Comparison of gene expression after intraperitoneal delivery of AAV2 or AAV5 in utero

Developing a second-generation clinical candidate AAV vector for gene therapy of familial hypercholesterolemia

Gene therapy for hypercholesterolemia offers the potential to sustainably ameliorate disease for life with a single dose. In this study, we demonstrate the combinatorial effects of codon and vector optimization, which significantly improve the efficacy of an adeno-associated virus (AAV) vector in the low-density lipoprotein receptor (LDLR)-deficient mouse model (Ldlr -/-, Apobec1 -/- double knockout [DKO]). This study investigated vector efficacy following the combination of intervening sequence 2 (IVS2) of the human beta-globin gene and codon optimization with the previously developed gain-of-function, human LDLR triple-mutant variant (hLDLR-L318D/K809R/C818A) in the treatment of homozygous familial hypercholesterolemia (HoFH). Vector doses as low as 3 × 1011 genome copies (GC)/kg achieved a robust reduction of serum low-density lipoprotein cholesterol (LDL-C) by 98% in male LDLR-deficient mice. Less efficient LDL-C reduction was observed in female mice, which was attributable to lower gene transfer efficiency in liver. We also observed persistent and stable transgene expression for 120 days, with LDL-C levels being undetectable in male DKO mice treated with the second-generation vector. In conclusion, codon and vector optimization enhanced transgene expression and reduced serum LDL-C levels effectively at a lower dose in LDLR-deficient mice. The second-generation clinical candidate vector we have developed has the potential to achieve therapeutic effects in HoFH patients.

A constitutive knockout of murine carbamoyl phosphate synthetase 1 results in death with marked hyperglutaminemia and hyperammonemia

The enzyme carbamoyl phosphate synthetase 1 (CPS1; EC 6.3.4.16) forms carbamoyl phosphate from bicarbonate, ammonia, and adenosine triphosphate (ATP) and is activated allosterically by N-acetylglutamate. The neonatal presentation of bi-allelic mutations of CPS1 results in hyperammonemia with reduced citrulline and is reported as the most challenging nitrogen metabolism disorder to treat. As therapeutic interventions are limited, patients often develop neurological injury or die from hyperammonemia. Survivors remain vulnerable to nitrogen overload, being at risk for repetitive neurological injury. With transgenic technology, our lab developed a constitutive Cps1 mutant mouse and reports its characterization herein. Within 24 hours of birth, all Cps1 ^-/- mice developed hyperammonemia and expired. No CPS1 protein by Western blot or immunostaining was detected in livers nor was Cps1 mRNA present. CPS1 enzymatic activity was markedly decreased in knockout livers and reduced in Cps1^+/- mice. Plasma analysis found markedly reduced citrulline and arginine and markedly increased glutamine and alanine, both intermolecular carriers of nitrogen, along with elevated ammonia, taurine, and lysine. Derangements in multiple other amino acids were also detected. While hepatic amino acids also demonstrated markedly reduced citrulline, arginine, while decreased, was not statistically significant; alanine and lysine were markedly increased while glutamine was trending towards significance. In conclusion we have determined that this constitutive neonatal mouse model of CPS1 deficiency replicates the neonatal human phenotype and demonstrates the key biochemical features of the disorder. These mice will be integral for addressing the challenges of developing new therapeutic approaches for this, at present, poorly treated disorder.

Transfer of Therapeutic Genes into Fetal Rhesus Monkeys Using Recombinant Adeno-Associated Type I Viral Vectors

Neuromuscular disorders such as Pompe disease (glycogen storage disease, type II), result in early and potentially irreversible cellular damage with a very limited opportunity for intervention in the newborn period. Pompe disease is due to deficiency in acid α-glucosidase (GAA) leading to lysosomal accumulation of glycogen in all cell types, abnormal myofibrillogenesis, respiratory insufficiency, neurological deficits, and reduced contractile function in striated muscle. Previous studies have shown that fetal delivery of recombinant adeno-associated virus (rAAV) encoding GAA to the peritoneal cavity of Gaa^-/- mice resulted in high-level transduction of the diaphragm. While progression of other genetic disorders may occur later in life, the potential of fetal gene delivery to avoid the onset of irreversible damage suggests it is an attractive option for many inherited diseases. In this study, rhesus monkey fetuses were administered 4.5 × 10¹² particles of rAAV type 1 expressing human GAA (rAAV1-CMV-hGAA), human α-1-antitrypsin (rAAV1-CBA-hAAT), or human mini-dystrophin (rAAV1-CMV-miniDMD) in the late first trimester using an established intraperitoneal ultrasound-guided approach. Fetuses were monitored sonographically and newborns delivered at term for postnatal studies. All animals remained healthy during the study period (growth, hematology, and clinical chemistry), with no evidence of adverse effects. Tissues were collected at a postnatal age of 3 months (∼7 months post-fetal gene transfer) for immunohistochemistry (IHC) and quantitative PCR. Both the diaphragm and peritoneum from vector-treated animals were strongly positive for expression of human GAA, AAT, or dystrophin by IHC, similar to findings when reporter genes were used. Protein expression in the diaphragm and peritoneum correlated with high vector copy numbers detected by real-time PCR. Other anatomical areas were negative, although the liver showed minimal evidence of human GAA, AAT, and DMD, vector genomes. In summary, delivery of rAAV vectors provided stable transduction of the muscular component of the diaphragm without any evidence of adverse effects.

