CMV-SaCas9HF AAV (Serotype 9)

Adeno-associated viruses (AAV) of the Parvoviridae family are small viruses without a lipid envelope, and their genetic material is single-stranded DNA. With a virion diameter of approximately 25 nanometers, AAV vectors are considered to be one of the smallest animal viruses. AAV has several favorable properties that make it a potential and attractive transgenic vector for human gene therapy. Wild-type AAV is non-pathogenic and has low immunogenicity. Unlike adenoviral vectors, recombinant AAV vectors lack nucleotide sequences encoding viral proteins and do not induce inflammatory responses; therefore, they do not interfere with the efficiency of therapeutic gene expression. In addition, recombinant AAV vectors do not integrate into the host genome but rather adopt an episomal form, thereby eliminating the risk of insertional mutagenesis associated with retroviruses. Another favorable property of rAAV vectors is their ability to infect both non-dividing and dividing cells, making them suitable for use in brain gene therapy. AAV vectors can be produced at high concentrations and remain stable during storage.

Gene therapy techniques are mainly based on in vivo or in vitro techniques. In vivo techniques involve the introduction of therapeutic genes directly into the patient using suitable viral or nonviral vectors. Although intravenous injection is the most convenient and common route for in vivo gene therapy, its effectiveness for central nervous system diseases is limited by the ability of the delivery system to cross the blood-brain barrier. Recombinant adeno-associated vectors (rAAV) have become the vector of choice for central nervous system treatment. These vectors are widely used due to their safety, stable gene expression, and a certain degree of neuronal tropism. In addition, rAAV9 has been shown to have the ability to cross the blood-brain barrier after intravenous injection. Notably, a 2020 clinical report on gene therapy for SMA type I demonstrated the safety and efficacy of intravenous application of rAAV9 vectors carrying therapeutic genes.