Metastasis Immunobiological Mechanisms And Immune Therapy

Cancer is serious hazard to public health, and is one of the worldwide leading causes of death. More than 90 percentage of cancer patients die from tumor metastasis. The formation of the immunosuppressive microenvironment is one of the major factors that enable escape of tumor cells from immune surveillance, promote proliferation, survival and migration of cells, and limit the clinical therapy of cancer. The immunosuppressive microenvironment is composed of suppressor cell populations, soluble immunosuppressive factors (cytokines, chemokines and enzymes). Accumulating studies have identified signal transducer and activator of transcription 3 (Stat3) as an important molecule induces immunosuppression at many levels. For example, the constitutive activation of Stat3 of tumor cells induces the establishment and development of the immunosuppressive microenvironment. Furthermore, the transcripts of Stat3 promote the outgrowth and metastasis of tumor cells. However, the mechanism how tumor cells maintain the constitutive activation of Stat3 has not been elucidated. Recently, some studies identified that tumor cells could actively or passively release damage associated molecular pattern molecules (DAMPs). The DAMPs can activate pattern recognition receptors (PRRs), then activate or inhibit the respective signal transduction pathway and induce the respective biological activity, which includes chronc inflammation, angiogenesis, stroma reconstitution and the establishment of the immunosuppressive microenvironment. In conclusion, DAMPs not only promote the proliferation and metastasis of tumor cells, but also induce the establishment the immunosuppressive microenvironment.TLRs are a family of important PRRs, and TLRs are able to mediate immune responses induced by both pathogen-associated molecular pattern molecules (PAMPs) and DAMPs. The interaction between the antigen and certain TLR subtypes enhances immune response, but the interaction between the same antigen with other TLR subtypes causes immune tolerance. For example, the interaction between the antigen with TLR4 induces immune activation, but the interaction between the same antigen and TLR2 induces immune suppression. Therefore, we assume that TLR2 can interact with DAMPs released by tumor cells, mediates the constitutive activation of Stat3 of tumor cells, and then induces the establishment of the immunosuppressive microenvironment. Firstly, we identified that multiple TLRs are expressed on many kinds of murine and human tumor cells. Additionally, Pg-LPS significantly induced phosphorylation of Stat3 through TLR2 on tumor cells and then mediated the release of suppressive factors, including IL-6 and IL-10. Thereafter, more research identified that tumor cells could actively maintain TLR2-Stat3 signal pathway and induce the establishment of the immunosuppressive microenvironment by a positive feedback mechanism. For example, the HSP60 released by tumor cells could activate TLR2 persistently, and then TLR2 activity maintained the constitutive activity of Stat3. Therefore, inhibiting TLR2 signaling of either B16F10 cells or host cells markedly attenuated pulmonary metastasis nodes and increased the survival of B16-bearing mice by inhibiting the activity of Stat3 and reversing immunosuppressive microenvironment. Our results identify that the activation of TLR2 is the main cause of the establishment of immune tolerance, and suggest that TLR2 might act as a potential therapeutic target in the treatment of cancer.CD 19 is an important marker molecule of B cells. Our early study found that CD 19 is also expressed on B16F10 melanoma cells. Some recent researches suggest that CD 19 is the important adaptor molecule of TLR signal pathway in B cells, and we also identified that the activation of TLR2 was the main cause of the constitutive activation of Stat3 in tumor cells. Therefore, we assume that CD 19 can interact with DAMPs released by tumor cells, mediate the constitutive activation of Stat3 of tumor cells, and then promote the proliferation and metastasis of tumor cells. As a result, we found that CD 19 mediated the constitutive activation of Stat3, which was induced by HSP60 through TLR2 activation. Moreover, blocking the CD 19 signal pathway, the constitutive activity of Stat3 was inhibited. Consequently, the expression of proteins(such as MMP-2, VEGF and c-Myc), which involve tumour-cell proliferation, survival and invasion, was down-regulated, epithelial-mesenchymal transition (EMT) was inhibited, and the secretion of immunosuppressive cytokines(such as IL-10) was also inhibited. Therefore, neutralizing anti-CD 19 antibody which was injected prophylactically or therapeutically, and inhibiting CD 19 signaling of either B16F10 cells or host cells markedly reversed immunosuppressive microenvironment, attenuated pulmonary metastasis nodes and increased the survival of B16-bearing mice. Furthermore, the therapeutic protocol by combining Gemcitabine with anti-CD 19 antibody is more effective in inhibiting the outgrowth and metastasis of tumor cells and improving the survival compared to Gemcitabine or anti-CD 19 antibody alone. Our results identify that CD 19 plays a critical role in the establishment of immune tolerance induced by tumor cells, and suggest that CD 19 might act as a potential therapeutic target in the treatment of cancer.