Evaluation of human antibodies from vaccinated volunteers for protection against Yersinia pestis infection

has a broad host range and has caused lethal bubonic and pneumonic plague in humans. With the emergence of multiple resistant strains and the potential for biothreat use, there is an urgent need for new therapeutic strategies that can protect populations from natural or deliberate infection. Targeting F1 has been proven to be the main strategy for developing vaccines and therapeutic antibodies, but data on anti-F1 antibodies, especially in humans, are scarce. To date, three human anti-F1 monoclonal antibodies (m252, αF1Ig2, and αF1Ig8) from naive populations have been reported. Here, we constructed an antibody library from vaccinees immunized with the plague subunit vaccine IIa by phage display. The genetic basis, epitopes, and biological functions of the obtained mAbs were assessed and evaluated in plague-challenged mice. Three human mAbs, namely, F3, F19, and F23, were identified. Their biolayer responses were 0.4, 0.6, and 0.6 nm, respectively. The dissociation constants (K