Our current finding revealed that DPP-4i enhanced tumor-infiltrating MPO+, CD4+, F4/80+, Foxp3+ cells, and MDSCs, but decreased CD8+ T lymphocytes in metastatic sites, indicating that DPP-4i may induce tumor-immunosuppressive microenvironment by enhancing tumor-infiltrating immune-suppressive cells. Here, CD4 is linked to neoplasm.