应用纳米组装技术克服治疗性疫苗载体免疫反应

The past two years have seen significant advance in cancer immunotherapy, while therapeutic cancer vaccine has yet in its infancy regardless of basic and clinical researches. One of the critical issues is the inability to elicit sufficient high targeting antibody but result in high titers of carrier antibody which is not necessary for therapy. The mechanism underlying this phenomenon is the known “epitopic competition” between the epitopics of antigen and carrier protein in recognition of B cells. To address the above issue, we propose herein a new vaccine strategy via nanotechnology based assembly, to overcome the immune response of carrier protein. The size of new vaccine will be in nanoscaled range facilitating the endocytosis of immune cells. More importantly, new vaccine features a core-shell structure where the carrier protein is selectively encapsulated in inner core to avoid the recognition of B cells. Assisted by this unique design, the antigen presented at the surface of nanostructures is much easier to be recognized and endocytosis by B cells specific to antigen. The recognition of vaccine by B cells specific to carrier epitopic will be thus largely suppressed. Specifically, the research will be systematically exploited by using four carrier protein including tetanus toxoid, and EGFR as the antigen.

近两年，癌症免疫治疗取得重要进展，然而抗体型治疗性疫苗无论是基础还是临床研究都处于探索阶段。其瓶颈问题在于不能产生具有足够治疗水平的内源抗体，而产生过高的非目标外源载体抗体。问题的主要原因在于内源抗原表位与外源载体表位在B细胞识别上存在严重的竞争劣势。针对以上问题，项目申请人基于熟练掌握的“纳米组装”技术，发展一种可克服载体表位免疫反应的新型治疗性疫苗构建方法。研究对象上将选取破伤风外毒素等四种外源免疫载体，选取相对成熟的EGFR的核心表位作为内源抗原表位，展开系统深入研究。新型纳米组装疫苗不仅具有纳米尺度，便于免疫细胞吞噬，且具有核壳结构特征，将外源性蛋白表位及内源性蛋白表位在空间上进行“分域放置”，前者置于核壳结构内部，后者置于结构表面。由于空间上的“隔离”，疫苗与针对外源蛋白表位特异的B细胞识别将被大大限制，从而为控制载体表位免疫反应提供一种有效手段。

治疗性疫苗的一个重要瓶颈问题在于不能产生具有足够治疗水平的内源抗体，而产生过高的非目标外源载体抗体。问题的根本原因之一在于内源抗原表位在与外源载体表位在B细胞识别上存在严重的竞争劣势。针对以上问题，项目负责人构建了一种新型纳米疫苗，其中无免疫原性的白蛋白（SA）作为纳米颗粒主要骨架，载体蛋白分布在内，抗原表位短肽偶联在外，空间上有序分布。动物实验验证了这种疫苗对载体蛋白和抗原表位抗体滴度水平的影响。研究发现，在优化的实验条件下，这种有序的分域隔离设计可有效减少KLH的免疫识别，使得KLH抗体得到大幅抑制。实验组目标表位的抗原滴度在45天之后远远高于对照组。综上，本项目发展的分域隔离设计可以有效避免KLH的免疫识别，极大降低载体蛋白的抗体水平，最终提高抗原肽段的免疫应答水平。本项目为克服载体蛋白抗体过表达的瓶颈问题提供新策略，而且有望为解决一般短肽疫苗普遍存在的表位抑制难题提供新思路。