PROS1 and COVID-19: The S protein-displaying nanoparticles with Quil-A/monophosphoryl lipid A successfully elicited a more consistent neutralizing antibody response compared with that with a trimeric form of S protein using the trimeric coiled-coil protein GCN4 and higher S-pseudotyped viral neutralizing titers than those in convalescent COVID-19 patient plasma, even in a single dose.