Synthetic double stranded RNA reliably induces innate immunity similar to a live viral vaccine in humans

Adjuvants are critical for the success of vaccines, and agonists for microbial pattern recognition receptors are promising new candidates. A mechanism for the immune enhancing role of adjuvants is to stimulate innate immunity. We studied the innate immune response in humans to synthetic double stranded RNA (poly ICLC), a ligand for TLR3 and MDA-5 cytosolic RNA helicase. Transcriptional analysis of blood samples from eight volunteers, after subcutaneous administration of poly ICLC showed upregulation of genes involved in multiple innate immune pathways in all subjects, including interferon and inflammasome signaling. Blocking of type I interferon receptor ex vivo significantly dampened the response to poly IC. Comparative transcriptional analysis showed that several innate pathways were similarly induced in volunteers immunized with the highly efficacious Yellow Fever Vaccine. Therefore a chemically defined microbial agonist like poly ICLC can be a reliable and authentic microbial mimic for inducing innate immunity, here for a live attenuated viral vaccine in humans.