Ⅲ、Ⅴ血清型B族链球菌新型糖缀合物疫苗的设计、合成与免疫活性评价

Group B Streptococcus (GBS) is one of the primary causes of life-threatening bacterial infection in neonates and pregnant women. The development of safe and effective GBS vaccine represents the most promising approach for GBS disease prevention, which has attracted much concern worldwide. However, there has been no GBS vaccine approved for clinical use until now. Developing conjugate vaccines using synthetic carbohydrate haptens was recently demonstrated as an efficient strategy. As the major virulent factors of GBS, the capsular polysaccharides (CPSs) are excellent targets for the development of carbohydrate-based vaccines. Furthermore, serotypes Ⅲ and Ⅴ GBS were shown to possess high association with GBS infection in neonate and adults and with the neonatal mortality. Consequently, this research proposal will aim at the design, synthesis, and immunological evaluation of novel glycoconjugate vaccines against GBS. Initially, we will synthesize a series of structurally well-defined carbohydrate haptens that designed according to the repeating units of types Ⅲ and Ⅴ GBS CPSs through a preactivation-based one-pot glycosylation strategy. Next, to result in T cell-dependent immunities, the synthetic carbohydrate haptens will be covalently coupled with immunologically active carriers, such as TT, CRM197 and MPLA, to form the semi-synthetic glycoprotein vaccines and the fully synthetic self-adjuvanting glycolipid vaccines. Additionally, this project will also evaluate immunological properties of the resultant glycoconjugates and their capability to induce protective immune responses against GBS in mice, so as to find the potential GBS vaccines or promising lead compounds worthy further investigation. In the meantime, study of their structure-activity relationships (SARs) will reveal the carbohydrate antigenic determinant, which will be very useful for guiding further optimization of the GBS vaccine design.

B族链球菌（GBS）感染可引起新生儿和围产期孕妇多种重症疾病，研发安全有效的疫苗是国际公认的应对GBS感染的理想措施，同时也是一项亟待解决的课题。基于合成糖半抗原进行糖缀合物疫苗研究是近年来发展的一种有效的糖疫苗研发策略。研究表明，GBS荚膜糖抗原是研发相关疫苗的理想靶标分子，并且Ⅲ、Ⅴ血清型GBS与新生儿和成人GBS感染以及与新生儿致死性感染紧密相关。鉴于此，本申请项目拟开展新型的GBS糖缀合物疫苗的设计、合成与免疫活性研究，即：以Ⅲ型和Ⅴ型GBS荚膜多糖结构为研究对象，设计并通过基于预活化的“一釜”糖基化方法高效合成相关荚膜糖半抗原，随后将其与具有免疫活性的载体蛋白（TT和CRM197）以及单磷酰类脂A通过共价键偶联以制备一系列新型的半合成和全合成GBS糖缀合物疫苗，结合免疫学活性评价，筛选出有效的候选疫苗，并阐明相关糖抗原的免疫决定簇。

B族链球菌（GBS）感染可引起新生儿和孕妇多种重症疾病，对围产期孕妇进行抗生素干预的策略无法有效应对GBS感染，并且会导致细菌耐药性不断增强，而目前临床尚无相关疫苗可用，因此研发安全有效的疫苗是国际公认的应对GBS感染的理想措施。利用结构明确的糖抗原制备糖缀合物疫苗是近年来发展的一种有效的疫苗研发策略。本项目主要开展基于合成糖抗原的新型GBS糖缀合物疫苗的合成和免疫活性研究。首先，根据不同血清型GBS荚膜寡糖抗原的结构特点，发展建立不同的合成策略，例如，使用预先组装的唾液酸化三糖模块并结合基于预活化的一釜糖苷化方法，高效实现V和VII型GBS荚膜寡糖重复片段及其二聚体的首次合成；利用对唾液酸化三糖进行原位组装的策略，实现Ia、II和III型GBS荚膜寡糖抗原的高效合成。随后，将化学合成的、结构确证的GBS荚膜寡糖抗原与载体蛋白进行位置选择性共价偶联以制备一系列糖蛋白缀合物。小鼠免疫活性评价发现部分糖蛋白缀合物可显著升高小鼠体内T细胞依赖的特异性IgG抗体滴度，这为研发具有临床应用前景的GBS糖疫苗提供活性较好的先导化合物。同时，基于合成糖抗原的结构确定性，本研究初步阐明了糖抗原免疫决定簇构效关系，为进一步优化GBS糖疫苗结构奠定基础。此外，我们发展了一种新颖高效的α-D-葡萄糖/氨基葡萄糖苷键构建方法，该方法底物适用性广、立体选择性专一，新方法的建立可为GBS糖抗原及其他类似寡糖的高效制备提供新合成思路。