Clinical Significance of Tumor Infiltrating Lymphocytes and Modulation by Neoadjuvant Chemotherapy in Colorectal...

Background: Colorectal cancer liver metastases (CRCLMs) are associated with treatment resistance, and poor survival. We aimed to measure the differences in the immune composition of primary colorectal tumors and CRCLMs to identify prognostic and potentially actionable differences in the tumor microenvironment (TME). Methods: We created two independent cohorts of patients that had surgical resection of primary colorectal tumor and CRCLM resection at the Yale Cancer Center, comprising of 84 and 95 cases arranged in tissue microarray (TMA) format. Using multiplex quantitative immunofluorescence (QIF) we measured CD4⁺, CD8⁺, and FOXP3⁺ immune cells across spatially-resolved compartments within the tumor samples. We then assessed the association of clinicopathologic variables and treatment-specific outcomes with immune cell composition. Results: CRCLMs showed significantly higher CD8⁺ effector T-cells and significantly lower FOXP3⁺ regulatory T-cell infiltration than primary tumors. In addition, high CD8⁺ T-cell infiltration within the cancer cell compartment of CRCLMs was prominently associated with longer overall survival in both cohorts (Cohort1: HR = 0.38, p = 0.032; Cohort2: HR = 0.23, p = 0.046). Neoadjuvant chemotherapy (NAC) was associated with a significant increase in CD8⁺ T-cells across all tumor tissue regions in CRCLMs (p < 0.01 in both cohorts). However, NAC was not associated with improved three-year progression-free survival in either cohort (Cohort1: HR = 0.75, p = 0.43; Cohort2: HR = 0.97, p = 0.93). Conclusions: The TME of CRCLMs is characterized by reduced Tregs and increased TILs in NAC-treated patients. Furthermore, increased CD8⁺ infiltration in the tumoral compartment within CRCLMs is associated with improved survival. Our results describe local adaptive anti-tumor immune responses seen in CRCLM and underscore the need for novel therapeutic strategies that leverage TME alterations.