Potential for germ line transmission after intramyocardial gene delivery by adeno-associated virus

Recombinant Adeno-Associated Virus Vectors for Gene Therapy of the Central Nervous System: Delivery Routes and Clinical Aspects

The Central Nervous System (CNS) is vulnerable to a range of diseases, including neurodegenerative and oncological conditions, which present significant treatment challenges. The blood-brain barrier (BBB) restricts molecule penetration, complicating the achievement of therapeutic concentrations in the CNS following systemic administration. Gene therapy using recombinant adeno-associated virus (rAAV) vectors emerges as a promising strategy for treating CNS diseases, demonstrated by the registration of six gene therapy products in the past six years and 87 ongoing clinical trials. This review explores the implementation of rAAV vectors in CNS disease treatment, emphasizing AAV biology and vector engineering. Various administration methods-such as intravenous, intrathecal, and intraparenchymal routes-and experimental approaches like intranasal and intramuscular administration are evaluated, discussing their advantages and limitations in different CNS contexts. Additionally, the review underscores the importance of optimizing therapeutic efficacy through the pharmacokinetics (PK) and pharmacodynamics (PD) of rAAV vectors. A comprehensive analysis of clinical trials reveals successes and challenges, including barriers to commercialization. This review provides insights into therapeutic strategies using rAAV vectors in neurological diseases and identifies areas requiring further research, particularly in optimizing rAAV PK/PD.

Lack of germline transmission in male mice following a single intravenous administration of AAV5-hFVIII-SQ gene therapy

Valoctocogene roxaparvovec (AAV5-hFVIII-SQ) is an adeno-associated virus serotype five gene therapy under investigation for the treatment of hemophilia A. Herein, we assessed the potential for germline transmission of AAV5-hFVIII-SQ in mice. Male B6.129S6-Rag2tm1Fwa N12 mice received a single intravenous dose of vehicle or 6 × 1013 vg/kg AAV5-hFVIII-SQ. Vehicle and AAV5-hFVIII-SQ-treated mice were mated with naïve females 4 days after dosing, when the concentration of vector genomes was expected to be at its peak in semen, and 37 days after dosing, when a full spermatogenesis cycle was estimated to be complete. Quantitative PCR was used to evaluate the presence of transgene DNA in liver and testes from F0 males dosed with AAV5-hFVIII-SQ and liver tissue of F1 offspring. Transgene DNA was detected in liver and testes of all F0 males dosed with AAV5-hFVIII-SQ, confirming successful transduction. Importantly, no transgene DNA was detected in any tested F1 offspring derived from F0 males dosed with AAV5-hFVIII-SQ. Using a novel 2-stage statistical model that takes into account the number of males dosed with AAV5-hFVIII-SQ and the number of offspring sired by these males, we estimate that the risk of germline transmission is <5% with a 99.2% confidence level.

Large-scale molecular epidemiological analysis of AAV in a cancer patient population

Recombinant adeno-associated viruses (rAAVs) are well-established vectors for delivering therapeutic genes. However, previous reports have suggested that wild-type AAV is linked to hepatocellular carcinoma, raising concern with the safety of rAAVs. In addition, a recent long-term follow-up study in canines, which received rAAVs for factor VIII gene therapy, demonstrated vector integration into the genome of liver cells, reviving the uncertainty between AAV and cancer. To further explore this relationship, we performed large-scale molecular epidemiology of AAV in resected tumor samples and non-lesion tissues collected from 413 patients, reflecting nine carcinoma types: breast carcinoma, rectal cancer, pancreas carcinoma, brain tumor, hepatoid adenocarcinoma, hepatocellular carcinoma, gastric carcinoma, lung squamous, and adenocarcinoma. We found that over 80% of patients were AAV-positive among all nine types of carcinoma examined. Importantly, the AAV sequences detected in patient-matched tumor and adjacent non-lesion tissues showed no significant difference in incidence, abundance, and variation. In addition, no specific AAV sequences predominated in tumor samples. Our data shows that AAV genomes are equally abundant in tumors and adjacent normal tissues, but lack clonality. The finding critically adds to the epidemiological profile of AAV in humans, and provides insights that may assist rAAV-based clinical studies and gene therapy strategies.

