The Prognostic Value of FoxP3+ Tumour-Infiltrating Lymphocytes in Rectal Cancer Depends on Immune Phenotypes Defined by CD8+ Cytotoxic T Cell Density.

Sören Schnellhardt,Marlen Haderlein,Arndt Hartmann,Luitpold Distel,Christoph Daniel,Maike Büttner-Herold,Johannes Hirneth,Rainer Fietkau

doi:10.3389/fimmu.2022.781222

Abstract

Tumour-infiltrating FoxP3+ regulatory T cells have been identified as both positive and negative prognostic factors in colorectal cancer (CRC) and rectal cancer (RC). In this study we investigated whether immune phenotypes, defined by CD8+ cytotoxic T cell density, may influence the prognostic association of FoxP3+ T cell densities in RC. Tissue microarrays from 154 rectal cancer resections were immunohistochemically double stained for CD8 and FoxP3. CD8+ and FoxP3+ cell densities were measured in the stromal and intraepithelial compartment. Stromal FoxP3+ cell densities were not associated with 10-year overall survival (OS). In the “immune-desert” phenotype, defined by very low stromal CD8+ cell density, a high density of stromal FoxP3+ T cells displayed a tendency towards an association with decreased 10-year OS (p = 0.179). In “inflamed” tumours, defined by high intraepithelial CD8+ T cell infiltration, the opposite was the case and high stromal FoxP3+ T cell densities were a positive prognostic factor (p = 0.048). Additionally, patients with an increased FoxP3/CD8 cell density ratio demonstrated a strong trend towards decreased 10-year OS (p = 0.066). These contrasting findings suggest functional heterogeneity within the group of FoxP3+ T cells. They are consistent with experimental studies which reported suppressive and non-suppressive populations of FoxP3+ T cells in CRC. Furthermore, our study demonstrates that CD8 immunohistochemistry may act as an instrument to identify tumours infiltrated by possibly functionally differing FoxP3+ T cell subtypes.

Highlights

The relevant relationship of immune cell infiltration in colorectal and rectal carcinomas (CRC) and patient prognosis has been established in numerous studies [1–4]
Cut-off values of these groups were defined by serial comparison of different CD8+ cell density thresholds for their impact on the prognostic significance of stromal forkhead box protein P3 (FoxP3)+ cell densities on overall survival (OS) and no-evidence-ofdisease survival rates (NED)
Tumours with stromal CD8+ cell densities of equal to or more than 40 cells/mm2 in combination with intraepithelial CD8+ cell densities of less than 170 cells/mm2 were assigned to the “immune-excluded” group, indicating a phenotype characterized by stromal accumulations of cytotoxic T cells with a simultaneous lack of intraepithelial infiltration (Figure 3D). 10-year OS was not associated with FoxP3+ cell densities in this group (Figure 3E)

Summary

Introduction

The relevant relationship of immune cell infiltration in colorectal and rectal carcinomas (CRC) and patient prognosis has been established in numerous studies [1–4]. Treg are an important element of immunological tolerance, both for selftolerance in healthy tissue and locally in tumours [9, 10] Targeting this cell type is regarded as a promising approach for improving the response rate of current immunotherapies [11]. Even the fundamental question of whether increased Treg infiltration in CRC is a favourable or unfavourable prognostic factor is still undecided and several studies have reported conflicting results [13, 14]. In this immunohistochemical study we investigated the prognostic relevance of FoxP3+ T cell density in the context of different degrees of intratumoural inflammation as signified by CD8+ T cell infiltration. Our results offer a possible explanation for inconsistent findings on the role of Treg in previous studies and give insights into the intricacies of Treg functionality in cancers

Methods

Results

Conclusion