Effect Of Inhibitory Receptor TIGIT On NK Cell Mediated Anti-tumor Immunity

Immune checkpoint-based anti-tumor immunotherapy has attracted a lot of attention at present,and many studies have shown that blocking immune checkpoints can enhance the effector functions of T cells and thus promote adaptive immune-mediated anti-tumor responses.And PD-1/PD-L1 or CTLA-4 blockade treatment have also achieved surprising clinical results.As an emerging inhibitory receptor,TIGIT promotes the exhuastion of T cells,inhibits T cell-mediated anti-tumor immune responses,and thus promotes the development of tumors.Nevertheless,in addition to antigen-trigged T cells,NK cells also play an important role in the anti-tumor immune response.However,the effects of TIGIT on NK cell exhaustion,and the effects on NK cells-mediated anti-tumor immune responses in tumor progression have not been explored.In this study,we reveals the relationship between TIGIT and NK cell-mediated antitumor responses during tumor development.1.TIGIT is highly expressed on tumor-infiltrating NK cells and promotes NK cell exhaustion.We collected fresh intratumoral(IT)and peritumoral(PT)regions from multiple tumor patients(colorectal cancer and breast cancer).And we found that,comparing with NK cells in PT resions,NK cells in IT regions significantly up-regulated TIGIT,indicating that tumor development promotes TIGIT highly expressed on NK cells.In order to further study the relationship between TIGIT and NK cells,we constructed six murine tumor models and detected the expression of the inhibitory receptors on tumor infiltrating NK cells and CTL cells,such as TIGIT,PD-1 and CTLA-4.It was found that during the development of tumors,the tumor-infiltrating NK cells are predominantly TIGIT+PD-1 CTLA-4,while the tumor-infiltrating TIGIT+CTL cells are mostly PD-1+ or CTLA-4+.It has been demonstrated that TIGIT is a more relevant regulator of NK cells during tumor progression,and that NK cells are more specifically regulated by TIGIT rather than PD-1 or CTLA-4.Next,by comparing the phenotype,effector function,and the apoptosis between tumor infiltrating TIGIT+NK and TIGIT-NK cells,we found that tumor infiltrating TIGIT+NK cells were more exhausted.Meanwhile tumor infiltrating NK cells were mostly TIGIT+,the results above demonstrate that tumor progression promotes TIGIT to be highly expressed on tumor-infiltrating NK cells and accelerated NK cell exhaustion.2.TIGIT deficiency reverses NK cell depletion and promote tumor clearance We performed tumor-bearing experiments in Tigitfl/fl-Ncr1iCre/+ mice(NK cell-specific deficiency of TIGIT).While comparing with control mice,tumor growth was inhibited in Tigitfl/fl-Ncr1iCre/+ mice and the survival was also significantly prolonged.And the function of tumor infiltrating NK cells and CTL cells was reversed.TIGIT highly expressed on NK cells promotes cell exhaustion and thereby accelerates tumor progression.3.TIGIT blockade alone reverses NK cell exhaustion and promotes tumor clearanceWe constructed a blockade monoclonal antibody that specifically recognizes TIGIT.We used this antibody to perform tumor immueotherapy experiments in vivo.It was found that the blockade of TIGIT significantly inhibits the growth of colon cancer,melanoma,breast cancer,and fibrosarcoma,and can also reverse the exhaustion of tumor-infiltrating NK cells and CTL cells.4.TIGIT-mediated NK cell exhaustion does not depend on adaptive immune systemIn adaptive immune-deficient mice(Rag2-/-,NOD-SCID and SCID),we constructed colon cancer model and found that tumor-infiltrating NK cells still highly expressed TIGIT,and tumor-infiltrating TIGIT+NK cells were still more functional exhausted.5.TIGIT blockade mediated the reversal of NK cells function does not depend on the adaptive immune systemColon cancer model was constructed in adaptive immune deficient mice(Rag2-/-,NOD-SCID,and SCID)and treated with anti-TIGIT antibody.It was found that TIGIT blockade still reversed NK cell function and inhibited tumor growth.6.TIGIT/PD-L1 blockade-mediated enhanced adaptive immune response is dependent on NK cellsWe first constructed a mouse melanoma model and depleted NK cells,and found that tumor metastasis was significantly increased and CTL cell exhaustion was exacerbated.In the absence of NK cells,even if blocking TIGIT,tumor growth cannot be inhibited and CTL cell function cannot be reversed.Next,we verified the conclusion in the colon cancer model.After depleting NK cells,mice were treaed with anti-TIGIT,anti-PD-L1,or anti-TIGIT plus anti-PD-L1,and we found that the effect of blockade treatment disappeared,with unconrtolled tumor growth and more exhausted CTL cells.7.TIGIT blockade alone can stimulate potential antitumor memory responses We used the cured mice from TIGIT blockade treatment(colon cancer and melanoma),re-injected the tumor cells to mice without any further treatment.Compared with the control group,we found that the cured mice had stronger anti-tumor function,and the overall survival of mice has been significantly extended.