This is a randomized, double-blind, placebo-controlled, multicenter study to evaluate the safety and tolerability of BX004-A in CF subjects with chronic PsA pulmonary infection. The study is divided into two parts, a single-ascending and multiple-dose phase (Part 1) and a multiple dose phase (Part 2). Subjects in both parts will be included in a 6-month safety follow-up. A Data Safety Monitoring Board will monitor safety in both parts. The purpose of the study is to evaluate safety and tolerability of BX004-A, and whether BX004-A reduces the PsA burden in the sputum of CF subjects with chronic PsA pulmonary infection. Clinically stable CF subjects with a confirmed diagnosis of CF and chronic PsA pulmonary infection will be enrolled.