Engineered AAV vector minimizes in vivo targeting of transduced hepatocytes by capsid-specific CD8+ T cells

Abstract

Recent clinical trials have shown that evasion of CD8+ T-cell responses against viral capsid is critical for successful liver-directed gene therapy with adeno-associated viral (AAV) vectors for hemophilia. Preclinicalmodels to test whether use of alternate serotypes or capsid variants could avoid this deleterious response have been lacking. Here, the ability of CD8+ T cells ("cap-CD8," specific for a capsid epitope presented by human B∗0702 or murine H2-Ld molecules) to target AAV-infected hepatocytes was investigated. In a murine model based on adoptive transfer of ex vivo expanded cap-CD8, AAV2- transduced livers showed CD8+ T-cell infiltrates, transaminitis, significant reduction in factor IX transgene expression, and loss of transduced hepatocytes. AAV8 gene transfer resulted in prolonged susceptibility to cap-CD8, consistent with recent clinical findings. In contrast, using an AAV2(Y-F) mutant capsid, which is known to be less degraded by proteasomes, preserved transgene expression and largely avoided hepatotoxicity. In vitro assays confirmed reduced major histocompatibility complex class I presentation of this capsid and killing of human or murine hepatocytes compared with AAV2. In conclusion, AAV capsids can be engineered to substantially reduce the risk of destruction by cytotoxic T lymphocytes, whereas use of alternative serotypes per se does not circumvent this obstacle.