An epitope vaccine derived by analyzing clinical trial samples safeguards hosts with prior exposure to S. aureus against reinfection

Humans, as natural carriers of Staphylococcus aureus (SA), have developed nonprotective immune imprints that can be reactivated by SA antigen vaccination and that contribute to the failure of SA vaccine trials. To test whether an epitope-focused vaccine strategy can overcome this issue, we explored the protective epitope of the notable SA antigen MntC. A surface loop of MntC (Loop101) was found to be essential for SA to absorb manganese(II) ion and survive oxidative stress. Our Loop101-deficient versus -competent MntC-based differential screening identified a Loop101-specific human monoclonal antibody (Hm0686). Hm0686 blocked SA from absorbing manganese(II) ion and exhibited a strong opsonophagocytic activity, suggesting that Hm0686-targeted Loop101 may be a protective epitope. A Loop101 epitope vaccine but not the whole MntC antigen protected against SA infection in mice with prior exposure-induced nonprotective imprints. Thus, this effective protective epitope-based vaccine strategy may be explored to overcome nonprotective immune imprints in humans.