Advances in RNA sensing by the immune system: separation of siRNA unwanted effects from RNA interference.

Small interfering RNAs (siRNAs) are routinely used as a genetic tool and hold promise for a range of therapeutic applications. However, one of the hurdles of making these agents a real therapeutic modality includes the activation of innate immunity and off-target effects. Therefore, the use of siRNAs in functional genomics and therapies depends on the development of new strategies to overcome these unwanted effects. It appears that the major innate immune response to chemically synthesized siRNAs is mediated by TLR7 and/or TLR8 in immune cells. Importantly, it has also been shown that the replacement of uridines with their 2'-modified counterparts can prevent immune activation. Similarly, 2'-modifications, particularly at the seed sequence reduced the number of unwanted off-target genes without interfering with siRNA silencing potency of the anticipated target gene. This chapter describes how to separate gene silencing from immunostimulation. Also, it discusses the impact of these findings on the design of effective cancer vaccines.