Gene therapy for monogenic liver diseases: clinical successes, current challenges and future prospects

Over the last decade, pioneering liver-directed gene therapy trials for haemophilia B have achieved sustained clinical improvement after a single systemic injection of adeno-associated virus (AAV) derived vectors encoding the human factor IX cDNA. These trials demonstrate the potential of AAV technology to provide long-lasting clinical benefit in the treatment of monogenic liver disorders. Indeed, with more than ten ongoing or planned clinical trials for haemophilia A and B and dozens of trials planned for other inherited genetic/metabolic liver diseases, clinical translation is expanding rapidly. Gene therapy is likely to become an option for routine care of a subset of severe inherited genetic/metabolic liver diseases in the relatively near term. In this review, we aim to summarise the milestones in the development of gene therapy, present the different vector tools and their clinical applications for liver-directed gene therapy. AAV-derived vectors are emerging as the leading candidates for clinical translation of gene delivery to the liver. Therefore, we focus on clinical applications of AAV vectors in providing the most recent update on clinical outcomes of completed and ongoing gene therapy trials and comment on the current challenges that the field is facing for large-scale clinical translation. There is clearly an urgent need for more efficient therapies in many severe monogenic liver disorders, which will require careful risk-benefit analysis for each indication, especially in paediatrics.

Benefits of Neuronal Preferential Systemic Gene Therapy for Neurotransmitter Deficiency

Aromatic L-amino acid decarboxylase (AADC) deficiency is a rare autosomal recessive disease that impairs synthesis of dopamine and serotonin. Children with AADC deficiency exhibit severe motor, behavioral, and autonomic dysfunctions. We previously generated an IVS6+4A>T knock-in mouse model of AADC deficiency (Ddc(KI) mice) and showed that gene therapy at the neonatal stage can rescue this phenotype. In the present study, we extended this treatment to systemic therapy on young mice. After intraperitoneal injection of AADC viral vectors into 7-day-old Ddc(KI) mice, the treated mice exhibited improvements in weight gain, survival, motor function, autonomic function, and behavior. The yfAAV9/3-Syn-I-mAADC-treated mice showed greater neuronal transduction and higher brain dopamine levels than AAV9-CMV-hAADC-treated mice, whereas AAV9-CMV-hAADC-treated mice exhibited hyperactivity. Therefore, neurotransmitter-deficient animals can be rescued at a young age using systemic gene therapy, although a vector for preferential neuronal expression may be necessary to avoid hyperactivity caused by this treatment.

Kidney-specific expression of GFP by in-utero delivery of pseudotyped adeno-associated virus 9

Gene therapy targeting of kidneys has been largely unsuccessful. Recently, a recombinant adeno-associated virus (rAAV) vector was used to target adult mouse kidneys. Our hypothesis is that a pseudotyped rAAV 2/9 vector can produce fetal kidney-specific expression of the green fluorescent protein (GFP) gene following maternal tail vein injection of pregnant mice. Pregnant mice were treated with rAAV2/9 vectors with either the ubiquitous cytomegalovirus promoter or the minimal NPHS1 promoter to drive kidney-specific expression of GFP. Kidneys from dams and pups were analyzed for vector DNA, gene expression, and protein. Vector DNA was identified in kidney tissue out to 12 weeks at low but stable levels, with levels higher in dams than that in pups. Robust GFP expression was identified in the kidneys of both dams and pups treated with the cytomegalovirus (CMV)-enhanced green fluorescent protein (eGFP) vector. When treated with the NPHS1-eGFP vector, dams and pups showed expression of GFP only in kidneys, localized to the glomeruli. An 80-fold increase in GFP mRNA expression in dams and a nearly 12-fold increase in pups was found out to 12 weeks of life. Selective targeting of the fetal kidney with a gene therapy vector was achieved by utilizing the pseudotyped rAAV 2/9 vector containing the NPHS1 promoter.

