The Study Of Relationship Between CD4~+CD25~+ Regulatory T Cells,PD-L1 And Ovarian Cancer

An organism has the function of immunologic surveillance that immune system may recognize and eliminate tumor cells that transformated from normal cells. As tumor cells express a series of tumor antigens, immune cells can recognize and eliminate tumor cells that express these antigens. The presence of TIL within the tumor microenvironment is considered to be an indication of the immune response to tumor antigens and is thought to reflect the dynamic process of"cancer immunoediting". But tumor cells may continuously grow by various kinds of ways or mechanisms that escape from immune system recognition and elimination. Regulation/Regulatory T cells maintain immunologic homeostasis, they also hamper immune responses that immune system aim directly at tumor, so they indirectly promote the growth of tumor and cause many troubles in tumor immunotherapy especially in tumor vaccine treatments. The programmed death-1(PD-1) /PD-LI pathway negatively regulates T cell activation and has been suggested to play an important role in regulating antitumor host immunity. Recent reports suggest that the aberrant expression of PD-LI on tumor cells impairs antitumor immunity, resulting in the immune evasion of the tumor cells.To clarify the involvement of regulatory T cells and PD-1/PD-L1 pathway in ovarian tumor, we have done the experiments described as follows. Firstly, we detected the levels of CD4+CD25+ T cells, CD3+CD4+T cells, CD3+CD8+T cells and CD4+/CD8+T cells ratios in peripheral blood mononuclear cells from patients with ovarian cancer. Then, we detected the expression of FOXP3 mRNA in peripheral blood with ovarian cancer. We also performed analysis for TILs (CD3+TILs,CD4+ TILs,CD8+ TILs,Treg and CD4+/CD8+ TILs ratios )in tumor stromal and intraepithelial from patients with ovarian cancer. Secondly, we observed the expression level of PD-L1 in human ovarian cancer and analyzed the relationship between PD-L1 expression and clinicopathological characteristics .Finally, we separated and cultivated TILs and tumor cells of/in ascites from patients with ovarian cancer, and analyzed subtypes and killing activity of TILs . We also observed whether the killing activity of TILs changed after the blockade of PD-1/PD-L1 pathway by anti-PD-L1 antibody.Results and analysis1. Firstly, we found that the number of CD4+CD25+Treg was markedly increased and the function of CD4+CD25+Treg was significantly enhanced in patients with ovarian cancer;these cells existed in intraepithelium of ovarian cancer. It demonstrated that tumor cells not only stimulated peripheral and local CD4+CD25+Treg proliferation and activation, but also stimulated CD4+CD25+Treg generation in thymus by series of unknown mechanisms CD4+CD25+Treg interfered immune effector cells response to tumor cells. It may be one of the mechanisms of tumor cells evading from immune elimination.2. Secondly, a substantial expression of PD-L1 was observed in all ovarian cancers investigated. PD-1/ PD-L1 pathway has been suggested to play an important role in regulating antitumor host immunity. In ovarian cancer, PD-L1 expression on tumors inhibits activation of T cell in which PD-1 expression upregulated, this mechanism improve the tumor survival and development. Therefore, the manipulation of tumor-associated PD-L1 may become a potential target for immunotherapy in human ovarian cancer. We also detected a significant association between PD-L1 expression and WHO grade. Tumor specimens from patients with higher WHO grade showed significantly higher percentages of tumor-associated PD-L1. Our results indicated that tumor-associated PD-L1 may be a significant prognostic factor.We also found that the blockade of PD-1/PD-L1 pathway by the application of anti-PD-L1 antibody enhanced the killing activity of TILs in ascites from patients with ovarian cancer greatly. Although various kinds of ways were used to activate TILs, which were used in tumor adoptive immunotherapy, the therapeutic efficacy was not remains indefinite. The changes of tumor microenvironment may involve in this problem. Blockade PD-L1, killing activity of CD8+TILs in ascites recovered . Blockade PD-L1 may become a beneficial strategy for tumor adoptive immunotherapy. As the killing activity of CD8+TILs in ascites recovered when the PD-1/PD-L1 pathway was blocked by the anti-PD-L1 antibody, the blockade of PD-1/PD-L1 pathway may become an efficient strategy for tumor adoptive immunotherapyTo sum up, our results indicated that CD4+CD25+Regulatory T cells and PD-1/ PD-L1 pathway may involve in the escape of tumor from immunologic surveillance, recognition and elimination. Though CD4+CD25+Treg are important in maintaining self homeostasis, its amplification, proliferation and activation in tumor development may protect tumor cells from recognition and elimination. Previous tumor immunotherapy may focus on how to enhance the cytotoxic effect of effector cells, and ignore the harmful effect of Treg to tumor immunotherapy. PD-1/ PD-L1 pathway has been suggested to play an important role in regulating antitumor host immunity by inhibiting the activation of T cell. Our study showed that the blockade of PD-L1 increased the killing activity of tumor-specific T cells. So a promising tumor immunotherapy target is a triple treatment therapy, which consists of the blockade of PD-1/PD-L1 pathway and the depletion of Treg.