The aim of the present study was to characterize infiltrated T cell clones that define the
tumor immune environment and are important in the response to treatment in patients with advanced
colorectal cancer (CRC). In order to explore predictive
biomarkers for the efficacy of immunochemotherapies,
T cell receptor (TCR) repertoire analysis was performed using blood samples and
tumor tissues obtained from patients with advanced CRC that had been treated with a combination of five-
cancer peptide vaccines and
oxaliplatin-based
chemotherapy. The TCR-α/β complementary DNAs (cDNAs), prepared from the messenger RNAs (mRNAs) obtained from 17
tumor tissues and 39 peripheral blood mononuclear cells of 9 CRC patients at various time points, were sequenced. The oligoclonal enrichment of certain TCR sequences was identified in
tumor tissues and blood samples; however, only a few TCR sequences with a frequency of >0.1% were commonly detected in pre- and post-treatment
tumor tissues, or in post-treatment blood and tissue samples. The average correlation coefficients of the TCR-α and TCR-β clonotype frequencies between the post-treatment
tumor tissues and blood samples were 0.023 and 0.035, respectively, and were much lower compared with the correlation coefficients of the TCR-α and TCR-β clonotype frequencies between pre- and post-treatment blood samples (0.430 and 0.370, respectively), suggesting that T cell populations in
tumor tissues vary from those in blood. Although the sample size was small, a tendency for the TCR diversity in
tumor tissues to drastically decrease during the treatment was indicated in two patients, who exhibited a longer progression-free survival time. The results of the present study suggest that TCR diversity scores in tissues may be a useful predictive
biomarker for the
therapeutic effect of immunochemotherapy for patients with advanced CRC.