Successful expression of human factor IX following repeat administration of adenoviral vector in mice

THE JEREMIAH METZGER LECTURE: TURNING GENES INTO MEDICINES: HIGHLIGHTS AND HURDLES IN THE DEVELOPMENT OF GENE THERAPY FOR GENETIC DISEASE

The journey from in vitro transfer of genes into mammalian cells to approved gene therapy products has spanned decades. This manuscript summarizes hurdles encountered and obstacles overcome in the development of successful adeno-associated viral (AAV) vectors for hemophilia B and for an inherited retinal dystrophy caused by mutations in the RPE65 gene. In the case of hemophilia B, careful analysis of the first unsuccessful attempts led to the realization that the human immune response to AAV vectors was preventing durable expression; elucidation of the response to the recombinant virion led to strategies that enabled successful long-lasting gene transfer. For RPE65 deficiency, a key to success was development and validation of a novel clinical endpoint for a disease that previously lacked a pharmacologic treatment.

Gene therapy - are we ready now?

Introduction

Haemophilia therapy has evolved from rudimentary transfusion‐based approaches to an unprecedented level of innovation with glimmers of functional cure brought by gene therapy. After decades of misfires, gene therapy has normalized factor (F)VIII and factor (F)IX levels in some individuals in the long term. Several clinical programmes testing adeno‐associated viral (AAV) vector gene therapy are approaching completion with imminent regulatory approvals.

Discussion

Phase 3 studies along with multiyear follow‐up in earlier phase investigations raised questions about efficacy as well as short‐ and long‐term safety, prompting a reappraisal of AAV vector gene therapy. Liver toxicities, albeit mostly low‐grade, occur in the first year in at least some individuals in all haemophilia A and B trials and are poorly understood. Extreme variability and unpredictability of outcome, as well as a slow decline in factor expression (seemingly unique to FVIII gene therapy), are vexing because immune responses to AAV vectors preclude repeat dosing, which could increase suboptimal or restore declining expression, while overexpression may result in phenotoxicity. The long‐term safety will need lifelong monitoring because AAV vectors, contrary to conventional wisdom, integrate into chromosomes at the rate that calls for vigilance.

Conclusions

AAV transduction and transgene expression engage the host immune system, cellular DNA processing, transcription and translation machineries in ways that have been only cursorily studied in the clinic. Delineating those mechanisms will be key to finding mitigants and solutions to the remaining problems, and including individuals who cannot avail of gene therapy at this time.

Hepatocarcinoma-intestine-pancreas/pancreatitis-associated protein (HIP/PAP) confers protection against hepatic fibrosis through downregulation of transforming growth factor β receptor II

Hepatocarcinoma-intestine-pancreas/pancreatitis-associated protein (HIP/PAP) has antimicrobial, antioxidant, anti-inflammatory, mitogenic, and antiapoptotic effects and thus exerts important functions in the maintenance of integrity and homeostasis of several organs, such as the gastrointestinal tract, pancreas, and liver. Although the potent hepatoprotective effect of HIP/PAP has been validated, its impact on liver fibrosis has not been reported. In this study, we evaluated the role of HIP/PAP on hepatic fibrosis and explored the possible underlying mechanisms. We found that the expression of HIP/PAP and its mouse counterpart, Reg3B, was markedly upregulated in fibrotic human or mouse livers. Intraperitoneal (i.p.) interleukin (IL)-10, IL-6, and TNF-α but not TGF-β1 significantly induced hepatic overexpression of Reg3B in mice. In both CCl₄ and BDL liver fibrosis models, adenovirus-mediated ectopic expression of HIP/PAP markedly alleviated liver injury, inflammation, collagen deposition, hepatic stellate cell activation, and the overexpression of profibrotic cytokines, including transforming growth factor β1 (TGF-β1), platelet-derived growth factor (PDGF)-A, B, connective tissue growth factor (CTGF), and plasminogen activator inhibitor-1 (PAI-1), in mice. In vitro experiments demonstrated that, in addition to suppressing hepatic stellate cell proliferation and accelerating hepatocyte proliferation, HIP/PAP mitigated TGF-β1-induced hepatic stellate cell activation, hepatocyte epithelial-mesenchymal transition (EMT) and upregulated expression of profibrotic cytokines in both hepatic stellate cells and hepatocytes. Moreover, HIP/PAP attenuated the overexpression of TGF-β receptor II (TGF-βRII) in fibrotic mouse livers and decreased the basal expression of TGF-βRII in nonfibrotic mouse livers as well as in cultured hepatocytes and hepatic stellate cells, which is at least partly attributable to the TGF-β1-antagonizing function of HIP/PAP. This study indicates that increased expression of hepatic HIP/PAP serves as a countermeasure against liver injury and fibrosis. Exogenous supplementation of HIP/PAP might be a promising therapeutic agent for hepatic fibrosis as well as liver injury.

Neonatal Genetic Delivery of Anti-Respiratory Syncytial Virus (RSV) Antibody by Non-Human Primate-Based Adenoviral Vector to Provide Protection against RSV

Respiratory syncytial virus (RSV) is one of the leading causes of lower respiratory tract infection in infants. Immunoprophylaxis with the anti-RSV monoclonal antibody, palivizumab, reduces the risk for RSV-related hospitalizations, but its use is restricted to high-risk infants due to the high costs. In this study, we investigated if genetic delivery of anti-RSV antibody to neonatal mice by chimpanzee adenovirus type 7 expressing the murine form of palivizumab (AdC7αRSV) can provide protection against RSV. Intranasal and intramuscular administration of AdC7αRSV to adult mice resulted in similar levels of anti-RSV IgG in the serum. However, only intranasal administration resulted in detectable levels of anti-RSV IgG in the bronchoalveolar lavage fluid. Intranasal administration of AdC7αRSV provided protection against subsequent RSV challenge. Expression of the anti-RSV antibody was prolonged following intranasal administration of AdC7αRSV to neonatal mice. Protection against RSV was confirmed at 6 weeks of age. These data suggest that neonatal genetic delivery of anti-RSV antibody by AdC7αRSV can provide protection against RSV.

Excessive irisin increases oxidative stress and apoptosis in murine heart

Irisin is an exercise-related myokine. The abundance of irisin is associated with many diseases, such as myocardial infarction, chronic kidney disease, metabolic syndrome, obesity, and diabetes mellitus. In cardiomyocytes, irisin modulates the mitochondrial thermogenesis, regulates ischemic responses, and affects calcium signaling. Previous studies suggested that irisin increases cardiomyoblast mitochondrial functions and protects ischemic and reperfusion injury in ex vivo murine heart. In human, clinical studies have shown that acute myocardial infarction patients with more elevated serum irisin abundances are associated with increased major adverse cardiovascular events. However, the mechanisms responsible for this discrepancy between in myocardial infarction patients and ex vivo murine heart is unclear. Based on the clinical observations, we hypothesized that excessive irisin might lead to mitochondrial dysfunctions and cardiomyocyte damages. Our data showed that overexpression of irisin in mice with the adenovirus resulted in enhanced mitochondrial respiration with a higher oxygen consumption rate. Enhanced irisin expression in heart and irisin treatment in cardiomyocytes increased reactive oxygen species production. Furthermore, irisin treatment in cardiomyocytes enhanced the apoptosis and the cleaved caspase 9 levels in hypoxic condition. Pathway analysis in the murine heart with the overexpression of irisin showed that angiopoietin-Tie2, IL-8, IL-13, TGF-β, and thrombopoietin signaling were affected by irisin. Collectively, these results supported that excessive irisin causes mitochondrial overdrive with a higher reactive oxygen species production, which results in increased apoptosis of cardiomyocytes in a hypoxic environment.

