Objective:To investigate the mechanism of cathepsin G(CatG) in improving the treatment efficacy of T cells in gliomas.Methods:(1) Clinical data of 397 glioma patients in the glioma database were collected, Kaplan-Meier method was used to perform survival analysis, and the correlation between CTSG and β2-microglobulin ( β2M) mRNA expressions in glioma tissues was analyzed. (2) Glioma stem cell (GSC) 387 and GSC3565 were isolated from glioblastoma and differentiated into differentiated glioma cell (DGC) 387 and DGC3565, respectively; GSC387 was divided into CatG group and CatG inhibitor group, and cells in the CatG group and CatG inhibitor group were cultured with 0.1 μg/μL recombinant human leukocyte antigen (HLA)-A*02:01 and HLA-B*15:01 combined with 4 ng/μL CatG or 10 mol/L CatG inhibitor for 10 min, respectively; the expressions of HLA-A*02:01 and HLA-B*15:01 were detected by Thomas bright blue staining, and the protein expressions of major histocompatibility complex (MHC)-I and MHC-DR were detected by Western blotting. (3) GSC387, GSC3565, DGC387, and DGC3565 were divided into 4 groups, including CatG group, CatG inhibitory group, blank antibody group 1 and blank antibody group 2, respectively; 4 ng/μL CatG, 10 μmol/L CatG inhibitor, blank antibody 1 and blank antibody 2 were added into the cells from the 4 groups for 24 h, and the expression of HLA-ABC was detected by flow cytometry. (4) GSC387, GSC3565, DGC387, and DGC3565 were divided into CatG group and CatG inhibitory group, respectively; luciferase assay was used to detect the influence of CatG in the killing effects of T cells and natural killer cells. Results:(1) The survival rate in patients from CTSG mRNA high expression group was significantly higher than that in patients from CTSG mRNA low expression group, and the survival rate in patients from β2M mRNA low expression group was statistically higher than that in patients from β2M mRNA high expression group ( P<0.05); a negative correlation between CTSG mRNA and β2M mRNA expressions was noted in glioma tissues ( r=-9.160, P=0.000). (2) Thomas bright blue staining showed that the expressions of HLA-A*02:01 and HLA-B*15:01 obviously increased in the CatG group as compared with those in the CatG inhibitor group; Western blotting showed that as compared with the CatG inhibitor group, the CatG group had increased MHC-I expression, and decreased expressions of α and β chains of MHC-DR. (3) Flow cytometry showed that the HLA-ABC expressions in GSC387 and GSC3565 of the CatG group were statistically higher than those in the CatG inhibitor group ( P<0.05). (4) Luciferase assay showed that, as compared with the CatG inhibitor group, the CatG group had statistically higher proportion of T cells killing GSCs ( P<0.05). Conclusion:CatG can improve the immunotherapy efficacy in GSCs, mainly by increasing the MHC-I expression on the cell surface.