Abstract
Intratumoral heterogeneity has been revealed in primary liver carcinoma (PLC). However, spatial heterogeneity of tumor-infiltrating lymphocytes (TILs), which reflects one dimension of a tumor's spatial heterogeneity, and the relationship between TIL diversity, local immune response and mutation burden remain unexplored in PLC. Therefore, we performed immune repertoire sequencing, gene expression profiling analysis and whole-exome sequencing in parallel on five regions of each tumor and on matched adjacent normal tissues and peripheral blood from five PLC patients. A significantly higher cumulative frequency of the top 250 most abundant TIL clones was observed in tumors than in peripheral blood. Besides, overlap rates of T cell receptor (TCR) repertoire for intratumor comparisons, significant higher than those for tumor-adjacent normal tissue comparisons and tumor-blood comparisons, which provide evidence for antigen-driven clonal expansion in PLC. Analysis of the percentage of ubiquitous TCR sequences, regional frequencies of each clone and TIL diversity suggested TIL clones varying between distinct regions of the same tumor, which indicated weak TCR repertoire similarity within a single tumor. Furthermore, correlation analysis revealed that TIL diversity significantly correlated with the expression of immune response genes rather than the mutation load. We conclude that intratumoural T-cell clones are spatially heterogeneous, which can lead to underestimate the immune profile of PLC from a single biopsy sample and may present challenge to adoptive cell therapy using autologous TILs. TIL diversity provides a reasonable explanation for the degree of immune response, implied TIL diversity can serve as a surrogate marker to monitor the effect of immunotherapy.
Highlights
Liver cancer is the third and second leading cause of cancer-related death among both men and women in China and worldwide, respectively [1, 2]
The number of unique TCR beta chain (TCRβ) reads was 2.55 × 105 to 9.88 × 105 for tumor tissues, 3.33 × 105 to 7.51 × 105 for adjacent noncancerous liver tissues, and 4.74 × to 1.27 × for peripheral blood, indicating that the average productive TCRβ reads between different tissue types were not significantly different, average unique TCRβ reads were significantly higher for peripheral blood than for tumor tissues or adjacent normal tissues
There was significantly higher overlap rates between tumor tissues than those between the tumor and other tissues.The results further suggested that the tumor-infiltrating lymphocytes (TILs) repertoire is more similar between tissues of the same tumor than that for tumor tissues compared to adjacent noncancerous tissue or peripheral blood (Figure 4), which agrees with findings published in esophageal cancer patients [16]
Summary
Liver cancer is the third and second leading cause of cancer-related death among both men and women in China and worldwide, respectively [1, 2]. PLC shows substantial heterogeneity at the genetic level in multiple clinical and genomic studies [6, 7]. Antigen-specific αβ-T cells account for the majority of TILs. simultaneously analyzing the thousands of TCR beta chain (TCRβ) CDR3 regions by next-generation sequencing (NGS) can reveal the T cell subclones from various diseases, including autoimmune diseases [13] chronic diseases [14], and even the spatial heterogeneity of the clonal composition of TILs [15,16,17]. Originating from livers with a history of chronic hepatocyte inflammation, PLC frequently displays significant heterogeneity between and even within tumors at genetic levels [6, 7]; whether spatial heterogeneity occurs in TIL populations in PLC remains unexplored
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