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

Liver lobe-specific hydrodynamic gene delivery to baboons: A preclinical trial for hemophilia gene therapy

Hydrodynamics-based gene transfer has been successfully employed for in vivo gene delivery to the liver of small animals by tail vein injection and of large animals using a computer-assisted and image-guided protocol. In an effort to develop a hydrodynamic gene delivery procedure clinically applicable for gene therapy, we have evaluated the safety and effectiveness of a lobe-specific hydrodynamic delivery procedure for hepatic gene delivery in baboons. Reporter plasmid was used to assess the gene delivery efficiency of the lobe-specific hydrodynamic gene delivery, and plasmid-carrying human factor IX gene was used to examine the pattern of long-term gene expression. The results demonstrated liver lobe-specific gene delivery, therapeutic levels of human factor IX gene expression lasting for >100 days, and the efficacy of repeated hydrodynamic gene delivery into the same liver lobes. Other than a transient increase in blood concentration of liver enzymes right after the injection, no significant adverse events were observed in animals during the study period. The results obtained from this first non-human primate study support the clinical applicability of the procedure for lobe-specific hydrodynamic gene delivery to liver.

Autologous bone marrow-derived MSCs engineered to express oFVIII-FLAG engraft in adult sheep and produce an effective increase in plasma FVIII levels

Introduction

Hemophilia A (HA) is the most common X-linked bleeding disorder, occurring in 1 in 5,000 live male births and affecting >1 million individuals worldwide. Although advances in protein-based HA therapeutics have improved health outcomes, current standard-of-care requires infusion 2-3 times per week for life, and 30% of patients develop inhibitors, significantly increasing morbidity and mortality. There are thus unmet medical needs requiring novel approaches to treat HA.

Methods

We tested, in a highly translational large animal (sheep) model, whether the unique immunological and biological properties of autologous bone marrow (BM)-derived mesenchymal stromal cells (MSCs) could enable them to serve as cellular delivery vehicles to provide long-term expression of FVIII, avoiding the need for frequent infusions.

Results

We show that autologous BM-MSCs can be isolated, transduced with a lentivector to produce high levels of ovine (o)FVIII, extensively expanded, and transplanted into adult animals safely. The transplanted cells engraft in multiple organs, and they stably produce and secrete sufficient quantities of FVIII to yield elevated plasma FVIII levels for at least 15 weeks.

Discussion

These studies thus highlight the promise of cellular-based gene delivery approaches for treating HA.

A simple adeno-associated virus-based approach for the generation of cardiac genetic models in rats

Background: Heart failure is a major health problem and progress in this field relies on better understanding of the mechanisms and development of novel therapeutics using animal models. The rat may be preferable to the mouse as a cardiovascular disease model due to its closer physiology to humans and due to its large size that facilitates surgical and monitoring procedures. However, unlike the mouse, genetic manipulation of the rat genome is challenging. Methods: Here we developed a simple, refined, and robust cardiac-specific rat transgenic model based on an adeno-associated virus (AAV) 9 containing a cardiac troponin T promoter. This model uses a single intraperitoneal injection of AAV and does not require special expertise or equipment. Results: We characterize the AAV dose required to achieve a high cardiac specific level of expression of a transgene in the rat heart using a single intraperitoneal injection to neonates. We show that at this AAV dose GFP expression does not result in hypertrophy, a change in cardiac function or other evidence for toxicity. Conclusions: The model shown here allows easy and fast transgenic based disease modeling of cardiovascular disease in the rat heart, and can also potentially be expanded to deliver Cas9 and gRNAs or to deliver small hairpin (sh)RNAs to also achieve gene knockouts and knockdown in the rat heart.

Generation of light-producing somatic-transgenic mice using adeno-associated virus vectors

We have previously designed a library of lentiviral vectors to generate somatic-transgenic rodents to monitor signalling pathways in diseased organs using whole-body bioluminescence imaging, in conscious, freely moving rodents. We have now expanded this technology to adeno-associated viral vectors. We first explored bio-distribution by assessing GFP expression after neonatal intravenous delivery of AAV8. We observed widespread gene expression in, central and peripheral nervous system, liver, kidney and skeletal muscle. Next, we selected a constitutive SFFV promoter and NFκB binding sequence for bioluminescence and biosensor evaluation. An intravenous injection of AAV8 containing firefly luciferase and eGFP under transcriptional control of either element resulted in strong and persistent widespread luciferase expression. A single dose of LPS-induced a 10-fold increase in luciferase expression in AAV8-NFκB mice and immunohistochemistry revealed GFP expression in cells of astrocytic and neuronal morphology. Importantly, whole-body bioluminescence persisted up to 240 days. We have validated a novel biosensor technology in an AAV system by using an NFκB response element and revealed its potential to monitor signalling pathway in a non-invasive manner in a model of LPS-induced inflammation. This technology complements existing germline-transgenic models and may be applicable to other rodent disease models.