Structural insights into adeno-associated virus serotype 5

The adeno-associated viruses (AAVs) display differential cell binding, transduction, and antigenic characteristics specified by their capsid viral protein (VP) composition. Toward structure-function annotation, the crystal structure of AAV5, one of the most sequence diverse AAV serotypes, was determined to 3.45-Å resolution. The AAV5 VP and capsid conserve topological features previously described for other AAVs but uniquely differ in the surface-exposed HI loop between βH and βI of the core β-barrel motif and have pronounced conformational differences in two of the AAV surface variable regions (VRs), VR-IV and VR-VII. The HI loop is structurally conserved in other AAVs despite amino acid differences but is smaller in AAV5 due to an amino acid deletion. This HI loop is adjacent to VR-VII, which is largest in AAV5. The VR-IV, which forms the larger outermost finger-like loop contributing to the protrusions surrounding the icosahedral 3-fold axes of the AAVs, is shorter in AAV5, creating a smoother capsid surface topology. The HI loop plays a role in AAV capsid assembly and genome packaging, and VR-IV and VR-VII are associated with transduction and antigenic differences, respectively, between the AAVs. A comparison of interior capsid surface charge and volume of AAV5 to AAV2 and AAV4 showed a higher propensity of acidic residues but similar volumes, consistent with comparable DNA packaging capacities. This structure provided a three-dimensional (3D) template for functional annotation of the AAV5 capsid with respect to regions that confer assembly efficiency, dictate cellular transduction phenotypes, and control antigenicity.

Role of antigen-specific regulatory CD4+CD25+ T cells in tolerance induction after neonatal IP administration of AAV-hF.IX

Neonatal AAV8-mediated Factor IX (F.IX) gene delivery was applied as a model for exploring mechanisms of tolerance induction during immune ontogeny. Intraperitoneal delivery of AAV8/ Factor IX (hF.IX) during weeks 1–4 of life, over a 20-fold dose range, directed stable hF.IX expression, correction of coagulopathy in F.IX-null hemophilia B mice, and induction of tolerance to hF.IX; however, only primary injection at 1–2 days of life enabled increasing AAV8-mediated hF.IX expression after re-administration, due to the absence of anti-viral capsid antibodies. Adoptive splenocyte transfer from tolerized mice demonstrated induction of CD4⁺CD25⁺ T regulatory (T_reg) populations that specifically suppressed anti-hF.IX antibody responses, but not responses to third party antigen. Induction of hF.IX antibodies was only observed in tolerized mice after in vivo CD4⁺CD25⁺ cell depletion and hF.IX challenge. Thus, primary injection of AAV during a critical period in the first week of life does not elicit antiviral responses, enabling re-administration of AAV and augmentation of hF.IX levels. Expansion of hF.IX-specific CD4⁺CD25⁺ T_regs has a major role in tolerance induction early in immune ontogeny. Neonatal gene transfer provides a useful approach for defining the ontogeny of immune responses and may suggest approaches for inducing tolerance in the context of genetic therapies.

Impact of age at administration, lysosomal storage, and transgene regulatory elements on AAV2/8-mediated rat liver transduction

Liver-directed gene transfer is being investigated for the treatment of systemic or liver-specific diseases. Recombinant vectors based on adeno-associated virus serotype 8 (AAV2/8) efficiently transduce liver cells allowing long term transgene expression after a single administration in animal models and in patients.We evaluated the impact on AAV2/8-mediated rat liver transduction of the following variables: i) age at vector administration, ii) presence of lysosomal storage in liver cells, and iii) regulatory elements included in the transgene expression cassette. We found that systemic administration of AAV2/8 to newborn rats results in vector genome dilution and reduced transduction efficacy when compared to adult injected animals, presumably due to hepatocyte proliferation. Accumulation of glycosaminoglycans in lysosomes does not impact on levels and distribution of AAV2/8-mediated liver transduction. Transgene expression occurs in hepatocytes but not in Kupffer or liver endothelial cells when the liver-specific thyroxine-binding-globulin promoter is used. However, extra-hepatic transduction is observed in the spleen and kidney of animals injected at birth. The use of target sequences for the hematopoietic-specific microRNA miR142-3p does not improve liver transduction efficacy neither reduce immune responses to the lysosomal enzyme arylsulfatase B. The inclusion of a variant of the Woodchuck hepatitis virus post-transcriptional regulatory element (WPRE-m) decreases AAV2/8-mediated liver transduction levels.As AAV2/8-mediated liver gene transfer is entering in the clinical arena, these data will provide relevant information to the design of efficient AAV2/8-based therapeutic strategies.

