Abstract 607: CD8+ T cell clones maintain a pool of memory-like Ly108+ cells in the tumor during their contraction phase
Authors: Takahashi Munetomo , Tsunoda Mikiya , Aoki Hiroyasu , Ogiwara Haru , Shichino Shigeyuki , Matsushima Kouji , Ueha Satoshi 
Published: April 2023

Abstract
The immune response against cancer is effectuated by the recruitment of expanding CD8+ T cell clones. However, the fate of these clonal populations that have migrated into the tumor environment - whether they persist, contract, and/or produce memory cells - is unknown. An improved understanding of clonal durability and potency will be essential for the development of novel cancer immunotherapies.
Here, we applied our previously developed bilateral tumor mouse model to track the fate of endogenous T cell clones responding to tumors in the same individual. This approach relied on the fact that the clonal composition of the two tumors is identical, allowing the sampling and comparison of tumor-infiltrating cells from the same clonal populations on different days in the same individual. Mice were inoculated bilaterally with Lewis lung carcinoma (LLC), and tumors were resected, one after the other, on days 14 and 21 post-inoculation. At each timepoint, sampled CD8+ T cells were gated on PD1, Ly108, and TIM-3 expression and subjected to T-cell receptor (TCR) sequencing to identify clones. We utilized this data to quantify changes in the fraction of memory-like (Ly108+TIM-3-) and exhausted (Ly108-TIM-3+, Ly108+TIM-3+) cells of individual clonal populations over time.
The majority (75%) of tumor-infiltrating CD8+ T cells on day 14 belonged to clonal populations that persisted on day 21. These clonal populations were classed as ‘expanding’ or ‘contracting’ based on changes in their clone size. Despite the polyclonal response to the tumor, almost all expanding clones contained a high fraction of memory-like (Ly108+TIM-3-) cells, whereas almost all ‘contracting’ clones contained a high fraction of exhausted (TIM-3+) cells. These characteristics were sufficient to predict whether a clonal population at day 14 would later expand or contract. We further quantified how the makeup of ‘contracting’ clonal populations changed over time. While all ‘contracting’ clonal populations lost a considerable number of exhausted (TIM3+) cells, half of the clonal populations maintained a pool of memory-like (Ly108+TIM-3-) cells in the tumor.
These results demonstrate that clonal dynamics can be predicted from static measurements, facilitating the development of novel methods to infer patient immune activity. The results also demonstrate the possibility of altering clonal fate. Reinvigoration of the pool of memory-like cells maintained in the tumor could re-expand contracting clonal populations, and thereby enhance the immune response against the tumor.
Citation Format: Munetomo Takahashi, Mikiya Tsunoda, Hiroyasu Aoki, Haru Ogiwara, Shigeyuki Shichino, Kouji Matsushima, Satoshi Ueha. CD8+ T cell clones maintain a pool of memory-like Ly108+ cells in the tumor during their contraction phase [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 607.