) cells per 24 hours and 1.4 +/- 0.1 IU/mL per 10(5) cells per 24 hours) than in control endografts (0.5 +/- 0.03 ng/mL per 10(5) cells per 24 hours and 0.07 +/- 0.00 IU/mL per 10(5) cells per 24 hours; P <.001). No graft stenosis was observed.

CONCLUSION

Retrovirally engineered vascular SMCs survived the implantation trauma, repopulated each graft, migrated into the underlying aorta, and expressed the transduced genes for the 7-month duration of the experiment. This bilayered Dacron endograft model provides a platform to study direct intravascular gene therapy.

Smooth muscle cells improve endothelial cell retention on polytetrafluoroethylene grafts in vivo

OBJECTIVE

We investigated the influence of smooth muscle cells (SMC) on endothelial cell (EC) retention on polytetrafluoroethylene (PTFE) grafts and the effect of SMC seeding on intimal hyperplasia in vivo in a rabbit model.

METHODS

Fibronectin-coated PTFE grafts (4 mm diameter) were seeded with either EC alone, SMC alone, or SMC followed 24 hours later by EC. The grafts were connected to an extracorporal aortic shunt for 1 hour or were individually implanted for 1, 30, and 100 days into the infrarenal aorta as an end-to-side bypass graft. The number of retained cells was compared at 1 hour and at 1 day after implantation. Neointimal thickness was measured 30 and 100 days after implantation.

RESULTS

After 1-hour exposure to blood flow, EC retention rate was greater (P <.005) if seeded on top of SMC (98% +/- 2%; n = 8) versus being seeded alone (65 +/- 11%; n = 8). SMC retention rate was 95 +/- 5% (n = 8) when seeded alone. Similar cell retention was obtained 1 day after implantation. After 30-day implantation the neointima was thicker in grafts seeded with EC and SMC (282 +/- 136 microm; n = 3) than with EC only (52 +/- 45 microm; n = 3; P <.001). However, the neointimal thickness for dual-cell-seeded grafts (126 +/- 60 microm; n = 3) was not significantly different (P =.09) from EC-seeded grafts (79 +/- 48 microm; n = 3) after 100-day implantation.

CONCLUSION

EC retention on PTFE grafts in vivo is improved if seeded over a layer of SMC. Further studies are needed to determine whether overlying EC modulate proliferation of underlying SMC.

Adenoviral-mediated transfer of tissue plasminogen activator gene into brain capillary endothelial cells in vitro

Tissue plasminogen activator (tPA) has a critical role in fibrinolysis, converting plasminogen into active protease plasmin. Because intravenous tPA has only limited effectiveness as acute stroke therapy, enhancement of endogenous tPA represents a potential alternative to stroke treatment. Adenoviral-mediated gene transfer was used to enhance production of tPA in bovine brain capillary endothelial cells (BEC). Antigen and activity levels of tPA and plasminogen activator inhibitor-1 (PAI-1) in media from BEC infected with AdCMVtPA were analyzed. Conditioned media were analyzed for thrombomodulin, the integral membrane antithrombotic molecule that co-activates protein C. BEC infected with AdCMVtPA demonstrated enhanced expression of tPA antigen (40.2 +/- 0.4 ng/mL vs 1.1 +/- 1.5 ng/mL [p<0.001] and 0.3 +/- 0.5 ng/mL [p<0.0001], respectively) and increased tPA enzymatic activity (27.4 +/- 5.7 IU/mL vs 8.3 +/- 1.7 IU/mL [p<0.05] and 13.3 +/- 3.2 IU/mL [p<0.05], respectively) compared to BEC infected with the control adenovirus (Adl327) or uninfected BEC. There was a moderate increase in PAI-1 protein 4 days after transfection with AdCMVtPA, and the integral membrane protein thrombomodulin was released into media by transfected BEC. These results demonstrate that adenoviral-mediated delivery in vitro of the human tPA gene resulted in high levels of expression of tPA in BEC. Transient overexpression of tPA by gene transfer might be a useful strategy to protect against thrombotic occlusion during the period of risk of acute stroke.

Dual cell seeding and the use of zymogen tissue plasminogen activator to improve cell retention on polytetrafluoroethylene grafts

OBJECTIVE

The purpose of this study was to enhance the retention of seeded endothelial cells (EC) on prosthetic vascular grafts. Dual-layer EC and smooth muscle cell (SMC) seeding and gene transfer of a zymogen tissue plasminogen activator gene (tPA) into seeded EC were studied.