Safety profile of recombinant adeno-associated viral vectors: focus on alipogene tiparvovec (Glybera®)

There has been great interest over the past two decades in developing gene therapies (GTs) to treat a variety of diseases; however, translating research findings into clinical treatments have proved to be a challenge. A major milestone in the development of GT has been achieved with the approval of alipogene tiparvovec (Glybera(®)) in Europe for the treatment of familial lipoprotein lipase deficiency. At this important stage with the evolution of GT into the clinic, this review will examine the safety aspects GT with adeno-associated virus (AAV) vectors. The topics that will be covered include acute reactions, immunological reactions to the AAV capsid and expressed transgene, viral biodistribution and shedding, DNA integration and carcinogenicity. These safety aspects of GT will be discussed with a focus on alipogene tiparvovec, in addition to other AAV vector GT products currently in clinical development.

AAV vectors for cardiac gene transfer: experimental tools and clinical opportunities

Since the first demonstration of in vivo gene transfer into myocardium there have been a series of advancements that have driven the evolution of cardiac gene delivery from an experimental tool into a therapy currently at the threshold of becoming a viable clinical option. Innovative methods have been established to address practical challenges related to tissue-type specificity, choice of delivery vehicle, potency of the delivered material, and delivery route. Most importantly for therapeutic purposes, these strategies are being thoroughly tested to ensure safety of the delivery system and the delivered genetic material. This review focuses on the development of recombinant adeno-associated virus (rAAV) as one of the most valuable cardiac gene transfer agents available today. Various forms of rAAV have been used to deliver "pre-event" cardiac protection and to temper the severity of hypertrophy, cardiac ischemia, or infarct size. Adeno-associated virus (AAV) vectors have also been functional delivery tools for cardiac gene expression knockdown studies and successfully improving the cardiac aspects of several metabolic and neuromuscular diseases. Viral capsid manipulations along with the development of tissue-specific and regulated promoters have greatly increased the utility of rAAV-mediated gene transfer. Important clinical studies are currently underway to evaluate AAV-based cardiac gene delivery in humans.

Partial restoration of left ventricular systolic function by asPLB gene transfer using ultrasound-mediated microbubble destruction

In vitro and in vivo studies have demonstrated that inhibition of phospholamban (PLB) expression in myocardium can restore left ventricular systolic function in failing heart. Ultrasound mediated microbubble destruction provides a new option for noninvasive gene transfer in heart. In this study, we transferred pAAV-antisense phospholamban (pAAV-asPLB) to the hearts of myocardial infarction (MI) mice, using ultrasound mediated microbubble destruction. Then we estimated the protein levels of PLB, Ser16-PLB and cardiac sarcoplasmic reticulum Ca(2+) ATPase (SERCA). The left ventricular ejection fraction (LVEF), fraction shortening (FS) and SERCA activity were measured as well. MI mice were generated by ligating the left anterior descending coronary artery. Microbubbles were prepared by sonicated perfluorocarbon gas with dextrose and albumin. A mixture of pAAV-asPLB plasmid and microbubble was injected via tail vein while the heart was simultaneously exposed to ultrasound via transthoracic insonation. Three weeks later, LVEF (48.2+/-5.18% vs 39.1+/-5.38%, p<0.05), FS (19.6+/-2.59% vs 16.0+/-2.29%, p<0.05), SERCA activity (3.00+/-0.29 vs 2.12+/-0.30, p<0.05) and Ser16-PLB protein level (0.8+/-0.25 vs 0.46+/-0.18, p<0.05) were increased while PLB protein level (1.45+/-0.38 vs 2.05+/-0.31, p<0.05) was decreased compared with the MI mice with saline injection. The above parameters in MI mice with only pAAV-asPLB plasmid injection or pAAV-asPLB plasmid combined with ultrasound alone were not significantly improved. pAAV-LacZ was used as a reporter gene to determine the efficiency and localization of transfection. The expression of beta-galactosidase was not found in liver, lung and brain, but found only in tubular epithelial cells of kidney and found in heart. These results confirm that asPLB gene transfection can be achieved by ultrasound mediated microbubble destruction with organ specificity. The effective transfection can partly restore heart function in MI mice.

