The Effect Of Tumor Cells On CD4~+CD25~+Treg

The functions of the immune system are closely related to the the occurrence and development of tumors. Although the body has all kindsof mechanisms of immune surveillance, but the immune system still can not complately prevent the occurrence of tumors. Through some mechanisms, tumor cells can induce immunotolerance to escape immune surveillance and make them grow and metastasis in the body. Studys show that whether in the cancer patients or in mouse tumor models, the immune system usually has weak immune response against tumor antigens, so which can not effectively clear the tumor cells, resulting in the occurrence of clinical oncology. At present, most scholars believe that there are two aspects mechanisms which can explain tumor cells escape from the immune system: one, the tumor-related immune escape mechanisms: deletion of the tumor antigen, MHC I molecule expression decreased, the lack of co-stimulatory molecules and death receptor signaling defects; two, host-related tumor immune escape mechanisms: the immune inhibitory factors, effector cells dysfunction, regulatory T cells' activation and tumor suppression of antitumor immunity, to maintain a relatively stable tumor nonresponse status. These are probably important factors that make tumor cells do not induce an effective immune response.Recently, through the study of the interaction of tumor cells and immune cells in the tumor microenvironment, people set up the concept of tumor immune microenvironment.As compared with normal tissues there are special characters of the tumor microenvironment, and the study of tumor microenvironment can help understand the mechanisms of tumor escaping immune surveillance. In the tumor immune microenvironment, there are many immune cells, especially the regulatory T cells which are taken much attention and may be the main factor of antitumor in body.The gathering of immune cells in tumor microenvironment are arised by the tumor, in which there are many informations about the interactions between immune system and tumor, so the intensive study of which is helpful to fully understanding the human tumor immunity. In the previous studies of our team, we found that in the cancer patients and in mouse tumor models, there were increase of CD4~+CD25~+Treg cells in number and function,and at the same time the function of immune surveillance was decreased,which indicated that CD4~+CD25~+Treg cells played a great role in tumor immunity. But it is still unclear that the mechanisms of how tumor cells induce CD4~+CD25~+Treg cells to participate in tumor immunotolerance.As a kind of typical pattern recognition receptors ( PRR), Toll-like receptors ( TLRs) is an important ingredient of innate immune system , and bearing the bridge between the adaptive immune response and the innate immune response, and which mainly through recognise the pathogen associated molecular patterns( PAMPs) to start immune response. In recent years, the studies of TLRs in the tumor immunity raised more and more intereset of researchers. Furthermore, in the process of research into the immune system, people found that TLRs can also be expressed on tumor cells, and may play an important role in the tumor pathonesis. In the previous studies of our team, we confirmed that the increase of the expression of TLR9 on APC cound affect the generation and function of CD4~+CD25~+Tregs, so the relation of TLRs and CD4~+CD25~+Treg cells' generation may very close. We speculate whether TLRs expressed on tumor cells have the similar effect with TLRs expressed on APC, which can influence CD4~+CD25~+Tregs by regulating some molecules and then help tumors escape from immune surveillance.Therefore, this study is making the co-culture system of Lewis lung cancer cells and splenic lymphocytes as object and aiming to explore the influence of tumor cells on CD4~+CD25~+Treg cells and the possible mechanisms involved, and which is carried out from the following two aspacts:1,The influence of Lewis lung cancer cells on CD4~+CD25~+Treg cellsIn order to explore the influence on CD4~+CD25~+Treg cells, number and function by the interactions of tumor cells with tumor microenvironment immune cells, we cocultured the Lewis lung cancer cells with splenic lymphocytes and used FACS and RT-PCR methods to test the number and function of cocultured splenic lymphocytes. The results showed that Lewis lung cancer cells can induce the increase of CD4~+CD25~+Treg cells in number and function. The results indicated tumor cells could induce the production of CD4~+CD25~+Treg cells, and made CD4~+CD25~+Treg cells take part in the induction and maintenance of tumor immunotolerance.2,The possible mechanisms of Lewis lung cancer cells affecting CD4~+CD25~+Treg cellsIn order to explore the possible mechanisms of tumor cells effect on CD4~+CD25~+Treg cells, we detected the changes of TLRs expression in Lewis lung cancer cells after co-cultured with splenic lymphocytes, and then further studied whether the tumor cells could affect the CD4~+CD25~+Treg cells through TLRs, and to contribute tumor immunologic escape. The results showed that spleenocytes could affect the expression of multiple TLRs on Lewis lung cancer cells after co-cultured with Lewis lung cancer cells, including the upregulation of TLR4,5,9; blocking TLR9 could reduce the number and function of CD4~+CD25~+Treg cells. The results indicated that the tumor cells could impact CD4~+CD25~+Treg cells through TLRs, which taken part in the induction and maintenance of tumor immunotolerance, tumor immunologic escape and promoted tumor occurrence and development. From above studies, we come to the following conclusions:1. Lewis lung cancer cells could induce the increase of CD4~+CD25~+Treg cells in number and function. Tumor cells could induce the production of CD4~+CD25~+Treg cells, and that may be one of the mechanisms of the formation of tumor immunotolerance;2. Lewis lung cancer cells could promote CD4~+CD25~+Treg cells in number and function through TLR9, which may participate in the formation of tumor immunotolerance, thus contributing to the occurrence and development of tumors.This research explored the influence of tumor cells on Treg cells and the mechanisms which may be involved in, and which provided new experimental evidences for fully understanding the tumor immunotolerance and immunologic escape mechanisms, and a new way for tumor immunotherapy based on the regulation of CD4~+CD25~+Treg cells via TLRs.