Stable human FIX expression after 0.9G intrauterine gene transfer of self-complementary adeno-associated viral vector 5 and 8 in macaques

Intrauterine gene transfer (IUGT) offers ontological advantages including immune naiveté mediating tolerance to the vector and transgenic products, and effecting a cure before development of irreversible pathology. Despite proof-of-principle in rodent models, expression efficacy with a therapeutic transgene has yet to be demonstrated in a preclinical nonhuman primate (NHP) model. We aimed to determine the efficacy of human Factor IX (hFIX) expression after adeno-associated-viral (AAV)-mediated IUGT in NHP. We injected 1.0-1.95 × 10(13) vector genomes (vg)/kg of self-complementary (sc) AAV5 and 8 with a LP1-driven hFIX transgene intravenously in 0.9G late gestation NHP fetuses, leading to widespread transduction with liver tropism. Liver-specific hFIX expression was stably maintained between 8 and 112% of normal activity in injected offspring followed up for 2-22 months. AAV8 induced higher hFIX expression (P = 0.005) and milder immune response than AAV5. Random hepatocellular integration was found with no hotspots. Transplacental spread led to low-level maternal tissue transduction, without evidence of immunotoxicity or germline transduction in maternal oocytes. A single intravenous injection of scAAV-LP1-hFIXco to NHP fetuses in late-gestation produced sustained clinically-relevant levels of hFIX with liver-specific expression and a non-neutralizing immune response. These data are encouraging for conditions where gene transfer has the potential to avert perinatal death and long-term irreversible sequelae.

Fetal gene therapy: recent advances and current challenges

INTRODUCTION

Fetal gene therapy (FGT) can potentially be applied to perinatally lethal monogenic diseases for rescuing clinically severe phenotypes, increasing the probability of intact neurological and other key functions at birth, or inducing immune tolerance to a transgenic protein to facilitate readministration of the vector/protein postnatally. As the field is still at an experimental stage, there are several important considerations regarding the practicality and the ethics of FGT.

AREAS COVERED

Here, through a review of FGT studies, the authors discuss the role and applications of FGT, the progress made with animal models that simulate human development, possible adverse effects in the recipient fetus and the mother and factors that affect clinical translation.

EXPERT OPINION

Although there are valid safety and ethical concerns, the authors argue that there may soon be enough convincing evidence from non-human primate models to take the next step towards clinical trials in the near future.

In vivo bioluminescent imaging (BLI): noninvasive visualization and interrogation of biological processes in living animals

In vivo bioluminescent imaging (BLI) is increasingly being utilized as a method for modern biological research. This process, which involves the noninvasive interrogation of living animals using light emitted from luciferase-expressing bioreporter cells, has been applied to study a wide range of biomolecular functions such as gene function, drug discovery and development, cellular trafficking, protein-protein interactions, and especially tumorigenesis, cancer treatment, and disease progression. This article will review the various bioreporter/biosensor integrations of BLI and discuss how BLI is being applied towards a new visual understanding of biological processes within the living organism.

Genetic modification of airway progenitors after lentiviral gene delivery to the amniotic fluid of murine fetuses

Lentiviral vectors with the firefly luciferase or enhanced green fluorescent protein (EGFP) transgenes were delivered to the amniotic fluid of murine fetuses at Embryonic Day (E) 14.5 or E16.5. Whole-body imaging of luciferase recipients after birth demonstrated transgene expression in the peritoneal and thoracic regions. Organ imaging showed luciferase expression in lung, skin, stomach, and/or intestine. Histological immunofluorescence analysis of EGFP recipients demonstrated that small clusters (≤ three cells) of EGFP-positive epithelial cells were present in the large and small airways of recipients at up to 7 months (n = 11). There was no difference in the frequency of transgene expression in mice injected at E14.5 or E16.5 in respiratory or nonrespiratory organs. Analysis of the bronchoalveolar duct junctions on tissue sections of recipient mice identified multiple EGFP-positive epithelial cells. Cells coexpressing EGFP, Clara cell 10-kd protein, and surfactant protein C (SPC) were also found in lungs, consistent with the transduction of bronchoalveolar stem cells. Next, naphthalene lung injury in both luciferase and EGFP recipients was performed to determine whether transduced cells could contribute to tissue repair. In luciferase recipients, the whole-body luciferase signal increased 2- to 20-fold at 2 weeks after naphthalene treatment. Remarkably, immunohistological analysis of the lungs of EGFP recipients after lung injury repair demonstrated repopulation of airways with long stretches of EGFP-positive epithelial cells (n = 4). Collectively, these data demonstrate that lentiviral gene delivery to the amniotic fluid of murine fetuses genetically modifies long-lived epithelial progenitors capable of contributing to lung injury repair.

