Gene therapy is currently one of the most advanced approaches investigated for the treatment of Huntington’s disease (HD). There is a high unmet need for disease-modifying HD therapy since to date, no clinical trials have demonstrated treatment efficacy. The therapeutic target in HD is the mutated huntingtin (Htt) and the goal of the gene therapy is to silence the gene with miRNAs expressed from an AAV5 vector.

Adeno-associated viral vector (AAV) expressing artificial miRNAs targeting the Htt gene is being developed by uniQure as an RNA interference (RNAi)-based gene therapy of HD. Three major approaches have been undertaken for the development of RNAi-based HD gene therapy: (1) total Htt knockdown by targeting exon 1, (2) targeting the CAG repeats in Htt exon 1 and (3) allele-specific inhibition of mutant Htt expression by targeting SNP rs362331 in exon 50 and SNP rs362307 in exon 67. Initially 100 artificial miRNAs targeting the wild-type and/or mutant Htt gene were designed and verified for their knock-down efficacy in vitro. In the first approach we identified the highly potent miHtt10 and miHtt12 targeting exon 1 therefore inducing strong total Htt knockdown. In the second approach, we tried to target the CAG repeats and discriminate between wt and mutant Htt based on differences in the secondary structure of the mRNA. In the third approach we identified miSNP50 and miSNP7 that specifically inhibited the mutant Htt allele while the wild-type Htt was mildly affected. Next, murine striata were transduced with AAV5-miHtt12, and AAV5-miSNP67 and a strong knockdown of Htt reporter gene was observed within 8 weeks post injection. Ongoing research aims to assess the neuroprotective effect of the non-selective and allele-specific miRNAs targeting Htt and expressed from AAV5 vectors in rodent HD models. Different viral delivery routes by direct intrastriatal injection or in the cerebrospinal fluid are being evaluated. Furthermore, the Htt RNAi silencing efficacy, safety and off-target potential are determined. AAV5 delivery of miRNAs targeting Htt provides a novel approach for HD therapy as it might allow specific inhibition of the mutant Htt gene expression and hence slow down disease progression.

Support provided by uniQure and EU-FP7 E!7900.