Integration-deficient lentiviral vectors expressing codon-optimized R338L human FIX restore normal hemostasis in Hemophilia B mice

Integration-deficient lentiviral vectors (IDLVs) have been shown to transduce a wide spectrum of target cells and organs in vitro and in vivo and to maintain long-term transgene expression in nondividing cells. However, epigenetic silencing of episomal vector genomes reduces IDLV transgene expression levels and renders these safe vectors less efficient. In this article, we describe for the first time a complete correction of factor IX (FIX) deficiency in hemophilia B mice by IDLVs carrying a novel, highly potent human FIX cDNA. A 50-fold increase in human FIX cDNA potency was achieved by combining two mechanistically independent yet synergistic strategies: (i) optimization of the human FIX cDNA codon usage to increase human FIX protein production per vector genome and (ii) generation of a highly catalytic mutant human FIX protein in which the arginine residue at position 338 was substituted with leucine. The enhanced human FIX activity was not associated with liver damage or with the formation of human FIX-directed inhibitory antibodies and rendered IDLV-treated FIX-knockout mice resistant to a challenging tail-clipping assay. A novel S1 nuclease-based B1-quantitative polymerase chain reaction assay showed low levels of IDLV integration in mouse liver. Overall, this study demonstrates that IDLVs carrying an improved human FIX cDNA safely and efficiently cure hemophilia B in a mouse model.

Ribosomal DNA integrating rAAV-rDNA vectors allow for stable transgene expression

Although recombinant adeno-associated virus (rAAV) vectors are proving to be efficacious in clinical trials, the episomal character of the delivered transgene restricts their effectiveness to use in quiescent tissues, and may not provide lifelong expression. In contrast, integrating vectors enhance the risk of insertional mutagenesis. In an attempt to overcome both of these limitations, we created new rAAV-rDNA vectors, with an expression cassette flanked by ribosomal DNA (rDNA) sequences capable of homologous recombination into genomic rDNA. We show that after in vivo delivery the rAAV-rDNA vectors integrated into the genomic rDNA locus 8-13 times more frequently than control vectors, providing an estimate that 23-39% of the integrations were specific to the rDNA locus. Moreover, a rAAV-rDNA vector containing a human factor IX (hFIX) expression cassette resulted in sustained therapeutic levels of serum hFIX even after repeated manipulations to induce liver regeneration. Because of the relative safety of integration in the rDNA locus, these vectors expand the usage of rAAV for therapeutics requiring long-term gene transfer into dividing cells.

Therapeutic in vivo gene transfer for genetic disease using AAV: progress and challenges

In vivo gene replacement for the treatment of inherited disease is one of the most compelling concepts in modern medicine. Adeno-associated virus (AAV) vectors have been extensively used for this purpose and have shown therapeutic efficacy in a range of animal models. Successful translation to the clinic was initially slow, but long-term expression of donated genes at therapeutic levels has now been achieved in patients with inherited retinal disorders and haemophilia B. Recent exciting results have raised hopes for the treatment of many other diseases. As we discuss here, the prospects and challenges for AAV gene therapy are to a large extent dependent on the target tissue and the specific disease.

Engineering biomaterial systems to enhance viral vector gene delivery

Integrating viral gene delivery with engineered biomaterials is a promising strategy to overcome a number of challenges associated with virus-mediated gene delivery, including inefficient delivery to specific cell types, limited tropism, spread of vectors to distant sites, and immune responses. Viral vectors can be combined with biomaterials either through encapsulation within the material or immobilization onto a material surface. Subsequent biomaterial-based delivery can increase the vector's residence time within the target site, thereby potentially providing localized delivery, enhancing transduction, and extending the duration of gene expression. Alternatively, physical or chemical modification of viral vectors with biomaterials can be employed to modulate the tropism of viruses or reduce inflammatory and immune responses, both of which may benefit transduction. This review describes strategies to promote viral gene delivery technologies using biomaterials, potentially providing opportunities for numerous applications of gene therapy to inherited or acquired disorders, infectious disease, and regenerative medicine.

An in vitro-identified high-affinity nucleosome-positioning signal is capable of transiently positioning a nucleosome in vivo

BACKGROUND

The physiological function of eukaryotic DNA occurs in the context of nucleosomal arrays that can expose or obscure defined segments of the genome. Certain DNA sequences are capable of strongly positioning a nucleosome in vitro, suggesting the possibility that favorable intrinsic signals might reproducibly structure chromatin segments. As high-throughput sequencing analyses of nucleosome coverage in vitro and in vivo have become possible, a vigorous debate has arisen over the degree to which intrinsic DNA:nucleosome affinities orchestrate the in vivo positions of nucleosomes, thereby controlling physical accessibility of specific sequences in DNA.

RESULTS

We describe here the in vivo consequences of placing a synthetic high-affinity nucleosome-positioning signal, the 601 sequence, into a DNA plasmid vector in mice. Strikingly, the 601 sequence was sufficient to position nucleosomes during an early phase after introduction of the DNA into the mice (when the plasmid vector transgene was active). This positioning capability was transient, with a loss of strong positioning at a later time point when the transgenes had become silent.

CONCLUSIONS

These results demonstrate an ability of DNA sequences selected solely for nucleosome affinity to organize chromatin in vivo, and the ability of other mechanisms to overcome these interactions in a dynamic nuclear environment.

Proteasome inhibitors decrease AAV2 capsid derived peptide epitope presentation on MHC class I following transduction

Adeno-associated viral (AAV) vectors are an extensively studied and highly used vector platform for gene therapy applications. We hypothesize that in the first clinical trial using AAV to treat hemophilia B, AAV capsid proteins were presented on the surface of transduced hepatocytes, resulting in clearance by antigen-specific CD8+ T cells and consequent loss of therapeutic transgene expression. It has been previously shown that proteasome inhibitors can have a dramatic effect on AAV transduction in vitro and in vivo. Here, we describe using the US Food and Drug Administration-approved proteasome inhibitor, bortezomib, to decrease capsid antigen presentation on hepatocytes in vitro, whereas at the same time, enhancing gene expression in vivo. Using an AAV capsid-specific T-cell reporter (TCR) line to analyze the effect of proteasome inhibitors on antigen presentation, we demonstrate capsid antigen presentation at low multiplicities of infection (MOIs), and inhibition of antigen presentation at pharmacologic levels of bortezomib. We also demonstrate that bortezomib can enhance Factor IX (FIX) expression from an AAV2 vector in mice, although the same effect was not observed for AAV8 vectors. A pharmacological agent that can enhance AAV transduction, decrease T-cell activation/proliferation, and decrease capsid antigen presentation would be a promising solution to obstacles to successful AAV-mediated, liver-directed gene transfer in humans.

