The objectives of this study are to assess the safety, tolerability, pharmacokinetics, pharmacodynamics and clinical outcome of patients who have severe pneumonia caused by Staphylococcus aureus (S. aureus) after a single intravenous administration of KBSA301 in addition of standard of care antibiotic treatment.

S. aureus is a leading cause of bloodstream, skin, soft tissue, and lower respiratory tract infections worldwide. The frequencies of both nosocomial and community-acquired S. aureus infections have increased steadily over the years and the treatment of these infections has become more challenging due to the emergence of multi-drug resistant strains (e.g. methicillin-resistant Staphylococcus aureus).

S. aureus has several virulence factors that contribute to the pathogenesis of the infection. Amongst them, alpha-toxin that is involved in the pathogenesis of pneumonia, as it leads to apoptosis and cell lysis, in particular lymphocytes, macrophages, alveolar epithelial cells, pulmonary endothelium, and thrombocytes.

In spite of preventive measures for S. aureus infections and current medical treatment (mostly antibiotic therapy, alone or in combination), there is a clear unmet medical need in the clinic for additional treatment options. Passive immunotherapy with monoclonal antibodies may improve treatment options for severe and life-threatening infections like those caused by S. aureus.

Inclusion Criteria:

• Adult male or female patients ≥ 18 years and ≤ 70 years of age
• Severe pneumonia caused by S. aureus (either methicillin-resistant or methicillin-sensitive) managed in an ICU
• APACHE II of ≤30 at the time of diagnosis
• Identification of S. aureus
• Written informed consent provided by the patient, the relatives or the designated trusted person and/or according to local guidelines

Exclusion Criteria:

• Women of child bearing potential are excluded from the participation from the study unless they have a negative pregnancy test at baseline and during the course of the study. Postmenopausal women or females that have been surgically sterilized are allowed to participate.
• Hypersensitivity to excipients or to any prescribed medication
• Severe neutropenia, lymphoma or anticipated chemotherapy
• Patients who have long-term tracheostomy
• Current or recent investigational drug (within 30 days of enrollment, or 5 half-lives of the investigational compound, whichever is longer)
• Presence of meningitis, endocarditis, or osteomyelitis
• Acquired immune deficiency syndrome (AIDS) with cluster of differentiation 4 (CD4) count <200 cells/ml
• Known bronchial obstruction or a history of post-obstructive pneumonia.
• Active primary lung cancer or another malignancy metastatic to the lungs
• Cystic fibrosis, known or suspected Pneumocystis jiroveci pneumonia, or known or suspected active tuberculosis
• Immunosuppressive therapy
• Liver function deficiency
• Moribund clinical condition