Neonatal Gene Therapy for Hemophilia B by a Novel Adenovirus Vector Showing Reduced Leaky Expression of Viral Genes

Gene therapy during neonatal and infant stages is a promising approach for hemophilia B, a congenital disorder caused by deficiency of blood coagulation factor IX (FIX). An adenovirus (Ad) vector has high potential for use in neonatal or infant gene therapy for hemophilia B due to its superior transduction properties; however, leaky expression of Ad genes often reduces the transduction efficiencies by Ad protein-mediated tissue damage. Here, we used a novel Ad vector, Ad-E4-122aT, which exhibits a reduction in the leaky expression of Ad genes in liver, in gene therapy studies for neonatal hemophilia B mice. Ad-E4-122aT exhibited significantly higher transduction efficiencies than a conventional Ad vector in neonatal mice. In neonatal hemophilia B mice, a single neonatal injection of Ad-E4-122aT expressing human FIX (hFIX) (Ad-E4-122aT-AHAFIX) maintained more than 6% of the normal plasma hFIX activity levels for approximately 100 days. Sequential administration of Ad-E4-122aT-AHAFIX resulted in more than 100% of the plasma hFIX activity levels for more than 100 days and rescued the bleeding phenotypes of hemophilia B mice. In addition, immunotolerance to hFIX was induced by Ad-E4-122aT-AHAFIX administration in neonatal hemophilia B mice. These results indicated that Ad-E4-122aT is a promising gene delivery vector for neonatal or infant gene therapy for hemophilia B.

Co-delivery of indoleamine 2,3-dioxygenase prevents loss of expression of an antigenic transgene in dystrophic mouse muscles

A significant problem affecting gene therapy approaches aiming at achieving long-term transgene expression is the immune response against the protein product of the therapeutic gene, which can reduce or eliminate the therapeutic effect. The problem is further exacerbated when therapy involves targeting an immunogenic tissue and/or one with a pre-existing inflammatory phenotype, such as dystrophic muscles. In this proof-of-principle study, we co-expressed a model antigen, bacterial β-galactosidase, with an immunosuppressive factor, indoleamine 2,3-dioxygenase 1 (IDO1), in muscles of the mdx mouse model of Duchenne muscular dystrophy. This treatment prevented loss of expression of the transgene concomitant with significantly elevated expression of T-regulatory (Treg) markers in the IDO1-expressing muscles. Moreover, co-expression of IDO1 resulted in reduced serum levels of anti-β-gal antibodies. These data indicate that co-expression of genes encoding immunomodulatory enzymes controlling kynurenine pathways provide a viable strategy for preventing loss of transgenes targeted into dystrophic muscles with pre-existing inflammation.

Evidence for contribution of CD4+ CD25+ regulatory T cells in maintaining immune tolerance to human factor IX following perinatal adenovirus vector delivery

Following fetal or neonatal gene transfer in mice and other species immune tolerance of the transgenic protein is frequently observed; however the underlying mechanisms remain largely undefined. In this study fetal and neonatal BALB/c mice received adenovirus vector to deliver human factor IX (hFIX) cDNA. The long-term tolerance of hFIX was robust in the face of immune challenge with hFIX protein and adjuvant but was eliminated by simultaneous administration of anti-CD25+ antibody. Naive irradiated BALB/c mice which had received lymphocytes from donors immunised with hFIX developed anti-hFIX antibodies upon immune challenge. Cotransplantation with CD4+CD25+ cells isolated from neonatally tolerized donors decreased the antibody response. In contrast, cotransplantation with CD4+CD25- cells isolated from the same donors increased the antibody response. These data provide evidence that immune tolerance following perinatal gene transfer is maintained by a CD4+CD25+ regulatory population.

Development of Gene Transfer for Induction of Antigen-specific Tolerance

Gene replacement therapies, like organ and cell transplantation are likely to introduce neo-antigens that elicit rejection via humoral and/or effector T cell immune responses. Nonetheless, thanks to an ever growing body of pre-clinical studies it is now well accepted that gene transfer protocols can be specifically designed and optimized for induction of antigen-specific immune tolerance. One approach is to specifically express a gene in a tissue with a tolerogenic microenvironment such as the liver or thymus. Another strategy is to transfer a particular gene into hematopoietic stem cells or immunological precursor cells thus educating the immune system to recognize the therapeutic protein as "self". In addition, expression of the therapeutic protein in pro-tolerogenic antigen presenting cells such as immature dendritic cells and B cells has proven to be promising. All three approaches have successfully prevented unwanted immune responses in pre-clinical studies aimed at the treatment of inherited protein deficiencies, e.g. lysosomal storage disorders and hemophilia, and of type I diabetes and multiple sclerosis. In this review we focus on current gene transfer protocols that induce tolerance, including gene delivery vehicles and target tissues, and discuss successes and obstacles in different disease models.

