Gene delivery to skeletal muscle results in sustained expression and systemic delivery of a therapeutic protein

Cardiac gene therapy with SERCA2a: from bench to bedside

While progress in conventional treatments is making steady and incremental gains to reduce mortality associated with heart failure, there remains a need to explore potentially new therapeutic approaches. Heart failure induced by different etiologies such as coronary artery disease, hypertension, diabetes, infection, or inflammation results generally in calcium cycling dysregulation at the myocyte level. Recent advances in understanding of the molecular basis of these calcium cycling abnormalities, together with the evolution of increasingly efficient gene transfer technology, have placed heart failure within reach of gene-based therapy. Furthermore, the recent successful completion of a phase 2 trial targeting the sarcoplasmic reticulum calcium pump (SERCA2a) ushers in a new era for gene therapy for the treatment of heart failure. This article is part of a Special Section entitled "Special Section: Cardiovascular Gene Therapy".

Strong foreign promoters contribute to innate inflammatory responses induced by adenovirus transducing vectors

E1-deleted adenovirus (FG Ad) transducing vectors are limited for use in vivo by their induction of strong innate and adaptive inflammatory responses. We have examined the contribution of the transgene cassette, particularly the foreign promoter driving transgene expression, in the induction of innate inflammation using a mouse ear model in which swelling is measured as a sensitive surrogate marker of the total innate inflammatory response. The commonly used cytomegalovirus major immediate early (CMV) promoter led to high-level swelling that was independent of transgene expression, while the Rous sarcoma virus and human ubiquitin C promoters led to intermediate levels of swelling and the Ad E1A promoter or no promoter led to equally low levels of swelling. Significant swelling was induced by a virus in which the E1A promoter directed pIX expression, supporting the possibility that activation of expression of Ad genes retained in the vector plays an important role in the inflammatory response. Taken together, our findings support the idea that strong foreign promoters likely play the limiting role in the induction of innate and adaptive immune responses that limit the duration of transgene expression after transduction by FG Ad vectors.

Post-Natal knockdown of fukutin-related protein expression in muscle by long-termRNA interference induces dystrophic pathology [corrected]

Limb-girdle muscular dystrophy 2I (LGMD2I) is caused by mutations in the fukutin-related protein (FKRP) gene. Unlike its severe allelic forms, LGMD2I usually involves slower onset and milder course without defects in the central nervous system. The lack of viable animal models that closely recapitulate LGMD2I clinical phenotypes led us to use RNA interference technology to knock down FKRP expression via postnatal gene delivery so as to circumvent embryonic lethality. Specifically, an adeno-associated viral vector was used to deliver short hairpin (shRNA) genes to healthy ICR mice. Adeno-associated viral vectors expressing a single shRNA or two different shRNAs were injected one time into the hind limb muscles. We showed that FKRP expression at 10 months postinjection was reduced by about 50% with a single shRNA and by 75% with the dual shRNA cassette. Dual-cassette injection also reduced a-dystroglycan glycosylation and its affinity to laminin by up to 70% and induced α-dystrophic pathology, including fibrosis and central nucleation, in more than 50% of the myofibers at 10 months after injection. These results suggest that the reduction of approximately or more than 75% of the normal level of FKRP expression induces chronic dystrophic phenotypes in skeletal muscles. Furthermore, the restoration of about 25% of the normal FKRP level could be sufficient for LGMD2I therapy to correct the genetic deficiency effectively and prevent dystrophic pathology.

Enhanced long-term transduction and multilineage engraftment of human hematopoietic stem cells transduced with tyrosine-modified recombinant adeno-associated virus serotype 2

The search for the ideal stem cell gene therapy vector continues as recognized problems persist. Although recombinant adeno-associated virus serotype 2 (rAAV2) mediates gene transfer into hematopoietic stem cells, identified restrictions to transgene expression reduce overall efficiency. Studies have shown that transduction efficiencies are significantly improved by preventing early proteasomal degradation after mutation of surface-exposed tyrosine residues on the capsid to phenylalanine. Here, we report that transduction of human cord blood CD34(+) stem cells by tyrosine-modified rAAV2 is significantly enhanced both in vitro and in vivo. Serial long-term in vivo bioluminescent imaging of immune-deficient recipients after xenotransplantation of CD34(+) cells transduced with tyrosine-modified rAAV2-luciferase revealed that modification of rAAV2 capsids led to a significant increase in the transduction of human CD34(+) cells, without adversely affecting engraftment capacity, or the ability to undergo multilineage differentiation and self-renewal. Together with observations of sustained high-level transgene expression in vivo and efficient persistence of rAAV genomes in human hematopoietic cells, these results suggest that, because of their ability to bypass restrictions to transduction, tyrosine-modified rAAV vectors, particularly Y500F, Y700F, Y444F, and Y704F, represent highly promising candidates for therapeutic evaluation for diseases of human hematopoietic stem cells.

The complex and evolving story of T cell activation to AAV vector-encoded transgene products

Original reports of adeno-associated virus (AAV) vector-mediated gene transfer to the muscle resulted in high-level β-galactosidase (β-gal) expression and the promise of a viral vector that was largely nonimmunogenic. Subsequent attempts to utilize these vectors for genetic vaccination, however, demonstrated that it was possible to activate cellular and humoral immunity to AAV-encoded antigens. These findings fueled years of investigation into factors impacting the immunogenicity of recombinant AAV-mediated gene delivery, including route of administration, dose, host species, capsid serotype, and transgene product. In cases where AAV vectors could avoid transgene-directed immunity, it became clear that mechanisms of tolerance were at work, varying between ignorance, anergy/deletion, or active suppression. Here, we follow the field of AAV gene therapy from inception, as investigators have worked to understand the delicate balance between AAV-mediated tolerance and the activation of immunity. This review discusses our current appreciation of AAV vector immunology, with a specific focus on the transgene-specific T cell response.

RH10 provides superior transgene expression in mice when compared with natural AAV serotypes for neonatal gene therapy

BACKGROUND

Neonatal gene therapy is a promising strategy for treating diseases diagnosed before or shortly after birth. Early and long-term expression of therapeutic proteins may limit the consequences of genetic mutations and result in a potential 'cure'. Adeno-associated viral vectors have shown promise in many areas of adult gene therapy but their properties have not been systematically investigated in the neonate.

METHODS

In these studies, using a constitutive promoter expressing luciferase, animals were administered one of ten serotypes of adeno-associated virus (AAV) on the second day of life. Examination of expression, organ growth and vector distribution, maintenance of expression and copy number were measured.

RESULTS

All serotypes demonstrated expression and, in general, transduction of all organs within 3 days, albeit with different biodistribution patterns and expression levels. The highest expression was detected with AAVrh10, whereas the lowest was detected with AAV4. Expression and genomes declined with growth over the first 10 weeks of life; thereafter, to day 100, expression and genomes remained relatively stable. With the highest expressing vectors, whole animal expression at 100 days declined to approximately 10% of that detected on the fifth day. AAVrh10 maintained the highest expression level and copy number throughout these studies.

CONCLUSIONS

The impact of tissue and organ growth on the stability of AAV expression will be important if neonatal gene transfer is to be considered as a modality for human gene therapy. Although all vectors did demonstrate expression, rh10 holds the greater promise of the vectors tested to maintain copy number in both mitotic and post-mitotic tissues.