METHODS

Polytetrafluoroethylene (PTFE) grafts were precoated with fibronectin, seeded with SMC followed by EC a day later, and then, 24 hours later, exposed to an in vitro flow system for 1 hour. Cell retention rates were determined for grafts seeded with EC only, a dual layer of EC on top of SMC, EC transduced with wild-type tPA, and EC transduced with zymogen tPA.

RESULTS

Seeding efficiency of PTFE pretreated with fibronectin was 260 +/- 8 cell/mm(2). After exposure to flow, only 39% +/- 14% of the EC were retained when EC were seeded alone, whereas 73% +/- 22% of EC remained on grafts when EC were seeded on top of SMC (P <.001, n = 10). The enzyme activity of a mutant zymogen tPA in absence of fibrin was 14 +/- 1 IU/mL, which is 3.6-fold lower than that in the presence of fibrin (50 +/- 19 IU/mL), whereas fibrin has no effect on the wild-type tPA activity. EC expressing a high level of wild-type tPA had a lower retention rate (37%) when compared with normal EC (45%). EC expressing the mutant zymogen tPA had an improved retention rate (54%, P =.001, n = 10) in absence of fibrin, whereas its retention rate was reduced to 43% when the cells were exposed to fibrin.

CONCLUSION

SMC seeded between EC and PTFE improves EC retention in vitro. Transduction of zymogen tPA increases thrombolytic ability of seeded cells with less adverse impact on cell retention than wild-type tPA.

Nonviral gene transfer into primary cultures of human and porcine mesothelial cells

Due to their abundance and accessibility, mesothelial cells may be suitable tools for recombinant reagent expression by gene transfer. Genetically modified porcine mesothelial cells (PMCs) may have the potential for the treatment of vascular diseases in humans. We studied the effect of various transfection reagents on the primary culture of PMCs and human mesothelial cells (HMCs). The cells were transfected with a plasmid encoding a reporter gene (luciferase or green fluorescent protein [GFP]) under the control of the cytomegalovirus promoter. Transfection was achieved using cationic lipids (DOSPER and DOTAP) or calcium phosphate/deoxyribonucleic acid coprecipitation or Fugene 6. Results showed that Fugene 6 was the most efficient and reproducible transfection reagent with both PMCs and HMCs. With Fugene 6, luciferase activity in PMCs (1.5 x 10(8) relative light units [RLU]/10(6) cells) was at least 2.5-fold higher than with the other transfection reagents, and it was 100-fold higher than in HMCs. However, the proportion of transfected cells expressing GFP was only 1%. These preliminary findings open up new avenues for developing experimental studies on the use of genetically modified PMCs.

Endothelial cell delivery for cardiovascular therapy

Obstructive atherosclerotic vascular disease stands as one of the greatest public health threats in the world. While a number of therapies have been developed to combat vascular disease, endothelial cell delivery has emerged as a distinct therapeutic modality. In this article, we will review the anatomy of the normal blood vessel and the biology of the intact endothelium, focusing upon its centrality in vascular biology and control over the components of the vascular response to injury so as to understand better the motivation for a cell-based form of therapy. Our discussion of cell delivery for cardiovascular therapy will be divided into surgical and interventional approaches. We will briefly recount the development of artificial grafts for surgical vascular bypass before turning our attention towards endothelial cell seeded vascular grafts, in which endothelial cells effectively provide local delivery of endogenous endothelial secretory products to maintain prosthetic integrity after surgical implantation. New techniques in tissue and genetic engineering of vascular grafts and whole blood vessels will be presented. Methods for percutaneous interventions will be examined as well. We will evaluate results of endoluminal endothelial cell seeding for treatment of restenosis and gene therapy approaches to enhance endogenous re-endothelialization. Finally, we will examine some innovations in endothelial cell delivery that may lead to the development of endothelial cell implants as a novel therapy for controlling proliferative vascular arteriopathy.

In vivo retention of endothelial cells adenovirally transduced with tissue-type plasminogen activator and seeded onto expanded polytetrafluoroethylene

PURPOSE

Seeding a prosthetic graft with genetically engineered vascular endothelial cells (ECs) has the potential to enhance the graft's antithrombotic properties. However, it has been reported that ECs transduced with tissue-type plasminogen activator (tPA) have very low levels of retention on grafts, probably because of increased proteolytic activity. We examined the retention of human tPA (htPA)-transduced ECs after the cells were seeded onto expanded polytetrafluoroethylene (ePTFE) grafts and implanted into dogs. We also examined the function of secreted htPA in this model.

