Adjunctive Therapy to Antibiotics in the Treatment of S. Aureus Ventilator-Associated Pneumonia With AR-301

Inclusion Criteria: 1. Written Informed Consent given by the patient or, if not possible, by a legally acceptable representative and/or an independent physician as authorized by the competent ethics committee (EC) or independent review board (IRB) and local regulations. 2. To be at least 18 years of age. Taiwan only: To be at least 20 years of age. South Korea only: To be at least 19 years of age. 3. Treated in an ICU at the time of enrollment. 4. Endotracheal tube in place (tracheostomy is allowed). 5. The patient is mechanically ventilated for at least 48 hours. 6. Diagnosis of pneumonia based on the following criteria (a, b, and c, all must be met): 1. One definitive chest X-ray diagnostic of pneumonia within 48 hours, 2. Hypoxemia based on PaO2/FiO2. 3. At least one of the following signs: i. Documented fever (e.g., body temperature greater than or equal to 38º Celsius). ii. Hypothermia (e.g., core body temperature less than or equal to 35º Celsius). iii. Total peripheral white blood cell (WBC) count greater than or equal to 10,000 cells/µL (or mm3). iv. Leukopenia with total WBC less than or equal to 4,500 cells/µL (mm3). v. Greater than 15 percent immature neutrophils (bands) noted on peripheral blood smear. 7. Documented pulmonary infection with Staphylococcus aureus obtained by bronchoalveolar lavage (BAL), mini-BAL, protected endotracheal aspiration/aspirate (ETA) (collectively 'airway specimen'). Exclusion Criteria 1. The subject is unlikely to survive for the study duration despite delivery of adequate antibiotics and supportive care for treatment of S. aureus pneumonia. 2. Effective antibacterial drug therapy for the index pneumonia administered continuously for 48 hours or more prior to initiation of study treatment. Effective antibiotics would include those typically used to treat S. aureus. 3. Plasmapheresis (ongoing or planned), extracorporeal membrane oxygenation (ECMO) or any procedure that would remove/filter out the monoclonal antibody/study drug. 4. Immunocompromised patients. 5. Known hereditary complement deficiency. 6. Liver dysfunction with a Child Pugh C score \> 9 (Child Pugh score of A or B are acceptable at discretion of the Principal Investigator \[PI\]). 7. Pulmonary disease that precludes evaluation of a therapeutic response (such as lung cancer resulting in bronchial obstruction or on the same side as the pneumonia, active tuberculosis, cystic fibrosis, granulomatous disease, fungal pulmonary infection, lung abscess, pleural empyema or post obstructive pneumonia). 8. Patient has received intravenous (IV) immunoglobulin therapy within 3 months prior to the Screening Visit. 9. Any woman of child-bearing potential (WOCBP) who does not have a negative pregnancy test result at Screening using SERUM or URINE testing based on Beta-subunit human chorionic gonadotropin (HCG) standard tests and methods from the local laboratory. 10. Any sexually active subject who is unwilling to use acceptable methods of contraception for 120 days after dosing. 11. Known lack of treatment compliance from prior studies or ongoing medical care based on medical records and PI's judgment and/or the capacity of the patient to comply with all study requirements. 12. Any medical, psychological, cognitive, social or legal conditions that would interfere in the ability to give an Informed Consent OR the absence of a legally valid representative of the patient or independent physician allowed and able to give consent on his/her behalf. 13. Participation as a subject in another interventional study within 30 days prior to the first dose of study treatment, or planned participation in such a study during the study or within 30 days of its completion by the patient.