Intracranial AAV administration dose-dependently recruits B cells to inhibit the AAV redosing

Recombinant adeno-associated virus (rAAV) is a widely used viral vector for gene therapy. However, a limitation of AAV-mediated gene therapy is that patients are typically dosed only once. In this study, we investigated the possibility of delivering multiple rounds of AAV through intracerebral injections in the mouse brain, and discovered a dose-dependent modulation of the second administration by the first-round AAV injection in a brain-wide scale. High-dose AAV injection increased chemokines CXCL9 and CXCL10 to recruit parenchymal infiltration of lymphocytes, whereas the blood-brain-barrier was relatively intact. Brain-wide dissection discovered the likely routes of the infiltrated lymphocytes through perivascular space and ventricles. Further analysis revealed that B lymphocytes played a critical role in inhibiting the redose. Choosing the right dosage for the first injection or switching the second AAV to a different serotype provided an effective way to antagonize the first-round AAV inhibition. Together, these results suggest that mammalian brains are not immunoprivileged for AAV infection, but multiple rounds of AAV gene therapy are feasible if designed carefully with proper doses and serotypes.