Teasing Apart The Immune Response To A Virus-Derived Adjuvant: Insights Into Type 1 Immunity Inducing Vaccine Development

Adjuvants boost and shape the immune response to killed and subunit vaccines. Currently there is a critical need for vaccine adjuvants that induce an immune response specific for intracellular pathogens, or type 1 immunity. As defective viral genomes are the primary immunostimulatory molecules during paramyxovirus infections, we tested whether a defective viral genome-derived oligonucleotide (DDO) induced type 1 immune responses when used as a vaccine adjuvant. We used a model influenza vaccine to examine the host response to DDO-adjuvanted vaccines. Using a combination of flow cytometry, ELISA, qPCR, and viral challenges we showed that DDO induces all the hallmarks of a type 1 immune response in mice. DDO induces IgG2c antibodies, Th1 CD4+ T-cells, and effector CD8+ T-cells. In addition to inducing robust type 1 immunity on its own, DDO synergizes with the mixed immunity inducing adjuvant AddaVax (the research equivalent of MF59) to induce even stronger type 1 immune responses. As CD8+ T-cell responses are difficult to induce in response to killed and subunit vaccination, we next examined the innate immune response to DDO to discover the requirements for CD8+ T-cell activation in response to vaccination. We determined that DDO requires the RNA sensor TLR3 and type I IFN signaling to induce type 1 conventional dendritic cell (cDC1) accumulation in the draining lymph node. cDC1 accumulation was required for CD8+ T-cell responses. Additionally, we show DDO induces a type I IFN and inflammatory response that is different from the double-stranded RNA mimic poly I:C. We have shown that DDO is a safe and effective type 1 immunity inducing adjuvant in mice. These studies illuminate aspects of the innate immune response that are required to induce a type 1 immune response and identify targets for adjuvant development and improvement.