No evidence of germ-line transmission by adenovirus-mediated gene transfer to mouse testes

OBJECTIVE

To investigate the risk of germ-line transmission of vector sequences after in vivo adenovirus-mediated gene transfer to mouse testes and to discuss whether an adenovirus vector could be used in the future to treat male factor infertility.

DESIGN

Experimental animal study.

SETTING

Laboratory research setting in the Department of Nephro-urology at Nagoya City University Graduate School of Medical Sciences in Japan.

ANIMAL(S)

Eight-week-old B6C3F1 mice.

INTERVENTION(S)

Adenovirus vector carrying a LacZ transgene as a marker was injected into the interstitial space (intratesticular injection) or seminiferous tubules (intratubular injection) of the mouse testis.

MAIN OUTCOME MEASURE(S)

An assessment by polymerase chain reaction (PCR) and histological analyses of the proportion of adenovirus vectors administered into the testis that can infect epididymal sperm and transmit to fetuses derived from these males 3, 7, 14, 28, and 35 days after intratesticular or intratubular adenovirus injection.

RESULT(S)

No PCR signal was identified in genomic DNA extracted from the epididymal sperm of all mice on each day after intratesticular or intratubular adenovirus injection. On reverse transcriptase (RT)-PCR analysis of mRNA isolated from fetuses derived from these males on each day after intratesticular or intratubular adenovirus injection, no fetuses had amplified products, although about 30% of the fetuses generated by microinjection into fertilized eggs had LacZ transcripts. On histochemical staining, no two-cell and 12.5 d.p.c. fetuses showed beta-gal activity. These sperm and fetus studies showed that adenovirus-mediated gene transfer to the testis does not cause infection of or transmission to the germ line or fetuses.

CONCLUSION(S)

The risk of germ-line transmission after adenovirus-mediated gene transfer to the testis is extremely low, and this method can be exploited in the future for the treatment of male factor infertility.

Gene therapy progress and prospects: Duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) is a severe muscle wasting disorder affecting 1/3500 male births. There is currently no effective treatment, but gene therapy approaches are offering viable avenues for treatment development. The last 10 years have seen the development of a number of strategies and tools for muscle gene therapy. However, the major hurdle has been the inability to deliver vectors at high enough efficiency via a systemic route. The last 2-3 years (reviewed here) have seen unrivalled progress in efficient systemic delivery of viral and non-viral gene transfer agents and antisense oligonucleotides. This progress, coupled with the successful completion of the first gene therapy clinical trial for DMD, has led to three more clinical trials planned for the immediate future.

rAAV-mediated angiogenin gene transfer induces angiogenesis and modifies left ventricular remodeling in rats with myocardial infarction

In vitro studies have demonstrated that bovine angiogenin (ANG) significantly stimulates both the migration of endothelial cells and the formation of tubelike structures. The aim of this study was to explore whether ANG gene transfer could enhance vascularization, modify left ventricular remodeling, and attenuate cardiac dysfunction in rats with myocardial infarction (MI). We constructed a recombinant adeno-associated virus vector encoding the ANG gene (rAAV-ANG) and evaluated its angiogenic potential after regional transfection by intramyocardial injection immediately after left anterior descending artery ligation in rats. Four weeks after coronary artery ligation, rAAV-ANG transfection upregulated the myocardium ANG protein expression level in both normal and MI rats, and immunohistochemistry showed that the overexpressed ANG was distributed in the cytoplasm of cardiomyocytes. In rats with MI, rAAV-ANG treatment altered left ventricular remodeling, as indicated by a decrease in left ventricular end diastolic diameter, left ventricular end systolic diameter, cardiomyocyte diameter, ventricular weight to body weight ratio and interstitial fibrosis infiltration. We also found an increase in capillary density and partly restored cardiac function in the group receiving rAAV-ANG treatment. These results confirmed that in rats with MI, ANG gene transfer could induce angiogenesis, alter left ventricular remodeling, and attenuate cardiac dysfunction. This study provides a new choice of treatment for ischemic heart disease.

