AAV PHP.B-CAG-mCherry

The development of effective gene therapies for neurological diseases depends on the availability of gene transfer vectors that can broadly and efficiently transduce cells of the central nervous system (CNS). Recombinant adeno-associated virus (AAV) vectors have become the platform of choice for the development of gene therapies for neurodegenerative diseases because they can efficiently transduce the CNS and express the target gene for a long time (potentially indefinitely). Prior to 2009, AAV gene transfer to the CNS was based on intraparenchymal injections, with distribution largely limited to the target structure, which is desirable in some cases but not necessarily for neurodegenerative diseases affecting the entire CNS. The discovery that AAV9 crosses the blood-brain barrier (BBB) ​​after systemic administration in mice ushered in a new era of intravascular gene therapy for CNS diseases. Despite this, AAV9 vectors delivered systemically to mature animals exhibit significant limitations, as the majority of transduced cells in the brain are astrocytes and endothelial cells, with very few neurons transduced.

In vivo screens using Cre recombinase-driven AAV capsid recognition to transduce AAV capsids into target cells in the CNS generated AAV-PHP.B and AAV-PHP.eB capsids that were 80- to 300-fold more efficient than AAV9. However, unlike AAV9, which exhibits consistent properties across species, AAV-PHP.B was only approximately 2-fold more efficient than AAV9 in rats18 and provided modest improvements in specific neuronal populations in marmosets, cats, and sheep. These findings in other species suggest that AAV-PHP.B is exploiting a non-evolutionarily conserved molecular mechanism to cross the BBB in mice with high efficiency.