biostudies-literaturePitiot ALuxembourg Government Ministry of Higher Education and ResearchInstitut National de la Santé et de la Recherche MédicaleNational Research FundEuropean Cooperation in Science and TechnologyUniversity of Tours105926https://www.ebi.ac.uk/biostudies/studies/S-EPMC12466147biostudies-literatureUnknown120<h4>Background</h4>Multidrug-resistant Pseudomonas aeruginosa raises major clinical concerns due to its capacity to cause a wide-array of infections in individuals with compromised immune defences and to withstand standard-of-care therapeutic treatments. Antibody-based approaches have proven to be efficient in the treatment of diverse infections. Here we propose an innovative approach harnessing the complement at the surface of bacteria for further killing.<h4>Methods</h4>We developed two Complement-activating Multimeric immunotherapeutic compleXes (CoMiX) targeting the bacterium through a single-chain variable fragment directed against the exopolysaccharide Psl, and carrying one of two different effector functions, Factor H Related protein 1 (FHR1) or a Fc dimer. Each CoMiX was assessed in vitro for their antibacterial activity, and further evaluated in a mouse model of acute pneumonia.<h4>Findings</h4>Both CoMiX-FHR1 and CoMiX-Fc effectively deposit C1q (for CoMiX-Fc), C3b, and C5b9 at the surface of multidrug-resistant clinical isolates, promoting their direct killing and/or opsonisation and subsequent phagocytosis for CoMiX-Fc (p < 0.001). Both CoMiX synergise with amikacin and protect epithelial cells against P. aeruginosa-induced cytotoxicity. Importantly, CoMiX administered intranasal to acutely infected mice significantly improve their survival (p < 0.001) by reducing local bacterial burden through the higher induction of C3b (opsonisation) and C5a (neutrophils recruitment and activation) and by decreasing lung inflammation.<h4>Interpretation</h4>Our proof-of-concept demonstrates the efficient, direct and indirect killing of P. aeruginosa by the complement, highlighting the therapeutic potential of CoMiX to combat multidrug-resistant bacteria.<h4>Funding</h4>Luxembourg National Research Fund, Ministry of Higher Education and Research of Luxembourg, COST action CA21145 EURESTOP, Institut National de la Santé et de la Recherche Médicale, and Tours University.EBioMedicineDirected-complement killing of Pseudomonas aeruginosa protects against lethal pneumonia.PMC12466147CA21145C22/BM/17380893/PSEUDOLIH GBB 98000005Zimmer JIserentant GSeguin-Devaux CChesnay ADervillez XSi-Tahar MServais JYPitiot AFouquenet DBriard BBrandus BRassam PDesoubeaux GMely YRolin CRichert LfalseDirected-complement killing of Pseudomonas aeruginosa protects against lethal pneumonia.<h4>Background</h4>Multidrug-resistant Pseudomonas aeruginosa raises major clinical concerns due to its capacity to cause a wide-array of infections in individuals with compromised immune defences and to withstand standard-of-care therapeutic treatments. Antibody-based approaches have proven to be efficient in the treatment of diverse infections. Here we propose an innovative approach harnessing the complement at the surface of bacteria for further killing.<h4>Methods</h4>We developed two Complement-activating Multimeric immunotherapeutic compleXes (CoMiX) targeting the bacterium through a single-chain variable fragment directed against the exopolysaccharide Psl, and carrying one of two different effector functions, Factor H Related protein 1 (FHR1) or a Fc dimer. Each CoMiX was assessed in vitro for their antibacterial activity, and further evaluated in a mouse model of acute pneumonia.<h4>Findings</h4>Both CoMiX-FHR1 and CoMiX-Fc effectively deposit C1q (for CoMiX-Fc), C3b, and C5b9 at the surface of multidrug-resistant clinical isolates, promoting their direct killing and/or opsonisation and subsequent phagocytosis for CoMiX-Fc (p < 0.001). Both CoMiX synergise with amikacin and protect epithelial cells against P. aeruginosa-induced cytotoxicity. Importantly, CoMiX administered intranasal to acutely infected mice significantly improve their survival (p < 0.001) by reducing local bacterial burden through the higher induction of C3b (opsonisation) and C5a (neutrophils recruitment and activation) and by decreasing lung inflammation.<h4>Interpretation</h4>Our proof-of-concept demonstrates the efficient, direct and indirect killing of P. aeruginosa by the complement, highlighting the therapeutic potential of CoMiX to combat multidrug-resistant bacteria.<h4>Funding</h4>Luxembourg National Research Fund, Ministry of Higher Education and Research of Luxembourg, COST action CA21145 EURESTOP, Institut National de la Santé et de la Recherche Médicale, and Tours University.2025-01-01T00:00:00Z2025 Oct2026-06-30T03:22:56.305Z2026-06-30T03:15:58.291ZS-EPMC124661474096150610.1016/j.ebiom.2025.105926