Diversity of draining lymph node-tumor overlapping T cell receptor repertoire reflects the anti-tumor effect of cancer immunotherapies

Abstract

Abstract CD8+ tumor-infiltrating lymphocytes, the main effector cells of anti-tumor immune responses, are composed of various T cell clones. Numerous studies have demonstrated the presence of tumor-reactive T cell clones with high frequency in tumors. However, it remains unclear as to which of the two mechanisms, the expansion of limited tumor-specific clones or the induction of diverse tumor-reactive ones, is more beneficial for the action of immune checkpoint inhibitors (ICIs). To address this question, we performed a T cell receptor repertoire analysis on B16F10 and on Lewis lung carcinoma tumor-bearing mice treated with immunotherapy including anti-PD-L1 monoclonal antibody (mAb) and anti-CD4 depletion mAb, which enhance the expansion of tumor-reactive CD8+ T cells. We focused on the T cell clones that overlapped between the tumor and draining lymph node (dLN) to analyze the T cell clones that were mobilized into the anti-tumor response after treatment. In anti-PD-L1 and anti-CD4 treated mice, the total frequency of CD8+ dLN-tumor overlapping clones in the tumor was increased. Surprisingly, although the expansion of the top10 overlapping clones did not differ, ICI treatment increased the total frequency of the 11th or lower overlapping clones, indicating the broadening of the tumor-reactive T cell repertoire. Moreover, the administration of FTY720 to tumor-bearing mice, which inhibits egress of T cells from the LNs to circulation, reduced the total frequency of the 11th or lower overlapping clones in the tumor and reduced the long-term anti-tumor effect of anti-PD-L1 treatment. These results suggest that mobilization of diverse tumor-reactive clones is essential for enhancing and persistent anti-tumor effect of ICIs.