Co‐expression of LAG3 and TIM3 identifies a potent Treg population that suppresses macrophage functions in colorectal cancer patients

Summary Regulatory T (Treg) cells are critical suppressors of inflammation and are thought to exert mainly deleterious effects in cancers. In colorectal cancer ( CRC ), Foxp3 + Treg accumulation in tumors was associated with poor prognosis. Hence, we examined the circulating Treg cells in CRC patients. Compared to controls, CRC patients presented mild upregulations in CD 4 + CD 25 +/hi T cells and in the more canonical CD 4 + CD 25 +/hi Foxp3 + Treg cells in peripheral blood mononuclear cells. Both of these Treg populations could be roughly divided into lymphocyte activation gene 3 negative T cell immunoglobulin and mucin‐domain containing‐3 negative ( LAG 3 − TIM 3 − ) and LAG 3 + TIM 3 + subsets. In CRC patients, the LAG 3 + TIM 3 + subset represented approximately half of CD 4 + CD 25 +/hi T cells and greater than 60% of CD 4 + CD 25 +/hi Foxp3 + Treg cells, which was significantly more frequent than in healthy controls. Compared to the LAG 3 − TIM 3 − CD 4 + CD 25 +/hi T cells, the LAG 3 + TIM 3 + CD 4 + CD 25 +/hi T cells presented considerably higher transforming growth factor‐β and slightly higher interleukin ( IL )‐10 secretion, together with higher cytotoxic T‐lymphocyte associated protein 4 and Foxp3 expression levels. Notably, macrophages following incubation with LAG 3 − TIM 3 − CD 4 + CD 25 +/hi T cells and LAG 3 + TIM 3 + CD 4 + CD 25 +/hi T cells displayed different characteristics. Macrophages incubated with LAG 3 + TIM 3 + CD 4 + CD 25 +/hi T cells presented lower expression of major histocompatibility complex class II , CD 80, CD 86, and tumor necrosis factor‐α but higher expression of IL ‐10, than macrophages incubated with LAG 3 − TIM 3 − CD 4 + CD 25 +/hi T cells. Together, our investigations demonstrated that CRC patients presented an enrichment of circulating Treg cells, in which the LAG 3 + TIM 3 + subset exhibited more potent expression of inhibitory molecules, and furthermore, the LAG 3 + TIM 3 + Treg cells could suppress the proinflammatory activation of macrophages more potently than the LAG 3 − TIM 3 − Treg cells.