Tolerance induction to cytoplasmic beta-galactosidase by hepatic AAV gene transfer: implications for antigen presentation and immunotoxicity

Background

Hepatic gene transfer, in particular using adeno-associated viral (AAV) vectors, has been shown to induce immune tolerance to several protein antigens. This approach has been exploited in animal models of inherited protein deficiency for systemic delivery of therapeutic proteins. Adequate levels of transgene expression in hepatocytes induce a suppressive T cell response, thereby promoting immune tolerance. This study addresses the question of whether AAV gene transfer can induce tolerance to a cytoplasmic protein.

Major Findings

AAV-2 vector-mediated hepatic gene transfer for expression of cytoplasmic β-galactosidase (β-gal) was performed in immune competent mice, followed by a secondary β-gal gene transfer with E1/E3-deleted adenoviral Ad-LacZ vector to provoke a severe immunotoxic response. Transgene expression from the AAV-2 vector in ∼2% of hepatocytes almost completely protected from inflammatory T cell responses against β-gal, eliminated antibody formation, and significantly reduced adenovirus-induced hepatotoxicity. Consequently, ∼10% of hepatocytes continued to express β-gal 45 days after secondary Ad-LacZ gene transfer, a time point when control mice had lost all Ad-LacZ derived expression. Suppression of inflammatory T cell infiltration in the liver and liver damage was linked to specific transgene expression and was not seen for secondary gene transfer with Ad-GFP. A combination of adoptive transfer studies and flow cytometric analyses demonstrated induction of Treg that actively suppressed CD8⁺ T cell responses to β-gal and that was amplified in liver and spleen upon secondary Ad-LacZ gene transfer.

Conclusions

These data demonstrate that tolerance induction by hepatic AAV gene transfer does not require systemic delivery of the transgene product and that expression of a cytoplasmic neo-antigen in few hepatocytes can induce Treg and provide long-term suppression of inflammatory responses and immunotoxicity.

A single intravenous injection of adeno-associated virus serotype-9 leads to whole body skeletal muscle transduction in dogs

The success of many gene therapy applications hinges on efficient whole body transduction. In the case of muscular dystrophies, a therapeutic vector has to reach every muscle in the body. Recent studies suggest that vectors based on adeno-associated virus (AAV) are capable of body-wide transduction in rodents. However, translating this finding to large animals remains a challenge. Here we explored systemic gene delivery with AAV serotype-9 (AAV-9) in neonatal dogs. Previous attempts to directly deliver AAV to adult canine muscle have yielded minimal transduction due to a strong cellular immune response. However, in neonatal dogs we observed robust skeletal muscle transduction throughout the body after a single intravenous injection. Importantly, systemic transduction was achieved in the absence of pharmacological intervention or immune suppression and it lasted for at least 6 months (the duration of study). We also observed several unique features not predicted by murine studies. In particular, cardiac muscle was barely transduced in dogs. Many muscular dystrophy patients can be identified by neonatal screening. The technology described here may lead to an effective early intervention in these patients.

Gene therapy for haemophilia

The ultimate goal of gene therapy is the replacement of a defective gene sequence with a corrected version to eliminate disease for the lifetime of the patient. This challenging task is not yet accomplished, however significant progress is evident. An initial spate of clinical trials attempting the treatment of haemophilia with gene transfer primarily resulted in the demonstration of good safety profiles, but without efficacy. Subsequent reengineering of vector plasmids and delivery systems resulted in markedly improved outcomes in animal models of the disease. The most recent clinical trial for the treatment of haemophilia B with gene transfer showed transient achievement of efficacy in the highest dose cohort tested, but also exposed a previously hidden barrier to the future success of these treatments. The progress and problems of gene therapies for haemorrhagic disorders will be discussed. This review will concentrate on approaches in or near clinical application.

The host response to adenovirus, helper-dependent adenovirus, and adeno-associated virus in mouse liver

Understanding host responses to viral gene therapy vectors is necessary for the development of safe and efficacious in vivo gene transfer agents. We describe the use of high-density spotted complementary DNA microarrays in monitoring the in vivo host transcriptional responses in mouse liver upon administration of either a "first-generation"adenoviral (Ad) vector, a helper-dependent "gutless" adenoviral (HD) vector, or an adeno-associated viral (AAV) vector containing human factor IX (hFIX) expression cassettes. Since HD and AAV do not contain any viral genes, they allow us to assess the host response to the viral capsid and packaged nonviral DNA in whole animals. Comparison of the host response to Ad and HD helps assess the importance of leaky adenoviral gene expression. While all three vectors induced characteristic temporally sequenced programs of gene expression, the gene expression programs induced by the Ad and HD adenovirus vectors were remarkably similar, including the induction of a prominent type I interferon (IFN)-dependent cluster within 6 hours of administration. In contrast, the AAV-based vector caused far fewer alterations of host-gene expression. Our results indicate that recognition of the Ad capsid or double-stranded DNA (of nonviral origin) in the vector elicits a robust type I IFN response that is, however, not elicited by AAV-derived vector transduction.

A comparative study of hFIX expression mediated by rAAV8 and rAAV1 administrated intramuscularly

BACKGROUND

Recombinant AAV serotype 8 (rAAV8) vector is relatively new for gene therapy. In this study, the hFIX expression mediated by rAAV8 injected intramuscularly was compared with that by rAAV1.

METHODS

rAAV8-hFIX or rAAV1-hFIX viruses were injected intramuscularly into two hind limbs of mice at doses of 5x10(10) gc and 2.5x10(12) gc (genome copy). The hFIX expression in the mouse plasma was detected by ELISA, APTT and Western blotting. The virus distribution was analyzed by immunohistochemical assay.

RESULTS

When the mice were infected with 5x10(10) gc virus, high levels of hFIX in the plasma of five rAAV8-hFIX virus-infected mice were detected 2 weeks after injection. A hFIX peak above 5000 ng/mL appeared between 2 and 6 weeks after injection. Relatively low levels of hFIX were detected in the plasma of rAAV1-hFIX virus-infected mice 2 weeks after injection. An hFIX peak above 3000 ng/mL appeared between 4 and 10 weeks after injection. However, much lower levels of hFIX were detected in mice infected with higher dose of rAAV8 virus. The hFIX in the mouse plasma was active biologically. The viruses were distributed mainly in the muscles of hind limbs.

DISCUSSION

Gene expression mediated by rAAV8 was sooner and stronger than that by rAAV1 after intramuscular administration. Inhibition might have been triggered markedly by rAAV8 at high doses.

Prolonged susceptibility to antibody-mediated neutralization for adeno-associated vectors targeted to the liver

Adeno-associated virus (AAV) vectors demonstrate highly efficient gene transfer to hepatocytes in vivo. One of the remaining obstacles to the treatment of hemophilia B patients with AAV vectors is the sensitivity of these vectors to antibody-mediated neutralization following systemic delivery. Testing and implementation of strategies to circumvent pre-existing antibodies requires knowledge of the clearance kinetics of AAV from circulation. In this study, AAV clearance kinetics were established for serotypes 2 and 8 in cell culture and in mice. Administration of pooled neutralizing serum subsequent to administration of the vector was used to define the time period in which the vector is susceptible to antibody-mediated neutralization. These experiments defined the in vivo clearance rates for both AAV2 and AAV8 vectors to be between 2 and 4 hours. In mice, portal vein and tail vein administration of each vector was tested with similar results. Cell culture studies in W162 cells established that cellular attachment and internalization both contribute to the clearance kinetics of AAV vectors. These studies characterize the in vivo clearance rates of AAV vectors for the first time and guide the development of future strategies for the avoidance of antibody-mediated AAV vector neutralization.

