Characterizing the T cell repertoire in lung squamous cell premalignancy and its association with lesion outcome.

Abstract

102 Background: The immune response to frank malignancy has been the focus of published work, but little is known about the adaptive immune response to bronchial premalignant lesions (PMLs), precursors of lung squamous cell carcinoma. This study was designed to characterize the T cell receptor (TCR) repertoire in PMLs and its association with clinical, pathological and molecular features. Methods: Endobronchial biopsies (n=294) and brushings (n=137) from high-risk subjects (n=50), undergoing lung cancer screening at approximately 1-year intervals via auto fluorescence bronchoscopy and CT, were profiled by RNA-Seq as part of the Pre-Cancer Genome Atlas (PCGA). We applied the TCR Repertoire Utilities for Solid Tissue/Tumor (TRUST) tool to identify TCR CDR3 sequences in the RNA-Seq data. We quantified the ratio of private (i.e., found in one patient only) and public (i.e. found in two or more patients) TCRs that are found in curated databases with known antigen specificities. We measured the correlation of TCR diversity with previously derived PML transcriptional signatures and molecular subtypes; and with mutational burden among a subset of biopsies (n=115) also profiled with whole exome sequencing. Results: We detected 40,421 unique TCR sequences, of which 3,396 (8.4%) were found in more than one sample and 1,057 (2.6%) were found in two or more patients (i.e. Public). TCRs with known antigen specificities were enriched among public TCRs (p < 0.001). In PMLs with a proliferative molecular subtype reflective of dysplasia (n=80), TCR diversity was decreased in PMLs that regressed versus PMLs that progressed (p=0.045). TCR diversity was negatively associated with a transcriptional signature of T-cell mediated immune activation (Spearman’s rho -0.26, p < 0.001) but was not associated with mutational burden. Conclusions: To our knowledge, this is the first characterization of the TCR repertoire associated with bronchial premalignant lesions. TCR diversity may help predict the efficacy of the host immune response to PMLs but it is not associated with mutational burden. Further studies are needed to leverage these findings and explore the potential for immunoprevention of PMLs.