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

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

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

Viral Infections and Male Infertility: A Comprehensive Review of the Role of Oxidative Stress

Viral infections have been a part of human existence to date, though viruses have posed a huge threat with various outbreaks lately. These threats are associated with reproductive health challenges, especially male infertility. The prime focus of this review is to highlight the mechanisms associated with viral infection-induced male infertility/subfertility and identify new treatment strategies with the aim to preserve male fertility. The reviewed data showed that viral infections stimulate inflammatory responses, resulting in the release of proinflammatory cytokines, which induces oxidative stress. This oxido-inflammatory cycle could continue in a vicious cycle and threaten male fertility. Existing data from human and experimental studies show that viral infection-induced oxido-inflammatory response results in testicular damage, atrophy of the seminiferous tubules and Sertoli cells, and reduced Leydig cell mass. This is accompanied by reduced circulatory testosterone, impaired spermatogenesis, reduced sperm motility, lipid peroxidation, DNA fragmentation and apoptosis of the sperm cells. Based on the available pieces of evidence, antioxidant therapy, in vivo and in vitro, may be beneficial and protects against the potential risk of male infertility from viral infection. It is, however recommended that more clinical studies be conducted to demonstrate the possible protective roles of antioxidants used as adjuvant therapy in viral infections, and in the in vitro treatment of semen samples for those utilizing semen washing and artificial reproductive techniques.

Infectivity of adeno-associated virus serotypes in mouse testis

Background

Recombinant adeno-associated viruses (AAVs) are emerging as favoured transgene delivery vectors for both research applications and gene therapy. In this context, a thorough investigation of the potential of various AAV serotypes to transduce specific cell types is valuable. Here, we rigorously tested the infectivity of a number of AAV serotypes in murine testis by direct testicular injection.

Results

We report the tropism of serotypes AAV2, 5, 8, 9 and AAVrh10 in mouse testis. We reveal unique infectivity of AAV2 and AAV9, which preferentially target intertubular testosterone-producing Leydig cells. Remarkably, AAV2 TM, a mutant for capsid designed to increase transduction, displayed a dramatic alteration in tropism; it infiltrated seminiferous tubules unlike wildtype AAV2 and transduced Sertoli cells. However, none of the AAVs tested infected spermatogonial cells.

Conclusions

In spite of direct testicular injection, none of the tested AAVs appeared to infect sperm progenitors as assayed by reporter expression. This lends support to the current view that AAVs are safe gene-therapy vehicles. However, testing the presence of rAAV genomic DNA in germ cells is necessary to assess the risk of individual serotypes.

Electronic supplementary material

The online version of this article (10.1186/s12896-018-0479-1) contains supplementary material, which is available to authorized users.

Deliverable transgenics & gene therapy possibilities for the testes

Male infertility and hypogonadism are clinically prevalent conditions with a high socioeconomic burden and are both linked to an increased risk in cardiovascular-metabolic diseases and earlier mortality. Therefore, there is an urgent need to better understand the causes and develop new treatments for these conditions that affect millions of men. The accelerating advancement in gene editing and delivery technologies promises improvements in both diagnosis as well as affording the opportunity to develop bespoke treatment options which would both prove beneficial for the millions of individuals afflicted with these reproductive disorders. In this review, we summarise the systems developed and utilised for the delivery of gene therapy and discuss how each of these systems could be applied for the development of a gene therapy system in the testis and how they could be of use for the future diagnosis and repair of common male reproductive disorders.

