Correlations between Circulating and Tumor-Infiltrating CD4 + T Cell Subsets with Immune Checkpoints in Colorectal Cancer.

T regulatory cells (Tregs) play different roles in the regulation of anti-tumor immunity in colorectal cancer (CRC), depending on the presence of different Treg subsets. We investigated correlations between different CD4 + Treg/T cell subsets in CRC patients with immune checkpoint-expressing CD4 + T cells. Positive correlations were observed between levels of different immune checkpoint-expressing CD4 + T cells, including PD-1, TIM-3, LAG-3, and CTLA-4 with FoxP3 + Tregs, Helios + T cells, FoxP3 + Helios + Tregs, and FoxP3 + Helios - Tregs in the tumor microenvironment (TME). However, negative correlations were observed between levels of these immune checkpoint-expressing CD4 + T with FoxP3 - Helios - T cells in the TME. These correlations in the TME highlight the role of cancer cells in the upregulation of IC-expressing Tregs. Additionally, positive correlations were observed between levels of FoxP3 + Tregs, Helios + T cells, FoxP3 + Helios + Tregs, and FoxP3 + Helios - Tregs and levels of CD4 + CTLA-4 + T cells and CD4 + PD-1 + T cells in peripheral blood mononuclear cells (PBMCs) and normal tissue-infiltrating lymphocytes (NILs). These observations suggest that CTLA-4 and PD-1 expressions on CD4 + T cell subsets are not induced only by the TME. This is the first study to investigate the correlations of different FoxP3 +/- Helios +/- T cell subsets with immune checkpoint-expressing CD4 + T cells in CRC patients. Our data demonstrated strong correlations between FoxP3 +/ Helios +/- Tregs but not FoxP3 - Helios +/- non-Tregs and multiple immune checkpoints, especially in the TME, providing a rationale for targeting these cells with highly immunosuppressive characteristics. Understanding the correlations between different immune checkpoints and Treg/T cell subsets in cancer patients could improve our knowledge of the underlying mechanisms of Treg-mediated immunosuppression in cancer.