The underlying mechanisms of tumor-induced immune suppression need to be fully understood. Regulatory T (Treg) cells have been shown to play an important role in tumor immune escape. Until now, many subsets of Treg cells have been described that can suppress T cell response via different mechanisms. CD69 is generally regarded as one of the activating markers; however, recent studies show that CD69 may exert regulatory function in the immune response. In this study, we have identified tumor-induced CD69+CD4+CD25− T cells as a new subset of CD4+ Treg cells. CD69+CD4+CD25− T cells increase dramatically along tumor progression, with up to 40% of CD4+ T cells in the advanced tumor-bearing mice. Distinct from the previously described CD4+ Treg cell subsets, CD69+CD4+CD25− T cells express high CD122, but they do not express Foxp3 and secrete IL-10, TGF-β1, IL-2, and IFN-γ. CD69+CD4+CD25− T cells are hyporesponsive and can suppress CD4+ T cell proliferation in a cell-cell contact manner. Interestingly, the fixed CD69+CD4+CD25− T cells still have suppressive activity, and neutralizing Abs against TGF-β1 can block their suppressive activity. We found that CD69+CD4+CD25− T cells express membrane-bound TGF-β1, which mediates suppression of T cell proliferation. Furthermore, engagement of CD69 maintains high expression of membrane-bound TGF-β1 on CD69+CD4+CD25− T cells via ERK activation. Our results demonstrate that CD69+CD4+CD25− T cells act as a new subset of regulatory CD4+ T cells, with distinct characteristics of negative expression of Foxp3, no secretion of IL-10, but high expression of CD122 and membrane-bound TGF-β1. Our data contribute to the better understanding of mechanisms for tumor immune escape.

Hepatocellular carcinoma (HCC) is one of the most common malignancies worldwide with limited therapeutic options. HCC‐induced immunosuppression often leads to ineffectiveness of immuno‐promoting therapies. Currently, suppressing the suppressors has become the potential strategy for cancer immunotherapy. So, figuring out the immunosuppressive mechanisms induced and employed by HCC will be helpful to the design and application of HCC immunotherapy. Here, we identified one new subset of human CD14+CTLA‐4+ regulatory dendritic cells (CD14+DCs) in HCC patients, representing ∼13% of peripheral blood mononuclear cells. CD14+DCs significantly suppress T‐cell response in vitro through interleukin (IL)‐10 and indoleamine‐2,3‐dioxygenase (IDO). Unexpectedly, CD14+DCs expressed high levels of cytotoxic T‐lymphocyte antigen‐4 (CTLA‐4) and programmed death‐1, and CTLA‐4 was found to be essential to IL‐10 and IDO production. So, we identified a novel human tumor‐induced regulatory DC subset, which suppresses antitumor immune response through CTLA‐4‐dependent IL‐10 and IDO production, thus indicating the important role of nonregulatory T‐cell‐derived CTLA‐4 in tumor‐immune escape or immunosuppression. Conclusions: These data outline one mechanism for HCC to induce systemic immunosuppression by expanding CD14+DCs, which may contribute to HCC progression. This adds new insight to the mechanism for HCC‐induced immunosuppression and may also provide a previously unrecognized target of immunotherapy for HCC. (Hepatology 2014;59:567–579)

The ␤2 integrins play a key role in inflammation and immune responses. The ␤2 integrin CD11b has been shown recently to be important in the maintenance of tolerance; however, the underlying mechanisms remain to be fully understood. Natural killer (

Regulatory T cells can restrict the uncontrolled immune response and inflammation, avoiding pathologic immune injury to the host and thus playing important roles in the maintenance of immune homeostasis. Until recently, many subsets of CD4 and CD8 regulatory T cells have been reported. In this study, we identified CD11chighCD8+ T cells as a new subset of CD8+ regulatory T cells. During Listeria monocytogenes and Staphylococcus aureus infection, two subsets of CD8 T cells were classified according to the expression level of CD11c, including CD11clowCD8+ and CD11chighCD8+ T cells. CD11clowCD8+ T cells, existing during the whole period of infection, act as conventional activated T cells to kill target cells in a perforin-dependent manner. Interestingly, CD11chighCD8+ T cells appeared only at a late stage of infection, expressed relatively high CD122 and low CD69, did not secrete IFN-γ, IL-10, TGF-β, and exhibited much more potent cytotoxicity against target cells via Fas ligand–Fas pathway in an Ag-independent manner. Ligation of CD11c was important in the cytotoxicity of CD11chighCD8+ T cells. Furthermore, CD11chighCD8+ T cells could directly kill the activated CD4 T cells both in vitro and in vivo, whereas CD11clowCD8+ T cells could not. Thus, we identified an infection-induced new subset of CD11chighCD8+ regulatory T cells, which might contribute to protect host from pathological immune injure. Our results indicate that CD11c+CD8+ T cells are constitute a heterogeneous population that can be divided further into regulatory CD11chighCD8+ T cell subset and effector CD11clowCD8+ T cell subset, thus adding insight to the role of CD8 T cells in immune response and regulation.