Antibodies against the capsid induced after intracranial AAV administration limits second administration in a dose dependent manner

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 possiblility to deliver multiple rounds of AAV through intracerebral injections in the mouse brain. We discovered a dose-dependent modulation of the second round AAV infection by the first round AAV injection in the brain-wide scales besides the injection region. High-dose AAV infection increases chemokines CXCL9 and CXCL10 to recruit the parenchymal infiltration of lymphocytes. Surprisingly, the blood-brain-barrier was relatively intact. Brain-wide dissection discovered the likely rountes of the infiltrated lymphocytes through perivascular space and ventricles. Further analysis using B-cell depleted mice revealed that B lymphocytes, but not T lymphocytes, played a critical role in inhibiting the second round AAV infection. Strategies against neutralizing antibodies had limited effects, while reducing the dosage for the first injection or switching the second AAV to a different serotype appeared to be more effective in antagonizing 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 still possible if designed carefully with proper doses and serotypes.