Non-clinical Safety and Efficacy of an AAV2/8 Vector Administered Intravenously for Treatment of Mucopolysaccharidosis Type VI

In vivo gene therapy with adeno-associated viral (AAV) vectors is safe and effective in humans. We recently demonstrated that AAV8-mediated liver gene transfer is effective in animal models of mucopolysaccharidosis type VI (MPS VI), a rare lysosomal storage disease that is caused by arylsulfatase B (ARSB) deficiency. In preparing for a first-in-human trial, we performed non-clinical studies to assess the safety of intravenous administrations of AAV2/8.TBG.hARSB produced under good manufacturing practice-like conditions. No toxicity was observed in AAV-treated mice, except for a transient increase in alanine aminotransferase in females and thyroid epithelial hypertrophy. AAV2/8.TBG.hARSB biodistribution and expression confirmed the liver as the main site of both infection and transduction. Shedding and breeding studies suggest that the risk of both horizontal and germline transmission is minimal. An AAV dose-response study in MPS VI mice was performed to define the range of doses to be used in the clinical study. Overall, these data support the non-clinical safety and efficacy of AAV2/8.TBG.hARSB and pave the way for a phase I/II clinical trial based on intravascular infusions of AAV8 in patients with MPS VI.

Risks, benefits and ethical, legal, and societal considerations for translation of prenatal gene therapy to human application

The still experimental nature of prenatal gene therapy carries a certain degree of risk, both for the pregnant mother as well as for the fetus. Some of the risks are procedural hazards already known from more conventional fetal medicine interventions. Others are more specific to gene therapy such as the potential for interference with normal fetal development, the possibility of inadvertent germ line gene transfer, and the danger of oncogenesis. This chapter reviews the potential risks in relation to the expected benefits of prenatal gene therapy. It discusses the scientific, ethical, legal, and social implications of this novel preventive approach to genetic disease and outlines preconditions to be met in preparation for a potential future clinical application.

Detection of EPO gene doping in blood

Gene doping--or the abuse of gene therapy--will continue to threaten the sports world. History has shown that progress in medical research is likely to be abused in order to enhance human performance. In this review, we critically discuss the progress and the risks associated with the field of erythropoietin (EPO) gene therapy and its applicability to EPO gene doping. We present typical vector systems that are employed in ex vivo and in vivo gene therapy trials. Due to associated risks, gene doping is not a feasible alternative to conventional EPO or blood doping at this time. Nevertheless, it is well described that about half of the elite athlete population is in principle willing to risk its health to gain a competitive advantage. This includes the use of technologies that lack safety approval. Sophisticated detection approaches are a prerequisite for prevention of unapproved and uncontrolled use of gene therapy technology. In this review, we present current detection approaches for EPO gene doping, with a focus on blood-based direct and indirect approaches. Gene doping is detectable in principle, and recent DNA-based detection strategies enable long-term detection of transgenic DNA (tDNA) following in vivo gene transfer.

Widespread endogenization of densoviruses and parvoviruses in animal and human genomes

Parvoviruses infect humans and a broad range of animals, from mammals to crustaceans, and generally are associated with a variety of acute and chronic diseases. However, many others cause persistent infections and are not known to be associated with any disease. Viral persistence is likely related to the ability to integrate into the chromosomal DNA and to establish a latent infection. However, there is little evidence for genome integration of parvoviral DNA except for Adeno-associated virus (AAV). Here we performed a systematic search for homologs of parvoviral proteins in publicly available eukaryotic genome databases followed by experimental verification and phylogenetic analysis. We conclude that parvoviruses have frequently invaded the germ lines of diverse animal species, including mammals, fishes, birds, tunicates, arthropods, and flatworms. The identification of orthologous endogenous parvovirus sequences in the genomes of humans and other mammals suggests that parvoviruses have coexisted with mammals for at least 98 million years. Furthermore, some of the endogenized parvoviral genes were expressed in eukaryotic organisms, suggesting that these viral genes are also functional in the host genomes. Our findings may provide novel insights into parvovirus biology, host interactions, and evolution.

