Route of administration determines induction of T-cell-independent humoral responses to adeno-associated virus vectors

Vectors based on adeno-associated viruses (AAV) type 2 show promise for treating chronic diseases because transgene expression appears to be stable. This study evaluated the impact of humoral immunity to the capsid proteins on vector uptake by hepatocytes following an intravascular approach. Route of vector administration in mice had a qualitative effect on antivector B cell responses. Administration of vector into the tail vein resulted in T-cell-dependent (TD) B cell responses that were completely inhibited with depleting CD4 antibody. Delivery of vector into the portal circulation via the spleen yielded B cell response that were partially T cell independent (TI) rendering strategies based on T cell inhibition ineffective in allowing vector readministration. The TI B cell response was short lived in comparison to the TD response. Rhesus monkeys produced a B cell memory response to intraportal vector which appeared to be T cell dependent based on Ig isotypes. Gene therapy strategies that require AAV vector readministration should consider vector biodistribution and its impact on B cell activation.