METHODS AND RESULTS

Canine jugular venous ECs were transduced with adenoviral vectors encoding htPA (Adex1CAhtPA) and beta-galactosidase (Adex1CALacZ). There was a positive relationship between the percentage of X-gal ECs staining and the multiplicity of infection (MOI) of Adex1CALacZ. The level of htPA production in vitro increased with the increasing MOI of Adex1CAhtPA, but decreased gradually 4 days after infection. ECs coinfected with Adex1CAhtPA and Adex1CALacZ (htPAEC) or ECs infected with Adex1CALacZ alone (LacZEC) were seeded onto ePTFE grafts at densities equivalent to confluence to visualize retained ECs in an in vivo flow study. The grafts were implanted into canine carotid arteries and harvested after 5 hours of exposure to blood flow. The harvested grafts showed patchy defects in ECs, most of which were covered with mural thrombi. There was no significant difference in retention between htPAEC (29.3% +/- 8.7%) and LacZEC (19.5% +/- 3. 6%). There was a significant negative correlation between the in vivo EC retention on the grafts and the in vitro cellular passage level of ECs (P =.041; r = -.40). htPAEC produced 210.3 +/- 22.2 ng htPA antigen/10(6) cells per 6 hours in vitro and continued to secrete htPA on the harvested graft.

CONCLUSIONS

We demonstrated that a large amount of functional htPA was produced by adenovirally modified canine ECs. The results of the in vivo study may suggest that overexpression of tPA has little effect on the short-term retention of early passage ECs seeded onto ePTFE grafts.

Human macrovascular endothelial cells: optimization of culture conditions

The purpose of this study is to identify optimal culture conditions to support the proliferation of human macrovascular endothelial cells. Two cell lines were employed: human saphenous vein endothelial cells (HSVEC) and human umbilical vein endothelial cells (HUVEC). The influence of basal nutrient media (14 types), fetal bovine serum (FBS), and mitogens (three types) were investigated in relation to cell proliferation. Additionally, a variety of extracellular matrix (ECM) substrate-coated culture dishes were also tested. The most effective nutrient medium in augmenting cell proliferation was MCDB 131. Compared to the more commonly used M199 medium, MCDB 131 resulted in a 2.3-fold increase in cell proliferation. Media containing 20% FBS increased cell proliferation 7.5-fold compared to serum-free media. Among the mitogens tested, heparin (50 microg/ml) and endothelial cell growth supplement (ECGS) (50 microg/ml) significantly improved cell proliferation. Epithelial growth factor (EGF) provided no improvement in cell proliferation. There were no statistical differences in cell proliferation or morphology when endothelial cells were grown on uncoated culture plates compared to plates coated with ECM proteins: fibronectin, laminin, gelatin, or collagen types I and IV. The culture environment yielding maximal HSVEC and HUVEC proliferation is MCDB 131 nutrient medium supplemented with 2 mM glutamine, 20% FBS, 50 microg/ml heparin, and 50 microg/ml ECGS. The ECM substrate-coated culture dishes offer no advantage.

Genetic engineering of stent grafts with a highly efficient pseudotyped retroviral vector

PURPOSE

The purpose of this study was first to compare the gene transfer efficiency of amphotrophic murine leukemia viral vector (ampho-MuLV) with the efficiency of MuLV pseudotyped with the vesicular stomatitis virus G glycoprotein (VSVG-MuLV) in tissue of vascular origin. The second purpose of this study was to determine cell retention after the implantation of genetically engineered stent grafts.

METHODS

Gene transfer efficiency was ascertained with the b-galactosidase assay. The target tissues included endothelial cells (ECs), smooth muscle cells (SMCs), and human saphenous veins (HSVs). Polyurethane stent grafts were suffused with lac Z-transduced ECs and SMCs that were harvested from porcine jugular vein. The grafts were implanted into the iliac artery of each pig whose jugular vein had been harvested. Cell retention was analyzed at 1 and 4 weeks with X-Gal staining.

RESULTS

VSVG-MuLV transduction efficiency exceeded that of ampho-MuLV in human ECs (VSVG-MuLV, n = 24, 89% +/- 6%; ampho-MuLV, n = 18, 14% +/- 6%; P <. 001), human SMCs (VSVG-MuLV, n = 5, 92% +/- 3%; ampho-MuLV, n = 4, 17% +/- 2%; P <.001), pig ECs (VSVG-MuLV, n = 4, 81% +/- 2%; ampho-MuLV, n = 4, 13% +/- 3%; P <.001), and pig SMCs (VSVG-MuLV, n = 5, 89% +/- 3%; ampho-MuLV, n = 4, 16% +/- 1%; P <.001). As much as a 10-fold higher transduction efficiency was observed with VSVG-MuLV in HSVs. After the stent graft implantation, the engineered cells were retained and proliferated on the stent membrane, with ingrowth into the underlying intima.

