Mapping the immunostimulatory activity of a Sendai virus defective viral genome (VIR5P.1152)

Abstract

Defective viral genomes (DVGs) generated during Sendai virus infection are the primary triggers of the host antiviral response. DVGs induce the expression type-I interferons (IFN) and other cytokines upon binding through the intracellular viral sensors RIG-I and MDA5. The molecular mechanism behind the superior immunostimulatory activity of DVGs is unknown. To identify RNA motifs that provide potent immunostimulatory activity to DVGs, we generated a series of deletion mutants of a prototype DVG derived from Sendai virus. In vitro transcribed RNA from these mutants were tested for their ability to induce type I IFNs upon transfection. In silico single strand RNA modeling of the mutants folding identified an AU-enriched stem loop domain formed by nucleotides 70-114 of the DVG that is essential for type I IFN induction. Consistent with this prediction, we demonstrate that mutants lacking this region lose their stimulatory activity, while mutants that kept intact this region preserved it Thus, a minimal RNA motif at the 5’ but not the 3’ complimentary sequence is critical for maximal DVG activity and oligonucleotides including such region may represent novel alternatives to be harnessed as potent adjuvants for vaccination.