Anti-capsule human monoclonal antibodies protect against hypervirulent and pandrug-resistantKlebsiella pneumoniae

SUMMARY The silent pandemic caused by antimicrobial resistance (AMR) requires innovative therapeutic approaches. Human monoclonal antibodies (mAbs), which are among the most transformative, safe and effective drugs in oncology and autoimmunity, are rarely used for infectious diseases and not yet used for AMR. Here we applied an antigen-agnostic strategy to isolate extremely potent human mAbs against Klebsiella pneumoniae (Kp) sequence type 147 (ST147), a hypervirulent and pandrug-resistant clonotype which is spreading globally. Isolated mAbs target the bacterial capsule and the O-antigen. Surprisingly, although both capsule- and O-antigen-specific mAbs displayed bactericidal activity in the picomolar range in vitro, only the capsule-specific mAbs were protective against fulminant ST147 bloodstream infection. Protection correlated with in vitro bacterial uptake by macrophages and enchained bacterial growth. Our study describes the only drug able to protect against pandrug-resistant Kp and provides a strategy to isolate mAbs and identify correlates of protection against AMR bacteria. Competing Interest Statement Patent application 102023000000924 describing isolated mAbs has been filed by Fondazione Toscana Life Sciences. R.R. hold shares in the GSK group of companies and declare no other financial and non-financial relationships and activities. Remaining authors declare no competing interests. Footnotes ↵13 Senior author The Materials and Methods section has been revised as follows: the paragraphs describing the purification procedures of Klebsiella pneumoniae capsule and O-antigen have been merged into a single one entitled "Purification of ST147NDM-1 capsule and purification of O-antigen from Kp strains".