Factors determining the risk of inadvertent retroviral transduction of male germ cells after in utero gene transfer in sheep

The possibility of permanent genetic changes to the germline is central to the bioethics of in utero gene therapy (IUGT) because of the concern of inadvertent potentially deleterious alterations to the gene pool. Despite presumed protection of the male germline due to early germ cell (GC) compartmentalization, we reported that GCs within the developing ovine testes are transduced at low levels after retrovirus-mediated IUGT, thus underscoring the need for a thorough understanding of GC development in clinically predictive models to determine the optimal time to perform IUGT and avoid germline modification. In the present studies, we used the fetal sheep model to analyze GCs for phenotype, location, proliferation, and incidence of transduction after IUGT at various fetal ages to learn when during development the nascent germline is likely to be at greatest risk of retrovirus-mediated alteration. Our studies show that although GCs were transduced at all injection ages, the levels of transduction varied by nearly 700-fold as a function of the age at transfer. After remaining largely quiescent as they migrated to/settled within nascent sex cords, GCs began active cycling before cord closure was complete, suggesting this is likely the point at which they would be most susceptible to retroviral transduction.Furthermore, we observed that compartmentalization of GCs continued into early postnatal life, suggesting the male germline may be vulnerable to low-level inadvertent retroviral vector modification throughout fetal life, but that this risk can be minimized by performing IUGT later in gestation.

Frequency and spectrum of genomic integration of recombinant adeno-associated virus serotype 8 vector in neonatal mouse liver

Neonatal injection of recombinant adeno-associated virus serotype 8 (rAAV8) vectors results in widespread transduction in multiple organs and therefore holds promise in neonatal gene therapy. On the other hand, insertional mutagenesis causing liver cancer has been implicated in rAAV-mediated neonatal gene transfer. Here, to better understand rAAV integration in neonatal livers, we investigated the frequency and spectrum of genomic integration of rAAV8 vectors in the liver following intraperitoneal injection of 2.0 x 10(11) vector genomes at birth. This dose was sufficient to transduce a majority of hepatocytes in the neonatal period. In the first approach, we injected mice with a beta-galactosidase-expressing vector at birth and quantified rAAV integration events by taking advantage of liver regeneration in a chronic hepatitis animal model and following partial hepatectomy. In the second approach, we performed a new, quantitative rAAV vector genome rescue assay by which we identified rAAV integration sites and quantified integrations. As a result, we find that at least approximately 0.05% of hepatocytes contained rAAV integration, while the average copy number of integrated double-stranded vector genome per cell in the liver was approximately 0.2, suggesting concatemer integration. Twenty-three of 34 integrations (68%) occurred in genes, but none of them were near the mir-341 locus, the common rAAV integration site found in mouse hepatocellular carcinoma. Thus, rAAV8 vector integration occurs preferentially in genes at a frequency of 1 in approximately 10(3) hepatocytes when a majority of hepatocytes are once transduced in the neonatal period. Further studies are warranted to elucidate the relationship between vector dose and integration frequency or spectrum.

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 for the fetus: is there a future?

Gene therapy uses the intracellular delivery of genetic material for the treatment of disease. A wide range of diseases - including cancer, vascular and neurodegenerative disorders and inherited genetic diseases - are being considered as targets for this therapy in adults. There are particular reasons why fetal application might prove better than application in the adult for treatment, or even prevention of early-onset genetic disorders such as cystic fibrosis and Duchenne muscular dystrophy. Research shows that gene transfer to the developing fetus targets rapidly expanding populations of stem cells, which are inaccessible after birth, and indicates that the use of integrating vector systems results in permanent gene transfer. In animal models of congenital disease such as haemophilia, studies show that the functionally immature fetal immune system does not respond to the product of the introduced gene, and therefore immune tolerance can be induced. This means that treatment could be repeated after birth, if that was necessary to continue to correct the disease. For clinicians and parents, fetal gene therapy would give a third choice following prenatal diagnosis of inherited disease, where termination of pregnancy or acceptance of an affected child are currently the only options. Application of this therapy in the fetus must be safe, reliable and cost-effective. Recent developments in the understanding of genetic disease, vector design, and minimally invasive delivery techniques have brought fetal gene therapy closer to clinical practice. However more research needs to be done in before it can be introduced as a therapy.

The impact of polyadenylation signals on plasmid nuclease-resistance and transgene expression

BACKGROUND

Efficient delivery and expression of plasmids (pDNA) is a major concern in gene therapy and DNA vaccination using non-viral vectors. Besides the use of adjuvants, the pDNA vector itself can be designed to maximize survival in nuclease-rich environments. Homopurine-rich tracts in polyadenylation sequences have been previously shown to be especially important in pDNA resistance.

METHODOLOGY

The effect of modifications in the poly A sequence of a model pDNA vector (pVAX1GFP) on nuclease resistance and transgene expression was investigated. Four poly A sequences were studied: bovine growth hormone (BGH), mutant BGH, SV40 and a synthetic poly A. Plasmid resistance (half-life) was assessed through in vitro incubations with mammalian nucleases. The impact in transgene expression was studied by quantifying pDNA, mRNA, and GFP expression in CHO, hybridoma and HeLa cells.

