DPP4 Inhibitor Enhances The Infiltration Of CAR-T Cells To Solid Tumor

Chimeric antigen receptor T cell(CAR-T)is a therapy that can specifically recognize and kill tumors by genetically modificating the patient’s own T lymphocytes.As a new effective method for the tumor immunotherapy,CAR-T therapy has achieved good therapeutic effect in the treatment of hematological tumors.However,the immunosuppressive microenvironment in solid tumors could limit CAR-T cells to infiltrate and persist.So,the efficacy of CAR-T therapy for solid tumors is not significant.Therefore,finding the way to enhance the infiltration of CAR-T cells into solid tumor tissues and improve the function and persistence of CAR-T cells in vivo have become the hot issue.Chemokines play an indispensable role in the migration of lymphocytes,while DPP4 can inhibit the activity of a variety of chemokines.In related studies,it was found that DPP4 inhibitors could increase the migration of lymphocyte to tumor and delay the growth of tumor.Thus,the combination of CAR-T cell therapy and DPP4 inhibitor will hopefully increase the infiltration of CAR-T cells into tumor and enhance the efficacy of CAR-T therapy for solid tumors.First,we examined the expression of CXCR3 in T cells,a chemokine receptor that is related to the migration of T cells.We found that CXCR3 is highly expressed on the surface of activated T cells.CXCL10,the ligand of CXCR3,is one of the substrates of DPP4.DPP4 can cleave the first two amino acids of CXCL10 in the amino terminus and make it lose activity.We detected the expression of CXCL10 and DPP4 in tumors by ELISA and examined the effect of both on T cell migration using transwell assay.The results showed that CXCL10 could recruit T cells,which is inhibit by DPP4.And the DPP4 inhibitor could increase the migration of T cell.To further determine the mechanism of the DPP4 inhibitor,we constructed cell models expressing different forms of CXCL10 by lentiviral vector technology.Transwell experiments revealed that the full-length CXCL10 can achieve T cell chemotaxis while the truncated CXCL10(3-77)has no recruitment function.Furthermore,the DPP4 inhibitor could increase the ability of CXCL10(1-77)to recruit T cells.The above results indicated that the DPP4 inhibitor could effectively promote T cell migration in vitro.Next,we investigated the effect of the DPP4 inhibitor on CAR-T infiltration in vivo using solid tumor mouse models.By detecting the DPP4 enzyme activity in the serum and tumor homogenate of mice,we found that the DPP4 enzyme activity in serum and tumor homogenate of the experimental group was significantly lower than that of the control group.It confirmed the DPP4 inhibitor’s effectiveness to inhibit the activity of DPP4 in vivo.By comparing the growth of tumors in each group,we found that combination therapy was able to delay the growth of tumors better than that of the single administration.More importantly,the number and proportion of tumor infiltrating lymphocytes in the combined group were significantly higher than in the control group,indicating that the DPP4 inhibitor can effectively promote the infiltration of CAR-T cells into tumor in vivo.In addition,the intratumoral CXCL10 expression of the combination group was higher than that of CAR-T group.It indicated that the DPP4 inhibitor could inhibit the cutting of CXCL10 by DPP4,prevent the cutting by other exogenous enzymes,and maintain the expression and biological activity of CXCL10,thus promoting the migration of CAR-T cells into tumor tissue.Taken together,we found that the DPP4 inhibitor could inhibit the cleavage of CXCL10 by DPP4,maintain the biological activity of CXCL10,promote the infiltration of CXCR3-expressing CAR-T cells into tumor,and effectively delay the growth of tumors.This research identified that DPP4 could influence T cell migration through the CXCL10/CXCR3 chemotaxis,studied and confirmed the role of the DPP4 inhibitor in the homing of CAR-T cells into solid tumors.And we established a treatment system to enhance the effect of CAR-T therapy targeted solid tumors,achieved the DPP4 inhibitor to a new application.The results of the study provided a new idea and laid the foundation for the combination therapy of solid tumors.