Isolation, selection, and characterization of potent human monoclonal antibodies against pandrug-resistant ST147NDM-1 Klebsiella pneumoniae

Antimicrobial resistance is a silent yet deadly threat to public health that requires immediate action at the global scale, calling for preparedness to rapidly develop novel therapeutic strategies. In this regard, in 2017 the World Health Organization (WHO) published a list of bacteria for which new antimicrobial solutions are urgently needed. Among the most critical group are the Gram-negative carbapenem-resistant enteric bacteria, including Klebsiella pneumoniae. In the last decades, K. pneumoniae acquired resistance to last-line classes of antibiotics due to the expression of carbapenemases such as the New Delhi metallo-β-lactamase 1 (NDM-1). To date, no vaccines or alternative therapies have been licensed against K. pneumoniae. Immunotherapy with monoclonal antibodies (mAbs) is being considered as an innovative solution for treating multidrug resistant infections, but experimental strategies for effective development have yet to be optimized for bacterial pathogens. We established an antigen-agnostic approach to efficiently screen human mAbs starting from blood of patients who recovered from K. pneumoniae infection, and we have successfully isolated extremely potent candidates against pandrug-resistant ST147 NDM-1-positive K. pneumoniae clinical isolates. These mAbs display antibacterial activity in the picomolar range in various in vitro assays and the selected top candidate has proved to be protective against bloodstream infections in vivo. Moreover, an ex vivo model of multidrug-resistant K. pneumoniae gut infection has been designed by employing human-derived intestinal organoids. The established model has been exploited on the one hand to deepen our understanding of the molecular processes that regulate host-pathogen interactions, on the other hand to further characterize bactericidal properties of the top candidate mAb. Overall, this study exemplifies a rationally designed pre-clinical approach for the development and characterization of innovative immunotherapies to target antimicrobial resistant pathogens and to address the silent pandemic caused by multidrug-resistant species.