RESULTS AND CONCLUSIONS

In vitro and cell culture studies indicate that plasmids containing the SV40 and the synthetic poly A sequences present significant improvements in nuclease resistance (up to two-fold increase in half-life). However, RT-PCR analysis demonstrated that significant reduction in mRNA steady-state levels were responsible for a decrease in transgene expression and detected transfection level of CHO and hybridoma cells when using the more resistant plasmids. Interestingly, transfection of HeLa cells demonstrated that both poly A efficiency and plasmid resistance interfere significantly in transgene expression. The results strongly suggest that the choice of the poly A is important, not only for mRNA maturation/stability, but also for pDNA resistance, and should thus be taken into consideration in the design and evaluation of pDNA vectors.

Post-transcriptional regulatory element boosts baculovirus-mediated gene expression in vertebrate cells

Baculoviruses can express transgenes in a wide range of vertebrate cells. However, in some cells transgene expression is weak. To enhance transgene expression, we studied the effect of the Woodchuck hepatitis virus post-transcriptional regulatory element (WPRE) on baculovirus (BV)-mediated gene expression of several transgenes. A significant increase in BV-mediated gene expression was detected in several cell lines. A 10-fold increase in transgene expression was observed with the WPRE as determined by the percentage of positive cells and mean fluorescence intensity (MFI). Furthermore, a combination of optimized cell culture medium and WPRE virus led to more than a 60-fold increase in gene expression. In accordance, elevated mRNA and protein levels were detected in WPRE-virus transduced cells. In HepG2 and RaaSMC, WPRE-mediated enhancement was comparable to the previously shown positive effect of sodium butyrate on BV-mediated gene expression. Thus, inclusion of the WPRE into a baculovirus vector provides a simple means to improve BV-mediated gene expression in vertebrate cells.

Molecular imaging of novel cell- and viral-based therapies

Drugs, surgery, and radiation are the traditional modalities of therapy in medicine. To these are being added new therapies based on cells and viruses or their derivatives. In these novel therapies, a cell or viral vector acts as a drug in its own right, altering the host or a disease process to bring about healing. Most of these advances originate from the significant recent advances in molecular medicine, but some have been around for some time. Blood transfusions and cowpox vaccinations are part of the history of medicine...but nevertheless are examples of cell- and viral-based therapies. This article focuses on the modern molecular incarnations of these therapies, and specifically on how imaging is used to track and guide these novel agents. We survey the literature dealing with imaging these new cell and viral particle therapies and provide a framework for understanding publications in this area. Leading technology of gene modifications are the fundamental modifications applied to make these new therapies amenable to imaging.

Utility of intraperitoneal administration as a route of AAV serotype 5 vector-mediated neonatal gene transfer

BACKGROUND

Gene transfer into a fetus or neonate can be a fundamental approach for treating genetic diseases, particularly disorders that have irreversible manifestations in adulthood. Although the potential utility of this technique has been suggested, the advantages of neonatal gene transfer have not been widely investigated. Here, we tested the usefulness of neonatal gene transfer using adeno-associated virus (AAV) vectors by comparing the administration routes and vector doses.

METHODS

To determine the optimal administration route, neonates were subjected to intravenous (i.v.) or intraperitoneal (i.p.) injections of AAV5-based vectors encoding the human coagulation factor IX (hfIX) gene, and the dose response was examined. To determine the distribution of transgene expression, vectors encoding lacZ or luciferase (luc) genes were used and assessed by X-gal staining and in vivo imaging, respectively. After the observation period, the vector distribution across tissues was quantified.

RESULTS

The factor IX concentration was higher in i.p.-injected mice than in i.v.-injected mice. All transgenes administered by i.p. injection were more efficiently expressed in neonates than in adults. The expression was confined to the peritoneal tissue. Interestingly, a sex-related difference was observed in transgene expression in adults, whereas this difference was not apparent in neonates.

CONCLUSIONS

AAV vector administration to neonates using the i.p. route was clearly advantageous in obtaining robust transgene expression. Vector genomes and transgene expression were observed mainly in the peritoneal tissue. These findings indicate the advantages of neonatal gene therapy and would help in designing strategies for gene therapy using AAV vectors.