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.

Hepatic gene transfer in neonatal mice by adeno-associated virus serotype 8 vector

For genetic diseases that manifest at a young age with irreversible consequences, early treatment is critical and essential. Neonatal gene therapy has the advantages of achieving therapeutic effects before disease manifestation, a low vector requirement and high vector-to-cell ratio, and a relatively immature immune system. Therapeutic effects or long-term rescue of neonatal lethality have been demonstrated in several animal models. However, vigorous cell proliferation in the newborn stage is a significant challenge for nonintegrating vectors, such as adeno-associated viral (AAV) vector. Slightly delaying the injection age, and readministration at a later time, are two of the alternative strategies to solve this problem. In this study, we demonstrated robust and efficient hepatic gene transfer by self-complementary AAV8 vector in neonatal mice. However, transduction quickly decreased over a few weeks because of vector dilution caused by fast proliferation. Delaying the injection age improved sustained expression, although it also increased neutralizing antibody (NAb) responses to AAV capsid. This approach can be used to treat genetic diseases with slow progression. For genetic diseases with early onset and severe consequences, early treatment is essential. A second injection of vector of a different serotype at a later time may overcome preexisting NAb and achieve sustained therapeutic effects.

AAV-based neonatal gene therapy for hemophilia A: long-term correction and avoidance of immune responses in mice

Hemophilia A gene therapy has been hampered by immune responses to vector-associated antigens and by neutralizing antibodies or inhibitors to the factor VIII (FVIII) protein; these ‘inhibitors’ more commonly effect hemophilia A patients than those with hemophilia B. A gene replacement strategy beginning in the neonatal period may avoid the development of these immune responses and lead to prolonged expression with correction of phenotype thereby avoiding long-term consequences. Serotype rh10 AAV was developed splitting the FVIII coding sequence into heavy and light chains with the chicken β-actin promoter/CMV enhancer for dual recombinant AAV vector delivery. Coinjection of virions of each FVIII chain intravenously to mice on the second day of life was performed. Mice express sustained FVIII antigen levels of ≥5% to 22 months of life without the development of antibodies to FVIII. Phenotypic correction was manifest in all AAV-FVIII-treated mice as demonstrated by functional assay and reduction in bleeding time. This study demonstrates the use of AAV in a gene replacement strategy in neonatal mice that establishes both long-term phenotypic correction of hemophilia A and lack of antibody development to FVIII in this disease model where AAV is administered shortly after birth. These studies support consideration of gene replacement therapy for diseases that are diagnosed in utero or in the early neonatal period.

Muscle-directed gene therapy for hemophilia B with more efficient and less immunogenic AAV vectors

BACKGROUND

Adeno-associated viral vector (AAV)-mediated and muscle-directed gene therapy is a safe and non-invasive approach to treatment of hemophilia B and other genetic diseases. However, low efficiency of transduction, inhibitor formation and high prevalence of pre-existing immunity to the AAV capsid in humans remain as main challenges for AAV2-based vectors using this strategy. Vectors packaged with AAV7, 8 and 9 serotypes have improved gene transfer efficiencies and may provide potential alternatives to overcome these problems.

OBJECTIVE

To compare the long-term expression of canine factor IX (cFIX) levels and anti-cFIX antibody responses following intramuscular injection of vectors packaged with AAV1, 2, 5, 7, 8 and 9 capsid in immunocompetent hemophilia B mice.

RESULTS

Highest expression was detected in mice injected with AAV2/8 vector (28% of normal), followed by AAV2/9 (15%) and AAV2/7 (10%). cFIX expression by AAV2/1 only ranged from 0 to 5% of normal levels. High incidences of anti-cFIX inhibitor (IgG) were detected in mice injected with AAV2 and 2/5 vectors, followed by AAV2/1. None of the mice treated with AAV2/7, 2/8 and 2/9 developed inhibitors or capsid T cells.

CONCLUSIONS

AAV7, 8 and 9 are more efficient and safer vectors for muscle-directed gene therapy with high levels of transgene expression and absence of inhibitor formation. The absence of antibody response to transgene by AAV7, 8 and 9 is independent of vector dose but may be due to the fact that these three serotypes are associated with high level distribution to, and transduction of, hepatocytes following i.m. injection.