Immunization of neonatal mice with LAMP/p55 HIV gag DNA elicits robust immune responses that last to adulthood

Successful T cell priming in early postnatal life that can generate effective long-lasting responses until adulthood is critical in HIV vaccination strategies because it prevents early sexual initiation and breastfeeding transmission of HIV. A chimeric DNA vaccine encoding p55 HIV gag associated with lysosome-associated membrane protein 1 (LAMP-1; which drives the antigen to the MIIC compartment), has been used to enhance cellular and humoral antigen-specific responses in adult mice and macaques. Herein, we investigated LAMP-1/gag vaccine immunogenicity in the neonatal period in mice and its ability to generate long-lasting effects. Neonatal vaccination with chimeric LAMP/gag generated stronger Gag-specific immune responses, as measured by the breadth of the Gag peptide-specific IFN-gamma, proliferative responsiveness, cytokine production and antibody production, all of which revealed activation of CD4+ T cells as well as the generation of a more robust CTL response compared to gag vaccine alone. To induce long-lived T and B cell memory responses, it was necessary to immunize neonates with the chimeric LAMP/gag DNA vaccine. The LAMP/gag DNA vaccine strategy could be particularly useful for generating an anti-HIV immune response in the early postnatal period capable of inducing long-term immunological memory.

Evaluation of hydrodynamic limb vein injections in nonhuman primates

The administration route is emerging as a critical aspect of nonviral and viral vector delivery to muscle, so as to enable gene therapy for disorders such as muscular dystrophy. Although direct intramuscular routes were used initially, intravascular routes are garnering interest because of their ability to target multiple muscles at once and to increase the efficiency of delivery and expression. For the delivery of naked plasmid DNA, our group has developed a hydrodynamic, limb vein procedure that entails placing a tourniquet over the proximal part of the target limb to block all blood flow and injecting the gene vector rapidly in a large volume so as to enable the gene vector to be extravasated and to access the myofibers. The present study was conducted in part to optimize the procedure in preparation for a human clinical study. Various injection parameters such as the effect of papaverine preinjection, tourniquet inflation pressure and duration, and rate of injection were evaluated in rats and nonhuman primates. In addition, the safety of the procedure was further established by determining the effect of the procedure on the neuromuscular and vascular systems. The results from these studies provide additional evidence that the procedure is well tolerated and they provide a foundation on which to formulate the procedure for a human clinical study.

Long-term luciferase expression monitored by bioluminescence imaging after adeno-associated virus-mediated fetal gene delivery in rhesus monkeys (Macaca mulatta)

The safety and efficiency of fetal adeno-associated virus (AAV) gene delivery in rhesus monkeys and long-term monitoring of transgene expression by bioluminescence imaging (BLI) were evaluated. Early second-trimester fetal monkeys were administered AAV2/5, AAV2/9, or AAV2/10 vector supernatant preparations expressing firefly luciferase under the control of the cytomegalovirus promoter, using an intrathoracic (n = 6) or intramyocardial (n = 6) approach and established ultrasound-guided techniques. Postnatal BLI was performed monthly up to 6 months postnatal age (n = 12) and then every 3 months thereafter to monitor transgene expression up to 24 months postnatal age (27 months after gene transfer; n = 6). All AAV serotypes showed greater than 1.0 x 10(9) photons/sec at all time points evaluated with limited biodistribution to nontargeted anatomical sites. The highest levels of bioluminescence (photons per second) observed were noted with AAV2/9 and AAV2/10 when the three vector constructs were compared. To correlate in vivo findings at the tissue level, specimens were collected from selected animals and analyzed. Three-dimensional reconstruction showed that firefly luciferase expression was consistent with imaging and morphometric measures. These findings suggest that (1) high levels of AAV-mediated firefly luciferase expression can be found after fetal AAV gene transfer and without any evidence of adverse effects; (2) the intercostal muscles, myocardium, and muscular component of the diaphragm of developing fetuses are readily transduced with AAV2/5, AAV2/9, or AAV2/10; and (3) postnatal outcomes and long-term luciferase expression can be effectively monitored by BLI in young rhesus monkeys.

AAV-directed muscular dystrophy gene therapy

IMPORTANCE OF THE FIELD

Muscle-directed gene therapy for genetic muscle diseases can be performed by the recombinant adeno-associated viral (rAAV) vector delivery system to achieve long-term therapeutic gene transfer in all affected muscles.

AREAS COVERED IN THIS REVIEW

Recent progress in rAAV-vector-mediated muscle-directed gene transfer and associated techniques for the treatment of muscular dystrophies (MD). The review covers literature from the past 2 - 3 years.

WHAT THE READER WILL GAIN

rAAV-directed muscular dystrophy gene therapy can be achieved by mini-dystrophin replacement and exon-skipping strategies. The additional strategies of enhancing muscle regeneration and reducing inflammation in the muscle micro-environment should be useful to optimize therapeutic efficacy. This review compares the merits and shortcomings of different administration methods, promoters and experimental animals that will guide the choice of the appropriate strategy for clinical trials.

TAKE HOME MESSAGE

Restoration of muscle histopathology and function has been performed using rAAV systemic gene delivery. In addition, the combination of gene replacement and adjuvant therapies in the future may be beneficial with regard to improving muscle regeneration and decreasing myofiber necrosis. The challenges faced by large animal model studies and in human trials arise from gene transfer efficiency and immune response, which may be overcome by optimizing the rAAV vectors utilized and the administration methods.

Gel-mediated delivery of AAV1 vectors corrects ventilatory function in Pompe mice with established disease

Pompe disease is a muscular dystrophy that results in respiratory insufficiency. We characterized the outcomes of targeted delivery of recombinant adeno-associated virus serotype 1 (rAAV2/1) vector to diaphragms of Pompe mice with varying stages of disease progression. We observed significant improvement in diaphragm contractile strength in mice treated at 3 months of age that is sustained at least for 1 year and enhanced contractile strength in mice treated at 9 and 21 months of age, measured 3 months post-treatment. Ventilatory parameters including tidal volume/inspiratory time ratio, minute ventilation/expired CO2 ratio, and peak inspiratory airflow were significantly improved in mice treated at 3 months and tested at 6 months. Despite early improvement, mice treated at 3 months and tested at 1 year had diminished normoxic ventilation, potentially due to attenuation of correction over time or progressive degeneration of nontargeted accessory tissues. However, for all rAAV2/1-treated mice (treated at 3, 9, and 21 months, assayed 3 months later; treated at 3 months, assayed at 1 year), minute ventilation and peak inspiratory flows were significantly improved during respiratory challenge. These results demonstrate that gel-mediated delivery of rAAV2/1 vectors can significantly augment ventilatory function at initial and late phases of disease in a model of muscular dystrophy.

