o Adeno-associated viruses (AAVs) are small viruses that infect humans and some other primate species. They are not known to cause disease and have a low immune response, making them suitable for gene therapy. AAVs can deliver genes by infecting cells and inserting the therapeutic gene into the cell's DNA. The limited cargo size is a significant challenge, often necessitating the use of smaller Cas9 variants or split Cas9 systems. Non-pathogenic, low immunogenicity, limited cargo capacity (~5 kb), stable expression in non-dividing cells.