CAG-FLEX-NES-jRGECO1a AAV (Serotype 9)

An important barrier to gene delivery in the central nervous system (CNS) is the blood-brain barrier (BBB), which prevents large or hydrophobic molecules such as viruses, macromolecular drugs, and many proteins from passively entering the brain. The BBB consists of three layers that separate the brain/spinal cord and cerebrospinal fluid from the blood, primarily located at the unique tight junctions of endothelial cells. These layers are called the brain capillary endothelium, the choroid plexus epithelium, and the arachnoid membrane, and each consists of a layer of cells connected by tight junctions.

Currently, there are 13 serotypes of AAV (AAV1-AAV13) based on the composition of the capsid protein, which differ in their tropism and transduction efficiency in different tissues. These differences in the various AAV serotypes can be exploited to selectively target specific specialized cells. Although different serotypes of AAV show different tropisms for various tissues, AAV9 has the highest tropism for the CNS among all serotypes that have been identified and characterized. As early as 2003, it was reported that adeno-associated virus serotype 2 (AAV2) could transduce neural cells after intravenous delivery after transient disruption of the blood-brain barrier with mannitol. Recent reports have shown that AAV9 is able to enter the central nervous system after intravenous (i.v.) delivery without the use of any blood-brain barrier permeabilizing agents.