Single amino acid changes can influence titer, heparin binding, and tissue tropism in different adeno-associated virus serotypes

Despite the high degree of sequence homology between adeno-associated virus (AAV) serotype 1 and 6 capsids (99.2%), these viruses have different liver transduction profiles when tested as vectors. Examination of the six amino acid residues that differ between AAV1 and AAV6 revealed that a lysine-to-glutamate change (K531E) suppresses the heparin binding ability of AAV6. In addition, the same mutation in AAV6 reduces transgene expression to levels similar to those achieved with AAV1 in HepG2 cells in vitro and in mouse liver following portal vein administration. In corollary, the converse E531K mutation in AAV1 imparts heparin binding ability and increases transduction efficiency. Extraction of vector genomes from liver tissue suggests that the lysine 531 residue assists in preferential transduction of parenchymal cells by AAV6 vectors in comparison with AAV1. Lysine 531 is unique to AAV6 among other known AAV serotypes and is located in a basic cluster near the spikes that surround the icosahedral threefold axes of the AAV capsid. Similar to studies with autonomous parvoviruses, this study describes the first example of single amino acid changes that can explain differential phenotypes such as viral titer, receptor binding, and tissue tropism exhibited by closely related AAV serotypes. In particular, a single lysine residue appears to provide the critical minimum charged surface required for interacting with heparin through electrostatic interaction and simultaneously plays an unrelated yet critical role in the liver tropism of AAV6 vectors.

Prevention of cytotoxic T lymphocyte responses to factor IX-expressing hepatocytes by gene transfer-induced regulatory T cells

Treatment of genetic disease such as the bleeding disorder hemophilia B [deficiency in blood coagulation factor IX (F.IX)] by gene replacement therapy is hampered by the risk of immune responses to the therapeutic gene product and to the gene transfer vector. Immune competent mice of two different strains were tolerized to human F.IX by hepatic gene transfer mediated by adenoassociated viral vector. These animals were subsequently challenged by systemic administration of an E1/E3-deleted adenoviral vector, which is known to induce a cytotoxic T lymphocyte response to the transgene product. Immune tolerance prevented cytotoxic T lymphocyte activation to F.IX and CD8(+) cellular infiltrates in the liver. Moreover, a sustained and substantial increase in hepatic F.IX expression from the adenoviral vector was achieved despite in vitro T cell responses to adenoviral antigens. Cytolytic responses to therapeutic and to viral vector-derived antigens had been prevented in vivo by activation of regulatory CD4(+) T cells, which mediated suppression of inflammatory lymphocyte responses to the liver. This result suggests that augmentation of regulatory T cell activation should provide new means to avoid destructive immune responses in gene transfer.

Intracoronary delivery of an adenovirus encoding fibroblast growth factor-4 in myocardial ischemia: effect of serum antibodies and previous exposure to adenovirus

The presence of anti-adenoviral serotype 5 (Ad5) antibodies may limit the efficacy of Ad5-mediated gene transfer. We therefore tested the hypothesis that intracoronary delivery of an adenovirus encoding human fibroblast growth factor type 4 (Ad5.FGF4) would improve regional myocardial function in an animal model of ischemia when high antibody levels preexist or after a prior intracoronary dose of Ad5. High anti-Ad5 antibody levels were generated in pigs by subcutaneous immunization with an adenovirus encoding LacZ (Ad5.lacZ). Neutralizing antibody levels increased 648-fold (range, 82- to 2108-fold) above preimmunization levels, and persisted for the duration of the study. Myocardial function during pacing-induced ischemia was improved in the ischemic region (p<0.001) at both 2 and 4 weeks after Ad5.FGF4 administration despite the presence of preexisting antibodies to Ad5. In a second set of experiments, the efficacy of a second intracoronary administration of Ad5 was determined by exposing the animals first to an intracoronary dose of Ad5.lacZ, followed 7 weeks later by the therapeutic dose of Ad5.FGF4. After delivery of Ad5.lacZ, anti-Ad5 antibody levels increased 8-fold (range, 1- to 18-fold), but this prior exposure to Ad5 did not prevent the therapeutic effects after subsequent intracoronary dosing with Ad5.FGF4 (p<0.001). In the porcine Ameroid constrictor model of myocardial ischemia the presence of anti-Ad5 antibodies or prior intracoronary dosing with adenovirus does not prevent the ability of Ad5.FGF4, delivered by intracoronary injection, from normalizing regional myocardial function.

Novel caprine adeno-associated virus (AAV) capsid (AAV-Go.1) is closely related to the primate AAV-5 and has unique tropism and neutralization properties

Preexisting humoral immunity to adeno-associated virus (AAV) vectors may limit their clinical utility in gene delivery. We describe a novel caprine AAV (AAV-Go.1) capsid with unique biological properties. AAV-Go.1 capsid was cloned from goat-derived adenovirus preparations. Surprisingly, AAV-Go.1 capsid was 94% identical to the human AAV-5, with differences predicted to be largely on the surface and on or under the spike-like protrusions. In an in vitro neutralization assay using human immunoglobulin G (IgG) (intravenous immune globulin [IVIG]), AAV-Go.1 had higher resistance than AAV-5 (100-fold) and resistance similar to that of AAV-4 or AAV-8. In an in vivo model, SCID mice were pretreated with IVIG to generate normal human IgG plasma levels prior to the administration of AAV human factor IX vectors. Protein expression after intramuscular administration of AAV-Go.1 was unaffected in IVIG-pretreated mice, while it was reduced 5- and 10-fold after administration of AAV-1 and AAV-8, respectively. In contrast, protein expression after intravenous administration of AAV-Go.1 was reduced 7.1-fold, similar to the 3.8-fold reduction observed after AAV-8 administration in IVIG-pretreated mice, and protein expression was essentially extinguished after AAV-2 administration in mice pretreated with much less IVIG (15-fold). AAV-Go.1 vectors also demonstrated a marked tropism for lung when administered intravenously in SCID mice. The pulmonary tropism and high neutralization resistance to human preexisting antibodies suggest novel therapeutic uses for AAV-Go.1 vectors, including targeting diseases such as cystic fibrosis. Nonprimate sources of AAVs may be useful to identify additional capsids with distinct tropisms and high resistance to neutralization by human preexisting antibodies.