Dendritic cell mediated delivery of plasmid DNA encoding LAMP/HIV-1 Gag fusion immunogen enhances T cell epitope responses in HLA DR4 transgenic mice

This report describes the identification and bioinformatics analysis of HLA-DR4-restricted HIV-1 Gag epitope peptides, and the application of dendritic cell mediated immunization of DNA plasmid constructs. BALB/c (H-2d) and HLA-DR4 (DRA1*0101, DRB1*0401) transgenic mice were immunized with immature dendritic cells transfected by a recombinant DNA plasmid encoding the lysosome-associated membrane protein-1/HIV-1 Gag (pLAMP/gag) chimera antigen. Three immunization protocols were compared: 1) primary subcutaneous immunization with 1×10⁵ immature dendritic cells transfected by electroporation with the pLAMP/gag DNA plasmid, and a second subcutaneous immunization with the naked pLAMP/gag DNA plasmid; 2) primary immunization as above, and a second subcutaneous immunization with a pool of overlapping peptides spanning the HIV-1 Gag sequence; and 3) immunization twice by subcutaneous injection of the pLAMP/gag DNA plasmid. Primary immunization with pLAMP/gag-transfected dendritic cells elicited the greatest number of peptide specific T-cell responses, as measured by ex vivo IFN-γ ELISpot assay, both in BALB/c and HLA-DR4 transgenic mice. The pLAMP/gag-transfected dendritic cells prime and naked DNA boost immunization protocol also resulted in an increased apparent avidity of peptide in the ELISpot assay. Strikingly, 20 of 25 peptide-specific T-cell responses in the HLA-DR4 transgenic mice contained sequences that corresponded, entirely or partially to 18 of the 19 human HLA-DR4 epitopes listed in the HIV molecular immunology database. Selection of the most conserved epitope peptides as vaccine targets was facilitated by analysis of their representation and variability in all reported sequences. These data provide a model system that demonstrates a) the superiority of immunization with dendritic cells transfected with LAMP/gag plasmid DNA, as compared to naked DNA, b) the value of HLA transgenic mice as a model system for the identification and evaluation of epitope-based vaccine strategies, and c) the application of variability analysis across reported sequences in public databases for selection of historically conserved HIV epitopes as vaccine targets.

Cardiac gene therapy

Heart failure is a chronic progressive disorder in which frequent and recurrent hospitalizations are associated with high mortality and morbidity. The incidence and the prevalence of this disease will increase with the increase in the number of the aging population of the United States. Understanding the molecular pathology and pathophysiology of this disease will uncover novel targets and therapies that can restore the function or attenuate the damage of malfunctioning cardiomyocytes by gene therapy that becomes an interesting and a promising field for the treatment of heart failure as well as other diseases in the future. Of equal importance are developing vectors and delivery methods that can efficiently transduce most of the cardiomyocytes that can offer a long-term expression and that can escape the host immune response. Recombinant adeno-associated virus vectors have the potential to become a promising novel therapeutic vehicles for molecular medicine in the future.

A detailed characterisation of the distribution and presentation of DNA vaccine encoded antigen

The association between plasmid DNA distribution, the amount of Ag produced, Ag persistence and the identity and localisation of cells presenting DNA-encoded Ag all have important consequences for both quantitative and qualitative aspects of T cell responses induced by DNA vaccines. Using a variety of approaches to detect and quantify the uptake of injected DNA, and the production and presentation of DNA-encoded antigen, we report that injected DNA vaccines rapidly enter the peripheral blood from the injection site and also reach muscle-draining lymph nodes directly as free DNA. 24 h after plasmid injection, MHCII⁺CD11b⁺B220⁻CD11c^low/− cells in the draining and distal LNs and spleen contain pDNA. Interestingly, we also observed pDNA⁺MHCII^low/−CD11b⁺ within the bone marrow. Concomitantly, we detected Ag-containing/expressing cells at both the injection site and in draining lymph nodes. Three days after plasmid injection we detected rare pMHC⁺CD11c⁺ cells within secondary lymphoid tissue and simultaneously observed Ag-specific CD4⁺ T cell accumulation and blastogenesis in these tissues. Our results show that the events that determine the induction of DNA vaccine immune responses occur within days of DNA injection and that the response becomes systemic very rapidly, possibly with involvement from resident BM cells.

Persistent expression of FLAG-tagged micro dystrophin in nonhuman primates following intramuscular and vascular delivery

Animal models for Duchenne muscular dystrophy (DMD) have species limitations related to assessing function, immune response, and distribution of micro- or mini-dystrophins. Nonhuman primates (NHPs) provide the ideal model to optimize vector delivery across a vascular barrier and provide accurate dose estimates for widespread transduction. To address vascular delivery and dosing in rhesus macaques, we have generated a fusion construct that encodes an eight amino-acid FLAG epitope at the C-terminus of micro-dystrophin to facilitate translational studies targeting DMD. Intramuscular (IM) injection of AAV8.MCK.micro-dys.FLAG in the tibialis anterior (TA) of macaques demonstrated robust gene expression, with muscle transduction (50-79%) persisting for up to 5 months. Success by IM injection was followed by targeted vascular delivery studies using a fluoroscopy-guided catheter threaded through the femoral artery. Three months after gene transfer, >80% of muscle fibers showed gene expression in the targeted muscle. No cellular immune response to AAV8 capsid, micro-dystrophin, or the FLAG tag was detected by interferon-gamma (IFN-gamma) enzyme-linked immunosorbent spot (ELISpot) at any time point with either route. In summary, an epitope-tagged micro-dystrophin cassette enhances the ability to evaluate site-specific localization and distribution of gene expression in the NHP in preparation for vascular delivery clinical trials.

Immune responses to T-cell epitopes of SARS CoV-N protein are enhanced by N immunization with a chimera of lysosome-associated membrane protein

In our previous study by Gupta et al, dominant T-cell epitopes of SARS CoV-N(N) protein were predicted by software. The spectrum of interferon (IFN)-gamma responses of Balb/c mice immunized against two different forms of SARS CoV-N plasmid was then analyzed. A cluster of dominant T-cell epitopes of SARS CoV-N protein was found in the N-terminus (amino acids 76-114). On the basis of this study, four different plasmids were constructed: (i) DNA encoding the unmodified N (p-N) or N(70-122) (p-N(70-122)) as an endogenous cytoplasmic protein or (ii) DNA encoding a lysosome-associated membrane protein (LAMP) chimera with N (p-LAMP/N) or N(70-122) (p-LAMP/N(70-122)). The immune responses of mice to these four constructs were evaluated. The results showed marked differences in the responses of the immunized mice. A single priming immunization with the p-LAMP/N construct was sufficient to elicit an antibody response. Enzyme-linked immunospot (ELISpot) assay indicated that p-LAMP/N(70-122) and p-LAMP/N plasmids both elicited a greater IFN-gamma response than p-N. p-N and p-N(70-122) constructs induced low or undetectable levels of cytokine secretion. We also found that the p-LAMP/N(70-122) construct promoted a long-lasting T-cell memory response without an additional boost 6 months after three immunizations. These findings show that DNA vaccines, even epitope-based DNA vaccines using LAMP as chimera, can elicit both humoral and cellular immune responses.

AAV9-mediated erythropoietin gene delivery into the brain protects nigral dopaminergic neurons in a rat model of Parkinson's disease

We have recently shown that intrastriatal injection of recombinant human erythropoietin (EPO) protects dopaminergic (DA) neurons in the substantia nigra (SN) from 6-hydroxydopamine (6-OHDA) toxicity in a rat model of Parkinson's disease. However, systemic administration of EPO did not protect nigral DA neurons, suggesting that the blood-brain barrier limits the passage of EPO protein into the brain. In the present study, we used an adeno-associated viral (AAV) serotype 9 (AAV9) vector to deliver the human EPO gene into the brain of 6-OHDA-lesioned rats. We observed that expression of the human EPO gene was robust and stable in the striatum and the SN for up to 10 weeks. EPO-immunoreactive (IR) cells were widespread throughout the injected striatum, and EPO-IR neurons and fibers were also found in the ipsilateral SN. Enzyme-linked immunosorbent assay and western blot analyses exhibited dramatic levels of EPO protein in the injected striatum. As a result, nigral DA neurons were protected against 6-OHDA-induced toxicity. Amphetamine-induced rotational asymmetry and spontaneous forelimb use asymmetry were both attenuated. Interestingly, we also observed that intrastriatal injection of AAV9-EPO vectors led to increased numbers of red blood cells in peripheral blood. This highlights the importance of using an inducible gene delivery system for EPO gene delivery.