Safety of direct administration of AAV2(CU)hCLN2, a candidate treatment for the central nervous system manifestations of late infantile neuronal ceroid lipofuscinosis, to the brain of rats and nonhuman primates

Late infantile neuronal ceroid lipofuscinosis (LINCL), a pediatric autosomal recessive neurodegenerative lysosomal storage disorder, results from mutations in the CLN2 gene and consequent deficiency in tripeptidyl-peptidase I (TPP-I) and progressive destruction of neurons. We have previously demonstrated that CNS gene transfer of AAV2(CU)hCLN2 (an AAV2-based vector expressing the human CLN2 cDNA) in rats and nonhuman primates mediates long-term TPP-I expression in the CNS neurons [Sondhi, D., Peterson, D.A., Giannaris, E.L., Sanders, C.T., Mendez, B.S., De, B., Rostkowski, A., Blancard, B., Bjugstad, K., Sladek, J.R., Redmond, D.E., Leopold, P.L., Kaminsky, S.M., Hackett, N.R., and Crystal, R.G. (2005). Gene Ther. 12, 1618-1632]. The present study tests the hypothesis that direct CNS administration of a clinical-grade AAV2(CU)hCLN2 vector to the CNS of rats and nonhuman primates at doses scalable to humans has a long-term safety profile acceptable for initiating clinical trials. Fischer 344 rats were injected bilaterally via the striatum with 2 x 10(10) particle units (PU) of AAV2(CU)hCLN2, using saline as a control. At 13, 26, and 52 weeks, vector and phosphate-buffered salineinjected rats were killed (n = 6 per time point), and blood, brain, and distant organs were assessed. There were no biologically significant differences between control and vector groups for complete blood count, serum chemistry, and neutralizing anti-AAV2 antibody levels. CNS administration of AAV2 CUhCLN2 did not result in any pathological changes in the brain that were attributable to the vector, although microscopic changes were observed along the track consistent with needle trauma. A total dose of 3.6 x 10(10) or 3.6 x 10(11) PU of AAV2(CU)hCLN2 was administered to the CNS of African Green monkeys at 12 locations, targeting the caudate nucleus, hippocampus, and overlying cortices. Monkeys (n = 3 at each dose) were killed 1, 13, 26, or 52 weeks after injection. Controls included sham-injected, saline-injected, and AAV2(CU)Null-injected (3.6 x 10(11) PU) monkeys. There were no biologically significant differences among vector-injected and control groups in any parameter of the general assessment, complete blood count, or serum chemistry assessed at multiple time points after vector administration. Importantly, no abnormal behavior was observed in any group in videotaped neurological assessment, where behaviors were quantified before administration and at multiple time points afterward. Histopathological examination of the CNS demonstrated that 1 week after administration, AAV2(CU)hCLN2 produced transient minor white matter edema with reactive glial cells in the corona radiata of the cerebrum along the injection track and in the surrounding white matter. This abnormality was not observed at 13, 26, or 52 weeks. Together with the long-term gene expression after gene transfer, these findings supported the initiation of clinical trials to assess the safety of AAV2(CU)hCLN2 administration to individuals with LINCL.

Chronic recurrent myocardial ischemic injury is significantly attenuated by pre-emptive adeno-associated virus heme oxygenase-1 gene delivery

OBJECTIVES

We assessed the hypothesis that overexpression of the antioxidant enzyme heme oxygenase (HO)-1 may protect against chronic recurrent ischemia/reperfusion injury.

BACKGROUND

Multiple and recurring episodes of myocardial ischemia can result in significant myocardial damage, including myocyte death, fibrosis, and wall thinning, leading to impaired ventricular function and cardiac failure.

