Immune checkpoint inhibitors (ICIs) have yielded remarkable responses in patients across multiple cancer types, but often lead to immune related adverse events (irAEs). Although a germline cause for irAEs has been hypothesized, no systematic genome wide association study (GWAS) has been performed and no individual variants associated with the overall likelihood of developing irAEs have yet been identified. We carried out a Genome-Wide Association Study (GWAS) of 1,751 patients on ICIs across 12 cancer types, with replication in an independent cohort of 196 patients and independent clinical trial data from 2275 patients. We investigated two irAE phenotypes: (i) high-grade (3-5) events defined through manual curation and (ii) all detectable events (including high-grade) defined through electronic health record (EHR) diagnosis followed by manual confirmation. We identified three genome-wide significant associations (p<5x10-8) in the discovery cohort associated with all-grade irAEs: rs16906115 near IL7 (combined p=1.6x10-11; hazard ratio (HR)=2.1), rs75824728 near IL22RA1 (combined p=6.6x10-9; HR=1.9), and rs113861051 on 4p15 (combined p=1.3x10-8, HR=2.0); with rs16906115 replicating in two independent studies. The association near IL7 colocalized with the gain of a novel cryptic exon for IL7, a critical regulator of lymphocyte homeostasis. Patients carrying the IL7 germline variant exhibited significantly increased lymphocyte stability after ICI initiation than non-carriers, and this stability was predictive of downstream irAEs and improved survival.

2507 Background: Myocarditis due to immune checkpoint inhibitors (ICIs) is uncommon; however, myocarditis due to ICIs leads to severe morbidity and even death in 20-40% of cases. The molecular underpinnings of ICI-associated myocarditis are poorly understood, and there is an unmet clinical need to identify therapeutic targets and biomarkers that can aid in disease management. Methods: Heart tissue was obtained through endomyocardial biopsy or autopsy of patients receiving ICIs and was profiled with paired single-cell RNA sequencing (scRNA-seq) and T cell receptor sequencing (TCR) using the 10x Genomics Chromium system. A control dataset was constructed using scRNAseq data of heart tissue from patients receiving ICIs but without myocarditis and a published dataset from healthy patients not receiving ICIs. Peripheral blood mononuclear cells (PBMCs) were collected at the time of myocarditis diagnosis in a larger cohort of patients and analyzed with ICI-treated controls. The CITE-Seq protocol was used to measure paired scRNA-seq, TCR, and surface proteomics in PBMCs, using serial timepoints where available. Results: Heart tissue from 13 patients with myocarditis, including three fatal cases, and seven controls yielded 77,712 single cells. Blood profiling from 27 patients with ICI myocarditis and ICI-treated controls across 54 samples yielded over 230,000 cells. ICI myocarditis tissue demonstrated an increased T cell infiltrate (OR 8.94, FDR = 0.0021). Expression of multiple inflammatory pathways, most notably interferon responses, was up-regulated across multiple immune and non-immune cell types in the setting of myocarditis, providing important pathophysiological insights. T cell clones were also found to be shared between blood and heart, enabling the identification of putative pathogenic T cell subsets. Conclusions: Increased intramyocardial T cells and the activation of interferon response gene networks were seen in the setting of ICI myocarditis. These preliminary findings highlight potential pathological pathways in ICI myocarditis that could serve as biomarkers or therapeutic targets.