Comparative Efficacy of Intratracheal Adeno-Associated Virus Administration to Newborn Rats

Transient local overexpression of genes that promote lung defense or repair may help to protect or promote alveolar development in premature neonates. We showed that the use of adenoviral vectors in neonates was limited by the induction of lung growth disorders. In the present work we compare the efficiency of gene transfer to the neonatal lung by three adeno-associated viral vectors: rAAV1, rAAV2, and rAAV5. Transduction efficiency was first measured in vitro, by infecting A549 immortalized human lung epithelial cells, and primary epithelial and mesenchymal cells isolated from human fetal lung. AAV vectors yielded similar low levels of luciferase gene expression in the different cell types. In vivo transduction efficiency was evaluated in newborn rats, with AAV-LacZ vectors being intratracheally instilled at 3 days of age. Both rAAV5 and rAAV1, but not rAAV2, induced significant lung beta-galactosidase expression, which persisted on day 35. Highest beta- galactosidase levels were measured with rAAV5, but remained far lower than those obtained with adenoviral vectors. A transient increase in alveolar macrophages was observed on day 6, but not on day 8, after rAAV5-LacZ instillation. Morphometric evaluation of lung structures was performed on day 21, and showed no altered lung growth. We conclude that rAAV1 or rAAV5 was more efficient at mediating gene transfer in the neonatal lung than was rAAV2, without adversely affecting lung development. However, in vivo transgene expression was relatively low, and needs to be improved for future therapeutic use of these adeno-associated vectors.

The inhibitory effects of anticoagulation on in vivo gene transfer by adeno-associated viral or adenoviral vectors

Identifying factors that influence gene transfer efficacy is critical for a successful gene-based clinical study. Here we demonstrate that in vivo AAV-2-mediated gene transfer is efficiently inhibited by unfractionated heparin, but not by a heparin preparation containing mainly low-molecular-weight forms (LMWH). Surprisingly, inhibitors of thrombin or factor Xa (F.Xa) significantly reduced AAV-2 transduction in a dose-dependent manner. These effects were independent of the vector promoter, transgene, or strain of mice. Expression by alternate AAV serotypes 5 and 8 was not affected by anticoagulant drugs, which suggests an AAV-2-specific effect. Moreover, AAV-2-mediated gene expression was diminished in mice with deficiency in thrombin generation (factor IX deficiency) and enhanced in mice with procoagulant phenotype due to factor V Leiden. In addition, inhibitors of F.Xa diminished adenovirus-mediated gene expression. These results demonstrated that coagulation activity itself is critical to ensure optimal viral vector transduction. Since intravascular delivery of vectors often requires the use of anticoagulants, the use of LMWH appears to be safe. These observations are of relevance for approaches using AAV-2 or adenoviral vectors, especially in early phase studies designed to identify the minimum therapeutic doses.

Gene therapy for murine glycerol kinase deficiency: Importance of murine ortholog

A glycerol kinase (Gyk) knock-out (KO) mouse model permits improved understanding of glycerol kinase (GK) deficiency (GKD) pathogenesis, however, early death of affected mice limits its utility. The purpose of this work was to delay death of affected males to investigate thoroughly their phenotypes. An adenoviral vector carrying the human (Adeno-XGK) or mouse (Adeno-XGyk) GK gene was injected into KO mice within 24 h of birth. Adeno-XGK did not change KO mouse survival time despite liver GK activity greater than 100% of wild type. However, Adeno-XGyk improved KO mouse survival time greater than two-fold. These investigations demonstrate that gene replacement therapy for Gyk KO mice is more efficacious using murine Gyk than human GK. These studies expand our understanding of GKD pathogenesis in the murine model, and show that while murine GKD is more severe than in humans, GKD mice have similar metabolic disturbances to affected humans with hypoglycemia and acidemia.

Porcine adenovirus serotype 3 internalization is independent of CAR and alphavbeta3 or alphavbeta5 integrin

Nonhuman adenoviruses including porcine adenovirus serotype 3 (PAd3) are emerging vectors for gene delivery. PAd3 efficiently transduces human and murine cells in culture, and circumvents preexisting humoral immunity in humans. The coxsackievirus-adenovirus receptor (CAR) serves as a primary receptor and alphavbeta3 or alphavbeta5 integrin as a secondary receptor for several human adenovirus (HAd) subtypes including HAd5. In this study, we deduced the role of CAR, alphavbeta3 or alphavbeta5 integrin in PAd3 internalization. Transduction experiments were conducted in human mammary epithelial (MCF-10A) cells using replication-defective PAd-GFP (PAd3 vector expressing green fluorescent protein [GFP]) and HAd-GFP (HAd5 vector expressing GFP). MCF-10A cells were treated with or without anti-human CAR, or anti-alphavbeta3 or anti-alphavbeta5 integrin antibodies prior to infection with HAd-GFP or PAd-GFP. Significant (P <0.05) inhibition in transduction by HAd-GFP was observed in antibody-treated cells as compared to untreated cells, whereas transduction by PAd-GFP remained to similar levels irrespective of the treatment. To study the adenoviral fiber knob-mediated virus interference, MCF-10A cells were treated with or without the recombinant HAd5 or PAd3 knob followed by infection with HAd-GFP or PAd-GFP. Significant (P <0.05) inhibition was observed only in transduction of the homologous vector. These results suggested that PAd3 internalization was CAR- as well as alphavbeta3 or alphavbeta5 integrin-independent and the primary receptor for HAd5 and PAd3 were distinct. CAR- and alphavbeta3 or alphavbeta5 integrin-independent entry of PAd3 vectors may have implications in targeting cell types that are not efficiently transduced by other adenoviral vectors.

Novel hemophilia B mouse models exhibiting a range of mutations in the Factor IX gene

Animal models have been critical to the development of novel therapeutics in hemophilia. A deficiency of current murine models of hemophilia B is that they are all due to gene deletions, a type of mutation that is relatively rare in the human hemophilia population. We generated mice with a range of mutations in the Factor IX (F.IX) gene; these more faithfully reflect the types of mutations that cause disease in the human population. Transgenic mice expressing either wild-type human F.IX (hF.IX), or F.IX variants with premature translation termination codons, or missense mutations, under the control of the murine transthyretin promoter, were generated and crossed with mice carrying a large deletion of the murine F.IX gene. Gene copy number, F.IX transcript levels in the liver, intrahepatocyte protein expression, and circulating levels of F.IX protein in the mice were determined and compared with data generated by transient transfection assays using the same F.IX variants. Mice were injected with a viral vector expressing hF.IX and displayed a range of immune responses to the transgene product, depending on the underlying mutation. These new mouse models faithfully mimic the mutations causing human disease, and will prove useful for testing novel therapies for hemophilia. (Blood. 2004;104:2767-2774)

A hemodynamic response to intravenous adenovirus vector particles is caused by systemic Kupffer cell-mediated activation of endothelial cells

Intravascular injection of adenoviral vectors may result in a toxic and potentially lethal reaction, the mechanism of which is poorly understood. We noted that mice demonstrated a transient change in behavior that was characterized by inactivity and lethargy within minutes after intravenous injection of relatively low doses of adenoviral vectors (including high-capacity gutless vectors). Moreover, immediately after vector injection a significant drop in blood pressure was measured that most probably was caused by the systemic activation of endothelial cells as monitored by detection of phosphorylated Akt/PKB kinase, activated endothelial nitric oxide synthase (eNOS), and nitrotyrosine. The activation of the endothelium was the result of the interaction of viral particles with Kupffer cells, which are resident macrophages of the liver representing the first line of defense of the innate immune system. Surprisingly, the uptake of vector particles by Kupffer cells not only resulted in their strong activation, but also in their nearly complete disappearance from the liver. Our results suggest that the toxicity of intravenously injected adenoviral vectors may be directly linked to the activation and destruction of Kupffer cells.

