Structural basis of liver de-targeting and neuronal tropism of CNS-targeted AAV capsids.

Crossing the blood-brain barrier while minimizing liver transduction is a key challenge in developing safe adeno-associated virus (AAV) vectors for treating brain disorders. In mice, the engineered capsid PHP.eB shows enhanced brain transduction, while the further engineered CAP-B10 is also de-targeted from astrocytes and liver. Here, we solve cryo-EM structures of CAP-B10 and its complex with AAV receptor (AAVR) domain PKD2, at 2.22 and 2.20 Å resolutions, respectively. These structures reveal a structural motif that hinders AAVR binding, which we confirm by measuring affinities. We show that this motif is transferable to other capsids by solving cryo-EM structures of AAV9-X1 and AAV9-X1.1, without and with PKD2, at 3.09, 2.51, and 2.18 Å, respectively. Using this structural information, we designed and validated novel AAV variants with reduced liver and altered brain cell tropism . Overall, our findings demonstrate that rationally modulating AAVR affinity can alter liver targeting and cellular tropism.