A Fraction of CD8+ T Cells from Colorectal Liver Metastases Preferentially Repopulate Autologous Patient-Derived Xenograft Tumors as Tissue-Resident Memory T Cells

SIMPLE SUMMARY: Treatment options for colorectal cancer (CRC) patients with liver metastases are often limited to liver surgery with or without chemotherapy. However, not all patients present operable colorectal liver metastases (CRLMs). Thus, alternative therapies that exploit the anti-tumor potential of tumor-infiltrating lymphocytes (TILs) are being evaluated. The establishment of markers connecting the phenotype to the function of tumor-reactive CD8+ TILs could aid diagnostic and therapeutic advances. In this regard, tissue-resident memory T cells (T(RM) cells) could be a potential candidate for therapies targeting TILs. Putative tumor-reactive T(RM) cells among CD8+ TILs likely co-express CD103 and CD39, since these markers indicate stable tumor residency and repeated response to antigens from the tumor environment, respectively. Our phenotypic and functional analyses of TILs in CRLM, with a specific focus on CD103+CD8+ T(RM) cells, may guide the improvement of TIL-mediated CRC treatments. ABSTRACT: The diversity of T cells in the human liver may reflect the composition of TILs in CRLM. Our ex vivo characterization of CRLM vs. adjacent liver tissue detected CD103+CD39+CD8+ T(RM) cells predominantly in CRLM, which prompted further assessments. These T(RM) cells responded to cognate antigens in vitro. As functional activities of autologous TILs are central to the implementation of personalized cancer treatments, we applied a patient-derived xenograft (PDX) model to monitor TILs’ capacity to control CRLM-derived tumors in vivo. We established PDX mice with CRLMs from two patients, and in vitro expansion of their respective TILs resulted in opposing CD4+ vs. CD8+ TIL ratios. These CRLMs also displayed mutated KRAS, which enabled trametinib-mediated inhibition of MEK. Regardless of the TIL subset ratio, persistent or transient control of CRLM-derived tumors of limited size by the transferred TILs was observed only after trametinib treatment. Of note, a portion of transferred TILs was observed as CD103+CD8+ T(RM) cells that strictly accumulated within the autologous CRLM-derived tumor rather than in the spleen or blood. Thus, the predominance of CD103+CD39+CD8+ T(RM) cells in CRLM relative to the adjacent liver and the propensity of CD103+CD8+ T(RM) cells to repopulate the autologous tumor may identify these TILs as strategic targets for therapies against advanced CRC.