Helper-Independent Sleeping Beauty transposon-transposase vectors for efficient nonviral gene delivery and persistent gene expression in vivo

Transposon-based vectors represent promising new tools for chromosomal transgene insertion and establishment of persistent gene expression in vivo. Here, we report the development of helper-independent transposon-transposase (HITT) vectors, which contain on single plasmids (i) a Sleeping Beauty (SB) transposon containing the transgene and (ii) a SB transposase expression cassette. To obtain an optimal level of transposase expression from HITT vectors, we determined the relative strength of a panel of different promoters in mouse liver and used these promoters to drive transposase expression from injected HITT vectors carrying a human alpha(1)-antitrypsin (hAAT) expression cassette flanked by transposon inverted repeats. By correlating promoter strength with stabilized serum hAAT levels, a narrow expression window supporting high-level transposition in the liver was defined. Peak levels of long-term gene expression were obtained with promoters 30- to 40-fold less active than CMV in mouse liver, whereas reduced stable levels of hAAT were detected with both weaker and stronger promoters. Injected HITT vectors induced transposase-dependent insertion of transposon DNA into the genome of at least 5-6% of transfected hepatocytes, generating levels of persistent hAAT expression that were 2- to 4-fold higher than with an optimized two-plasmid approach. In addition, we show that HITT vectors carrying a human factor IX (hFIX)-containing transposon support (i) long-term hFIX expression in normal mice and (ii) partial phenotypic correction in a mouse model of hemophilia B. SB-based HITT vectors represent a major advance in the establishment of persistent transgene expression from nonviral gene delivery systems and should prove useful for gene transfer to tissues or cell types in which transfection efficiencies are low.

Neonatal gene transfer with a retroviral vector results in tolerance to human factor IX in mice and dogs

The effect of neonatal gene transfer on antibody formation was determined using a retroviral vector (RV) expressing human factor IX (hFIX). Normal mice from different strains injected intravenously with RV as newborns achieved therapeutic levels of hFIX without antibody production and were tolerant as adults to challenge with hFIX. Neonatal hemophilia B mice that received different amounts of RV achieved stable and dose-related expression of hFIX without anti-hFIX antibody formation. After protein challenge, antibody formation was markedly reduced for animals that expressed hFIX at levels higher than 14 ng/mL (0.3% of normal). However, antibodies developed for animals that received the lowest dose of RV and expressed hFIX at approximately 2 ng/mL before protein challenge. In dogs, neonatal injection of a high dose of RV resulted in 500 ng/mL hFIX in plasma without antibody formation. We conclude that neonatal gene transfer with RV does not induce antibody responses to hFIX in mice or dogs and that mice achieving levels greater than 3 x 10-10 M hFIX are usually tolerant to protein injection as adults. Low-dose gene therapy or frequent protein injections in the neonatal period might induce tolerance to subsequent injections of protein with a low risk for adverse effects.

Preclinical in vivo evaluation of pseudotyped adeno-associated virus vectors for liver gene therapy

We report the generation and use of pseudotyped adeno-associated viral (AAV) vectors for the liver-specific expression of human blood coagulation factor IX (hFIX). Therefore, an AAV-2 genome encoding the hfIX gene was cross-packaged into capsids of AAV types 1 to 6 using efficient, large-scale technology for particle production and purification. In immunocompetent mice, the resultant vector particles expressed high hFIX levels ranging from 36% (AAV-4) to more than 2000% of normal (AAV-1, -2, and -6), which would exceed curative levels in patients with hemophilia. Expression was dose- and time-dependent, with AAV-6 directing the fastest and strongest onset of hFIX expression at all doses. Interestingly, systemic administration of 2 x 1012 vector particles of AAV-1, -4, or -6 resulted in hFIX levels similar to those achieved by portal vein delivery. For all other serotypes and particle doses, hepatic vector administration yielded up to 84-fold more hFIX protein than tail vein delivery, corroborated by similarly increased vector DNA copy numbers in the liver, and elicited a reduced immune response against the viral capsids. Finally, neutralization assays showed variable immunologic cross-reactions between most of the AAV serotypes. Our technology and findings should facilitate the development of AAV pseudotype-based gene therapies for hemophilia B and other liver-related diseases.

Long-term transgene expression by administration of a lentivirus-based vector to the fetal circulation of immuno-competent mice

Inefficient gene transfer, inaccessibility of stem cell compartments, transient gene expression, and adverse immune and inflammatory reactions to vector and transgenic protein are major barriers to successful in vivo application of gene therapy for most genetic diseases. Prenatal gene therapy with integrating vectors may overcome these problems and prevent early irreparable organ damage. To this end, high-dose attenuated VSV-G pseudotyped equine infectious anaemia virus (EIAV) encoding beta-galactosidase under the CMV promoter was injected into the fetal circulation of immuno-competent MF1 mice. We saw prolonged, extensive gene expression in the liver, heart, brain and muscle, and to a lesser extent in the kidney and lung of postnatal mice. Progressive clustered hepatocyte staining suggests clonal expansion of cells stably transduced. We thus provide proof of principle for efficient gene delivery and persistent transgene expression after prenatal application of the EIAV vector and its potential for permanent correction of genetic diseases.

Neonatal or hepatocyte growth factor-potentiated adult gene therapy with a retroviral vector results in therapeutic levels of canine factor IX for hemophilia B

Hemophilia B is a bleeding disorder resulting from factor IX (FIX) deficiency that might be treated with gene therapy. Neonatal delivery would correct the disease sooner than would transfer into adults, and could reduce immunological responses. Neonatal mice were injected intravenously with a Moloney murine leukemia virus-based retroviral vector (RV) expressing canine FIX (cFIX). They achieved 150% to 280% of normal cFIX antigen levels in plasma (100% is 5 microg/mL), which was functional in vitro and in vivo. Three newborn hemophilia B dogs that were injected intravenously with RV achieved 12% to 36% of normal cFIX antigen levels, which improved coagulation tests. Only one mild bleed has occurred during 14 total months of evaluation. This is the first demonstration of prolonged expression after neonatal gene therapy for hemophilia B in mice or dogs. Most animals failed to make antibodies to cFIX, demonstrating that neonatal gene transfer may induce tolerance. Although hepatocytes from newborns replicate, those from adults do not. Adult mice therefore received hepatocyte growth factor to induce hepatocyte replication prior to intravenous injection of RV. This resulted in expression of 35% of normal cFIX antigen levels for 11 months, although all mice produced anti-cFIX antibodies. This is the first demonstration that high levels of FIX activity can be achieved with an RV in adults without a partial hepatectomy to induce hepatocyte replication. We conclude that RV-mediated hepatic gene therapy is effective for treating hemophilia B in mice and dogs, although the immune system may complicate gene transfer in adults.

