Tumor-Targeted Delivery of IL-2 by NKG2D Leads to Accumulation of Antigen-Specific CD8+ T Cells in the Tumor Loci and Enhanced Anti-Tumor Effects

Interleukin-2 (IL-2) has been shown to promote tumor-specific T-cell proliferation and differentiation but systemic administration of IL-2 results in significant toxicity. Therefore, a strategy that can specifically deliver IL-2 to the tumor location may alleviate concerns of toxicity. Because NKG2D ligands have been shown to be highly expressed in many cancer cells but not in healthy cells, we reason that a chimeric protein consisting of NKG2D linked to IL-2 will lead to the specific targeting of IL-2 to the tumor location. Therefore, we created chimeric proteins consisting of NKG2D linked to Gaussia luciferase (GLuc; a marker protein) or IL-2 to form NKG2D-Fc-GLuc and NKG2D-Fc-IL2, respectively. We demonstrated that NKG2D linked to GLuc was able to deliver GLuc to the tumor location in vivo. Furthermore, we showed that TC-1 tumor-bearing mice intramuscularly injected with DNA encoding NKG2D-Fc-IL2, followed by electroporation, exhibited an increased number of luciferase-expressing E7-specific CD8+ T cells at the tumor location. More importantly, treatment with the DNA construct encoding NKG2D-Fc-IL2 significantly enhanced the therapeutic anti-tumor effects generated by intradermal vaccination with therapeutic HPV DNA in tumor-bearing mice. Therefore, by linking NKG2D to IL2, we are able to specifically deliver IL-2 to the tumor location, enhancing antigen-specific T-cell immune response and controlling tumor growth. Our approach represents a platform technology to specifically deliver proteins of interest to tumor loci.

白细胞介素-2（Interleukin-2, IL-2）已被证实可促进肿瘤特异性T细胞的增殖与分化，但IL-2的全身给药会引发显著毒性。因此，能够将IL-2特异性递送至肿瘤部位的策略，或可缓解毒性相关顾虑。鉴于NKG2D配体（NKG2D ligand）已被证实在多种癌细胞中高表达，而正常细胞中无此特征，我们推测将NKG2D与IL-2融合的嵌合蛋白，可实现IL-2向肿瘤部位的特异性靶向递送。据此，我们构建了分别由NKG2D与高斯荧光素酶（Gaussia luciferase, GLuc，一种标记蛋白）或IL-2融合的嵌合蛋白，即NKG2D-Fc-GLuc与NKG2D-Fc-IL2。我们证实，与GLuc融合的NKG2D可在活体中将GLuc递送至肿瘤部位。进一步实验显示，对接种TC-1肿瘤的小鼠肌内注射编码NKG2D-Fc-IL2的DNA后辅以电穿孔，其肿瘤部位的表达荧光素酶的E7特异性CD8+ T细胞数量有所增加。更为关键的是，编码NKG2D-Fc-IL2的DNA治疗，可显著增强荷瘤小鼠皮内接种治疗性HPV DNA疫苗所产生的抗肿瘤治疗效果。综上，通过将NKG2D与IL-2融合，我们可实现IL-2向肿瘤部位的特异性递送，强化抗原特异性T细胞免疫应答并抑制肿瘤生长。本方法可作为一种将目标蛋白特异性递送至肿瘤位点的平台技术。