Treatment with a fusion protein of the extracellular domains of NKG2D to IL-15 retards colon cancer growth in mice.

Tumor-targeted cytokines are a new class of pharmaceutical anticancer agents often considered superior to the corresponding unconjugated cytokines for therapeutic purposes. We generated a new fusion protein， dsNKG2D-IL-15， in which double NKG2D extracellular domains were fused to IL-15， in Escherichia coli. This fusion protein promoted the activation， proliferation， and cytotoxicity of NK cells， and bound to NKG2D ligand-positive tumor cells. These tumor cells were also more susceptible to NK-cell attack when decorated with dsNKG2D-IL-15. The administration of mouse dsNKG2D-IL-15 protein in vivo significantly retarded the growth of transplanted colon cancers and prolonged the survival of tumor-bearing mice. Treatment with dsNKG2D-IL-15 increased the frequencies of NK and CD8 T cells in spleen and tumor tissues. The antitumor effect mediated by dsNKG2D-IL-15 was significantly decreased with in vivo depletion of NK cells or CD8 T cells. Recombinant dsNKG2D-IL-15 thus inhibited NKG2D ligand-positive tumor growth effectively by activating lymphocytes. This new biological fusion protein could potentially be used to elicit immunity in tumor-targeting treatments.