The Role of Recombinant AAV in Precise Genome Editing.

Swati Bijlani,Ka Ming Pang,Saswati Chatterjee,Venkatesh Sivanandam,Amanpreet Singh

doi:10.3389/fgeed.2021.799722

Swati Bijlani, Ka Ming Pang + Show 3 more

Open Access

https://doi.org/10.3389/fgeed.2021.799722

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Abstract

The replication-defective, non-pathogenic, nearly ubiquitous single-stranded adeno-associated viruses (AAVs) have gained importance since their discovery about 50 years ago. Their unique life cycle and virus-cell interactions have led to the development of recombinant AAVs as ideal genetic medicine tools that have evolved into effective commercialized gene therapies. A distinctive property of AAVs is their ability to edit the genome precisely. In contrast to all current genome editing platforms, AAV exclusively utilizes the high-fidelity homologous recombination (HR) pathway and does not require exogenous nucleases for prior cleavage of genomic DNA. Together, this leads to a highly precise editing outcome that preserves genomic integrity without incorporation of indel mutations or viral sequences at the target site while also obviating the possibility of off-target genotoxicity. The stem cell-derived AAV (AAVHSCs) were found to mediate precise and efficient HR with high on-target accuracy and at high efficiencies. AAVHSC editing occurs efficiently in post-mitotic cells and tissues in vivo. Additionally, AAV also has the advantage of an intrinsic delivery mechanism. Thus, this distinctive genome editing platform holds tremendous promise for the correction of disease-associated mutations without adding to the mutational burden. This review will focus on the unique properties of direct AAV-mediated genome editing and their potential mechanisms of action.

Highlights

The completion of the sequencing of the human genome marked the start of the race to create targeted modifications for the study of gene function, generation of disease models, and therapeutic applications (Li et al, 2020; Galichet and Lovell-Badge, 2021)
The mechanism of associated virus (AAV) gene targeting has yet to be definitively delineated, we have recently shown that AAV editing requires homology to targeted chromosomal sequence, singlestranded AAV editing genomes, and the presence of BRCA2 in target cells (Smith et al, 2018) (Figure 1)
AAVbased editing incorporates the key hallmarks of homologous recombination (HR), including the absolute requirement for BRCA2 and homology between the repair template and the genomic target

Summary

INTRODUCTION

The completion of the sequencing of the human genome marked the start of the race to create targeted modifications for the study of gene function, generation of disease models, and therapeutic applications (Li et al, 2020; Galichet and Lovell-Badge, 2021). The ability to precisely and permanently correct pathogenic mutations at the level of the genome without adding to the mutational burden has the potential to be transformative for genetic therapies of inherited and acquired diseases. AAVs have emerged as efficient genetic modification vehicles due to efficient in vivo infectivity, non-pathogenicity, widespread tissue tropism, rare genomic integration, and their ability to infect and persist in non-dividing cells (Gaj et al, 2016; Epstein and Schaffer, 2017). AAV infection of target cells in the absence of helper virus coinfection results in latency which is the basis for the use of AAV as delivery vehicles for genetic material. Recombinant AAV vectors are doubly replicationdeficient in the absence of AAV Rep/Cap genes and helper virus functions and do not undergo replication. Recombinant AAV vectors have proven to be safe, welltolerated, and effective gene therapy vectors for treating genetic diseases. AAV vectors are well on their way to becoming established genetic therapies

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CONCLUSION