Inhibitor of PI3Kδ/γ, such as (S)-(-)-N-[2-(3-Hydroxy-1H-indol-3-yl)-methyl]-acetamide (SNA), (-)-4-O-(4-O-β-D-glucopyranosylcaffeoyl) quinic acid (QA), and IPI-145, reversed the suppressive effects of G-MDSCs on the proliferation of T lymphocytes through significantly reducing the expression of NOS2 and Arg1 transcript levels in G-MDSCs and promoting cytotoxic T-cell-mediated tumor regression, resultantly enhancing the therapeutic efficacy of anti-PD1 treatment in osteosarcoma tumor (111), colon tumor (112), and oral cancer (121), respectively. The gene discussed is NOS2; the disease is neoplasm.