Sustained transgene expression despite T lymphocyte responses in a clinical trial of rAAV1-AAT gene therapy

Alpha-1 antitrypsin (AAT) deficiency is well-suited as a target for human gene transfer. We performed a phase 1, open-label, dose-escalation clinical trial of a recombinant adeno-associated virus (rAAV) vector expressing normal (M) AAT packaged into serotype 1 AAV capsids delivered by i.m. injection. Nine AAT-deficient subjects were enrolled sequentially in cohorts of 3 each at doses of 6.9 x 10(12), 2.2 x 10(13), and 6.0 x 10(13) vector genome particles per patient. Four subjects receiving AAT protein augmentation discontinued therapy 28 or 56 days before vector administration. Vector administration was well tolerated, with only mild local reactions and 1 unrelated serious adverse event (bacterial epididymitis). There were no changes in hematology or clinical chemistry parameters. M-specific AAT was expressed above background in all subjects in cohorts 2 and 3 and was sustained at levels 0.1% of normal for at least 1 year in the highest dosage level cohort, despite development of neutralizing antibody and IFN-gamma enzyme-linked immunospot responses to AAV1 capsid at day 14 in all subjects. These findings suggest that immune responses to AAV capsid that develop after i.m. injection of a serotype 1 rAAV vector expressing AAT do not completely eliminate transduced cells in this context.

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 muscle-targeting peptide displayed on AAV2 improves muscle tropism on systemic delivery

Adeno-associated virus (AAV) has become a leading gene transfer vector for striated muscles. However, the AAV vectors also exhibit broad tropisms after systemic delivery. In an attempt to improve muscle tropism, we inserted a 7-amino-acid (ASSLNIA) muscle-targeting peptide (MTP) in the capsids of AAV2 at residue 587 or 588, generating AAV(587)MTP and AAV(588)MTP. In vitro studies showed that both viruses diminished their infectivity on non-muscle cell lines as well as on un-differentiated myoblasts; however, preserved or enhanced their infectivity on differentiated myotubes. AAV(587)MTP, but not AAV(588)MTP, also abolished its heparin-binding capacity and infected myotubes in a heparin-independent manner. Furthermore, in vivo studies by intravenous vector administration in mice showed that AAV(587)MTP enhanced its tropism to various muscles and particularly to the heart (24.3-fold of unmodified AAV2), whereas reduced its tropism to the non-muscle tissues such as the liver, lungs, spleen and so on. This alteration of tissue tropism is not simply because of the loss of heparin-binding, as a mutant AAV2 (AAVHBSMut) containing heparin-binding site mutations lost infectivity on both non-muscle and muscle cells. Furthermore, free MTP peptide, but not the scrambled control peptide, competitively inhibited AAV(587)MTP infection on myotubes. These results suggest that AAV2 could be re-targeted to the striated muscles by a MTP inserted after residue 587 of the capsids. This proof of principle study showed first evidence of peptide-directed muscle targeting on systemic administration of AAV vectors.

Does the use of recombinant AAV5 in pulmonary gene therapy lead to lung damage?

This study investigated whether repeated administration of recombinant adeno-associated virus type 5 (rAAV5) to the airways induces inflammatory processes in the lungs of BALB/c-mice, with mechanical and histologic changes. Saline was instilled intratracheally in the control group, and rAAV5-green fluorescence protein (GFP) (4x10(11)particles) in the virus group (VR). These groups were subdivided into four subgroups: one dose analyzed 3 weeks later (VR1d3w) and two doses analyzed 1 (VR2d1w), 2 (VR2d2w) and 3 weeks (VR2d3w) after the second dose. Lung morphometry, mechanical parameters, airway responsiveness, rAAV5-GFP transduction and the expression of inflammatory cytokines were investigated. No significant differences in lung mechanics, airway responsiveness, and morphometry were observed. Re-administration of rAAV5 vector resulted in a decrease in GFP mRNA expression in the VR2d3w group. There was no evidence of inflammatory response or apoptosis in any group. rAAV5 did not induce an inflammatory process, mechanical or morphometric changes in the lungs. AAV5 may be an appropriate vector for lung gene therapy.

Additive effect of AAV-mediated angiopoietin-1 and VEGF expression on the therapy of infarcted heart

Vascular endothelial growth factor (VEGF) is a key angiogenic factor and has been used experimentally for induction of neovasculature in ischemic myocardium. However, blood vessels induced by VEGF are immature. Angiopoietin-1 (ang-1) has the ability to recruit and sustain periendothelial support cells and promote vascular maturation. Thus, co-expression of the two may yield a better result than expression of either one alone. Two adeno-associated viral vectors (AAV), CMVVEGF and CMVang-1 with the CMV promoter driving VEGF or ang-1 gene expression, respectively, were injected into ischemic mouse hearts individually or together in different ratios. The results show that co-injected groups had more capillaries than the CMVang-1 group and similar densities of capillaries and alpha-actin positive vessels as the CMVVEGF group. Neovasculature induced by CMVVEGF was leaky. In contrast, neovasculature in CMVang-1-injected or CMVVEGF and CMVang-1 co-injected hearts was less leaky than that in CMVVEGF-injected hearts. The group that received CMVang-1 and CMVVEGF in a 1:1 ratio had the smallest infarct size and best cardiac function and regional wall movement among all the groups. We conclude that ang-1 and VEGF can compensate for each others' shortcomings and yield a better therapeutic effect by acting together.

Gene therapy following subretinal AAV5 vector delivery is not affected by a previous intravitreal AAV5 vector administration in the partner eye

PURPOSE

In an earlier study we found normal adeno-associated viral vector type 2 (AAV2)-mediated GFP expression after intravitreal injection to one eye of normal C57BL/6J mice. However, GFP expression was very poor in the partner eye of the same mouse if this eye received an intravitreal injection of the same vector one month after the initial intravitreal injection. We also found both injections worked well if they were subretinal. In this study, we tested whether the efficiency of subretinal AAV vector transduction is altered by a previous intravitreal injection in the partner eye and more importantly whether therapeutic efficiency is altered in the rd12 mouse (with a recessive RPE65 mutation) after the same injection series.

METHODS

One microl of scAAV5-smCBA-GFP (1 x 10(13) genome containing viral particles per ml) was intravitreally injected into the right eyes of four-week-old C57BL/6J mice and 1 microl of scAAV5-smCBA-hRPE65 (1 x 10(13) genome containing viral particles per ml) was intravitreally injected into the right eyes of four-week-old rd12 mice Four weeks later, the same vectors were subretinally injected into the left eyes of the same C57BL/6J and rd12 mice. Left eyes of another cohort of eight-week-old rd12 mice received a single subretinal injection of the same scAAV5-smCBA-hRPE65 vector as the positive control. Dark-adapted electroretinograms (ERGs) were recorded five months after the subretinal injections. AAV-mediated GFP expression in C57BL/6J mice and RPE65 expression and ERG restoration in rd12 mice were evaluated five months after the second subretinal injection. Frozen section analysis was performed for GFP fluorescence in C57BL/6J mice and immunostaining for RPE65 in rd12 eyes.

RESULTS

In rd12 mice, dark-adapted ERGs were minimal following the first intravitreal injection of scAAV5-smCBA-RPE65. Following subsequent subretinal injection in the partner eye, dramatic ERG restoration was recorded in that eye. In fact, ERG b-wave amplitudes were statistically similar to those from the eyes that received the initial subretinal injection at a similar age. In C57BL/6J mice, GFP positive cells were detected in eyes following the first intravitreal injection around the injection site. Strong GFP expression in both the retinal pigment epithelium (RPE) and photoreceptor (PR) cells was detected in the partner eyes following the subsequent subretinal injection. Immunostaining of retinal sections with anti-RPE65 antibody showed strong RPE65 expression mainly in the RPE cells of subretinally injected eyes but not in the intravitreally injected eyes except minimally around the injection site.

