AAV Vectors for Delivery of RNAi
Adeno-associated virus (AAV) vectors have become an important tool for human gene therapy. They have shown high transduction efficiency in a wide range of target tissues, good safety in animal models and human clinical trials, and prospective long-term gene expression. RNA interference (RNAi) has become another important tool in human gene therapy, enabling scientists to move on from classical gene transfer to gene silencing methods or combinations. At Creative Biolabs, we are currently able to provide AAV vector design and construction services for the delivery of RNAi.
Introduction of RNAi
RNAi, first discovered 20 years ago, is an evolutionary conservative mechanism of sequence-specific post-transcriptional gene silencing mediated by a double-stranded (ds) RNA molecule that matches the target gene sequence. Since then, the field of gene therapy has recognized the potential of this technology in the treatment of previously undruggable diseases and has used this new strategy as a tool to complement traditional gene transfer approaches. At present, RNAi has become another important tool for human gene therapy.
Post-transcriptional gene silencing by small interfering RNA (siRNA) has rapidly become a powerful tool for genetic analysis of mammalian cells, and has the potential to produce new therapies. The delivery of siRNA into mammalian cells is usually achieved by transfection of small hairpin RNA (shRNA) plasmids driven by ds oligonucleotides or RNA polymerase III (Pol-III) promoters. In order to overcome the problem of inefficient transfection of plasmid vectors, some viral vectors have recently been used to transfer siRNA.
Figure 1. RNAi and miRNA biogenesis. (Borel, 2014)
AAV Vectors for Delivery of RNAi at Creative Biolabs
Vector-derived RNAi is a vector used to express RNA transcripts (e.g., shRNAs or microRNAs (miRNAs)), which are eventually processed to produce siRNAs in the target cells. AAV is currently one of the most attractive gene therapy vectors. In recent years, evidence of the success of recombinant AAV (rAAV) vectors in clinical trials (especially Leber's congenital melanoma, hemophilia B and lipoprotein lipase deficiency) has continued to increase their safety. We have successfully developed an AAV-based vector for siRNA delivery by using rAAV-2, in which rep and cap genes have been removed. Fully evaluated, the results indicate that the rAAV vector containing the siRNA expression cassette can be efficiently packaged, and the target cells can be successfully infected under high frequency and low toxicity conditions.
Figure 2. Schematic representation of a modified AAV vector for the delivery of p53 siRNA. (Tomar, 2003)
Features of AAV Vector-derived RNAi
- With AAV, RNAi has the potential of lifelong persistence, where tissue specificity can be achieved;
- The use of AAV-based vectors is advantageous because these viruses can be prepared with very high titers;
- Based on rAAV's extensive preclinical and clinical trial experience, the use of rAAV as an RNAi platform to transform into a successful clinical product is only a matter of time.
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References
- Borel, F.; et al. (2014). Recombinant AAV as a platform for translating the therapeutic potential of RNA interference. Molecular Therapy. 22(4): 692-701.
- Tomar, R.S.; et al. (2003). Use of adeno-associated viral vector for delivery of small interfering RNA. Oncogene. 22(36): 5712.
