The Role And Molecular Mechanism Of TIGIT-CD155 Signal Axis In The Immune Escape Of Oral Squamous Cell Carcinoma

Tumor cells can evade and suppress the host anti-tumor immune response,which is one of the main characteristics of malignant tumors.Tumor cells interact directly or indirectly with the tumor microenvironment to regulate the proportion and function of effector cells and immunosuppressive cells,and then affect the prognosis of patients.Numerous studies have shown that the continuous overexpression of immune checkpoint molecules such as PD-1 and CTLA-4 is the chief mechanism of tumor immunosuppression.The application of monoclonal antibodies to blockade immune checkpoints has achieved great success in multiple tumors,activating patients’anti-tumor immune responses and significantly increasing the overall survival.However,only a limited percentage of patients can achieve response in immune checkpoint blockade therapy,which indicates that a deeper knowledge is needed to explore different mechanisms of interaction between tumor cells and tumor microenvironment in immune escape.TIGIT is a novel immune checkpoint molecule that can bind to its ligand CD155 to induce the exhaustion of effector T cells and promote immunosuppression.The specific role of TIGIT-CD155 signal axis in oral squamous cell carcinoma has not been elucidated.TIGIT is restrictedly expressed on effector T cells,regulatory T cells(Tregs)and natural killer cells(NK cells),and CD155 can be widely expressed in tumor cells and tumor-associated myeloid cells.Our previous studies found that Tregs and myeloid-derived suppressor cells(MDSCs)play an important role in the immune escape of oral squamous cell carcinoma.This study mainly explores the expression,function and mechanism of TIGIT-CD155signal axis in oral squamous cell carcinoma,and analyzes the application prospects of its combined blocking with PD-1-PD-L1 pathway.Part oneStudy on the regulatory function of TIGIT-CD155 signal axis in the immune escape of OSCCObjective:Studies have shown that the TIGIT-CD155 signal axis stands out as a new type of immune checkpoint pathway and can lead to the exhaustion of effector T cells and NK cells.However,the function and intrinsic mechanisms of this pathway in oral squamous cell carcinoma have not been elucidated.Therefore,our group aimed to explore the role of the TIGIT-CD155 signal axis in oral squamous cell carcinoma and its possibility as a potential target for immunotherapy of oral squamous cell carcinoma.Methods:We used flow cytometry to detect the expression of TIGIT in human oral squamous cell carcinoma tissues and transgenic mouse models;human oral squamous cell carcinoma tissue microarray was used to detect the expression level of CD155.Finally,preclinical in vivo studies were performed on transgenic mouse model to investigate the specific efficacy of TIGIT m Ab on tumor growth,and analyzed the changes of immune cells in mouse model by flow cytometry;in vitro co-culture experiments were performed to explore the potential mechanism.Results:TIGIT was overexpressed on tumor-infiltrating CD8~+and CD4~+T cells in both OSCC patients and mouse models,and was correlated with immune checkpoint molecules(PD-1,TIM-3,LAG-3).TIGIT was also highly expressed in mouse regulatory T cells and associated with immunosuppression.CD155 was expressed in tumor and tumor-infiltrating myeloid cells,and also indicated poor all-over survival.TIGIT m Ab treatment significantly prevented tumor growth in transgenic OSCC mouse models with enhanced antitumor immune response by activating CD8~+T cell effector function and reducing the population of Tregs.In vitro coculture study showed that TIGIT m Ab significantly abrogated the immunosuppressive capacity of MDSCs and Tregs.Conclusions:The TIGIT-CD155 signal axis is highly expressed in oral squamous cell carcinoma and is involved in mediating immune escape of oral squamous cell carcinoma.Blocking the TIGIT-CD155 signal axis can effectively inhibit tumor growth and improve anti-tumor immunity.The TIGIT-CD155 signal axis may be a potential target for OSCC immunotherapy.Part two Study on the role of combined application of anti-TIGIT with anti-PD-L1 monoclonal antibody in reversing immunotherapy resistance of OSCCObjective: To further investigate the potential clinical value of TIGIT-CD155 signal axis blockade,we used human specimens and transgenic mouse models to analyze the correlation of TIGIT-CD155 and PD-1-PD-L1 signal axes,as well as the relationship between the co-expression level and immune escape in the tumor microenvironment.Through monoclonal antibodies blockade in vivo,we aimed to explore the combined application of TIGIT and PD-L1 m Ab in enhancing the anti-tumor immunity of transgenic mice.Methods: We performed flow cytometry to detect the co-expression level of CD155 and PD-L1 on MDSCs in human TILs,and analyzed the correlation between the enrichment level of CD155~+PD-L1~+ MDSCs and CD3~+ T cell.We also investigated the co-expression level of CD155 and PD-L1 on MDSCs in the peripheral immune organs and TILs of transgenic mouse models.The correlation between the enrichment level of CD155~+PD-L1~+ MDSCs and tumor progression was also analyzed.Subsequently,we combined the use of TIGIT m Ab and PD-L1 m Ab to treat OSCC transgenic mice model to explore the combination therapeutic effect on tumor growth,and the analysis of effector T cells,myeloid cells and memory T cells in the tumor microenvironment of transgenic mice were performed by flow cytometry.Results: CD155 and PD-L1 were highly co-expressed on MDSCs cells in human OSCC.The co-expression level of CD155 and PD-L1 was inversely associated with the percentages of CD3~+ T and effector memory T cells in the tumor microenvironment.Subsequently,CD155~+PD-L1~+ MDSCs in transgenic mouse model were gradually enriched in the tumor microenvironment in the middle and late stages of tumor progression.Application of PD-L1 monoclonal antibody alone in the transgenic mouse model up-regulated the expression of CD155 on MDSCs,while application of TIGIT monoclonal antibody up-regulated the expression of PD-L1 on MDSCs.Then the combined blockade of TIGIT-CD155 and PD-1-PD-L1 signal axis in transgenic mouse models significantly inhibited tumor growth,and enhanced the percentages of T cells in the tumor microenvironment,and increased the level of CD226 expression on effector T cells and cytokine secretion.Potential immune memory effects were also found in the draining lymph nodes.Conclusions: CD155~+PD-L1~+ MDSCs are enriched in the tumor microenvironment of human and transgenic mouse models.Blocking TIGIT-CD155 and PD-1-PD-L1 signal axis can effectively enhance the response rate of OSCC to PD-L1 m Ab therapy,and activate effector T cells,and can stimulate potential anti-tumor immune memory effects.These data suggest the clinical potential of co-targeting the TIGIT-CD155 and PD-1-PD-L1 signal axes.