Bronchoalveolar lavage fluid analysis in patients with checkpoint inhibitor pneumonitis

<bold>Objectives</bold>: Bronchoalveolar lavage fluid (BALF) analysis was a useful diagnostic approach for interstitial lung disease. However, BALF features were inconsistent in different studies of checkpoint inhibitor pneumonitis (CIP). <bold>Methods:</bold> We retrospectively reviewed the medical records of 154 patients with pathology-confirmed malignancy suffering from CIPs between July 2018 and December 2022. Patients who were arranged with bronchoalveolar lavage were enrolled in our study. <bold>Results:</bold> There were 42 CIP patients with results of BALF differential cell count and lymphocyte subset analysis. There were 32 males (76.2%). The mean age at the diagnosis of CIP were 62.0 ± 10.4 (range: 31-78) years old. The median time to onset of CIP was 98.5 days after the first dose of immune checkpoint inhibitors. There were 18 patients (42.9%) with low-grade CIPs and 24 patients (57.1%) with high-grade CIPs. The mean lymphocyte percentage was (36.7 ± 22.5) %. There were 34 (81%) CIP patients with lymphocytic cellular pattern. The median ratio of CD3+CD4+/ CD3+CD8+lymphocyte was 0.5 (0.3, 1.0). The ration was less than 1.0 in 31 CIP patients (73.8%). However, there was no significant difference in BALF feature between patients with low-grade vs. high-grade CIPs. <bold>Conclusions:</bold> CD3+CD8+ lymphocytosis pattern was the main BALF inflammatory profile in this cohort of CIP patients. <fig><object-id>erj;64/suppl_68/OA3786/F1</object-id><object-id>F1</object-id><object-id>F1</object-id><graphic></graphic></fig>