CYstic Fibrosis bacterioPHage Study at Yale (CYPHY)

Inclusion Criteria: 1. Capable of giving signed informed consent; 2. Stated willingness to comply with all study procedures and availability for the duration of the study; 3. Age ≥18; 4. CF diagnosis based upon genetics, sweat chloride testing, or clinical manifestations; 5. Able to provide repeated induced sputum samples; 6. Able to use a nebulizer; 7. PsA culture positive on one occasions within past 2 years and in sputum at screening visit; 8. FEV1 \>40%; 9. Clinically stable lung disease, defined as no decrease in FEV1 \>10% or pulmonary exacerbations in the 4 weeks prior to screening; 10. If on CF modulator therapy (e.g., ivacaftor, ivacaftor/elexacaftor/tezacaftor), then subject remains on the same modulator therapy for at least 2 months prior to enrollment; 11. For females of reproductive potential: use of effective contraception for at least 1 month prior to screening and agreement to use 2 methods of effective contraception during study participation and for an additional 6 weeks after the end of YPT-01 administration; 12. Males of non-reproductive potential (e.g., documented congenital bilateral absence of vas deferens) or males of reproductive potential (e.g., non-vasectomized males or males vasectomized less than 120 days prior to study start) that agree to use condoms with spermicide while engaging in sexual activity or be sexually abstinent. Exclusion Criteria: 1. History of solid organ transplant (e.g., lung or liver); 2. Severe neutropenia, as defined by absolute neutrophil count (ANC) of \< 500 per microliter; 3. No YPT-01 phage identified that effectively targets sputum PsA; 4. Treatment for pulmonary exacerbation within the prior 4 weeks; 5. Change in pulmonary medications within the prior 4 weeks; 6. Subjects who are pregnant, who intend to become pregnant, or who do not wish to use contraception; 7. Subjects who are breastfeeding; 8. Participation in another clinical research study concurrently or within the prior 2 months; 9. Known allergy to soy, egg, yeast, or meat. 10. Any genetic or acquired (including medication-induced) immunocompromised condition, beyond the level of immunocompromise typically associated with CF and its management.