AAVs Anatomy: Roadmap for Optimizing Vectors for Translational Success
Angela M. Mitchell, Sarah C. Nicolson, Jayme K. Warischalk and R. Jude Samulski
Affiliation: UNC Gene Therapy Center, University of North Carolina at Chapel Hill, 7119 Thurston Bowles Building, (104 Manning Drive), Campus Box 7352, Chapel Hill, NC 27599- 7352; USA.
Keywords: Adeno-associated virus, clinical trials, directed evolution, gene delivery, immune response, capsid modification, targeting, AAV's Anatomy, rAAV, capsid modification targeting, Gene therapy, RNAs, virus-like particles, PEGylation, Bactofection, Baculoviruses, bacteriophage, Herpes Simplex Virus, Adenovirus, Reoviruses, Vesicular Stomatitis Virus, Measles Virus, cancer immunotherapy, X-linked adrenoleukodystrophy, Parvoviridae, Dependovirus, Inverted terminal repeats, Vac-cinia virus, Human Papillomavirus, Cystic Fibrosis, CFTR, Hemophilia B, Le-ber Congenital Amerosis type 2, RPE65 gene, CNS, Canavan disease, Parkinson's disease, Alzheimer's disease, amyotrophic lateral sclerosis, choroderaemia, epilepsy, GABA, GDNF, melanoma, carcinoma, muscular dystrophy, Vector Tropism, biopanning, avadin affinity chromatography, PCR, blood brain barrier, HPMA, hTERT, glucose transporter isoform 1, neoantigen, Capsid Topology, Transencapsidated Vectors
Adeno-Associated Virus based vectors (rAAV) are advantageous for human gene therapy due to low inflammatory responses, lack of toxicity, natural persistence, and ability to transencapsidate the genome allowing large variations in vector biology and tropism. Over sixty clinical trials have been conducted using rAAV serotype 2 for gene delivery with a number demonstrating success in immunoprivileged sites, including the retina and the CNS. Furthermore, an increasing number of trials have been initiated utilizing other serotypes of AAV to exploit vector tropism, trafficking, and expression efficiency. While these trials have demonstrated success in safety with emerging success in clinical outcomes, one benefit has been identification of issues associated with vector administration in humans (e.g. the role of pre-existing antibody responses, loss of transgene expression in non-immunoprivileged sites, and low transgene expression levels). For these reasons, several strategies are being used to optimize rAAV vectors, ranging from addition of exogenous agents for immune evasion to optimization of the transgene cassette for enhanced therapeutic output. By far, the vast majority of approaches have focused on genetic manipulation of the viral capsid. These methods include rational mutagenesis, engineering of targeting peptides, generation of chimeric particles, library and directed evolution approaches, as well as immune evasion modifications. Overall, these modifications have created a new repertoire of AAV vectors with improved targeting, transgene expression, and immune evasion. Continued work in these areas should synergize strategies to improve capsids and transgene cassettes that will eventually lead to optimized vectors ideally suited for translational success.
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