Modulation of dendritic cell maturation and function by siRNA-bearing 5'-triphosphate

Small interfering RNAs (siRNAs) have emerged as a powerful technique for sequence-specific gene silencing in a wide variety of organisms. However, it has been shown that in vitro transcribed siRNA can activate innate immunity through RIG-1 helicase, a cytosolic sensor of viral RNA. We recently demonstrated that the activation of RIG-1 by siRNA-bearing 5'-triphosphate can be used to enhance dendritic cell maturation and function. Indeed, immature DCs that had been transfected with siRNA-bearing 5'-triphosphate activated T cells, indicating that, even in the absence of external stimuli such as TNF-alpha, those DCs were sufficiently mature to initiate T cell activation. Also, a recent study has shown that 5'-bearing siRNAs targeting Bcl-2 can induce apoptosis in tumour cells, further supporting the use of this strategy to combat cancer. This chapter describes the in vitro synthesis of siRNA targeting indoleamine 2,3-dioxygenase (IDO), an enzyme that plays a critical role in hindering immunity against tumours.