CONCLUSIONS

These results show that an initial intravitreal injection of AAV vectors to one eye of a mouse does not influence AAV-mediated gene expression or related therapeutic effects in the other eye when vectors are administered to the subretinal space. This suggests that the subretinal space possesses a unique immune privilege relative to the vitreous cavity.

Gene therapy for cystic fibrosis

Cystic Fibrosis (CF) is an autosomal recessive disorder due to mutations in the CF transmembrane conductance regulator (CFTR) gene that lead to defective ion transport in the conducting pulmonary airways and exocrine glands. Through a process that is not fully understood, CFTR defects predispose affected patients to chronic endobronchial infections with organisms such as Pseudomonas aeruginosa and Staphylococcus aureus. Following the discovery of the CFTR gene in 1989, CF became one of the primary targets for gene therapy research. Early enthusiasm surrounded the new field of gene therapy during most of the 1990s and it led academics and clinicians on a big effort to apply gene therapy for cystic fibrosis. Clinical studies have been pursued using recombinant adenovirus, recombinant adeno-associated virus, cationic liposomes, and cationic polymer vectors. Although to this date no dramatic therapeutic benefits have been observed, a lot of information has been gained from the pre-clinical and clinical studies that were performed. This learning curve has led to the optimization of vector technology and an appreciation of immune and mechanical barriers that have to be overcome for successful delivery.

Striatal readministration of rAAV vectors reveals an immune response against AAV2 capsids that can be circumvented

Recombinant adeno-associated virus (rAAV) expresses no viral genes after transduction. In addition, because the brain is relatively immunoprivileged, intracranial rAAV transduction may be immunologically benign due to a lack of antigen presentation. However, preexposure to AAV allows neutralizing antibodies (nAbs) to block brain transduction and rAAV readministration in the brain leads to an inflammatory response in the second-injection site. In this study, we replicate our striatal rAAV2/2-GDNF readministration results and extend this effect to a second transgene, green fluorescent protein (GFP). Unlike rAAV2/2-GDNF readministration, striatal rAAV2/2-GFP readministration leads to a loss of transgene in the second site in the absence of detectable circulating nAbs. In order to determine whether the transgene or the AAV2 capsid is the antigenic stimulus in brain for the immune response in the second site, we readministered rAAV2/2-GFP using two different rAAV serotypes (rAAV2/2 followed by rAAV2/5). In this case, there was no striatal inflammation or transgene loss detected in the second-injection site. In addition, striatal readministration of rAAV2/5-GFP also resulted in no detectable immune response. Furthermore, delaying rAAV2/2 striatal readministration to a 11-week interval abrogated the immune response in the second-injection site. Finally, while striatal readministration of rAAV2/2 leads to significant loss of transgene in the second-injection site, this effect is not due to loss of vector genomes as determined by quantitative real-time PCR. We conclude that intracellular processing of AAV capsids after transduction is the immunogenic antigen and capsid serotypes that are processed more quickly than rAAV2/2 are less immunogenic.

The Jeremiah Metzger Lecture: gene therapy for inherited disorders: from Christmas disease to Leber's amaurosis

This paper will focus on recent developments in the field of gene therapy for inherited disorders. From a historical perspective, this Metzger lecture is a follow-on to one presented by Dr. William Kelley in 1987, entitled "Current Status of Human Gene Therapy" (Transactions Am Clin. Climatol. Assoc. 99:152-169) (1). In 1987, gene transfer studies in human subjects were yet to be undertaken; the first clinical studies, infusion of genetically modified autologous T cells into two young girls with ADA-SCID, would not take place until 1990 (2). Today's lecture will summarize progress since that time in one area, that of in vivo gene transfer for genetic disease. I will describe progress in two areas, gene therapy for the bleeding disorder hemophilia B, and for a subset of retinal degenerative disorders termed Leber's congenital amaurosis, due to mutations in the gene encoding retinal pigment epithelium-specific 65 kilodalton protein (RPE65). This lecture will demonstrate the interconnected nature of progress in these two areas, as careful delineation of the obstacles in hemophilia led to the realization that success could be achieved in Leber's.

Antigen-specific humoral tolerance or immune augmentation induced by intramuscular delivery of adeno-associated viruses encoding CTLA4-Ig-antigen fusion molecules

This study initially sought to investigate the immunostimulatory properties of recombinant adeno-associated virus (rAAV) with a view to developing a genetic vaccine for malaria using muscle as a target tissue. To augment humoral immunity, the AAV-encoded antigen was genetically fused with CTLA4-Ig, a recombinant molecule that binds B7 costimulatory molecules. At 10(9) vg, CTLA4-Ig fusion promoted the humoral immune response 100-fold and was dependent on CTLA4-Ig binding with B7 costimulatory molecules, confirming plasmid DNA models using this strategy. In distinct contrast, 10(12)-10(13) vg of rAAV1 specifically induced long-lived humoral tolerance through a mechanism that is independent of CTLA4-Ig binding with B7. This finding was unexpected, as rAAV delivery to muscle, unlike liver, has shown that this tissue provides a highly immunogenic environment for induction of humoral immunity against rAAV transgene products. An additional unpredicted consequence of antigen fusion with CTLA4-Ig was the enhancement of antigen expression by approximately one log, an effect mapped to the hinge and Fc domain of IgG(1,) but not involving antigen dimerization or the neonatal Fc receptor. Collectively, these findings significantly advance the potential of rAAV both as a vaccine or immunotherapeutic platform for the induction of antigen-specific humoral immunity or tolerance and as a gene therapeutic delivery system.

Relative persistence of AAV serotype 1 vector genomes in dystrophic muscle

The purpose of this study was to assess the behavior of pseudotyped recombinant adeno-associated virus type 1 (rAAV2/1) vector genomes in dystrophic skeletal muscle. A comparison was made between a therapeutic vector and a reporter vector by injecting the hindlimb in a mouse model of Limb Girdle Muscular Dystrophy Type 2D (LGMD-2D) prior to disease onset. We hypothesized that the therapeutic vector would establish long-term persistence through prevention of myofiber turnover. In contrast, the reporter vector genome copy number would diminish over time due to disease-associated muscle degradation.

One day old alpha sarcoglycan knockout mice (sgca^-/-) were injected with 1 × 10¹¹ vector genomes of rAAV2/1-tMCK-sgca in one hindlimb and the same dose of rAAV2/1-tMCK-LacZ in the contra lateral hindlimb. Newborn mice are tolerant of the foreign transgene allowing for long-term expression of both the marker and the therapeutic gene in the null background. At 2 time-points following vector administration, hindlimb muscles were harvested and analyzed for LacZ or sarcoglycan expression. Our data demonstrate prolonged vector genome persistence in skeletal muscle from the hindlimbs injected with the therapeutic transgene as compared to hindlimbs injected with the reporter gene. We observed loss of vector genomes in skeletal muscles that were there were not protected by the benefits of therapeutic gene transfer. In comparison, the therapeutic vector expressing sarcoglycan led to reduction or elimination of myofiber loss. Mitigating the membrane instability inherent in dystrophic muscle was able to prolong the life of individual myofibers.

