Ly6Clo monocytes drive immunosuppression and confer resistance to anti-VEGFR2 cancer therapy

Current anti-VEGF therapies for colorectal cancer (CRC) provide limited survival benefit, as tumors rapidly develop resistance to these agents. Here, we have uncovered an immunosuppressive role for nonclassical Ly6C(lo) monocytes that mediates resistance to anti-VEGFR2 treatment. We found that the chemokine CX3CL1 was upregulated in both human and murine tumors following VEGF signaling blockade, resulting in recruitment of CX3CR1(+)Ly6C(lo) monocytes into the tumor. We also found that treatment with VEGFA reduced expression of CX3CL1 in endothelial cells in vitro. Intravital microscopy revealed that CX3CR1 is critical for Ly6C(lo) monocyte transmigration across the endothelium in murine CRC tumors. Moreover, Ly6C(lo) monocytes recruit Ly6G(+) neutrophils via CXCL5 and produce IL-10, which inhibits adaptive immunity. Preventing Ly6C(lo) monocyte or Ly6G(+) neutrophil infiltration into tumors enhanced inhibition of tumor growth with anti-VEGFR2 therapy. Furthermore, a gene therapy using a nanoparticle formulated with an siRNA against CX3CL1 reduced Ly6C(lo) monocyte recruitment and improved outcome of anti-VEGFR2 therapy in mouse CRCs. Our study unveils an immunosuppressive function of Ly6C(lo) monocytes that, to our knowledge, has yet to be reported in any context. We also reveal molecular mechanisms underlying antiangiogenic treatment resistance, suggesting potential immunomodulatory strategies to enhance the long-term clinical outcome of anti-VEGF therapies.