The goal of this Phase 2b clinical trial is to see if nebulized phage (BX004) can treat chronic Pseudomonas aeruginosa (PsA) lung infection in CF subjects. The primary goal is to see if 8 weeks of twice daily BX004 can reduce the amount of PsA in the sputum compared to placebo (on top of background CF therapy).

This is a randomized, double-blind, placebo-controlled, multicenter study to evaluate BX004 in CF subjects with chronic PsA pulmonary infection. The main purpose of the study is to evaluate whether BX004 reduces the PsA burden in the sputum of CF subjects with chronic PsA pulmonary infection. Secondary endpoints are to see how well BX004 works in improving lung function and quality of life, reducing the amount of PsA in the sputum, getting negative sputum cultures for PsA, and safety and tolerability. Clinically stable CF subjects with a confirmed diagnosis of CF and chronic PsA pulmonary infection will be enrolled. Subjects will be included in a 6-month post-dose safety follow-up. A Data Safety Monitoring Board of the CF Foundation will monitor safety.

Key Inclusion Criteria:

• Cystic fibrosis patients with chronic Pseudomonas aeruginosa pulmonary infection receiving standard of care inhaled antibiotics (cycling or continuous regimen) or no inhaled antibiotics
• Age ≥ 18 years
• FEV1 40%-80% predicted
• Clinically stable lung disease
• Willing and able to provide adequate sputum samples, using any method (spontaneously expectorated, induced, from home or clinic) at designated study visits.

Key Exclusion Criteria:

• Known hypersensitivity to bacteriophages or excipients in the formulation.
• Receipt of prior bacteriophage therapy within the 6 months prior to Screening or Day 1
• Detection of Burkholderia cenocepacia from respiratory tract within 1 year prior to Screening or from Screening culture
• Currently receiving systemic treatment for allergic bronchopulmonary aspergillosis
• Currently receiving treatment for active infection with non-tuberculous mycobacteria or prior detection of Mycobacterium abscessus in 12 months prior to Screening
• History of severe neutropenia
• History of lung transplant
• History of solid organ transplant
• Acquired or primary immunodeficiency syndrome
• Initiation or change in type of CFTR modulator less than 3 months prior to Screening
• Pregnant or breastfeeding female

Blinded clinical trial