text: As with all gene therapies, a number of safety and toxicity issues need to be evaluated during the development of DDRNAI therapeutics.
  Oncogene activation by viral insertion: Some gene therapy vectors integrate into the host genome, thereby acting as insertional mutagens. This was a particular issue with early retroviral vectors where insertions adjacent to oncogenes resulted in the development of lymphoid tumors. AAV vectors are considered low-risk for host-genome integration, as adeno-associated virus infection has not been associated with the induction of cancers in humans despite widespread prevalence across the general population. Moreover, extensive clinical use of AAV vectors has provided no evidence of carcinogenicity. While lentiviral vectors do integrate into the genome they do not appear to show a propensity to activate oncogene expression.
  Immune response to gene therapy vectors: An immunological response to an adenoviral vector resulted in the death of a patient in an early human trial. Careful monitoring of potential toxicities in preclinical testing and analyses of pre-existing antibodies to gene therapy vectors in patients minimizes such risks.
  Innate immune response: siRNAs have been shown to activate immune responses through interaction with Toll-like receptors leading to interferon responses. These receptors reside on the cell's surface and so DDRNAIconstructs – delivered directly into intracellular space – are not expected to induce this response.
  Toxic effects due to over-expression of shRNAs: High-level expression of shRNAs has been shown to be toxic. Strategies to minimize levels of shRNA expression or promote precise processing of shRNAs can overcome this problem.
  Off-target effects: Unintended silencing of genes that share sequence homology with expressed shRNAs can theoretically occur. Careful selection of shRNA sequences and thorough preclinical testing of constructs can circumvent this issue.