The purpose of this study is to confirm and extend the Phase 1-2 KB001 findings of an airway anti-inflammatory effect in CF individuals with chronic Pseudomonas aeruginosa (Pa) airway infection. It is hypothesized that steady-state levels of KB001-A in CF subjects with airway Pa infection will be safe and well-tolerated, and will increase the time-to-need for antibiotic treatment (IV, inhaled, or oral) for worsening of respiratory tract signs and symptoms compared with placebo.

Inclusion Criteria:

• Individuals with CF who are older than 50 years of age may participate if treated with 2 or more courses of antibiotics (IV and/or oral) for respiratory sign and symptoms (CF exacerbation) in the 12 months before the Screening Visit
• Confirmed diagnosis of CF
• At least 2 respiratory tract cultures in the previous 12 months, with Pa present. The most recent positive Pa culture must be within 12 weeks before the Screening Visit (or obtain a positive culture at screening)
• FEV1 % levels within acceptable ranges (per the study protocol)
• Received inhaled ABX for equivalent of 8 weeks or greater in the 26 weeks before the Day 0 Visit

Exclusion Criteria:

• Treatment with antibiotics for acute illness within the 4 weeks before the Day 0 Visit
• Use of systemic corticosteroids within the 4 weeks before the Day 0 Visit
• Any change in regimen of CF maintenance therapies within the 4 weeks before the Day 0 Visit
• History of sputum cultures positive for B. cepacia complex in the 2 years before the Screening Visit
• History of organ transplantation
• Current smoker (tobacco, marijuana, or any other material). Use of smokeless inhalers/vaporizers for these materials is also prohibited
• History of drug addiction or alcohol abuse in the 12 months before the Screening Visit
• History of hepatic disease (clinical cirrhosis or portal hypertension), renal dysfunction
• Breast-feeding or pregnancy as evidenced by a positive blood pregnancy test
• Receiving any investigational drug in the 16 weeks (or 5 half lives) before the Day 0 Visit, whichever is longer