Comprehensive analysis of RNA sequencing data from the CGGA and TCGA databases and single-cell sequencing data from the GSE70630 and GSE89567 databases showed that the loss of chromosome 19q altered the tumor immune microenvironment by downregulating the immunosuppressive function of TIM-3 and its ligand Galectin-9 in glioma patients with 1p/19q codeletion, which may further affect the tumor sensitivity to chemotherapy and immunotherapy. The gene discussed is LGALS9; the disease is glioma.