Investigation of intracellular innate immune responses to AAV gene therapy in the retina.

Abstract

Purpose : Gene therapy using recombinant adeno-associated viral (AAV) vectors holds great promise for treating inherited retinal dystrophies. Recent research has established intracellular innate immune mechanisms for the detection of viral DNA and restriction of several pathogenic viruses, including HIV, hepatitis B and human papilloma virus. However, little is known about this response in relation to AAV, which is generally thought to have low immunogenicity. We investigated intracellular innate immunity to AAV transduction in the retina, with the aim of uncovering its impact on the efficacy of retinal gene therapy.

Methods : An AAV2 vector encoding green fluorescent protein (GFP) was injected subretinally into 4 week old female C57BL/6 mice, with sham injections of phosphate-buffered saline undertaken in the contralateral eye (n=3 per time point). RNA was extracted from the mouse retina at baseline and on day 3, 7 and 15 post-injection. The expression of a panel of genes implicated in intracellular innate immunity was quantified using reverse transcription qPCR.

Results : GFP expression was observed in the AAV injected eyes at all time points analysed. A range of cytosolic viral nucleic acid sensors (cGas, Trim21, Rig-I and Sting) and anti-viral cytokines (Tnf-α, Cxcl10, Isg15 and Ifn-γ) were upregulated 7 days post-injection in the AAV injected eyes. Furthermore, by day 7, the expression of Apobec3 and Apobec1 were upregulated 16 and 10 fold respectively compared to sham. The induction of Apobec3 and Apobec1, which both encode enzymes implicated in the deamination and degradation of viral DNA in the nucleus, was statistically significant both relative to sham and baseline expression (ANOVA followed by Tukey HSD or paired 2-tailed Student’s t-test respectively; p<0.05). There was no detectable change in other Apobec family members (Apobec2 and Aicda).

Conclusions : Intracellular innate immune responses involving anti-viral sensors (Apobec3, Apobec1, cGAS and Rig-I), mediators (Sting) and effectors (Trim21 and pro-inflammatory cytokines) are activated in response to AAV gene therapy in the retina, independent of surgical trauma. Further work is needed to elucidate the effects of these responses on the efficacy and longevity of gene therapy.

This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.