Adjuvancy effects of a RIG-I agonist (RIG101) on H1N1 HA antigen intranasally vaccinated mice and human nasal epithelium/PBMCs co-culture

<bold>Background:</bold> Although systemic vaccination against influenza and SARS-CoV-2 reduced hospitalisation and mortality, it showed limited effects on local viral infection. Mucosal vaccines offer an attractive approach to prevent respiratory virus infections. The development of adjuvants to enhance effectiveness of mucosal vaccines may be critical to future therapeutic success. <bold>Aim:</bold> To evaluate adjuvancy effects of a RIG-I agonist (RIG101 nanoemulsion: RIGImmune Inc.) on recombinant H1N1 Hemagglutinin (HA) intranasally vaccinated mice and in human nasal epithelium and PBMC co-cultured system. <bold>Methods:</bold> HA antigen was administered intranasally twice in 28 days apart, and live H1N1 PR8 was challenged intranasally on 28 days post booster. Lung/nasal tissue and lavage were collected on Day 5 post infection to determine viral load and inflammatory cells. RIG101 nanoemulsion or CPG-ODN was treated intranasally together with HA antigen. PBMCs treated with L-leucyl-L-leucine methyl ester were treated with HA with/without RIG101 and IgM was determined by ELISPOT. <bold>Results:</bold> Addition of RIG101 to H1N1 HA antigen was more effective on reduction of viral load and inflammation, and prevention of virus-induced body weight loss compared with HA antigen vaccination alone and CPG-ODN addition. In PBMC-nasal epithelium co-culture, RIG101 clearly enhanced IgM production in LLME-treated PBMCs compared with H1N1 HA alone. <bold>Conclusion:</bold> RIG101, a RIG-I agonist, is promising adjuvant to boost mucosal vaccine effects against respiratory virus.