Safety and Efficacy of AON-D21 in Severe Community-Acquired Pneumonia.

Inclusion Criteria: Community-acquired pneumonia, confirmed or suspected of bacterial or viral origin. Admitted to an ICU (or similar unit). Requiring respiratory support by HFO ≥ 30 L/min with FiO2 ≥ 30% or NIV or IMV or ECMO. CRP ≥ 50 mg/L. PaO2/FiO2 ratio ≤ 300 mmHg. Treatment initiation no more than 48 h after initiation of respiratory support (HFO ≥ 30 L/min with FiO2 ≥ 30%, NIV, IMV or ECMO). Written informed consent. Age ≥ 18 years to ≤ 85 years. Body mass index ≥ 17.5 kg/m² and ≤ 40 kg/m². For female participants of childbearing potential, agreement to use dual methods of contraception until Day 60. For male participants with female partners of childbearing potential, agreement to use barrier method of contraception until Day 60 and to refrain from donating sperm during the study and for 3 months after the last infusion. Exclusion Criteria: Refractory septic shock. Not expected to survive 72 hours. Hospital-acquired or ventilator-associated pneumonia or known or suspected pneumonia due to aspiration or other physical injury or trauma or tuberculosis. Known or suspected hypersensitivity to AON-D21 or any components of the formulation used (e.g., PEG, mannitol or EDTA) or a history of clinically relevant allergy requiring continuous treatment, or of anaphylaxis. Known fibrotic lung disease, bronchiectasis or any other known severe chronic respiratory disease. Active malignant disease. Factors other than a pathogen suspected or confirmed to be causative for the respiratory insufficiency. Hepatocellular injury defined by an ALT or AST value ≥ 3 times the ULN. Known acute or chronic liver disease with Child-Pugh C (See Appendix 13.6.2). Any medical disease or condition that, in the opinion of the investigator(s), compromises the participant's safety or compromises the interpretation of the results. Receiving chronic immunosuppressive therapy in relevant doses. Known immunodeficiency disease/condition. Nursing and pregnant women (defined as the state after conception until the termination of gestation, screened in all women of child-bearing potential with a chorionic gonadotrophin (hCG) blood test (local laboratory). Current or recent participation in an investigational trial. Systemic treatment with any complement inhibitor. Known complement deficiency. Unlikely to remain at the investigational site beyond 96 h.