Adeno-associated virus-binding antibodies detected in cats living in the Northeastern United States lack neutralizing activity

Durable contraception in the female domestic cat using viral-vectored delivery of a feline anti-Müllerian hormone transgene

Eighty percent of the estimated 600 million domestic cats in the world are free-roaming. These cats typically experience suboptimal welfare and inflict high levels of predation on wildlife. Additionally, euthanasia of healthy animals in overpopulated shelters raises ethical considerations. While surgical sterilization is the mainstay of pet population control, there is a need for efficient, safe, and cost-effective permanent contraception alternatives. Herein, we report evidence that a single intramuscular treatment with an adeno-associated viral vector delivering an anti-Müllerian hormone transgene produces long-term contraception in the domestic cat. Treated females are followed for over two years, during which transgene expression, anti-transgene antibodies, and reproductive hormones are monitored. Mating behavior and reproductive success are measured during two mating studies. Here we show that ectopic expression of anti-Müllerian hormone does not impair sex steroids nor estrous cycling, but prevents breeding-induced ovulation, resulting in safe and durable contraception in the female domestic cat.

Biodistribution of Adeno-Associated Virus Gene Therapy Following Cerebrospinal Fluid-Directed Administration

Adeno-associated virus (AAV)-based gene therapies, exemplified by the approved therapy for spinal muscular atrophy, have the potential to deliver disease-course-altering treatments for central nervous system (CNS) indications. However, several clinical trials have reported severe adverse events, including patient deaths following high-dose systemic administration for muscle-directed gene transfer, highlighting the need to explore approaches utilizing lower doses when targeting the CNS. Animal models of disease provide insight into the response to new AAV therapies. However, translation from small to larger animals and eventually to humans is hampered by anatomical and biological differences across the species and their impact on AAV delivery. We performed a literature review of preclinical studies of AAV gene therapy biodistribution following cerebrospinal fluid (CSF) delivery (intracerebroventricular, intra-cisterna magna, and intrathecal lumbar). The reviewed literature varies greatly in the reported biodistribution of AAV following administration into the CSF. Differences between studies, including animal model, vector serotype used, method used to assess biodistribution, and route of administration, among other variables, contribute to differing outcomes and difficulties in translating these preclinical results. For example, only half of the published AAV-based gene therapy studies report vector copy number, the most direct readout following administration of a vector; none of these studies reported details such as the empty:full capsid ratio and quality of encapsidated genome. Analysis of the last decade's literature focusing on AAV-based gene therapies targeting the CNS underscores limitations of the body of knowledge and room for continued research. In particular, there is a need to understand the biodistribution achieved by different CSF-directed routes of administration and determining if specific cell types/structures of interest will be transduced. Our findings point to a clear need for a more systematic approach across the field to align the assessments and elements reported in preclinical research to enable more reliable translation across animal models and into human studies.

Preexisting Neutralizing Antibodies against Different Adeno-Associated Virus Serotypes in Humans and Large Animal Models for Gene Therapy

Gene therapy is a potential cure for several inherited retinal dystrophies, and adeno-associated virus (AAV) has emerged as a vector of choice for therapeutic gene delivery to the retina. However, prior exposure to AAVs can cause a humoral immune response resulting in the presence of antibodies in the serum, which can subsequently interfere with the AAV-mediated gene therapy. The antibodies bind specifically to a serotype but often display broad cross-reactivity. A subset of these antibodies called neutralizing antibodies (NABs) can render the AAV inactive, thereby reducing the efficacy of the therapy. The preexisting NAB levels against different serotypes vary by species, and these variations need to be considered while designing studies. Since large animals often serve as preclinical models to test gene therapies, in this review we compile studies reporting preexisting NABs against commonly used AAV serotypes in humans and large animal models and discuss strategies to deal with NABs.

[Prokaryotic expression of a recombinant protein of adeno-associated virus capsid conserved regions and preparation of its polyclonal antibody]

OBJECTIVE

To express and purify the antigenic peptide of adeno-associated virus (AAV) capsid conserved regions in prokaryotic cells and prepare its rabbit polyclonal antibody.

