Characterization of the T-cell receptor beta chain repertoire in tumor-infiltrating lymphocytes

Tumor-infiltrating lymphocytes (TILs) are direct effectors of tumor immunity, and their characterization is important for further development of immunotherapy. Recent advances in high-throughput sequencing technologies have enabled a comprehensive analysis of T-cell receptor (TCR) complementarity-determining region 3 (CDR3) sequences, which may provide information of therapeutic importance. We developed a high-fidelity target sequencing method with the ability for absolute quantitation, and performed large-scale sequencing of TCR beta chain (TCRB) CDR3 regions in TILs and peripheral blood lymphocytes (PBLs). The estimated TCRB repertoire sizes of PBLs from four healthy individuals and TILs from four colorectal cancer tissue samples were 608,664-1,003,098 and 90,228-223,757, respectively. The usage of J- and V-regions was similar in PBLs and TILs. Proportions of CDR3 amino acid (aa) sequences occupying more than 0.01% of the total molecular population were 0.33-0.43% in PBLs and 1.3-3.6% in TILs. Additional low coverage sequencing of 15 samples identified five CDR3 aa sequences that were shared by nine patients, one sequence shared by 10 patients, and one sequence shared by 12 patients. The estimated size of the TCRB repertoire in TILs was significantly smaller than that in PBLs. The proportion of abundant species (>0.01%) in TILs was larger than that in PBLs. Shared CDR3 aa sequences represent a response to common antigens, and the identification of such CDR3 sequences may be beneficial in developing clinical biomarkers.