Molecular characterization of immune-related severe adverse events (irSAE).

Abstract

3076 Background: Immune checkpoint inhibitors (ICIs; anti-CTLA-4 and anti-PD-1) have shown clinical success in many cancers, but may cause rare irSAE. The molecular features of irSAE have not been extensively explored. Therefore, we characterized the immune composition of tissue affected by ICI-mediated inflammation with a focus on colitis and neurologic toxicity. Methods: We performed retrospective T-cell receptor (TCRβ) sequencing, RNA-sequencing (HTG EdgeSeq; > 2500 immune-related genes), and digital spatial profiling (NanoString) for 20 protein markers in 10 regions across tissues representing ICI-induced colitis, autoimmune inflammation (e.g. Crohn’s) and normal colon. Matched tumors were also included in a subset. We also analyzed the encephalitic and healthy brain of a unique presentation of anti-PD-1-induced encephalitis. Results: Patient-matched melanoma and colitis biopsies (n = 3) demonstrated shared T cell clones in all samples ranging from several shared clones to several hundred (0.4%, 2.7%, and 3% of rearrangements, respectively), including high-frequency clones. Shared TCRβ sequences were also identified among and between colon-irSAE and Crohn’s specimens. Gene expression patterns of inflammation in colon-irSAE resembled that of Crohn’s disease in principle components and clustering analysis, highlighting likeness between these diseases/SAEs. NanoString digital spatial profiling of regions of inflammation across samples showed higher CD68 and PD-L1 positivity in colon-irSAE specimens versus normal colon or Crohn’s specimens and reduced beta-catenin levels in both Crohn’s and colon-irSAE specimens relative to normal controls. Finally, we detected a high degree of TCR clonality in the encephalitic brain, including a single sequence present in ~20% of > 12,000 T cells, suggesting a distinct antigen-specific response. Conclusions: We report the molecular characteristics of irSAE in colon and brain specimens from patients receiving ICIs. Highly clonal TCRβ sequences were frequently detected, particularly in a unique case of encephalitis-irSAE. Furthermore, we identify molecular distinctions and similarities between autoimmune and colon-irSAEs at the gene expression and proteomic levels.