A Powassan virus domain III nanoparticle immunogen elicits neutralizing and protective antibodies in mice

Powassan virus (POWV) is an emerging tick borne flavivirus (TBFV) that causes severe neuroinvasive disease. Currently, there are no approved treatments or vaccines to combat POWV infection. Here, we generated and characterized a nanoparticle immunogen displaying domain III (EDIII) of the POWV E glycoprotein. Immunization with POWV EDIII presented on nanoparticles resulted in significantly higher serum neutralizing titers against POWV than immunization with monomeric POWV EDIII. Furthermore, passive transfer of EDIII-reactive sera protected against POWV challenge in vivo. We isolated and characterized a panel of EDIII-specific monoclonal antibodies (mAbs) and identified several that potently inhibit POWV infection and engage distinct epitopes within the lateral ridge and C-C ' loop of the EDIII. By creating a subunit-based nanoparticle immunogen with vaccine potential that elicits antibodies with protective activity against POWV infection, our findings enhance our understanding of the molecular determinants of antibody-mediated neutralization of TBFVs. Author summaryPowassan virus (POWV) is an emerging tick-borne flavivirus that circulates in North America. Infection can cause severe neuro-invasive disease, and currently there is no treatment or vaccine against POWV. We generated a novel POWV immunogen that displays the EDIII of the envelope glycoprotein on the surface of a self-assembling protein nanoparticle. We found that immunization of the EDIII-displaying nanoparticle in mice elicited potently neutralizing and protective antibodies. We further characterized EDIII-specific neutralizing mAbs and mapped their epitopes to specific regions within the POWV EDIII. Our study sheds light on determinants of antibody-mediated neutralization and protection against POWV and other TBFVs. It also informs EDIII-based vaccine and antiviral efforts to combat POWV infection.