Syn-FLEX-NES-jRCaMP1a AAV (Serotype 9)

Gene therapy aims to manipulate the genetic material in cells to restore gene function by editing, adding or deleting gene expression, thereby altering living cells for therapeutic purposes. Gene therapy is most commonly delivered via viral vectors, with recombinant AAV vectors currently being the most commonly used. AAV was originally discovered as a contaminant in adenovirus preparations and belongs to the Parvoviridae and Dependovirus genus. It relies on co-infection with other viruses (primarily adenoviruses) for replication, hence its name. It is therefore a replication-incompetent virus and therefore lacks the disease associated with wild-type viruses. AAV is able to transduce both dividing and non-dividing cells, has the potential for long-term transgene expression, and is capable of packaging up to ∼4.7 kilobases of therapeutic DNA.

For the generation of AAV viral vectors, two important genes are required, Rep and Cap. Rep is required for viral genome replication and packaging, while Cap expresses the viral capsid protein that encapsulates the packaged genome and is involved in cell binding and internalization. The viral genome is flanked by inverted terminal repeats (ITRs), which are required for genome replication and packaging. There are at least 12 known AAV serotypes (AAV1-AAV12), driven by differences in the Cap, which directs different tissue tropisms for genome internalization. Cap engineering can increase tissue targeting and specificity. A third gene, encoding the assembly-activating protein (AAP) from an alternative reading frame in the Cap, has been shown to be important for promoting stability and interactions between AAV viral proteins and nucleocapsid assembly.