Adenoviral-mediated gene transfer in human and animal vein grafts using clinically relevant exposure times, pressures, and viral concentrations

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.

Cardiovascular gene delivery: The good road is awaiting

Atherosclerotic cardiovascular disease is a leading cause of death worldwide. Despite recent improvements in medical, operative, and endovascular treatments, the number of interventions performed annually continues to increase. Unfortunately, the durability of these interventions is limited acutely by thrombotic complications and later by myointimal hyperplasia followed by progression of atherosclerotic disease over time. Despite improving medical management of patients with atherosclerotic disease, these complications appear to be persisting. Cardiovascular gene therapy has the potential to make significant clinical inroads to limit these complications. This article will review the technical aspects of cardiovascular gene therapy; its application for promoting a functional endothelium, smooth muscle cell growth inhibition, therapeutic angiogenesis, tissue engineered vascular conduits, and discuss the current status of various applicable clinical trials.

Pressure-Induced Vector Transport in Human Saphenous Vein

The efficiency of gene therapy as a pretreatment for saphenous vein coronary artery bypass grafts can be improved by increasing the transport of vector into the tunica media. The purpose of this study was to determine the effect of increasing transmural pressure on vector delivery depth in human saphenous vein segments. Specifically, we introduced adenovirus-sized microspheres luminally to observe changes in transport efficiency into the intimal and medial layers with increasing pressure. Our results indicate that transmural pressures of 100 and 400 mmHg increase the intimal concentration of microspheres as compared to 0 mmHg (p < 0.03), but do not significantly affect medial concentrations. We did not find increasing concentrations with increasing pressure above 100 mmHg. These results suggest that low or intermediate transmural pressures are adequate for intimal vector delivery and that techniques other than increasing pressure are required to deliver gene therapy vectors (> or = 100 nm) to medial smooth muscle cells. Also, our data support previous models designating the internal elastic lamina as the primary barrier to particle transport. Finally, our ex vivo microsphere perfusion experiment represents a novel way to explore functional vein permeabilities to gene therapy vectors and, ultimately, optimize vascular gene therapy protocols.

Sustained inhibition of experimental neointimal hyperplasia with a genetically modified herpes simplex virus

OBJECTIVE

Reported herein is a potential strategy for sustained smooth muscle cell (SMC) inhibition with a virulence-attenuated herpes simplex virus (HSV). Experiments were conducted in vitro to demonstrate selective SMC cytotoxicity and in vivo to demonstrate reduced neointimal hyperplasia (NIH) in a clinically relevant animal model.

METHODS

In vitro: Cultured human umbilical artery smooth muscle cells (UASMC) and venous endothelial cells (HUVEC) were exposed to varying multiplicities of infection (MOI) of a gamma(1)34.5-deleted HSV-1 virus (R849). Cell survival was assessed at 48 and 72 hours with a colorimetric MTT viability assay. In vivo: New Zealand White rabbit external jugular veins (n = 21) were exposed to R849 (2.5 x 10(6) pfu/mL) or culture medium at 110 to 120 mm Hg for 10 minutes, then fashioned as vein patches on carotid arteries. Carotid arteries were ligated distally to decrease blood flow and stimulate a hyperplastic response (ultra-low shear stress model). After 2, 4, 12, and 24 weeks, patched segments were perfusion-fixed with glutaraldehyde and morphometrically examined for NIH formation.

RESULTS

In vitro: At 48 hours, R849 exhibited preferential cytotoxicity to UASMC compared with HUVEC, with 11% +/- 10% of UASMCs and 49% +/- 8% of HUVECs surviving after infection with MOI = 25 (P <.05). Higher MOI resulted in poor survival of both cell lines. In vivo: Blood flow was similarly reduced in all animals both at surgery (0.9 +/- 0.1 mL/min vs 1.6 +/- 0.3 mL/min) and at harvest (2.7 +/- 0.4 mL/min vs 2.5 +/- 0.5 mL/min). R849-infected patches exhibited markedly less NIH than control patches did at 2 weeks (162 +/- 14 microm vs 49 +/- 6 microm; P <.05), 4 weeks (190 +/- 27 microm vs 67 +/- 8 microm; P <.05), and 12 weeks (233 +/- 18 microm vs 113 +/- 2 microm; P <.05).

CONCLUSION

The virulence-attenuated HSV strain R849 demonstrates selective cytotoxicity for SMC and is capable of sustained inhibition of NIH in an experimental model of vein graft failure.

Prevention of restenosis by a herpes simplex virus mutant capable of controlled long-term expression in vascular tissue in vivo

Neointimal hyperplasia resulting from vascular smooth muscle cell (SMC) proliferation and luminal migration is the major cause of autologous vein graft failure following vascular coronary or peripheral bypass surgery. Strategies to attenuate SMC proliferation by the delivery of oligonucleotides or genes controlling cell division rely on the use of high concentrations of vectors, and require pre-emptive disruption of the endothelial cell layer. We report a genetically engineered herpes simplex virus (HSV-1) mutant that, in an in vivo rabbit model system, infects all vascular layers without prior injury to the endothelium; expresses a reporter gene driven by a viral promoter with high efficiency for at least 4 weeks; exhibits no systemic toxicity; can be eliminated at will by administration of the antiviral drug acyclovir; and significantly reduces SMC proliferation and restenosis in vein grafts in immunocompetent hosts.

Gene therapy for acute diseases

The use of gene transfer systems to study cell function makes it apparent that overexpression of a transgene can restore or improve the function of a protein and positively influence cell function in a predetermined manner for purposes of counterbalancing cellular pathophysiology. The ability of some gene transfer vehicles to produce transgene product within hours of delivery positions gene transfer as a unique pharmaceutical administration system that can quickly affect production of biologic response modifiers in a highly compartmentalized fashion. This approach can be expected to overcome many of the adverse effects and high costs of systemic delivery of recombinant pharmaceuticals. This review highlights recent advances toward development of gene therapies for acute illnesses with particular emphasis on preclinical models of disease. In this context, a growing body of data suggests that gene therapies for polygenic and non-genetic diseases such as asthma, cardiogenic and non-cardiogenic pulmonary edema, stroke, subarachnoid hemorrhage, seizures, acute myocardial infarction, endovascular thrombosis, and infections may someday be options for the treatment of patients.