CXCL11 and neoplasm: Further studies are required to determine the anti-tumor mechanisms of CXCL9- and CXCL11-expressing tumor tissues, which are resistant to DPP4, to elucidate the immunosuppressive role of DPP4 in the tumor microenvironment, and to test whether DPP4 inhibitors restore the anti-tumor activity of IFN-inducible chemokines in an immunocompetent mouse model.