Tumors can recruit, induce, and expand regulatory T cells (Tregs) to suppress antitumor immune responses for survival and progression. The complicated tumor-related Treg subsets and their functional mechanisms are not fully addressed yet. We have previously identified a novel CD4⁺CD69⁺Foxp3⁻ Treg subset in tumor-bearing mice, which suppresses CD4 T cell response via membrane-bound transforming growth factor beta 1 (mTGF-β1) and then promotes tumor progression. In hepatocellular carcinoma patients, here, we identified tumor-infiltrating human CD4⁺CD69⁺ Tregs which represent ~67.2 % of tumor-infiltrating CD4 T cells that is significantly higher than conventional CD4⁺CD25⁺Foxp3⁺ Tregs. They expressed mTGF-β1, PD-1, and CTLA-4, but not CD25 or Foxp3, and only produced a little interleukin (IL)-10 and TGF-β1. More importantly, they significantly suppressed CD4 T cell response via mTGF-β1 in vitro. Furthermore, the percentage of these CD4⁺CD69⁺ Tregs in tumor tissue was significantly correlated with tumor progression, which is more pronounced at the late stage of cancer patients. Thus, we have identified a tumor-induced new population of human CD4⁺CD69⁺ Tregs in cancer patients with phenotype of CD25⁻Foxp3⁻mTGF-β1⁺CTLA-4⁺PD-1⁺, and these Tregs can suppress antitumor immune response via mTGF-β1. Our results not only enrich the family of Treg subsets, providing new mechanistic insight to tumor-induced immune suppression in human, but also suggest a potential target for cancer immunotherapy.
Key message: CD4⁺CD69⁺Foxp3⁻ regulatory T cells were identified in hepatocellular carcinoma patients. These Treg cells inhibit T cell response via membrane-bound TGF-β. The percentage of these cells was significantly correlated with tumor progression. The percentage of these cells was higher than conventional CD4⁺CD25⁺Foxp3⁺ Tregs. These Treg cells not only exist in tumor-bearing mice, but also in cancer patients.