Transduction of the mammary epithelium with adenovirus vectors in vivo

Because the mammary parenchyma is accessible from the exterior of an animal through the mammary duct, adenovirus transduction holds promise for the short-term delivery of genes to the mammary epithelium for both research and therapeutic purposes. To optimize the procedure and evaluate its efficacy, an adenovirus vector (human adenovirus type 5) encoding a green fluorescent protein (GFP) reporter and deleted of E1 and E3 was injected intraductally into the mouse mammary gland. We evaluated induction of inflammation (by intraductal injection of [(14)C]sucrose and histological examination), efficiency of transduction, and maintenance of normal function in transduced cells. We found that transduction of the total epithelium in the proximal portion of the third mammary gland varied from 7% to 25% at a dose of 2 x 10(6) PFU of adenovirus injected into day 17 pregnant mice. Transduction was maintained for at least 7 days with minimal inflammatory response; however, significant mastitis was observed 12 days after transduction. Adenovirus transduction could also be used in the virgin animal with little mastitis 3 days after transduction. Transduced mammary epithelial cells maintained normal morphology and function. Our results demonstrate that intraductal injection of adenovirus vectors provides a versatile and noninvasive method of investigating genes of interest in mouse mammary epithelial cells.

In utero gene transfer of human factor IX to fetal mice can induce postnatal tolerance of the exogenous clotting factor

The fundamental hypotheses behind fetal gene therapy are that it may be possible (1) to achieve immune tolerance of transgene product and, perhaps, vector; (2) to target cells and tissues that are inaccessible in adult life; (3) to transduce a high percentage of rapidly proliferating cells, and in particular stem cells, with relatively low absolute virus doses leading to clonal transgene amplification by integrating vectors; and (4) to prevent early disease manifestation of genetic diseases. This study provides evidence vindicating the first hypothesis; namely, that intravascular prenatal administration of an adenoviral vector carrying the human factor IX (hFIX) transgene can induce immune tolerance of the transgenic protein. Following repeated hFIX protein injection into adult mice, after prenatal vector injection, we found persistence of blood hFIX and absence of hFIX antibodies in 5 of 9 mice. Furthermore, there was substantial hFIX expression after each of 2 reinjections of vector without detection of hFIX antibodies. In contrast, all adult mice that had not been treated prenatally showed a rapid loss of the injected hFIX and the development of high hFIX antibody levels, both clear manifestations of a strong immune reaction.

Long-term correction of glycogen storage disease type II with a hybrid Ad-AAV vector

We administered an adenovirus-adeno-associated virus (Ad-AAV) vector encoding human acid alpha-glucosidase (hGAA) to acid alpha-glucosidase-knockout (GAA-KO) mice on day 3 of life by gastrocnemius injection. In contrast to previous results for muscle-targeted Ad vector in adult GAA-KO mice, the muscles of the hindlimb showed reduced glycogen content and persistent hGAA for as long as 6 months after neonatal Ad-AAV vector administration. Not only the injected gastrocnemius muscles, but also the hamstrings and quadriceps muscles produced therapeutic levels of hGAA as a result of widespread transduction with the Ad-AAV vector; moreover, hGAA activity was 50-fold elevated as compared to normal mice. Vector RNA was detected in the hindlimb muscles, the hearts, and the livers by northern blot analysis and/or by RT-PCR for as long as 6 months. The low levels of hGAA detected in the heart were attributable to transduction with the Ad-AAV vector, not to secretion of hGAA by the injected muscle and uptake by the heart. Finally, although an antibody response to hGAA was present, it did not prevent the correction of glycogen storage in the skeletal muscle of GAA-KO mice.

Negative-strand RNA viral vectors: intravenous application of Sendai virus vectors for the systemic delivery of therapeutic genes

Treatment by gene replacement is critical in the field of gene therapy. Suitable vectors for the delivery of therapeutic genes have to be generated and tested in preclinical settings. Recently, extraordinary features for a local gene delivery by Sendai virus vectors (SeVV) have been reported for different tissues. Here we show that direct intravenous application of SeVV in mice is not only feasible and safe, but it results in the secretion of therapeutic proteins to the circulation, for example, human clotting Factor IX (hFIX). In vitro characterization of first-generation SeVV demonstrated that secreted amounts of hFIX were at least comparable to published results for retroviral or adeno-associated viral vectors. Furthermore, as a consideration for application in humans, SeVV transduction led to efficient hFIX synthesis in primary human hepatocytes, and SeVV-encoded hFIX proteins could be shown to be functionally active in the human clotting cascade. In conclusion, our investigations demonstrate for the first time that intravenous administration of negative-strand RNA viral vectors may become a useful tool for the wide area of gene replacement requirements.

Free DNA ends are essential for concatemerization of synthetic double-stranded adeno-associated virus vector genomes transfected into mouse hepatocytes in vivo

Recombinant adeno-associated virus (rAAV) vectors stably transduce hepatocytes in vivo. In hepatocyte nuclei, the incoming single-stranded (ss) vector genomes are converted into various forms of double-stranded (ds) genomes including extrachromosomal linear and circular monomers and concatemers, and a small portion of the vector genomes integrate into chromosomes. The mechanism of genome conversion is not well understood. In the present study, we analyzed the role of inverted terminal repeat (ITR) sequences of ds circular or linear rAAV vector intermediates in concatemerization. We synthesized supercoiled ds circular monomers with a double-D ITR (DDITR) (C+), and ds linear monomers with an ITR at each end (L+), and their control molecules, C- and L-, which lack the ITR-derived sequences, and transfected mouse hepatocytes with these molecules in vivo to assess their capacity for concatemerization. The transfected L+ or L-, but not C+ or C- molecules, concatemerized in vivo irrespective of the presence or absence of the ITRs. In addition, our results suggested that transfected C+ or C- species were not efficient substrates for integration. Based on these observations, we propose a model whereby ds linear molecules with free DNA ends, but not circular molecules, play an important role in rAAV vector genome concatemerization.

Selective depletion or blockade of Kupffer cells leads to enhanced and prolonged hepatic transgene expression using high-capacity adenoviral vectors

Tissue macrophages, in particular hepatic Kupffer cells (KCs), contribute to early inflammatory responses following adenoviral vector administration. This study evaluates the effect of selective and transient (3 days) depletion of KCs by a single injection of clodronate liposomes on the in vivo performance of high-capacity adenoviral (HC-Ad) vectors. In KC-depleted C57BL/6 and C3H mice increased and stabilized hAAT levels were observed following intravenous injection of HC-Ad vectors expressing human alpha-1 anti-trypsin (hAAT) either from the hAAT promoter or from the human cytomegalovirus promoter. Comparable increases in hAAT levels were obtained in mice preinjected with a transcriptionally silent HC-Ad vector. Interestingly, in the majority of animals of both strains depletion of KCs was sufficient to prevent the generation of anti-hAAT antibodies, resulting in prolonged transgene expression. Thus, short-term and selective depletion of hepatic macrophages at the same time significantly increased hepatic transgene expression and reduced the humoral immune response to the transgenic protein.

