EPS9.10 Could anti-Pseudomonas aeruginosa antibodies be a useful marker in monitoring the effect of ETI treatment on airways’ microbiology in cystic fibrosis (CF)?

Objectives: CF patients in treatment with Elexacaftor, Tezacaftor, and Ivacaftor (ETI) show a reduction of airways secretion and expectoration is more difficult. This affects both the culture results and the definition of P. aeruginosa (Pa) chronicity, usually based on Leeds criteria. The aim of this work was to monitor Pa isolation and antibody response in patients in treatment with ETI. Methods: in patients attending our Centre we recorded the microbiology data 1-year before and 1-year after the beginning of ETI in the last 2 years. In addition, the titre of antibodies to Pa antigens (St-Ag) (serogroups 1–17) was assessed by ELISA (positive cut off >2.96 EU). Results: One hundred eighty-seven patients (median age 24.8 yrs; range 6.1–58.1) in treatment with ETI were analyzed. An average of 4.5 ± 1.9 microbiological culture (1.6 ± 1.9 pharyngeal swab, 2.8 ± 2.6 sputum) were tested for each patient. Fifty-six patients were Pa-free, 56 chronic and 27 intermittent according to the Leeds criteria, in 48 cases we had no quarterly cultures to define microbiological status. After one year, an average of 3.1 ± 2.1 microbiological cultures (1.7 ± 1.7 pharyngeal swabs, 1.4 ± 2 sputum) were taken; 48 patients were Pa-free, 41 chronic, 5 intermittent, in 93 cases we had no quarterly cultures to define microbiological status. In a subgroup of 37 Pa-positive patients, antibody titer decreased from 31.2 ± 52.2 EU before therapy to 15.1 ± 20.0 EU after therapy (P < .05). Moreover, after therapy, the antibody titre was 2.3 ± 1.4 EU in Pa intermittent patients and 21.6 ± 22.6 EU in chronic Pa patients (P < .05). Conclusions: ETI therapy had an effect on decreasing Pa isolation in respiratory samples and anti-Pa antibody titre. In this context, the definition of Pa chronicity becomes difficult to apply based only on microbiological criteria, and the utility of antibodies needs to be better evaluated since they remain positive in chronic patients. Acknowledgments: Niels Høiby for providing the Pa antigens. Journal of Cystic Fibrosis 22S2 (2023) S64–S199