Prognostic association of FoxP3 regulatory T cells with tumor infiltrating CD8 cytotoxic T cells quantified on resected liver colorectal metastases (LCM)

Abstract

Background: The adaptive Th1 immune response (CD3/CD8/CD45RO T-cells) is a strong prognostic factor for the survival of the patients after colorectal primary tumor and metastases resection. The prognostic impact of regulatory T-cells (FoxP3) in metastatic settings is less characterized. Methods: Metastatic colorectal patients undergoing curative liver surgery for all resected LCM were investigated. For this cohort, we previously reported the prognostic role of an immune score based (IS) for T (CD3/CD8/CD45RO) and B (CD20) cells infiltration . The FoxP3 and CD8 cells infiltrating the center (CT ) and the invasive margin (IM) of LCM were immunohistochemically stained and their densities quantified on whole slides with a dedicated image analysis software. The mean value of the 3 most infiltrated areas (0.64 mm²) was calculated. The CT and IM densities of FoxP3 and CD8 were classified into high (Hi) or low (Lo) according to the minimum p-value cut-off. The total number of Hi densities determined the IS : 0-2 Hi (low IS) or 3-4 Hi (high IS). Cumulative DFS/OS analyses were performed using the Kaplan-Meier estimator. The hazard ratio for OS/DFS comparing (IS 0-2 vs 3-4) was determined using univariate Cox regression and the significance by log-rank tests. Results: 294 LCM from 88 patients (Male/Female 1.1, mean 3.3/patient, synchronous/metachronous 5.8) were included. Inter-metastatic heterogeneity for FoxP3 and CD8 (CT/IM) is high and observed among all patients. For the least infiltrated LCM/patient: a high IS is prognostic for DFS (HR:0.31 95%IC 0.18-0.53; p = 0.0006) and OS (HR:0.29 95%IC 0.14-0.64; p = 0.001). Independently of CD8 cells, a high FoxP3 density in both regions (CT/IM) is not prognostic for DFS (HR:0.53 95%IC 0.28-0.97; p = 0.74) but for OS (HR:0.16 95%IC 0.02-1.17; p = 0.04). Conclusions: Regulatory T cells associated with cytotoxic T cells in both tumor regions (CT/IM) of the least infiltrated LCM/patient are highly prognostic after curative resection. These results confirm the important role of tumor regions and FoxP3 for modulating the tumor immune response