Background Immune checkpoint inhibitors (ICI) are associated with a distinct spectrum of toxicities. Data on irAE hospitalization rates and clinical course of patients with thoracic malignancies are lacking. Methods Patients with advanced thoracic malignancy treated with ICI (2/2016 -6/2021) were retrospectively identified. Demographic and clinical data of confirmed irAE hospitalizations were extracted from the medical record and a descriptive analysis was performed. ResultsFrom February 2016 to June 2021, 1,312 patients with thoracic malignancy received ICI (monotherapy, combination with 2nd ICI or other agents) with 102 patients (7.7%) hospitalized for irAEs . Treatment intent was first-line therapy with ICI in most patients (N= 50, 49%) and adjuvant ICI in 9% (N =9). 59% (N =60) received ICI alone, 32% (N =33) chemo plus immunotherapy, and 7% (N =7) dual ICI. The average age on admission was 68 years in both genders. The median time between ICI initiation and admission was 64 days (1-935). The most common evidenced irAEs were pneumonitis (N = 38, 37%), hepatitis (N = 20, 20%), myocarditis (N = 14, 14%) and colitis (N = 13, 13%). Nearly half (N = 18, 47%) of patients with pneumonitis were treated with prior thoracic radiation and received first line (N = 22, 58%) ICI. Pneumonitis cases had the highest 60-day readmission rate (37%, N = 14) with a 60-day mortality rate of 53% (N = 20). 60-day re-admission and mortality rates were 19% (N = 17) and 29% (N = 26), respectively, among the rest of the cohort. Multi-organ toxicity occurred in 36% (N = 37) of patients. Myocarditis patients often had a concomitant irAE (79%; 11/14) with 36% (N = 5) presenting overlapping neuromuscular toxicity. Overall, 64% (N = 65) received IV corticosteroids for a median duration of 42.5 days (0-527) and 18% (N = 18) required second line immunosuppression. irAEs solved to grade 1 or less after immunosuppression in 63 patients. Seven patients (7%) experienced a grade 5 event while admitted. ICI rechallenge occurred in 14 patients. Median OS was 360 days; (16 -2219, table 1). Conclusions Severe irAE requiring inpatient admission, though infrequent, results in considerable morbidity, mortality, and healthcare utilization. Pneumonitis was the most common irAE requiring inpatient management in our lung cancer population with a significant risk of mortality despite the use of guideline-directed systemic immunosuppression. This study highlights the continued need for prospective research to optimally manage severe toxicities, particularly pneumonitis. Ethics Approval The study obtained IRB approval.Protocol #: 2017P000501.

Introduction: Myocarditis due to immune checkpoint inhibitors (ICIs), a type of cancer immunotherapy, is associated with high morbidity and mortality. The cellular and molecular pathogenesis of ICI myocarditis remains largely unknown. Identification of circulating factors associated with intracardiac pathology may aid new clinical approaches. Hypothesis: We hypothesized that ICI myocarditis is associated with increased abundance of intracardiac immune cells and upregulated inflammatory genes in the heart and serum. Methods: Heart tissue from 13 patients with ICI myocarditis was acquired by endomyocardial biopsy or autopsy; peripheral blood mononuclear cells (PBMCs) were also collected from ten of these patients and eight additional ICI myocarditis patients. Control heart tissue was derived from six hearts declined for transplantation (non-ICI-exposed) and from the biopsy and autopsy of one ICI-treated patient without myocarditis. The 10x Genomics Chromium system was used to generate single-cell RNA sequencing (scRNAseq) data from heart and PBMC specimens. Serum proteins were measured by core lab assay (for troponin T) or by multiplexed Luminex immunoassay. Results: Unbiased clustering of scRNAseq data from 77,071 cells recovered from heart samples revealed 37 cell subsets across 10 cell lineages. Myocarditis heart tissue demonstrated enrichment of T/NK cells (odds ratio 8.3, p=0.0006), B/plasma cells (OR 5.1, p=0.01), and dendritic cells (DCs) (OR 9.2, p=0.006) relative to controls. Circulating DC abundance was decreased in fatal (n=3) versus nonfatal (n=15) myocarditis cases (p=0.008), while intracardiac DC abundance was directly associated with serum troponin T values (p=0.02). The levels of five immunomodulatory factors - IL-15, CXCL9, CCL3, TNFα, and CCL21 - were found to be significantly upregulated transcriptionally in at least one intracardiac cell subset and at the protein level in the serum of myocarditis cases. Conclusions: Fatality status and troponin level associated with intracardiac DC abundance and multiple immunomodulatory genes were upregulated in both the heart and serum in ICI myocarditis. These observations may guide novel diagnostic and therapeutic strategies.

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