Intraocular route of AAV2 vector administration defines humoral immune response and therapeutic potential

PURPOSE

Safety and efficiency are critical for successful gene therapy. Adeno-associated viral (AAV) vectors are commonly used for gene transfer in both human and animal studies. However, administration of AAV vectors can lead to development of neutralizing antibodies against the vector capsid, thus decreasing the efficiency of therapeutic gene transfer and preventing effective vector readministration. We investigated immune responses to different routes of ocular administration and readministration of AAV vectors, and the effect of previous exposure of AAV vector in one eye on the transduction efficacy of subsequent intraocular AAV-mediated gene delivery to the partner eye.

METHODS

We tested two vector systems. One contained a cDNA encoding a secreted pigment epithelial derived factor (PEDF) cDNA under the control of a Cytomegalovirus (CMV) enhancer and chicken beta-actin promoter (CBA; AAV2-CBA-PEDF) and was tested in a murine model of laser-induced choroidal neovascularization (CNV). The other vector contained a cDNA encoding the intracellular reporter green fluorescent protein (GFP) under the control of the same promoter (AAV2-CBA-GFP). Animals were divided into groups and received sequential injections at different combinations of either intravitreal or subretinal routes. CNV was evaluated by fluorescein angiographic choroidal flat-mount image analysis. The expression of GFP was analyzed in retinal sections by direct fluorescence imaging. Antibodies against AAV2 capsid and transgenes were analyzed by ELISA using serum samples collected before injection and different time points after the injection. Neutralizing antibodies were characterized by in vitro assays.

RESULTS

Various ocular compartments responded to AAV administration differently. Intravitreal administration of AAV vectors, which resulted in transduction of inner retina (primarily retinal ganglion cells), generated a humoral immune response against AAV capsid that blocked vector expression upon readministration via the same route into the partner eye. In contrast, it had no effect on vector readministered into the subretinal space of the partner eye. Additionally, subretinal administration of vector did not trigger any humoral immune response against AAV capsid, and had no effect on subsequent administration of vector either intravitreally or subretinally into the partner eye.

CONCLUSIONS

These findings have important clinical implications for the design of AAV-mediated ocular gene transfer for retinal diseases, particularly if both eyes require sequential treatment.

Tissue specific promoters improve specificity of AAV9 mediated transgene expression following intra-vascular gene delivery in neonatal mice

The AAV9 capsid displays a high natural affinity for the heart following a single intravenous (IV) administration in both newborn and adult mice. It also results in substantial albeit relatively lower expression levels in many other tissues. To increase the overall safety of this gene delivery method we sought to identify which one of a group of promoters is able to confer the highest level of cardiac specific expression and concurrently, which is able to provide a broad biodistribution of expression across both cardiac and skeletal muscle. The in vivo behavior of five different promoters was compared: CMV, desmin (Des), alpha-myosin heavy chain (α-MHC), myosin light chain 2 (MLC-2) and cardiac troponin C (cTnC). Following IV administration to newborn mice, LacZ expression was measured by enzyme activity assays. Results showed that rAAV2/9-mediated gene delivery using the α-MHC promoter is effective for focal transgene expression in the heart and the Des promoter is highly suitable for achieving gene expression in cardiac and skeletal muscle following systemic vector administration. Importantly, these promoters provide an added layer of control over transgene activity following systemic gene delivery.

Recombinant adeno-associated virus type 8-mediated extensive therapeutic gene delivery into skeletal muscle of alpha-sarcoglycan-deficient mice

Autosomal recessive limb-girdle muscular dystrophy type 2D (LGMD 2D) is caused by mutations in the alpha-sarcoglycan gene (alpha-SG). The absence of alpha-SG results in the loss of the SG complex at the sarcolemma and compromises the integrity of the sarcolemma. To establish a method for recombinant adeno-associated virus (rAAV)-mediated alpha-SG gene therapy into alpha-SG-deficient muscle, we constructed rAAV serotypes 2 and 8 expressing the human alpha-SG gene under the control of the ubiquitous cytomegalovirus promoter (rAAV2-alpha-SG and rAAV8-alpha-SG). We compared the transduction profiles and evaluated the therapeutic effects of a single intramuscular injection of rAAVs into alpha-SG-deficient (Sgca(-/-)) mice. Four weeks after rAAV2 injection into the tibialis anterior (TA) muscle of 10-day-old Sgca(-/-) mice, transduction of the alpha-SG gene was localized to a limited area of the TA muscle. On the other hand, rAAV8-mediated alpha-SG expression was widely distributed in the hind limb muscle, and persisted for 7 months without inducing cytotoxic and immunological reactions, with a reversal of the muscle pathology and improvement in the contractile force of the Sgca(-/-) muscle. This extensive rAAV8-mediated alpha-SG transduction in LGMD 2D model animals paves the way for future clinical application.

Large-scale production of recombinant adeno-associated viral vectors

Current and future demands of viral vectors for the development of successful pre-clinical and clinical studies in human gene therapy and possible commercialization of gene therapy products require well-established large-scale production processes. One of the most promising vectors for human gene therapy is recombinant adeno-associated virus vectors (rAAVs). Some of the attractive features of rAAV are broad tissue tropism, low immunogenicity, ability to transduce both mitotic and post-mitotic cells, and long-term gene expression in non-dividing cells. Recently, we developed a novel technology for the production of these vectors exploiting baculovirus expression vectors (BEV: ) in insect cell cultures. Initially developed in small, shake flask format, this process has been successfully scaled to larger volumes. In an effort to standardize rAAV production in stirred tank bioreactors, we characterized the culture conditions to derive a set of parameters correlated with high rAAV yields. Measuring capacitance and dielectric spectroscopy with a permittivity probe enabled us to determine optimal times of infection and harvest. Consistent yields of rAAV, 2 x 10(13) DNase-resistant vector genomes (vg) [1 x 10(12) transducing units (tu)] per liter of cell culture were obtained in bioreactors with working volumes ranging from 10 to 40 l. This represents significant progress toward establishing a robust large-scale process at industry level.

Optimization of recombinant adeno-associated viral vectors for human beta-globin gene transfer and transgene expression

Therapeutic levels of expression of the beta-globin gene have been difficult to achieve with conventional retroviral vectors without the inclusion of DNase I-hypersensitive site (HS2, HS3, and HS4) enhancer elements. We generated recombinant adeno-associated viral (AAV) vectors carrying an antisickling human beta-globin gene under the control of either the beta-globin gene promoter/enhancer or the erythroid cell-specific human parvovirus B19 promoter at map unit 6 (B19p6) without any enhancer, and tested their efficacy in a human erythroid cell line (K-562) and in primary murine hematopoietic progenitor cells (c-kit(+)lin()). We report here that (1) self-complementary AAV serotype 2 (scAAV2)-beta-globin vectors containing only the HS2 enhancer are more efficient than single-stranded AAV (ssAAV2)-beta-globin vectors containing the HS2+HS3+HS4 enhancers; (2) scAAV2-beta-globin vectors recombine with scAAV2-HS2+HS3+HS4 vectors after dual-vector transduction, leading to transgene expression; (3) scAAV2-beta-globin as well as scAAV1-beta-globin vectors containing the B19p6 promoter without the HS2 enhancer element are more efficient than their counterparts containing the HS2 enhancer/beta-globin promoter; and (4) scAAV2-B19p6-beta-globin vectors in K-562 cells, and scAAV1-B19p6-beta-globin vectors in murine c-kit(+)lin() cells, yield efficient expression of the beta-globin protein. Thus, the combined use of scAAV vectors and the parvovirus B19 promoter may lead to expression of therapeutic levels the beta-globin gene in human erythroid cells, which has implications in the use of these vectors in gene therapy of beta-thalassemia and sickle cell disease.

