The genome of self-complementary adeno-associated viral vectors increases Toll-like receptor 9-dependent innate immune responses in the liver

Although adeno-associated viral (AAV) vectors have been successfully used in hepatic gene transfer for treatment of hemophilia and other diseases in animals, adaptive immune responses blocked long-term transgene expression in patients on administration of single-stranded AAV serotype-2 vector. More efficient vectors have been developed using alternate capsids and self-complimentary (sc) genomes. This study investigated their effects on the innate immune profile on hepatic gene transfer to mice. A mild and transient upregulation of myeloid differentiation primary response gene (88), TLR9, TNF-α, monocyte chemotactic protein-1, IFN-γ inducible protein-10, and IFN-α/β expression in the liver was found after single-stranded AAV vector administration, regardless of the capsid sequence. In contrast, scAAV vectors induced higher increases of these transcripts, upregulated additional proinflammatory genes, and increased circulating IL-6. Neutrophil, macrophage, and natural killer cell liver infiltrates were substantially higher on injection of scAAV. Some but not all of these responses were Kupffer cell dependent. Independent of the capsid or expression cassette, scAAV vectors induced dose-dependent innate responses by signaling through TLR9. Increased innate responses to scAAV correlated with stronger adaptive immune responses against capsid (but not against the transgene product). However, these could be blunted by transient inhibition of TLR9.