Subgenomic satellite particle generation in recombinant AAV vectors results from DNA lesion/breakage and non-homologous end joining

Recombinant AAV (rAAV) vectors have been developed for therapeutic treatment of genetic diseases. Nevertheless, current rAAV vectors administered to patients often contain non-vector related DNA contaminants. Here, we present a thorough molecular analysis of the configuration of non-standard AAV genomes generated during rAAV production. In addition to the sub-vector genomic size particles containing incomplete AAV genomes, our results found that rAAV preparations were contaminated with multiple categories of subgenomic particles with either snapback genomes or vector genomes with deletions in the mid regions. Through CRISPR and restriction enzyme-based in vivo and in vitro modeling, we identified that the main mechanism leading to the formation of non-canonical genome particles occurred through nonhomologous end joining of fragmented vector genomes caused by genome lesions or DNA breaks that were generated by the host cell/environment. The results of this study advance our understanding of AAV vectors and provide new clues on improving vector efficiency and safety profile for use in human gene therapy.