METHODS

In this study we used a closed-chest rodent model of chronic recurring myocardial ischemia and reperfusion to investigate the efficacy of pre-emptive gene therapy in overexpressing the antioxidant enzyme HO-1, using adeno-associated virus (AAV)-2 as the delivery vector.

RESULTS

We show that constitutive overexpression of HO-1 can prevent myocardial wall thinning, inflammation, fibrosis, and deterioration of cardiac function (as measured by echocardiography, histology, and immunohistochemistry) induced by repeated transient myocardial ischemia and reperfusion injury. With HO-1 therapy, there was a significant reduction in apoptosis as determined by levels of markers of survival proteins and terminal deoxynucleotidyltransferase dUTP nick end-labeling staining. This prevention of tissue damage was also associated with reduction in superoxide generation.

CONCLUSIONS

Taken together we provide the first evidence of the therapeutic efficacy of pre-emptive AAV-HO-1 delivery for prevention against multiple ischemic injury. This approach protects myocytes by simultaneously activating protective response and inhibiting pathological left ventricular remodeling and, therefore, may be a useful cardio-protective strategy for patients with coronary artery disease at a high risk for recurrent myocardial ischemia.

Gene therapy for renal disorders

During the last 20 years there have been major improvements in renal replacement therapy, including dialysis and kidney transplantation; however, the treatment options for renal diseases are still limited. Gene therapy is a potential modality for many renal diseases for which we are as yet unable to offer specific treatment. This article reviews the recent data on gene therapy in animal models applicable to human renal diseases and evaluates its efficacy, safety and clinical relevance. Several approaches appear to be promising, including adeno-associated viral vectors for long-term gene expression, electroporation for muscular gene delivery, ultrasound/microbubble-mediated gene targeting, macrophage-based gene therapy and small interfering RNAs.

No evidence for germ-line transmission following prenatal and early postnatal AAV-mediated gene delivery

BACKGROUND

Recombinant adeno-associated viruses have been used successfully in a number of pre-clinical and clinical gene therapy studies. Since there is a broad consensus that gene therapy must not lead to germ-line transmission, the potential of such vectors for inadvertent gene transfer into germ cells deserves special attention. This applies in particular to pre- or perinatal vector application which has been considered for diseases presenting with morbidity already at birth.

METHODS

AAV serotype 2 derived vectors carrying a beta-galactosidase reporter gene or human clotting factor IX cDNA were injected intraperitoneally or via a yolk sac vein into mouse fetuses or administered intravascularly to newborn mice. Tissue samples of the treated animals including the gonads as well as sperm DNA, obtained by differential lysis of one testis of each male animal, and the offspring of all treated mice were investigated for the presence of vector DNA by nested PCR. In positive samples, the copy number of the vector was determined by quantitative real-time PCR.

RESULTS

AAV vectors administered intraperitoneally or intravascularly to fetal or newborn mice reached the gonads of these animals and persisted there for time periods greater than one year. Intravascular injection of the vector resulted more frequently in gene transfer to the gonads than intraperitoneal injection. Vector copy numbers in the gonads ranged from 0.3 to 74 per 10(4) cell equivalents. However, neither in isolated sperm DNA from the treated animals nor in their offspring were vector sequences detectable.

CONCLUSIONS

These data suggest the risk of inadvertent germ-line transmission following prenatal or early postnatal AAV type 2 mediated gene delivery to be very low.

Recombinant adeno-associated viral (rAAV) vectors as therapeutic tools for Duchenne muscular dystrophy (DMD)

Duchenne muscular dystrophy (DMD) is a lethal genetic muscle disorder caused by recessive mutations in the dystrophin gene. The size of the gene (2.4 Mb) and mRNA (14 kb) in addition to immunogenicity problems and inefficient transduction of mature myofibres by currently available vector systems are formidable obstacles to the development of efficient gene therapy approaches. Adeno-associated viral (AAV) vectors overcome many of the problems associated with other vector systems (nonpathogenicity and minimal immunogenicity, extensive cell and tissue tropism) but accommodate limited transgene capacity (<5 kb). As a result of these observations, a number of laboratories worldwide have engineered a series of microdystrophin cDNAs based on genotype-phenotype relationship in Duchenne (DMD) and Becker (BMD) dystrophic patients, and transgenic studies in mdx mice. Recent progress in characterization of AAV serotypes from various species has demonstrated that alternative AAV serotypes are far more efficient in transducing muscle than the traditionally used AAV2. This article summarizes the current progress in the field of recombinant adeno-associated viral (rAAV) delivery for DMD, including optimization of recombinant AAV-microdystrophin vector systems/cassettes targeting the skeletal and cardiac musculature.

