After tumor - derived exosomal HSP70 binds to TLR2 on the surface of MDSCs, it activates STAT3 phosphorylation, induces the expression of arginase 1 (Arg1) and inducible nitric oxide synthase (iNOS), and enhances the immunosuppressive activity of MDSCs (90). Here, NOS2 is linked to neoplasm.