AAV serotype-1 mediates early onset of gene expression in mouse hearts and results in better therapeutic effect

Adeno-associated viral vectors (AAV) are attractive tool for gene therapy for coronary artery disease. However, gene expression in myocardium mediated by AAV serotype 2 (AAV2) does not peak until 4-6 weeks after gene transfer. This delayed gene expression may reduce its therapeutic potential for acute cardiac infarction. To determine whether earlier gene expression and better therapeutic effect could be achieved using a different serotype, CMV promoter driving the EPO gene (AAV-EPO) was packaged into AAV serotypes 1-5 capsids and injected into mouse myocardium. EPO expression was studied by measuring the hematocrits and EPO mRNA. After we found that AAV1 mediates the highest gene expression after 4 days of gene transduction, AAV-LacZ (CMV promoter driving LacZ gene expression) and MLCVEGF (hypoxia-inducible and cardiac-specific VEGF expression) were packaged into AAV1 and 2 capsids. LacZ expression was detected in AAV1-LacZ but not in AAV2-LacZ-injected hearts 1 day after vector injection. Compared to AAV2-MLCVEGF that mediated no significant VEGF expression, AAV1-MLCVEGF mediated 13.7-fold induction of VEGF expression in ischemic hearts 4 days after gene transduction and resulted in more neovasculatures, better cardiac function and less myocardial fibrosis. Thus, AAV1 mediates earlier and higher transgene expression in myocardium and better therapeutic effects.

Robust systemic transduction with AAV9 vectors in mice: efficient global cardiac gene transfer superior to that of AAV8

It has been recently shown that recombinant adeno-associated virus serotype 8 (rAAV8) is a robust alternative serotype vector that overcomes many of the limitations of rAAV2 and transduces various tissues efficiently and globally through systemic vector administration. AAV9 is a serotype newly isolated from human tissues, but our knowledge of the biology of rAAV9 in vivo is currently limited. Here, we demonstrate by a series of comprehensive side-by-side experiments with rAAV8 and 9 vectors delivered via different routes or at various doses in mice that rAAV9 vectors share the robustness of rAAV8, i.e., (1) very high liver transduction efficiency irrespective of whether vectors are administered intravascularly or extravascularly and (2) substantial transduction in the heart, skeletal muscle, and pancreas by peripheral vein injection. Importantly, rAAV9 transduced myocardium 5- to 10-fold higher than rAAV8, resulting in over 80% cardiomyocyte transduction following tail vein injection of as low as 1.0 x 10(11) particles per mouse. Thus rAAV9, as well as rAAV8, is a robust vector for gene therapy applications and rAAV9 is superior to rAAV8 specifically for cardiac gene delivery by systemic vector administration.

Gene Therapy Progress and Prospects – Vectorology: design and production of expression cassettes in AAV vectors

Adeno-associated virus (AAV) derived vectors are considered highly eligible vehicles for human gene therapy. Not only do they possess many great potential for clinical applications due to their wide range of tissue targets but also their excellent preclinical safety profile makes them particularly suitable candidates for treating serious diseases. Initial clinical trials have yielded encouraging results and prompted further improvements in their design and methods of production. Many studies have been performed to modify the tropism of recombinant (r)AAV by capsid modification. However, the precise control of spatial and temporal gene expression, which may be important in determining the safety and efficacy of gene transfer, lies in a rational choice and a subtle combination of various regulatory genetic elements to be inserted into the expression cassette. Moreover, new strategies based on such genetic sequences open new perspectives for enhancing vector genome persistence, disrupting or reducing pathogenic gene expression and even targeting genes.

Different Osteogenic Potentials of Recombinant Human BMP-6 Adeno-Associated Virus and Adenovirus in Two Rat Strains

The osteogenic potential of AAV5hBMP6 was compared with that of ADhBMP6 in immunodeficient and immunocompetent rats. AAV5hBMP6 (2.3 x 10(12) particles) and ADhBMP6 (5 x 10(7) PFU) elicited viral antibody production in immunocompetent rats. Among rats that received AAV5hBMP6, the earliest time points at which the bone was visible under CT scanner were 30 days in 2-month-old Sprague-Dawley (SD) rats and 60 days in 18-month-old SD rats. The mean volumes of ectopic bone 90 days after viral injection were 0.31 +/- 0.14 cm(3) in athymic nude rats, 0.64 +/- 0.12 cm(3) in 2-month-old SD rats, and 0.21 +/- 0.10 cm(3) in 18-month-old SD rats. In contrast, among rats that received ADhBMP6, the earliest time points to observe the bone formation by CT scan were 15 days in 2-month-old rats and no bone formation in 18-month-old SD rats. The mean volumes of ectopic bone were 4.17 +/- 0.05 cm(3) in athymic nude rats and 0.06 +/- 0.03 cm(3) in 2-month-old SD rats. Although both types of viruses induced an immune response in immunocompetent animals, this response played different roles in the process of bone formation induced by the BMP6 vectors.

