Structure of ClfA002 in Complex With Neutralizing Antibody AZD7745 Provides Insight into Its Broad Neutralization Mechanism in Staphylococcus aureus Infection.

backgroundComplications due to Staphylococcus aureus infections are a major health concern as current therapies lack broad coverage; therefore, development of a broad neutralizing therapy is critical. We previously showed that a monoclonal antibody combination comprising suvratoxumab and AZD7745, targeting respectively alpha toxin and clumping factor A (ClfA), 2 S aureus virulence factors, provided broad strain coverage in a mouse model. To understand the basis for the broad strain coverage of AZD7745, the epitope was determined. Moreover, we surveyed a global collection of bacteremia isolates to study AZD7745 epitope conservation and neutralizing activity.

methodsAZD7745 epitope was determined from the co-crystal structure of AZD7745 Fab with the N2N3 fibrinogen binding domain of ClfA (at 1.58 Å). A geographically diverse collection of 174 S aureus bacteremia isolates was collected between 2022 and 2023. Whole genome sequencing was performed to determine the presence of the clfA gene and AZD7745 epitope conservation. AZD7745 neutralizing activity was tested in vitro against a representative strain of each ClfA variant in a fibrinogen/ClfA binding assay.

resultsThe AZD7745 epitope contains 12 binding residues on the ClfA N3 domain. Among the 174 isolates, we identified 45 ClfA subtypes with 29 presenting amino acid variations on contact residues. Nonetheless, AZD7745 exhibited neutralizing activity against each subtype. We showed that AZD7745 binding to ClfA N3 domain imposes a conformational change that prevents fibrinogen binding to ClfA.

conclusionsClfA is ubiquitously present on S aureus global clinical isolates, and AZD7745 epitope is highly conserved. This suggests that AZD7745 can confer broad coverage against S aureus.