OR05

Recombinant adeno-associated viral vectors (rAAV) are successful viral vectors for in vivo gene therapy. However, in several clinical trials using high-doses of vectors, adverse events related to the host immune system activation and/or vector toxicity, have been described. Here, we investigated the impact of the immune response in the liver after high-dose systemic injection of rAAV9 in a rat model.

Rats were injected with a high dose of rAAV9 (1e14vg/kg) expressing the GFP reporter gene (n= 21 rats). IFN-γ lymphocyte secretion against transgene product (GFP) was observed as early as day 7 post-injection, and against AAV9 capsid after one month post injection. Surprisingly, despite a comparable peripheral immune response against the vector in all injected rats, our results show that in almost 30% of animals (n=6/21), the GFP protein was no more detected in the liver starting from one month after injection. Thus, we carried out a short term in situ hepatic analyses to investigate the selective loss of transgene expression in some individuals. At day 7 post-injection (n=6), at the time of a transaminase peak, we have systematically observed a liver inflammation with inter-individual variable characteristics.

Hence, our study shows that the delivery of high doses of rAAV9 vector in rats results in persisting liver transgene expression in 70% animals, despite a peripheral immune response. Our rat gene transfer model appears relevant as it seems to reflect the inter-individual differences and the balance between immunity and long-term expression described in pre-clinical and even clinical studies of liver gene transfer.