Liver Gene Transfer of Interkeukin-15 Constructs That Become Part of Circulating High Density Lipoproteins for Immunotherapy

Apolipoprotein A-I (Apo A-I) is a major component of high density lipoproteins (HDL) that transport cholesterol in circulation. We have constructed an expression plasmid encoding a chimeric molecule encompassing interleukin-15 (IL-15) and Apo A-I (pApo-hIL15) that was tested by hydrodynamic injections into mice and was co-administered with a plasmid encoding the sushi domain of IL-15Rα (pSushi) in order to enhance IL-15 trans-presentation and thereby bioactivity. The pharmacokinetics of the Apo A-I chimeric protein were much longer than non-stabilized IL-15 and its bioactivity was enhanced in combination with IL-15Rα Sushi. Importantly, the APO-IL-15 fusion protein was incorporated in part into circulating HDL. Liver gene transfer of these constructs increased NK and memory-phenotype CD8 lymphocyte numbers in peripheral blood, spleen and liver as a result of proliferation documented by CFSE dilution and BrdU incorporation. Moreover, the gene transfer procedure partly rescued the NK and memory T-cell deficiency observed in IL-15Rα−/− mice. pApo-hIL15+ pSushi gene transfer to the liver showed a modest therapeutic activity against subcutaneously transplanted MC38 colon carcinoma tumors, that was more evident when tumors were set up as liver metastases. The improved pharmacokinetic profile and the strong biological activity of APO-IL-15 fusion protein holds promise for further development in combination with other immunotherapies.

载脂蛋白A-I（Apolipoprotein A-I）是循环中负责转运胆固醇的高密度脂蛋白（High Density Lipoprotein，HDL）的核心组成成分。本研究构建了一种编码包含白细胞介素15（Interleukin-15，IL-15）与Apo A-I的嵌合分子的表达质粒（命名为pApo-hIL15），通过小鼠水动力注射开展功能验证，并与编码IL-15受体α（IL-15Rα）sushi结构域的质粒（pSushi）联合给药，以增强IL-15的跨呈递效率，进而提升其生物活性。该Apo A-I嵌合蛋白的药代动力学时长显著长于未稳定化的IL-15，且与IL-15Rα sushi结构域联合使用时，其生物活性得到进一步增强。值得关注的是，APO-IL-15融合蛋白可部分整合至循环HDL中。通过肝脏基因转导递送上述质粒，可使外周血、脾脏及肝脏中的NK细胞与记忆表型CD8淋巴细胞数量显著升高，该效应通过CFSE增殖稀释实验与BrdU掺入实验证实的细胞增殖过程得以验证。此外，该基因转导策略可部分挽救IL-15Rα基因敲除（IL-15Rα−/−）小鼠中观察到的NK细胞与记忆T细胞缺陷。对肝脏实施pApo-hIL15联合pSushi的基因转导，对皮下移植的MC38结肠腺癌肿瘤展现出轻度治疗活性，而当肿瘤以肝转移灶形式构建时，该治疗效果更为显著。APO-IL-15融合蛋白所具备的优化药代动力学特性与强效生物活性，为其与其他免疫治疗手段联合应用的后续开发提供了良好前景。