Protective effect of recombinant adeno-associated virus 2/8-mediated gene therapy from the maternal hyperphenylalaninemia in offsprings of a mouse model of phenylketonuria

Phenylketonuria (PKU) is an autosomal recessively inherited metabolic disorder caused by a deficiency of phenylalanine hydroxylase (PAH). The accumulation of phenylalanine leads to severe mental and psychomotor retardation, and the fetus of an uncontrolled pregnant female patient presents with maternal PKU syndrome. We have reported previously on the cognitive outcome of biochemical and phenotypic reversal of PKU in a mouse model, Pahenu2, by the AAV serotype 2-mediated gene delivery of a human PAH transgene. However, the therapeutic efficacy had been limited to only male PKU mice. In this study, we generated a pseudotyped recombinant AAV2/8-hPAH vector and infused it into female PKU mice through the hepatic portal vein or tail vein. Two weeks after injection, complete fur color change to black was observed in female PKU, as in males. The PAH activity in the liver increased to 65-70% of the wild-type activity in female PKU mice and to 90% in male PKU mice. Plasma phenylalanine concentration in female PKU mice decreased to the normal value. In addition, the offsprings of the treated female PKU mice can rescue from the harmful effect of maternal hyperphenylalaninemia. These results indicate that recombinant AAV2/8-mediated gene therapy is a potential therapeutic strategy for PKU.

Correction of murine PKU following AAV-mediated intramuscular expression of a complete phenylalanine hydroxylating system

Phenylketonuria (PKU) caused by phenylalanine hydroxylase (PAH) deficiency leads to toxic accumulation of phenylalanine (Phe). PAH is predominantly expressed in liver and its activity requires a supply of tetrahydrobiopterin (BH(4)) cofactor, but we propose that expression of a complete Phe hydroxylating system (PAH plus BH(4) synthetic enzymes) in skeletal muscle will lead to therapeutic reduction of blood Phe levels in Pah(enu2) mice, a model of human PKU. In order to test this hypothesis, we first developed transgenic Pah(enu2) mice that lack liver PAH activity but coexpress, in their skeletal muscle, PAH and guanosine triphosphate cyclohydrolase I (GTPCH). The latter is responsible for the committing enzymatic step in BH(4) biosynthesis. Despite sufficient muscle enzyme expression, these mice remained hyperphenylalaninemic, thereby suggesting that expression of additional BH(4) synthetic enzymes would be necessary. A recombinant triple-cistronic adeno-associated virus-2 (AAV2) pseudotype 1 vector expressing PAH along with GTPCH and 6-pyruvoyltetrahydrobiopterin synthase (PTPS), the next step in BH(4) synthesis, was generated. Injection of this vector into the gastrocnemius muscles of Pah(enu2) mice led to stable and long-term reduction of blood Phe and reversal of PKU-associated coat hypopigmentation. We propose that muscle-directed gene therapy will be a viable alternative treatment approach to PKU and other inborn errors of metabolism.

Adeno‐associated virus (AAV)‐mediated transduction of male germ line stem cells results in transgene transmission after germ cell transplantation

We explored whether exposure of mammalian germ line stem cells to adeno-associated virus (AAV), a gene therapy vector, would lead to stable transduction and transgene transmission. Mouse germ cells harvested from experimentally induced cryptorchid donor testes were exposed in vitro to AAV vectors carrying a GFP transgene and transplanted to germ cell-depleted syngeneic recipient testes, resulting in colonization of the recipient testes by transgenic donor cells. Mating of recipient males to wild-type females yielded 10% transgenic offspring. To broaden the approach to nonrodent species, AAV-transduced germ cells from goats were transplanted to recipient males in which endogenous germ cells had been depleted by fractionated testicular irradiation. Transgenic germ cells colonized recipient testes and produced transgenic sperm. When semen was used for in vitro fertilization (IVF), 10% of embryos were transgenic. Here, we report for the first time that AAV-mediated transduction of mammalian germ cells leads to transmission of the transgene through the male germ line. Equally important, this is also the first report of transgenesis via germ cell transplantation in a nonrodent species, a promising approach to generate transgenic large animal models for biomedical research.