Barriers for retinal gene therapy: separating fact from fiction

The majority of recent preclinical gene therapy studies targeting the retina have used adeno-associated virus (AAV) as the gene transfer vector. However, AAV has several limitations including the ability to generate innate inflammatory responses, the ability to cause insertional mutagenesis at a frequency of up to 56% in some tissues and a limited cloning capacity of 4.8Kb. Furthermore, AAV is known to generate limiting immune responses in humans despite the absence of similar immune responses in preclinical canine and murine studies. Three clinical trials to treat Leber's congenital amaurosis using AAV are under way. A clinical trial to treat Stargardt's using lentivirus vectors has also been recently announced. However, very limited evidence currently exists that lentivirus vectors can efficiently transduce photoreceptor cells. In contrast, very few preclinical ocular gene therapy studies have utilized adenovirus as the gene therapy vector. Nonetheless, the only two ocular gene therapy clinical trials performed to date have each used adenovirus as the vector and more significantly, in these published trials there has been no observed serious adverse event. These trials appear to be poised for Phase II/III status. Activation of cytotoxic T lymphocytes limits duration of transgene expression in the retina from first generation adenovirus vectors. However, an advanced class of adenovirus vectors referred to as Helper-dependent Adenovirus (Hd-Ad) have recently been shown to be capable of expressing transgenes in ocular tissues for more than one year. Hd-Ad vectors have many properties that potentially warrant their inclusion in the retinal gene therapy toolbox for the treatment of retinal degenerative diseases.

Silencing of T lymphocytes by antigen-driven programmed death in recombinant adeno-associated virus vector-mediated gene therapy

Recombinant adeno-associated virus (rAAV) vectors are considered promising for human gene replacement because they facilitate stable expression of therapeutic proteins in transduced tissues. Whether the success of gene therapy will be influenced by cellular immune responses targeting transgene-encoded proteins that are potentially immunogenic is unknown. Here we characterized CD8(+) T-cell activity against beta-galactosidase and enhanced green fluorescent protein, model antigens containing major histocompatibility complex (MHC) class I epitopes that are constitutively produced in murine skeletal muscle after rAAV vector transduction. Antigen-specific CD8(+) T cells were detected in the spleen and liver of mice within 7 days of muscle transduction. CD8(+) T-cell frequencies in these organs were stable, and effector functions were intact for months despite ongoing antigen production in muscle. CD8(+) T cells also infiltrated transduced muscle, where frequencies were at least 5-fold higher than in untransduced spleen and liver. Significantly, the majority of antigen-specific CD8(+) T cells in vector-transduced muscle were not functional. Loss of function in the muscle was associated with programmed death of the effector cells. Stable gene expression therefore depended on selective death of CD8(+) T cells at the site of antigen production, an effective mechanism for subverting immunity that is also potentially reversible.

Safety and efficacy of regional intravenous (r.i.) versus intramuscular (i.m.) delivery of rAAV1 and rAAV8 to nonhuman primate skeletal muscle

We developed a drug-free regional intravenous (r.i.) delivery protocol of recombinant adeno-associated virus (rAAV) 1 and 8 to an entire limb in the nonhuman primate (NHP), and compared the results with those produced by intramuscular (i.m.) delivery of the same dose of vector. We show that r.i. delivery of both serotypes was remarkably well tolerated with no adverse side-effects. After i.m., muscle transduction was restricted to the site of injection with a high number of vector copies per cell for rAAV1. In contrast, although r.i. delivery resulted in a lower vector copy per cell, it was detectable in the vast majority of muscles of the injected limb. The amounts of circulating infectious rAAV were similar for both serotypes and modes of delivery. At autopsy at up to 34 months after vector administration, similar biodistribution patterns were found for both vectors and for both modes of delivery, with numerous organs found to be positive for vector sequence when assayed using PCR and Southern blot. Altogether, we demonstrated that r.i. is a simple and efficient transduction protocol in NHPs, resulting in higher expression of the transgene with a lower number of vector genomes per cell. However, regardless of the mode of delivery, concerns continue to be raised by the presence of vector sequences detected at distant sites.

Gene delivery to intestinal epithelial cells in vitro and in vivo with recombinant adeno-associated virus types 1, 2 and 5

Intestinal disorders such as inflammatory bowel disease (IBD) result in chronic illness requiring lifelong therapy. Our aim was to evaluate the efficacy of recombinant adeno-associated virus (AAV) vector-mediated gene delivery to intestinal epithelial cells in vitro and in vivo. Human colon epithelial cell lines and colon biopsies were transduced using AAV pseudotypes 2/1, 2/2, and 2/5 encoding green fluorescence protein (GFP). Mice were administered the same vectors through oral, enema, intraperitoneal (IP) injection and superior mesenteric artery (SMA) injection routes. Tropism and efficiency were determined by microscopy, flow cytometry, immunohistochemistry and PCR. Caco2 cells were more permissive to AAV transduction. Human colon epithelial cells in organ culture were more effectively transduced by AAV2/2. SMA injection provided the most effective means of vector gene transfer to small intestine and colonic epithelial cells in vivo. Transgene detection 80 days post AAV treatment suggests transduction of crypt progenitor cells. This study shows the feasibility of AAV-mediated intestinal gene delivery, applicable for the investigation of IBD pathogenesis and novel therapeutic options, but also revealed the need for further studies to identify more efficient pseudotypes.

AAV serotype 1 mediates more efficient gene transfer to pig myocardium than AAV serotype 2 and plasmid

Adeno-associated virus (AAV) has many properties of an ideal vector for delivery of therapeutic genes into the myocardium. Previous studies in a mouse model of myocardial infarction showed that AAV serotype 1 (AAV1) is superior to AAV serotypes 2-5 to transfer genes into the myocardium by direct injection. Since vectors may behave differently in humans and because the human and the pig hearts resemble each other closely, we tested whether AAV1 is also superior to AAV2 in transferring genes into the pig myocardium. We also compared gene transduction efficiency between AAV vectors and plasmid. We injected CMVLacZ and CMVVEGF (vectors with the cytomegalovirus (CMV) promoter driving LacZ and VEGF gene expression) unpackaged or packaged in AAV serotypes 1 or 2 capsids into pig myocardium. Hearts were collected 3, 14 and 28 days after the injection. Gene expression was analyzed by real-time reverse-transcription polymerase chain reaction (RT-PCR) and histological staining. Capillaries and smooth muscle alpha-actin (SMA)-positive vessels were quantified. Potential lymphocyte infiltration at the injection sites was analyzed by immunostaining using specific antibodies. As in the mouse, AAV1 mediated better gene transduction than AAV2. Plasmid mediated minimal gene expression only. More capillaries and SMA-positive vessels were detected at AAV1CMVVEGF- and AAV2CMVVEGF-injected than AAV1CMVLacZ-injected sites. We did not detect inflammatory cell infiltration at the injection sites. In conclusion, by direct injection, AAV1 is more efficient than AAV2, and plasmid is inefficient in mediating gene transfer into the pig myocardium. AAV-mediated VEGF gene transfer can also induce neovascular formation in the pig myocardium.