Encapsulation of recombinant adenovirus into alginate microspheres circumvents vector-specific immune response

Pre-existing immunity against adenoviruses may compromise the efficacy of adenoviral vectors for vaccination and gene therapy. The purpose of this study was to determine whether encapsulation of adenovirus recombinants into biodegradable alginate microparticles could circumvent the vector-specific immune response. Mice were immunized either intranasally (i.n.) or intraperitoneally (i.p.) with human adenovirus type 5 (HAd5), resulting in the development of virus-specific antibodies. Immunized and nai;ve mice were inoculated with AdCA36lacZ (an E1-deleted HAd5 recombinant containing the bacterial beta-galactosidase (LacZ) gene), encapsulated (E) into alginate microparticles, or nonencapsulated (NE) ie, as a virus suspension. LacZ expression in animals immunized once (1x) or twice (2x) with HAd5 and subsequently inoculated with NE-AdCA36lacZ (NE-Z) was significantly (P<0.001) reduced compared to those levels observed in NE-Z inoculated nai;ve mice, suggesting that the immune response against the vector adversely affected transgene expression. In contrast, there was only slight reduction (P>0.05) in LacZ expression in mice immunized 1x or 2x with HAd5 that were subsequently inoculated with E-AdCA36lacZ (E-Z) compared to those levels obtained in E-Z inoculated nai;ve animals. Similar results were obtained with i.n. or i.p. inoculated animals. These results indicate that microencapsulation of recombinant adenovirus effectively circumvented the vector-specific immune response.

Effect of intratracheal adenoviral vector administration on lung development in newborn rats

Local overexpression of genes that promote lung defense or repair may be helpful in protecting the immature neonatal lung from injuries, but whether the vectors used to administer these genes affect physiological postnatal lung growth has not been investigated. We explored the effect on alveolarization of E1-deleted Adnull vector (Ad5-LMP-null) given intratracheally to 3-day-old rats. Three Adnull doses were evaluated 10(8), 5 x 10(8), and 10(9) TCID(50). Lung morphometry on day 21 showed significant growth disorders with the two higher doses. With 5 x 10(8) TCID(50), absolute lung volume increased significantly (+16%), as did absolute (+20%) and specific (+32%) alveolar airspace volumes, whereas alveolar surface density decreased by 13% (p < 0.009 for all parameters). Lung inflammation was mild, nonsignificant, and occurred mainly with the highest Adnull dose, indicating that it was unlikely to contribute to our results. Adnull instillation induced a significant#10; decrease in terminal bronchiolar cell proliferation as evaluated by proliferating cell nuclear antigen immunostaining (p = 0.02), as well as a 23% decrease in absolute parenchyma elastic fiber length (p = 0.02). Furthermore, lung tropoelastin mRNA content decreased by 25% (p < 0.02). In conclusion, E1-deleted adenoviral vectors can induce lung growth disorders when instilled into the airways of neonatal rats. Interactions with lung matrix turnover may be the main explanation to these deleterious effects.

PEGylation of E1-deleted adenovirus vectors allows significant gene expression on readministration to liver

Systemic administration of adenoviral vectors leads to activation of innate and antigen-specific immunity. In an attempt to diminish T and B cell-specific immune responses to E1-deleted adenoviral vectors, capsid proteins were modified with various activated monomethoxypolyethylene glycols (MPEGs). The impact of this modification was studied in a murine model of liver-directed gene transfer in which an E1-deleted adenovirus expressing the lacZ gene was given intravenously. The efficiency of vector transduction of hepatocytes in vivo was not compromised by any of the polymer chemistries. PEGylation of the virus, however, diminished the activation of cytotoxic T lymphocytes and helper T cells of the type 1 subset (Th1 cells) against native viral antigens; neutralizing antibodies to native virus were also diminished. PEGylation prolonged transgene expression and allowed partial readministration with native virus or with a virus PEGylated with a heterologous chemical moiety. Apparently, modification of the capsid leads to a shift in antigenic epitopes because vector readministration was not possible when the immunizing vector had been modified by the same PEGylation chemistry used to modify the second vector. In light of these results, the concept of improving the performance of adenoviral vectors through modification of the capsid with PEG shows promise.

Improved hepatic gene transfer by using an adeno-associated virus serotype 5 vector

Adeno-associated viral (AAV) vectors have been shown to direct stable gene transfer and expression in hepatocytes, which makes them attractive tools for treatment of inherited disorders such as hemophilia B. While substantial levels of coagulation factor IX (F.IX) have been achieved using AAV serotype 2 vectors, use of a serotype 5 vector further improves transduction efficiency and levels of F.IX transgene expression by 3- to 10-fold. In addition, the AAV-5 vector transduces a higher proportion of hepatocytes ( approximately 15%). The subpopulations of hepatocytes transduced with either vector widely overlap, with the AAV-5 vector transducing additional hepatocytes and showing a wider area of transgene expression throughout the liver parenchyma.

Determinants of hepatitis C translational initiation in vitro, in cultured cells and mice

Hepatitis C virus (HCV) is an RNA virus infecting 1 in every 40 people worldwide. Development of new therapeutics for treating HCV has been hampered by the lack of small-animal models. We have adapted existing hydrodynamic transfection methods to optimize the delivery of RNAs to the cytoplasm of mouse liver cells in vivo. Transfected HCV genomic RNA failed to replicate in mouse liver, suggesting a post-entry block to viral replication. Real-time imaging of HCV internal ribosome entry site (IRES) firefly luciferase reporter mRNA translation in living mice demonstrated that the HCV IRES was functional in mouse liver. We then used this system as a model for studying HCV RNA translation in mice. We compared translation by several mutant HCV IRES variants in cell lysates, cultured cells, and mouse liver. We measured the contribution to translation of a cap, HCV 3'-untranslated region (UTR), poly(A) tail, domains II, IIIb, IIIabc, IIIabcd, IIId, and the initiator codon. Efficient translation required a 3'-UTR in mice and HeLa cells, but not in rabbit reticulocyte lysates. Translational regulation of transfected RNAs was stringent in mice. The method we describe could be useful for studies in mice of antisense or ribozyme inhibitors targeting the IRES as well as other RNA biochemical studies in vivo.

Toxicity of a first-generation adenoviral vector in rhesus macaques

We constructed a first-generation adenovirus vector (AVC3FIX5) that we used to assess the rhesus macaque as a nonhuman primate model for preclinical testing of hemophilia B gene therapy vectors. Although we succeeded in our primary objective of demonstrating expression of human factor IX we encountered numerous toxic side effects that proved to be dose limiting. Following intravenous administration of AVC3FIX5 at doses of 3.4 x 10(11) vector particles/kg to 3.8 x 10(12) vector particles/kg, the animals in our study developed antibodies against human factor IX, and dose-dependent elevations of enzymes specific for liver, muscle, and lung injury. In addition, these animals showed dose-dependent prolongation of clotting times as well as acute, dose-dependent decreases in platelet counts and concomitant elevation of fibrinogen and von Willebrand factor. These abnormalities may be caused by the direct toxic effects of the adenovirus vector itself, or may result indirectly from the accompanying acute inflammatory response marked by elevations in IL-6, a key regulator of the acute inflammatory response. The rhesus macaque may be a useful animal model in which to evaluate mechanisms of adenovirus toxicities that have been encountered during clinical gene therapy trials.