text: The gene silencing effects of transfected designed siRNA are generally transient, but this difficulty can be overcome through an RNAi approach. Delivering this siRNA from DNA templates can be done through several recombinant viral vectors based on retrovirus, adeno-associated virus, adenovirus, and lentivirus. The latter is the most efficient virus that stably delivers siRNA to target cells as it can transduce nondividing cells as well as directly target the nucleus. These specific viral vectors have been synthesized to effectively facilitate siRNA that is not viable for transfection into cells. Another aspect is that in some cases synthetic viral vectors can integrate siRNA into the cell genome which allows for stable expression of siRNA and long-term gene knockdown. This technique is advantageous because it is in vivo and effective for difficult to transfect cell. However problems arise because it can trigger antiviral responses in some cell types leading to mutagenic and immunogenic effects.
  This method has potential use in gene silencing of the central nervous system for the treatment of Huntington's disease.