Abstract 1346: T cell receptor repertoire sequencing reveals chemotherapy-driven clonal expansion in colorectal liver metastases
Authors: Høye Eirik , Dagenborg Vegar Johansen , Torgunrud Annette , Lund-Andersen Christin , Fretland Åsmund Avdem , Lorenz Susanne , Edwin Bjørn , Hovig Eivind , Ree Anne Hansen , Flatmark Kjersti 
Published: June 2022

Abstract
Background: Colorectal liver metastasis (CLM) is a leading cause of cancer-related mortality in the industrialized world, and only a small fraction of patients are eligible for curative resections. While immune checkpoint inhibition (ICI) has resulted in major breakthroughs in some cancers, the response in microsatellite stable (MSS) colorectal cancer has been disappointing. High density of infiltrating T cells has been associated with improved overall survival and response to ICI. We previously found that T cell infiltration varied considerably in a cohort of MSS CLM cases, which could reflect varying sensitivity to ICI treatment. The aim of this study was to quantify and characterize T cell infiltration in CLM using T cell receptor (TCR) repertoire sequencing (TCRR-seq).
Methods: Resection specimens were collected from 85 patients with CLM included in the Oslo CoMet trial (NCT01516710). Of these, 37 and 13 patients had received neoadjuvant chemotherapy (NACT) within a short or long interval, respectively, prior to resection, while 35 had not (no-NACT group). TCRR-seq libraries were prepared from DNA extracted from CLM tissue using the hsTCRB kit from Adaptive Biotechnologies, which allows both quantitative and qualitative analysis of TCR repertoires. The T cell fraction relative to the total number of cells was estimated for each CLM sample. Repertoire clonality was analyzed using Hill diversity profiles, a mathematical framework for determining species diversity derived from the ecological literature. Network analyses were conducted to analyze convergence of clonal T cell receptor amino acid sequences in each repertoire.
Results: The mean CLM T cell fraction was 8.1% (0.4-31.3%), and tumors with high T cell fraction had more monoclonal repertoires (p=1.86E-6). Interestingly, CLM from patients in the short interval group had increased T cell infiltration compared to the no-NACT and long interval groups (mean 10.5% and 6.3%, respectively; p=0.04), and these repertoires were also more monoclonal (p=0.003). Network analysis revealed that clonally expanded T cells tended to exhibit little overall receptor similarity to other T cells in the repertoire. Clonally expanded T cells were overall also private (unique) to each patient.
Conclusion: A short interval between exposure to cytotoxic chemotherapy and surgical resection was associated with increased T cell infiltration in CLM samples, and the increase was associated with clonal expansion. The findings suggest that chemotherapy could be a driver of clonal expansion in this setting, possibly by induction of immunogenic cell death. Furthermore, the CLM neo-antigen landscape appears to be diverse and private to the individual patient.
Citation Format: Eirik Høye, Vegar Johansen Dagenborg, Annette Torgunrud, Christin Lund-Andersen, Åsmund Avdem Fretland, Susanne Lorenz, Bjørn Edwin, Eivind Hovig, Anne Hansen Ree, Kjersti Flatmark. T cell receptor repertoire sequencing reveals chemotherapy-driven clonal expansion in colorectal liver metastases [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1346.