Perinatal gene transfer to the liver

The liver acts as a host to many functions hence raising the possibility that any one may be compromised by a single gene defect. Inherited or de novo mutations in these genes may result in relatively mild diseases or be so devastating that death within the first weeks or months of life is inevitable. Some diseases can be managed using conventional medicines whereas others are, as yet, untreatable. In this review we consider the application of early intervention gene therapy in neonatal and fetal preclinical studies. We appraise the tools of this technology, including lentivirus, adenovirus and adeno-associated virus (AAV)-based vectors. We highlight the application of these for a range of diseases including hemophilia, urea cycle disorders such as ornithine transcarbamylase deficiency, organic acidemias, lysosomal storage diseases including mucopolysaccharidoses, glycogen storage diseases and bile metabolism. We conclude by assessing the advantages and disadvantages associated with fetal and neonatal liver gene transfer.

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.

Improved induction of immune tolerance to factor IX by hepatic AAV-8 gene transfer

Gene therapy for hemophilia B has been shown to result in long-term expression and immune tolerance to factor IX (F.IX) after in vivo transduction of hepatocytes with adeno-associated viral (AAV-2) vectors in experimental animals. An optimized protocol was effective in several strains of mice with a factor 9 gene deletion (F9(-/-)). However, immune responses against F.IX were repeatedly observed in C3H/HeJ F9(-/-) mice. We sought to establish a gene transfer protocol that results in sustained expression without a requirement for additional manipulation of the immune system. Compared with AAV-2, AAV-8 was more efficient in transgene expression and induction of tolerance to F.IX in three different strains of wild-type mice. At equal vector doses, AAV-8 induced transgene product-specific regulatory CD4(+)CD25(+)FoxP3(+) T cells at significantly higher frequency. Moreover, sustained correction of hemophilia B in C3H/HeJ F9(-/-) mice without antibody formation was documented in all animals treated with > or =4 x 10(11) vector genomes (VG)/kg and in 80% of mice treated with 8 x 10(10) VG/kg. Therefore, it is possible to develop a gene transfer protocol that reliably induces tolerance to F.IX largely independent of genetic factors. A comparison with other studies suggests that additional parameters besides plateau levels of F.IX expression contributed to the improved success rate of tolerance induction.

Hepatic gene transfer as a means of tolerance induction to transgene products

The liver is a preferred target organ for gene therapy not only for liver-specific diseases but also for disorders that require systemic delivery of a protein. Diseases that could benefit from hepatic gene transfer include hemophilia, metabolic disorders, lysosomal storage disorders, and others. For a successful delivery of the transgene and sustained expression, the protocol must avoid immune responses in order to be efficacious. A growing number of studies have demonstrated that liver-directed transfer can induce transgene product-specific immune tolerance. Tolerance obtained via this route requires optimal engineering of the vector to eliminate transgene expression in antigen presenting cells while restricting high levels of therapeutic expression to hepatocytes. Innate immune responses may prevent tolerance induction, cause toxicity, and have to be minimized. Discussed in our review is the crucial role of CD4(+)CD25(+) regulatory T cells in tolerance to the hepatocyte-derived gene product, the immunobiology of the liver and our current understanding of its tolerogenic properties, current and proposed research as to the mechanisms behind the liver's unique cellular environment, as well as development of the tools for tolerance induction such as advanced vector systems.

The EBV-encoded dUTPase activates NF-kappa B through the TLR2 and MyD88-dependent signaling pathway

The innate immune response plays a key role as the primary host defense against invading pathogens including viruses. We have previously shown that treatment of human monocyte-derived macrophages with EBV-encoded dUTPase induces the expression of proinflammatory cytokines through the activation of NF-kappaB. However, the receptor responsible for EBV-encoded dUTPase-mediated biological effects is not known. In this study, we demonstrate that the purified EBV-encoded dUTPase activates NF-kappaB in a dose-dependent manner through TLR2 and requires the recruitment of the adaptor molecule MyD88 but not CD14. Furthermore, activation of NF-kappaB was abrogated by anti-TLR2, anti-EBV-encoded dUTPase blocking Abs and the overexpression of a dominant negative construct of MyD88 in human embryonic kidney 293 cells expressing TLR2. In addition, treatment of human monocyte-derived macrophages with the anti-EBV-encoded dUTPase Ab 7D6 or the anti-TLR2 Ab blocked the production of IL-6 by the EBV-encoded dUTPase. To our knowledge, this is the first report demonstrating that a nonstructural protein encoded by EBV is a pathogen-associated molecular pattern and that it has immunomodulatory functions. Although additional studies are necessary to define the signaling pathways activated by the EBV-encoded dUTPase and to determine its role in modulating immune responses to EBV infection, our results suggest that the dUTPase could be a potential target for the development of novel therapeutic agents against infections caused by EBV.

