Corbett’s team grew spike protein in the lab — lots of it -- and stored it frozen in vials. Then with the first research doses of vaccine Moderna dubbed “mRNA-1273,” the NIH researchers immunized dozens of mice. Days later, they started collecting blood samples to check if the mice were producing antibodies against that all-important spike protein. One early test: Mix the mouse samples with thawed spike protein and various color-eliciting trackers, and if antibodies are present, they bind to the protein and glow.