CONCLUSION

VSVG-MuLV significantly increased the gene transfer efficiency in vascular SMCs and ECs and in organ-cultured HSVs. The cells were retained and proliferated on stent grafts for the short term in the pig.

Gene therapy for vascular disease

Atherosclerosis is a degenerative process characterized by endothelial cell dysfunction, inflammatory cell adhesion and infiltration, and the accumulation of cellular and matrix elements leading to the formation of fibrocellular plaques. In the end stages, advanced occlusive plaques limit blood flow and oxygen delivery resulting in the well-known ischemic syndromes of the coronary, skeletal muscle, mesenteric, and cerebrovascular circulation. Moreover, sudden critical ischemic events may be precipitated by plaque disturbance, rupture, hemorrhage, and/or thrombosis. Traditional pharmacologic approaches have been effective in reducing serum cholesterol and controlling thrombosis but, in the main, have had little impact on the treatment of advanced lesions. The purpose of this review is to examine the current status of gene therapy for vascular proliferation, aberrant endothelial function, thrombosis, peripheral ischemia, and modification of the blood/biomaterial interface.

Gene therapy and vascular disease: potential applications in vascular surgery

Advances in molecular biology have generated methods that are used to enhance diagnosis and treatment of a variety of human diseases. More recently modification of gene expression in cells by gene transfer has been introduced as a new therapeutic modality. The targeting of vascular cells with this method is appealing not only for anatomical reasons, but also because endovascular techniques provide access to the vasculature and makes site-specific delivery possible. Over the past few years, gene transfer has been widely used to explore the pathophysiology of vascular diseases in experimental models and available data suggests that this method may eventually become a therapeutic alternative for vascular disorders such as restenosis, graft failure, and critical ischaemia. In the following we discuss the methodology of gene transfer, its tentative use in vascular diseases related to vascular surgery, and the problems associated with this new technology.

Retroviral-mediated transduction of endothelial cells with the lac Z gene impairs cellular proliferation in vitro and graft endothelialization in vivo

PURPOSE

An endothelialized lumen within a synthetic graft that expresses recombinant proteins with anticoagulant or antiproliferative activity has the potential to improve graft function. However, preliminary data suggest that genetic modification of endothelial cells (ECs) impairs their proliferation. The purpose of this investigation was to test the hypothesis that retroviral transduction of cultured ECs with the lac Z gene encoding for beta-galactosidase would decrease EC proliferation in vitro and graft endothelialization in vivo.

METHODS

In vitro studies compared canine EC proliferation over a 14-day period among early-passage ECs (two and three) and late-passage ECs (six and nine) transduced with the BAG vector (containing the lac Z gene and the neomycin resistance gene), ECs transduced with the neomycin resistance gene only, the nontransduced ECs. In vivo canine studies assessed endothelialization of expanded polytetrafluoroethylene thoracoabdominal grafts seeded with autologous lac Z-transduced ECs (n = 7) or nontransduced ECs (n = 3) compared with that of nonseeded grafts (n = 3). Histochemical staining and DNA polymerase chain reaction was used 6 weeks after implantation to detect the presence of the lac Z gene in the grafts' cellular linings and perigraft tissues. Endothelialization was assessed by light microscopy and electron microscopy.

RESULTS

Proliferation of late-passage lac Z-transduced ECs in vitro was significantly decreased compared with neomycin resistance-transduced ECs or nontransduced ECs. Among early-passage ECs smaller but significant decreases in proliferation were noted among lac Z-transduced cells compared with nontransduced cells. Six of seven expanded polytetrafluoroethylene grafts seeded with transduced ECs showed lac Z gene expression. Lac Z gene expression was not found on grafts seeded with nontransduced ECs or nonseeded grafts. The endothelialized luminal surface area was significantly less in grafts seeded with lac Z-transduced ECs compared with grafts seeded with nontransduced ECs.

CONCLUSIONS

Retroviral-mediated transduction of canine ECs with the lac Z gene encoding for beta-galactosidase impairs EC proliferation in vitro and the ability of transduced ECs to form a confluent EC monolayer on the luminal surface of synthetic grafts in vivo.