Muscle as a target for supplementary factor IX gene transfer

Immune responses to the factor IX (F.IX) transgene product are a concern in gene therapy for the X-linked bleeding disorder hemophilia B. The risk for such responses is determined by several factors, including the vector, target tissue, and others. Previously, we have demonstrated that hepatic gene transfer with adeno-associated viral (AAV) vectors can induce F.IX-specific immune tolerance. Muscle-derived F.IX expression, however, is limited by a local immune response. Here, skeletal muscle was investigated as a target for supplemental gene transfer. Given the low invasiveness of intramuscular injections, this route would be ideal for secondary gene transfer, thereby boosting levels of transgene expression. However, this is feasible only if immune tolerance established by compartmentalization of expression to the liver extends to other sites. Immune tolerance to human F.IX established by prior hepatic AAV-2 gene transfer was maintained after subsequent injection of AAV-1 or adenoviral vector into skeletal muscle, and tolerized mice failed to form antibodies or an interferon (IFN)-gamma(+) T cell response to human F.IX. A sustained increase in systemic transgene expression was obtained for AAV-1, whereas an increase after adenoviral gene transfer was transient. A CD8(+) T cell response specifically against adenovirus-transduced fibers was observed, suggesting that cytotoxic T cell responses against viral antigens were sufficient to eliminate expression in muscle. In summary, the data demonstrate that supplemental F.IX gene transfer to skeletal muscle does not break tolerance achieved by liver-derived expression. The approach is efficacious, if the vector for muscle gene transfer does not express immunogenic viral proteins.

Gene therapy for treatment of inherited haematological disorders

Gene therapy, a molecular medicine based on vector-mediated transfer of therapeutic genes, holds promise for a cure of monogenetic inherited diseases. In recent years, tremendous progress has been reported in the treatment of haematological disorders: clinical trials in severe combined immune deficiencies have been successful by using retroviral vectors to express target genes in haematopoietic stem cells, which after transplantation efficiently reconstituted the immune system concomitant with substantial improvement in the clinical status of patients. Conversely, unexpected adverse events were also encountered. In other work, progress towards clinical studies on ex vivo gene transfer for Fanconi anaemia and haemoglobinopathies has been made. Each approach features a unique treatment strategy and also faces various impediments to success. In the case of the X-linked bleeding disorder haemophilia, several Phase I/II clinical trials were conducted, including in vivo administration of viral vectors to skeletal muscle and liver. Adeno-associated viral gene transfer of coagulation Factor IX has been documented in human subjects, reaching therapeutic levels after infusion into a hepatic blood vessel. However, sustained expression of therapeutic levels (as shown in large animal models of haemophilia) has not yet been achieved in humans. In general, long-term follow-up will be important for assessment of the safety of all existing gene therapy strategies.

High expression reduces an antibody response after neonatal gene therapy with B domain-deleted human factor VIII in mice

BACKGROUND

Gene therapy could prevent bleeding in patients with hemophilia A, but might induce antibodies that block factor VIII (FVIII) function.

OBJECTIVES

To test the efficacy of gene therapy in the newborn period for preventing a response to human FVIII (hFVIII) because of immaturity of the immune system.

METHODS

Varying doses of a retroviral vector (RV) expressing a B domain-deleted hFVIII cDNA were injected i.v. into newborn hemophilia A C57BL/6 or normal C3H mice. Mice were evaluated for hFVIII expression, hemostasis, and development of anti-hFVIII antibodies with inhibitory activity.

RESULTS AND CONCLUSIONS

Injection of a high RV dose [10(10) transducing units (TU) kg(-1)] into newborn hemophilia A or C3H mice resulted in 61% and 13% of normal hFVIII antigen in plasma, respectively; most mice did not produce anti-hFVIII antibodies, and hemophilia A mice did not bleed. Furthermore, most mice with >20 ng mL(-1) of hFVIII in plasma (10% normal, 1 x 10(-10) m) were tolerant to hFVIII, as an antibody response was markedly reduced after challenge with hFVIII with or without adjuvant. However, most RV-treated animals with lower antigen levels developed antibodies before or after challenge. Thus, initiation of a gene therapy trial with low RV doses might increase inhibitor formation. Furthermore, frequent hFVIII infusions in newborns with hemophilia A might reduce inhibitor formation. Finally, difficulties in achieving tolerance after gene therapy for hemophilia A as compared to hemophilia B may relate to lower expression of FVIII than FIX, as high antigen levels are most effective at inducing tolerance.