Evaluation of prenatal intra-amniotic LAMB3 gene delivery in a mouse model of Herlitz disease

Prenatal gene therapy has been considered for Herlitz junctional epidermolysis bullosa (H-JEB), a lethal genodermatosis caused by the absence of any of the three subunits of laminin-5, resulting from birth in widespread blistering and erosions of skin and mucosae. To investigate this strategy in an animal model, adenovirus type 5- and adeno-associated virus (AAV) type 2-derived vectors carrying a beta-galactosidase reporter gene or LAMB3 cDNA encoding the beta3 chain of laminin-5 were generated, tested for stability in amniotic fluid and evaluated in vitro on murine H-JEB keratinocytes, and in vivo by prenatal injection into the amniotic cavities of laminin-5 beta3-deficient mice. The different vectors were administered individually or combined at maximum doses on day 14 post coitum. Adenoviral vectors infected preferentially the foetal epidermis, whereas AAV delivered the transgene mainly to mucous membranes of the airways and the upper digestive tract. The LAMB3 transgene was expressed in target epithelia of newborn laminin-5 beta3-deficient mice, and the transgenic beta3 chain was shown to assemble with its endogenous partner chains, resulting in detectable amounts of laminin-5 in the basement membranes of skin and mucosae and in a lower extent of tissue separation in the skin. However, only combined delivery of the two vector types led to a minor increase of the life span of H-JEB mice. Failure to rescue diseased animals was, at least in part, due to abandonment of any conspicuous pup by the heterozygous mother. This is the first study of a prenatal gene therapy approach to a heritable blistering disorder. Although our findings indicate that prenatal combined administration of adenoviral and adeno-associated LAMB3 vectors provides therapeutic benefit to H-JEB mice, this animal model appears unsuitable for long-term investigations of the therapeutic concept.

Inadvertent Germline Transmission of AAV2 Vector: Findings in a Rabbit Model Correlate with Those in a Human Clinical Trial

The risk of germline transmission of vector sequences in humans is a major safety concern, because the enrollment of subjects of reproductive age in early-phase clinical trials of gene transfer continues to increase. In a study of adult men with hemophilia B, adeno-associated virus serotype 2 (AAV2) delivered to the liver via the hepatic artery resulted in unexpected transient vector dissemination to the semen. Here we report that intravenous AAV2 injection in rabbits proved a useful model to assess biologic parameters of vector dissemination to the semen. Detectable vector sequences in semen disappeared in a dose-dependent and time-dependent fashion. AAV infectious particles were present only as long as day 4 after injection and were undetectable thereafter. The kinetics of vector clearance was faster in the semen fractions enriched for motile sperm than in the total semen. In addition, increased frequency of semen sampling accelerated the clearance of vector sequences from semen. Long-term follow-up, spanning hundreds of spermatogenesis cycles, showed that there was no recurrence of detectable vector sequences in semen, thus reducing the probability of inadvertent transduction of early spermatogonia not committed to differentiation at the time of vector injection. We conclude that AAV2 presents minimal germline transmission risk for humans.

Genetic correction of the fetal brain increases the lifespan of mice with the severe multisystemic disease mucopolysaccharidosis type VII

Neurogenetic diseases typically have globally distributed lesions, and pathology usually develops early in life, requiring early diagnosis and treatment. We investigated the effects of transferring a corrective gene into the fetal brain before the onset of pathology in the mucopolysaccharidosis (MPS) type VII mouse, a model of a lysosomal storage disease. A single adeno-associated virus serotype 1 vector injection into the ventricle at 15.5 days of gestation resulted in widespread distribution and lifelong expression of the normal gene in the brain and spinal cord. The normal enzyme was distributed to neighboring cells (as expected) and completely prevented the development of storage lesions throughout the central nervous system (CNS). No vector transfer was found outside the CNS, including the gonads, but a small amount of enzyme was present in visceral tissues, consistent with transfer from cerebrospinal fluid to venous circulation. The enzyme was present peripherally in such low amounts that it did not result in the severe skeletal dysmorphology that occurs readily when systemic treatment is used in neonates. However, the survival probability of the treated animals was significantly increased. The results suggest that the nervous system disease may contribute to the overall physiologic health of the animal in this type of disease.