Auto-reactive antibodies as predictive markers for immune checkpoint–induced pneumonitis

2554 Background: Certain immune-related adverse events (irAEs) that emerge with immune checkpoint blockade share clinical features of autoimmune conditions. Preexisting auto-reactive antibodies and their contribution to irAEs have not been well defined, and observations are limited. Methods: We longitudinally collected patient plasma samples from a clinical trial that combines immune checkpoint inhibitors, Ipilimumab, and Nivolumab (I+N) with subsequent radiation therapy (Lonestar, NCT03391869). Plasma samples were collected at baseline, after 12 weeks of I+N (induction), and at the time of Grade ≥ 2 pneumonitis (CTCAEv5.0). Auto reactive antibody profiles were analyzed using a fluorescence-based assay system that measures more than 130 antigens and is capable of assaying antibody reactivity for IgG and IgM fractions, including nuclear-cytosolic and tissue-specific antigens. Selected antibodies had a reportable result range, reference intervals, and reproducibility with quality controls. A paired t-test was used to compare the mean of longitudinally collected baseline and toxicity samples. An unpaired t-test was used to compare differences between groups. The False Discovery Rate was used to control the Type I error rate of multiple comparisons. Results: In the study cohort, G≥2 pneumonitis was observed in 11 patients out of 194 (5.6%). Serum was collected at baseline for all 11 patients, and 9 of the 11 patients had a serum sample collected at the time of pneumonitis event. Longitudinal serum samples (baseline and post-induction) collected from 32 patients without any irAEs were used as control. At baseline AChR3 and calmodulin antibodies were elevated in patients who developed pneumonitis, compared with baseline samples from controls (p≤0.05). At the time of pneumonitis IgM antibodies against AChR3, CXCL10, NSE, BAFF, CA242, Cytokeratin 19 were noted to be elevated in serum for pneumonitis cases compared with post induction samples from control (p≤0.005). Conclusions: We identified auto reactive antibodies associated with a higher risk of immunotherapy associated pneumonitis in patients treated with ipilimumab and nivolumab. These included auto reactive antibodies against proteins associated with lung injury (AChR3), lung inflammation (BAFF, CXCL10) and against alveolar epithelium (Cytokeratin 19). Future studies are warranted to determine if auto-reactive antibodies can be used as pre-treatment risk markers or to diagnose pneumonitis and may offer insights into to mechanisms that predispose toward pneumonitis.