Induction and role of regulatory CD4+CD25+ T cells in tolerance to the transgene product following hepatic in vivo gene transfer

Gene replacement therapy is complicated by the risk of an immune response against the therapeutic transgene product, which in part is determined by the route of vector administration. Our previous studies demonstrated induction of immune tolerance to coagulation factor IX (FIX) by hepatic adeno-associated viral (AAV) gene transfer. Using a regulatory T-cell (T(reg))-deficient model (Rag-2(-/-) mice transgenic for ovalbumin-specific T-cell receptor DO11.10), we provide first definitive evidence for induction of transgene product-specific CD4(+)CD25(+) T(regs) by in vivo gene transfer. Hepatic gene transfer-induced T(regs) express FoxP3, GITR, and CTLA4, and suppress CD4(+)CD25(-) T cells. T(regs) are detected as early as 2 weeks after gene transfer, and increase in frequency in thymus and secondary lymphoid organs during the following 2 months. Similarly, adoptive lymphocyte transfers from mice tolerized to human FIX by hepatic AAV gene transfer indicate induction of CD4(+)CD25(+)GITR(+) that suppresses antibody formation to FIX. Moreover, in vivo depletion of CD4(+)CD25(+) T(regs) leads to antibody formation to the FIX transgene product after hepatic gene transfer, which strongly suggests that these regulatory cells are required for tolerance induction. Our study reveals a crucial role of CD4(+)CD25(+) T(regs) in preventing immune responses to the transgene product in gene transfer.

Improvements in mucopolysaccharidosis I mice after adult retroviral vector-mediated gene therapy with immunomodulation

Mucopolysaccharidosis I (MPS I) is caused by deficient alpha-L-iduronidase (IDUA) activity and results in the accumulation of glycosaminoglycans and multisystemic disease. Gene therapy could program cells to secrete mannose 6-phosphate-modified IDUA, and enzyme in blood could be taken up by other cells. Neonatal retroviral vector (RV)-mediated gene therapy has been shown to reduce the manifestations of murine MPS I; however, intravenous injection of RV into adults was ineffective owing to a cytotoxic T lymphocyte (CTL) response against transduced cells. In this study, prolonged inhibition of CD28 signaling with CTLA4-Ig, or transient administration of CTLA4-Ig with an anti-CD40 ligand antibody or with an anti-CD4 antibody, resulted in stable expression in most mice that received RV as adults. Mice with stable expression had 81 +/- 41U/ml IDUA activity in serum. This resulted in reductions in bone disease, improvements in hearing and vision, and reductions in biochemical and pathological evidence of lysosomal storage in most organs. Improvements in brain were likely due to diffusion of enzyme from blood. However, aortic disease was refractory to treatment. This demonstrates that most manifestations of MPS I can be prevented using adult gene therapy if an immune response is blocked.

Immune response after neonatal transfer of a human factor IX-expressing retroviral vector in dogs, cats, and mice

INTRODUCTION

Gene therapy could prevent bleeding in hemophilia. However, antibodies could inhibit coagulation, while cytotoxic T lymphocytes could destroy modified cells. The immaturity of the newborn immune system might prevent these immune responses from occurring after neonatal gene therapy.

MATERIALS AND METHODS

Newborn dogs, cats, or mice were injected intravenously with a retroviral vector expressing human Factor IX. Plasma was evaluated for antigen and anti-human Factor IX antibodies. Cytotoxic T lymphocyte responses were evaluated indirectly by analysis of retroviral vector RNA in liver. Lymphocytes were evaluated for cytokine secretion and the ability to suppress an immune response to human Factor IX in mice.

RESULTS AND CONCLUSIONS

Hemophilia B dogs that achieved 942+/-500 ng/ml (19% normal) or 5+/-0.4 ng/ml (0.1% normal) of human Factor IX in plasma only bled 0 or 1.2 times per year, respectively, and were tolerant to infusion of human Factor IX. Normal cats expressed human Factor IX at 118+/-29 ng/ml (2% normal) in plasma without antibody formation. However, plasma human Factor IX disappeared at late times in 1 of 4 cats, which was probably due to a cytotoxic T lymphocyte response that destroyed cells with high expression. C3H mice were tolerant to human Factor IX after neonatal gene therapy, which may involve clonal deletion of human Factor IX-responsive cells. These data demonstrate that neonatal gene therapy does not induce antibodies to human Factor IX in dogs, cats, or mice. The putative cytotoxic T lymphocyte response in one cat requires further study.

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.

Unresolved issues in diagnosis and management of inherited bleeding disorders in the perinatal period: A White Paper of the Perinatal Task Force of the Medical and Scientific Advisory Council of the National Hemophilia Foundation, USA

Haemophilia and inherited bleeding disorders in newborns and their carrier mothers pose unique challenges. The pattern of bleeding and the causes and risk factors for bleeding are decidedly different than an older child or an adult with haemophilia/inherited bleeding disorder. This document outlines the needs for further research and education, summarizes the state of the art background information and provides guidance regarding research, education and access to care issues in this population.