Gene therapy: the first two decades and the current state-of-the-art

The concept of gene therapy was envisioned soon after the emergence of restriction endonucleases and subcloning of mammalian genes in phage and plasmids. Over the ensuing decades, vectors were developed, including nonviral methods, integrating virus vectors (gammaretrovirus and lentivirus), and non-integrating virus vectors (adenovirus, adeno-associated virus, and herpes simplex virus vectors). Preclinical data demonstrated potential efficacy in a broad range of animal models of human diseases, but clinical efficacy in humans remained elusive in most cases, even after decades of experience in over 1000 trials. Adverse effects from gene therapy have been observed in some cases, often because of viral vectors retaining some of the pathogenic potential of the viruses upon which they are based. Later generation vectors have been developed in which the safety and/or the efficiency of gene transfer has been improved. Most recently this work has involved alterations of vector envelope or capsid proteins either by insertion of ligands to target specific receptors or by directed evolution. The disease targets for gene therapy are multiple, but the most promising data have come from monogenic disorders. As the number of potential targets for gene therapy continues to increase, and a substantial number of trials continue with both the standard and the later generation vector systems, it is hoped that a therapeutic niche for gene therapy will emerge in the coming decades.

Complement is an essential component of the immune response to adeno-associated virus vectors

Adeno-associated virus (AAV) vectors are associated with relatively mild host immune responses in vivo. Although AAV induces very weak innate immune responses, neutralizing antibodies against the vector capsid and transgene still occur. To understand further the basis of the antiviral immune response to AAV vectors, studies were performed to characterize AAV interactions with macrophages. Primary mouse macrophages and human THP-1 cells transduced in vitro using an AAV serotype 2 (AAV2) vector encoding green fluorescent protein did not result in measurable transgene expression. An assessment of internalized vector genomes showed that AAV2 vector uptake was enhanced in the presence of normal but not heat-inactivated or C3-depleted mouse/human serum. Enhanced uptake in the presence of serum coincided with increased macrophage activation as determined by the expression of NF-kappaB-dependent genes such as macrophage inflammatory protein 2 (MIP-2), interleukin-1beta (IL-1beta), IL-8, and MIP-1beta. AAV vector serotypes 1 and 8 also activated human and mouse macrophages in a serum-dependent manner. Immunoprecipitation studies demonstrated the binding of iC3b complement protein to the AAV2 capsid in human serum. AAV2 did not activate the alternative pathway of the complement cascade and lacked cofactor activity for factor I-mediated degradation of C3b to iC3b. Instead, our results suggest that the AAV capsid also binds complement regulatory protein factor H. In vivo, complement receptor 1/2- and C3-deficient mice displayed impaired humoral immunity against AAV2 vectors, with a delay in antibody development and significantly lower neutralizing antibody titers. These results show that the complement system is an essential component of the host immune response to AAV.

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.

Quiescent subpopulations of human CD34-positive hematopoietic stem cells are preferred targets for stable recombinant adeno-associated virus type 2 transduction

We have previously demonstrated recombinant adeno-associated viral (rAAV) transduction of human CD34(+) hematopoietic stem cells (HSCs) capable of serial engraftment in vivo. Here we evaluated the capacity of rAAV2 to mediate gene transfer into nondividing, quiescent, primitive CD34(+) cells subdivided on the basis of metabolic, mitotic, and phenotypic properties. Results revealed that CD34(+)CD38() marrow cells are the most quiescent, exist primarily in G(0) at isolation and are the only population to remain nondividing during the entire exposure to free rAAV. Despite significant differences in the extended clonogenic capacities of CD34(+) subsets in stromal cultures, the frequency of rAAV marking of colonies derived from primitive progenitors was similar in all three populations, suggesting that both primitive and more differentiated progenitors were initially transduced at equal levels. After transduction, episomal and integrated rAAV genomes were detected in all CD34(+) subsets. However, the more quiescent cells displayed higher levels of integrated rAAV than did rapidly dividing cells. Importantly, stable long-term integration was observed only in the most primitive, quiescent CD34(+)CD38(-) subset, indicating that this HSC compartment comprises the preferred substrate for stable rAAV2 transduction. Previously described rate limitations to transgene expression were observed in transduced CD34(+) cells and could be overcome by tyrphostin pretreatment, which resulted in augmented second-strand synthesis. These results represent the first demonstration of rAAV-mediated gene transfer to primitive, quiescent human CD34(+)CD38(-) stem cells and reveal that nondividing CD34(+)CD38(-) HSCs are the optimal CD34(+) targets for rAAV transduction.

How not to be seen: immune-evasion strategies in gene therapy

The development of efficient and safe vectors for gene delivery paved the way for evolution of gene therapy as a new modality for treatment of various inherited disorders and for cancer. The current vectors, viral and non-viral, have their limitations. Innate and adaptive immune responses to vector particles and components may restrict the efficiency of gene transfer and the persistence of expression of the transgene. Results from preclinical studies in animals and more recently data from clinical studies have demonstrated the potential impact of the cellular and the humoral immune response on the therapeutic efficacy. Not only the vector components, but also the transgene products may induce an immune response that negatively affects the therapeutic efficacy. The induction of a cytotoxic T-cell response to transgene-encoded peptides, as well as the production of antibodies directed against secreted proteins have been reported in preclinical and clinical studies, and these may thwart those applications that require long-term expression. Here we will review some of the options to blunt the acquired immune responses to transgene-encoded polypeptides.

Process optimization of large-scale production of recombinant adeno-associated vectors using dielectric spectroscopy

A well-characterized manufacturing process for the large-scale production of recombinant adeno-associated vectors (rAAV) for gene therapy applications is required to meet current and future demands for pre-clinical and clinical studies and potential commercialization. Economic considerations argue in favor of suspension culture-based production. Currently, the only feasible method for large-scale rAAV production utilizes baculovirus expression vectors and insect cells in suspension cultures. To maximize yields and achieve reproducibility between batches, online monitoring of various metabolic and physical parameters is useful for characterizing early stages of baculovirus-infected insect cells. In this study, rAAVs were produced at 40-l scale yielding ~1 x 10(15) particles. During the process, dielectric spectroscopy was performed by real time scanning in radio frequencies between 300 kHz and 10 MHz. The corresponding permittivity values were correlated with the rAAV production. Both infected and uninfected reached a maximum value; however, only infected cell cultures permittivity profile reached a second maximum value. This effect was correlated with the optimal harvest time for rAAV production. Analysis of rAAV indicated the harvesting time around 48 h post-infection (hpi), and 72 hpi produced similar quantities of biologically active rAAV. Thus, if operated continuously, the 24-h reduction in the production process of rAAV gives sufficient time for additional 18 runs a year corresponding to an extra production of ~2 x 10(16) particles. As part of large-scale optimization studies, this new finding will facilitate the bioprocessing scale-up of rAAV and other bioproducts.

Long-term skeletal muscle protection after gene transfer in a mouse model of LGMD-2D

Limb girdle muscular dystrophy (LGMD) describes a group of inherited diseases resulting from mutations in genes encoding proteins involved in maintaining skeletal muscle membrane stability. LGMD type-2D is caused by mutations in alpha-sarcoglycan (sgca). Here we describe muscle-specific gene delivery of the human sgca gene into dystrophic muscle using an adeno-associated virus 1 (AAV1) capsid and creatine kinase promoter. Delivery of this construct to adult sgca(-/-) mice resulted in localization of the sarcoglycan complex to the sarcolemma and a reduction in muscle fiber damage. Sgca expression prevented disease progression as observed in vivo by T(2)-weighted magnetic resonance imaging (MRI) and confirmed in vitro by decreased Evan's blue dye accumulation. The ability of recombinant AAV-mediated gene delivery to restore normal muscle mechanical properties in sgca(-/-) mice was verified by in vitro force mechanics on isolated extensor digitorum longus (EDL) muscles, with a decrease in passive resistance to stretch as compared with untreated controls. In summary, AAV/AAV-sgca gene transfer provides long-term muscle protection from LGMD and can be non-invasively evaluated using magnetic resonance imaging.