Fetal gene transfer using lentiviral vectors and the potential for germ cell transduction in rhesus monkeys (Macaca mulatta)

Genetic modification of germ cells in somatic gene therapy protocols is a concern, particularly with fetal approaches. This study focused on the potential for germ cell gene transfer post-fetal gene delivery using a human immunodeficiency virus type 1 (HIV-1)-derived lentiviral vector pseudotyped with the vesicular stomatitis virus-glycoprotein (VSV-G). Rhesus monkey fetuses (n = 47) were administered vector supernatant (10(7) infectious particles per fetus) via the intraperitoneal (IP), intrapulmonary (Ipu), or intracardiac routes (Ica) under ultrasound guidance. Tissue harvests were performed near term or 3 months postnatal age, and genomic DNA obtained to analyze for vector sequences from collected sections of gonads and gonadal cells obtained by laser capture microdissection (germ cells, stroma, epithelium). Results indicated no evidence of germ cell gene transfer in fetuses or infants with Ipu or Ica routes of administration. However, evidence of the transgene (1.33 +/- 0.78 enhanced green fluorescent protein [EGFP] copies per copy epsilon-globin) was found in females, but not males, when using the IP administration approach (p < 0.05). The highest EGFP copies were detected on the surface epithelium (p < 0.05). The results of these studies suggest that the HIV-1-derived lentiviral vector pseudotyped with VSV-G may transduce a subpopulation of gonadal cells in female fetuses with IP administration, whereas no evidence of gene transfer was shown to occur in males or with organ-targeting approaches.

In utero gene therapy: current challenges and perspectives

Over the past few years, considerable progress in prenatal diagnosis and surgery combined with improvements in vector design vindicate a reappraisal of the feasibility of in utero gene therapy for serious monogenetic diseases. As adult gene therapy gathers pace, several apparent obstacles to its application as a treatment may be overcome by pre- or early postnatal treatment. This review will examine the concepts and practice of prenatal vector administration. We aim to highlight the advantages of early therapeutic intervention focusing on diseases that could benefit greatly from a prenatal gene therapy approach. We will pay special attention to the strategies and vectors that are most likely to be used for this application and will speculate on their expected developments for the near future.

Unrestricted hepatocyte transduction with adeno-associated virus serotype 8 vectors in mice

Recombinant adeno-associated virus (rAAV) vectors can mediate long-term stable transduction in various target tissues. However, with rAAV serotype 2 (rAAV2) vectors, liver transduction is confined to only a small portion of hepatocytes even after administration of extremely high vector doses. In order to investigate whether rAAV vectors of other serotypes exhibit similar restricted liver transduction, we performed a dose-response study by injecting mice with beta-galactosidase-expressing rAAV1 and rAAV8 vectors via the portal vein. The rAAV1 vector showed a blunted dose-response similar to that of rAAV2 at high doses, while the rAAV8 vector dose-response remained unchanged at any dose and ultimately could transduce all the hepatocytes at a dose of 7.2 x 10(12) vector genomes/mouse without toxicity. This indicates that all hepatocytes have the ability to process incoming single-stranded vector genomes into duplex DNA. A single tail vein injection of the rAAV8 vector was as efficient as portal vein injection at any dose. In addition, intravascular administration of the rAAV8 vector at a high dose transduced all the skeletal muscles throughout the body, including the diaphragm, the entire cardiac muscle, and substantial numbers of cells in the pancreas, smooth muscles, and brain. Thus, rAAV8 is a robust vector for gene transfer to the liver and provides a promising research tool for delivering genes to various target organs. In addition, the rAAV8 vector may offer a potential therapeutic agent for various diseases affecting nonhepatic tissues, but great caution is required for vector spillover and tight control of tissue-specific gene expression.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Characterization of Coelenterazine Analogs for Measurements of Renilla Luciferase Activity in Live Cells and Living Animals

In vivo imaging of bioluminescent reporters relies on expression of light-emitting enzymes, luciferases, and delivery of chemical substrates to expressing cells. Coelenterazine (CLZN) is the substrate for a group of bioluminescent enzymes obtained from marine organisms. At present, there are more than 10 commercially available CLZN analogs. To determine which analog is most suitable for activity measurements in live cells and living animals, we characterized 10 CLZN analogs using Renilla luciferase (Rluc) as the reporter enzyme. For each analog, we monitored enzyme activity, auto-oxidation, and efficiency of cellular uptake. All CLZN analogs tested showed higher auto-oxidation signals in serum than was observed in phosphate buffer or medium, mainly as a result of auto-oxidation by binding to albumin. CLZN-f, -h, and -e analogs showed 4- to 8-fold greater Rluc activity, relative to CLZN-native, in cells expressing the enzyme from a stable integrant. In studies using living mice expressing Rluc in hepatocytes, administration of CLZN-e and -native produced the highest signal. Furthermore, distinct temporal differences in signal for each analog were revealed following intravenous or intraperitoneal delivery. We conclude that the CLZN analogs that are presently available vary with respect to hRluc utilization in culture and in vivo, and that the effective use of CLZN-utilizing enzymes in living animals depends on the selection of an appropriate substrate.