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

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

Immune deviation by mucosal antigen administration suppresses gene-transfer-induced inhibitor formation to factor IX

Formation of inhibitory antibodies is a serious complication of protein or gene replacement therapy for hemophilias, congenital X-linked bleeding disorders. In hemophilia B (coagulation factor IX [F.IX] deficiency), lack of endogenous F.IX antigen expression and other genetic factors may increase the risk of antibody formation to functional F.IX. Here, we developed a protocol for reducing inhibitor formation in gene therapy by prior mucosal (intranasal) administration of a peptide representing a human F.IX-specific CD4(+) T-cell epitope in hemophilia B mice. C3H/HeJ mice with a F.IX gene deletion produced inhibitory IgG to human F.IX after hepatic gene transfer with an adeno-associated viral vector. These animals subsequently lost systemic F.IX expression. In contrast, repeated intranasal administration of the specific peptide resulted in reduced inhibitor formation, sustained circulating F.IX levels, and sustained partial correction of coagulation following hepatic gene transfer. This was achieved through immune deviation to a T-helper-cell response with increased IL-10 and TGF-beta production and activation of regulatory CD4(+)CD25(+) T cells.

Optimal haemophilia care versus the reality

Haemophilia A and B are inherited bleeding disorders whose diagnosis and management is generally well established and best provided by specialists in a comprehensive care setting. Patients may be put at unnecessary risk if appropriate expertise is not sought for the management of accidents and surgery. The delivery of a high quality comprehensive service to patients with bleeding disorders depends upon defined standards and a network of haemophilia centres in the UK with similar models in other countries. In developing countries, despite a shortage or absence of treatment products, development of local expertise results in an improved outlook and reduction in mortality. Optimal care for severe haemophilia includes accurate diagnosis, early and adequate factor replacement for bleeding episodes and the provision of prophylaxis from an early age to prevent joint bleeding and the consequent arthropathy. Haemophilia treatment is expensive resulting in considerable inequity in provision of care across the world. Despite decades of experience, optimal treatment levels are not robustly defined. Transfusion-transmitted infections continue to have a significant impact on patient management. The development of inhibitory antibodies seriously complicates the management both in morbidity and cost. While gene therapy has not yet produced the hoped-for cure, new technologies will produce improved products.

Sustained FVIII expression and phenotypic correction of hemophilia A in neonatal mice using an endothelial-targeted sleeping beauty transposon

Hemophilia A, deficiency of coagulation factor VIII (FVIII), is an attractive candidate for gene therapy as expression of modest amounts of FVIII can provide therapeutic benefit. Most gene transfer approaches for hemophilia have focused on the liver, as this is the major source of endogenous FVIII; however, increasing evidence suggests that endothelial cells are capable of synthesis and release of FVIII. Here the Sleeping Beauty (SB) transposon is employed to target long-term expression of the human B-domain-depleted FVIII gene (approved gene symbol F8) within lung endothelia of hemophilic mice. As the formation of inhibitory antibodies to FVIII has been a significant impediment toward achieving therapeutic plasma levels after gene or protein therapy, we chose to perform gene transfer in neonatal mice, which are more likely to be immune tolerant. Using this approach, low therapeutic levels of FVIII ( approximately 10%), as well as phenotypic correction of the bleeding disorder, were achieved in all animals that received the FVIII transposon and functional transposase throughout the duration of the study (24 weeks). Rechallenge of these animals with additional gene transfer did not result in significant increases in FVIII levels, due mainly to increases in inhibitory antibodies. These studies demonstrate the feasibility of using endothelial-targeted SB transposons for the treatment of hemophilia A.

Tolerance induction by viral in vivo gene transfer

Treatment of genetic disease by protein or gene replacement therapy is hampered by immune responses to the therapeutic protein. An excellent example is formation of inhibitory antibodies to coagulation factors in treatment of the X-linked bleeding disorder hemophilia. Experiments in murine and canine models of hemophilia B (deficiency in factor IX) have demonstrated sustained therapeutic levels of factor IX transgene expression following hepatic adeno-associated viral gene transfer in animals with deletion and nonsense mutations in the factor IX gene. This article reviews experimental evidence for induction of immune tolerance to the factor IX transgene product by hepatic adeno-associated viral gene transfer, which has been shown to limit T helper cell responses and to substantially reduce the risk of antibody responses. Tolerance induction is associated with activation of regulatory CD4(+) T cells capable of suppressing antibody formation to factor IX protein. Hepatic administration of adeno-associated viral vector expressing ovalbumin in mice transgenic for a T cell receptor specific for this antigen provided direct evidence for induction of CD4(+) T cell tolerance, including T cell anergy and clonal deletion. Taken together, these data indicate the potential for viral in vivo gene transfer not only to provide sustained systemic expression, but moreover to induce immunological hypo-responsiveness to the therapeutic gene product.