Adeno-associated viral vector delivers cardiac-specific and hypoxia-inducible VEGF expression in ischemic mouse hearts

It has been shown that the adeno-associated virus (AAV) vector can deliver the VEGF gene efficiently into the ischemic mouse myocardium. However, the AAV genomes can be found in extracardiac organs after intramyocardial injection. To limit unwanted VEGF expression in organs other than the heart, we tested the use of the cardiac myosin light chain 2v (MLC-2v) promoter and the hypoxia-response element to mediate cardiac-specific and hypoxia-inducible VEGF expression. An AAV vector, MLCVEGF, with 250 bp of the MLC-2v promoter and nine copies of the hypoxia-response element driving VEGF expression, was constructed. Gene expression was studied in vitro by infection of rat cardiomyocytes, rat skeletal myocytes, and mouse fibroblasts with the vector and in vivo by direct injection of the vector into normal and ischemic mouse hearts. With MLCVEGF infection, VEGF expression was higher in cardiomyocytes than the other two cell lines and was hypoxiainducible. VEGF expression was also higher in ischemic hearts than in normal hearts. No VEGF expression was detectable in organs with detectable MLCVEGF vectors other than the heart. MLCVEGF-injected ischemic hearts had more capillaries and small vessels around the injection site, smaller infarct size, and better cardiac function than the negative controls. Hence, MLCVEGF can mediate cardiac-specific and hypoxia-inducible VEGF expression, neoangiogenesis, infarct-size reduction, and cardiac functional improvement.

Endothelium-Targeted Gene and Cell-Based Therapies for Cardiovascular Disease

Most common cardiovascular diseases are accompanied by endothelial dysfunction. Because of its predominant role in the pathogenesis of cardiovascular disease, the vascular endothelium is an attractive therapeutic target. The identification of promoter sequences capable of rendering endothelial-specific transgene expression together with the recent development of vectors with enhanced tropism for endothelium may offer opportunities for the design of new strategies for modulation of endothelial function. Such strategies may be useful in the treatment of chronic diseases such as hypertension, atherosclerosis, and ischemic artery disease, as well as in acute myocardial infarction and during open heart surgery for prevention of ischemia and reperfusion (I/R)-induced injury. The recent identification of putative endothelial progenitor cells in peripheral blood may allow the design of autologous cell-based strategies for neovascularization of ischemic tissues and for the repair of injured blood vessels and bioengineering of vascular prosthesis. "Proof-of-concept" for some of these strategies has been established in animal models of cardiovascular disease. However the successful translation of these novel strategies into clinical application will require further developments in vector and delivery technologies. Further characterization of the processes involved in mobilization, migration, homing, and incorporation of endothelial progenitor cells into the target tissues is necessary, and the optimal conditions for therapeutic application of these cells need to be defined and standardized.

Gene transfer vector biodistribution: pivotal safety studies in clinical gene therapy development

Techniques allowing for gene transfer vectors biodistribution investigation, in the frame of preclinical gene therapy development, are exposed. Emphasis is given on validation and test performance assessment. In the second part, specific gene vector distribution properties are reviewed (adenovirus, AAV, plasmid, retroviruses, herpes-derived vectors, germline transmission risks). The rationale for biodistribution by quantitative PCR, animal study and result interpretation is discussed. The importance and pivotal role of biodistribution study in gene transfer medicine development is shown through the determination of target organs for toxicity, germline transmission assessment and determination of risks of shedding and spreading of vectors in the gene transfer recipient and the environment.