METHODS

The DNA sequence encoding the conserved regions of AAV capsid protein was synthesized and cloned into the vector pET30a to obtain the plasmid pET30a-AAV-CR for prokaryotic expression and purification of the conserved peptides. Coomassie blue staining and Western blotting were used to identify the AAV conserved peptides. Japanese big ear white rabbits were immunized with AAV conserved region protein to prepare polyclonal antibody, with the rabbits injected with PBS as the control group. The antibody titer was determined with ELISA, and the performance of the antibody for recognizing capsid protein sequences of AAV1-AAV10 was assessed with Western blotting and immunofluorescence assay.

RESULTS

The plasmid pET30a-AAV-CR was successfully constructed, and a recombinant protein with a relative molecular mass of 17000 was obtained. The purified protein induced the production of antibodies against the conserved regions of AAV capsid in rabbits, and the titer of the purified antibodies reached 1:320 000. The antibodies were capable of recognizing a wide range of capsid protein sequences of AAV1-AAV10.

CONCLUSION

We successfully obtained the polyclonal antibodies against AAV capsid conserved region protein from rabbits, which facilitate future studies of AAV vector development and the biological functions of AAV.

Adeno-Associated Viruses (AAV) and Host Immunity - A Race Between the Hare and the Hedgehog

Adeno-associated viruses (AAV) have emerged as the lead vector in clinical trials and form the basis for several approved gene therapies for human diseases, mainly owing to their ability to sustain robust and long-term in vivo transgene expression, their amenability to genetic engineering of cargo and capsid, as well as their moderate toxicity and immunogenicity. Still, recent reports of fatalities in a clinical trial for a neuromuscular disease, although linked to an exceptionally high vector dose, have raised new caution about the safety of recombinant AAVs. Moreover, concerns linger about the presence of pre-existing anti-AAV antibodies in the human population, which precludes a significant percentage of patients from receiving, and benefitting from, AAV gene therapies. These concerns are exacerbated by observations of cellular immune responses and other adverse events, including detrimental off-target transgene expression in dorsal root ganglia. Here, we provide an update on our knowledge of the immunological and molecular race between AAV (the “hedgehog”) and its human host (the “hare”), together with a compendium of state-of-the-art technologies which provide an advantage to AAV and which, thus, promise safer and more broadly applicable AAV gene therapies in the future.

Adeno-Associated Vector-Delivered CRISPR/SaCas9 System Reduces Feline Leukemia Virus Production In Vitro

Feline leukemia virus (FeLV) is a retrovirus of cats worldwide. High viral loads are associated with progressive infection and the death of the host, due to FeLV-associated disease. In contrast, low viral loads, an effective immune response, and a better clinical outcome can be observed in cats with regressive infection. We hypothesize that by lowering viral loads in progressively infected cats, using CRISPR/SaCas9-assisted gene therapy, the cat’s immune system may be permitted to direct the infection towards a regressive outcome. In a step towards this goal, the present study evaluates different adeno-associated vectors (AAVs) for their competence in delivering a gene editing system into feline cells, followed by investigations of the CRISPR/SaCas9 targeting efficiency for different sites within the FeLV provirus. Nine natural AAV serotypes, two AAV hybrid strains, and Anc80L65, an in silico predicted AAV ancestor, were tested for their potential to infect different feline cell lines and feline primary cells. AAV-DJ revealed superior infection efficiency and was thus employed in subsequent transduction experiments. The introduction of double-strand breaks, using the CRISPR/SaCas9 system targeting 12 selected FeLV provirus sites, was confirmed by T7 endonuclease 1 (T7E1), as well as Tracking of Indels by Decomposition (TIDE) analysis. The highest percentage (up to 80%) of nonhomologous end-joining (NHEJ) was found in the highly conserved gag and pol regions. Subsequent transduction experiments, using AAV-DJ, confirmed indel formation and showed a significant reduction in FeLV p27 antigen for some targets. The targeting of the FeLV provirus was efficient when using the CRISPR/SaCas9 approach in vitro. Whether the observed extent of provirus targeting will be sufficient to provide progressively FeLV-infected cats with the means to overcome the infection needs to be further investigated in vivo.