Abstract
Systemic delivery of adeno-associated viral (AAV) vectors has been evaluated for the treatment of several liver diseases, including homozygous familial hypercholesterolemia, ornithine transcarbamylase deficiency, and hemophilia. Here, we evaluated this approach for the treatment of Crigler-Najjar syndrome. We administered wild-type rhesus macaques with 1.0 × 1013 or 2.5 × 1013 genome copies/kg of an AAV serotype 8 vector expressing a codon-optimized version of human uridine diphosphate glucuronosyl transferase 1A1 (UGT1A1) from a liver-specific promoter. We extensively studied vector biodistribution, transgene expression, and immune responses following vector administration. All rhesus macaques survived until their scheduled necropsy at day 56 and showed no clinical abnormalities during the course of the study. Macaques administered with either vector dose developed a T cell response to the AAV capsid and/or transgene. We mapped the immunodominant epitope in the human UGT1A1 sequence, and we found no correlation between peripheral and tissue-resident lymphocyte responses. Upon further investigation, we characterized CD107a+, granzyme B+, CD4+, and CD8+ transgene-specific cellular responses that were restricted to tissue-resident T cells. This study highlights the importance of studying immune responses at the vector transduction site and the limited usefulness of blood as a surrogate to evaluate tissue-restricted T cell responses.
Highlights
Liver gene replacement therapy has the potential to effectively treat, and even cure, a number of diseases resulting from the lack of a single gene product in hepatocytes
During the in-life phase of the study, we monitored the macaques for immune responses to the AAV8 capsid and the hUGT1A1 transgene by interferon gamma enzyme-linked immunospot (IFN-g ELISPOT) of blood samples collected on days 0, 14, 28, 42, and 56
We have shown complete and stable correction of hyperbilirubinemia in a mouse model of Crigler-Najjar syndrome at 2.5 Â 1012 genome copies (GC)/kg, which is 10-fold lower than the upper dose studied in this non-human primate (NHP) toxicity study, suggesting an attractive therapeutic window.[8,23]
Summary
Liver gene replacement therapy has the potential to effectively treat, and even cure, a number of diseases resulting from the lack of a single gene product in hepatocytes. Systemic delivery of gene therapy vectors packaged with the adeno-associated viral (AAV) serotype 8 capsid results in extensive liver transduction and has been previously evaluated by our group for non-clinical efficacy in the treatment of homozygous familial hypercholesterolemia,[1,2,3] ornithine transcarbamylase deficiency,[4] and hemophilia.[5,6,7] We sought to evaluate the effectiveness of a similar approach for the treatment of Crigler-Najjar syndrome.[8]. The only curative therapy is a liver transplant prior to the onset of neurological damage. The continuous synthesis of UGT1A1 by the liver following systemic delivery of a gene therapy vector expressing UGT1A1 has the potential to be a simpler and safer treatment than liver transplantation
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