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.

Liver-directed neonatal gene therapy prevents cardiac, bone, ear, and eye disease in mucopolysaccharidosis I mice

Mucopolysaccharidosis I (MPS I) due to deficient alpha-L-iduronidase (IDUA) activity results in accumulation of glycosaminoglycans in many cells. Gene therapy could program liver to secrete enzyme with mannose 6-phosphate (M6P), and enzyme in blood could be taken up by other cells via the M6P receptor. Newborn MPS I mice were injected with 10(9) (high dose) or 10(8) (low dose) transducing units/kg of a retroviral vector (RV) expressing canine IDUA. Most animals achieved stable expression of IDUA in serum at 1240 +/- 147 and 110 +/- 31 units/ml, respectively. At 8 months, untreated MPS I mice had aortic insufficiency, increased bone mineral density (BMD), and reduced responses to sound and light. In contrast, MPS I mice that received high-dose RV had normal echocardiograms, BMD, auditory-evoked brain-stem responses, and electroretinograms. This is the first report of complete correction of these clinical manifestations in any model of mucopolysaccharidosis. Biochemical and pathologic evaluation confirmed that storage was reduced in these organs. Mice that received low-dose RV and achieved 30 units/ml of serum IDUA activity had no or only partial improvement. We conclude that high-dose neonatal gene therapy with an RV reduces some major clinical manifestations of MPS I in mice, but low dose is less effective.

Absence of a desmopressin response after therapeutic expression of factor VIII in hemophilia A dogs with liver-directed neonatal gene therapy

Hemophilia A (HA) is a bleeding disorder caused by factor VIII (FVIII) deficiency. FVIII replacement therapy can reduce bleeding but is expensive, inconvenient, and complicated by development of antibodies that inhibit FVIII activity in 30% of patients. Neonatal hepatic gene therapy could result in continuous secretion of FVIII into blood and might reduce immunological responses. Newborn HA mice and dogs that were injected i.v. with a retroviral vector (RV) expressing canine B domain-deleted FVIII (cFVIII) achieved plasma cFVIII activity that was 139 +/- 22% and 116 +/- 5% of values found in normal dogs, respectively, which was stable for 1.5 yr. Coagulation tests were normalized, no bleeding had occurred, and no inhibitors were detected. This is a demonstration of long-term fully therapeutic gene therapy for HA in a large animal model. Desmopressin (DDAVP; 1-deamino-[d-Arg(8)]vasopressin) is a drug that increases FVIII activity by inducing release of FVIII complexed with von Willebrand factor from endothelial cells. It has been unclear, however, if the FVIII is synthesized by endothelial cells or is taken up from blood. Because the plasma cFVIII in these RV-treated dogs derives primarily from transduced hepatocytes, they provided a unique opportunity to study the biology of the DDAVP response. Here we show that DDAVP did not increase plasma cFVIII levels in the RV-treated dogs, although von Willebrand factor was increased appropriately. This result suggests that the increase in FVIII in normal dogs after DDAVP is due to release of FVIII synthesized by endothelial cells.

Fetal and neonatal gene therapy: benefits and pitfalls

The current approaches to gene therapy of monogenetic diseases into mature organisms are confronted with several problems including the following: (1) the underlying genetic defect may have already caused irreversible pathological changes; (2) the level of sufficient protein expression to ameliorate or prevent the disease requires prohibitively large amounts of gene delivery vector; (3) adult tissues may be poorly infected by conventional vector systems dependent upon cellular proliferation for optimal infection, for example, oncoretrovirus vectors; (4) immune responses, either pre-existing or developing following vector delivery, may rapidly eliminate transgenic protein expression and prevent future effective intervention. Early gene transfer, in the neonatal or even fetal period, may overcome some or all of these obstacles. The mammalian fetus enjoys a uniquely protected environment in the womb, bathed in a biochemically and physically supportive fluid devoid of myriad extra-uterine pathogens. Strong physical and chemical barriers to infection might, perhaps, impede the frenetic cell division. The physical support and the biochemical support provided by the fetal-maternal placental interface may, therefore, minimize the onset of genetic diseases manifest early in life. The fetal organism must prepare itself for birth, but lacking a mature adaptive immune system may depend upon more primordial immune defences. It is the nature of these defences, and the vulnerabilities they protect, that are poorly understood in the context of gene therapy and might provide useful information for approaches to gene therapy in the young, as well as perhaps the mature organism.