Table 4_Distinct effects of adjuvants on B cell responses to protein or polysaccharide antigens contained in glycoconjugate vaccines.xlsx

BackgroundProtein-polysaccharide conjugate vaccines rely on the induction of T-cell-dependent responses that support germinal center (GC) reactions to potentiate the expansion of antigen-specific memory B-cell (MBC) populations and high-avidity antibody responses. The effects of adjuvants on B-cell and antibody responses are well described for protein antigens but remain largely unexplored for conjugated polysaccharidic antigens.
MethodsWe assessed the effects of five adjuvants present in licensed vaccines (AS01, AS03, AS04, and aluminum hydroxide [Alum]) or under clinical evaluation (AS37) on the magnitude and quality of antigen-specific antibody responses and local/systemic B-cell responses. Naive mice received three immunizations of adjuvanted or non-adjuvanted model glycoconjugate vaccine containing Staphylococcus aureus (SA) capsular polysaccharide serotypes 5/8 (CP5/8) conjugated to a tetanus toxoid carrier and inactivated SA HlaH35L toxin.
ResultsAll AS-containing vaccines increased CP5/8-specific antibody titers and B-cell immunity relative to Alum- or non-adjuvanted formulations. After two immunizations, AS03 (α-tocopherol-containing oil-in-water emulsion) most robustly enhanced CP5/8-specific immunity relative to the other adjuvants or no adjuvant. AS03 induced higher responses of high-avidity antibodies persisting for at least 25 weeks post-immunization and greater expansions of populations of splenic GC B cells, mature MBCs in the lymph node or spleen, and long-lived plasma cells in the bone marrow. These effects increased with each immunization, suggesting the presence of avidity maturation and highlighting the role of the carrier in improving the quality of GC reactions. While HlaH35L-specific responses were augmented by each adjuvant, they lacked significant inter-group differences, pointing to profound differences in the adjuvants’ effects on polysaccharide vs. protein antigens in the mice of the present study.
ConclusionInvestigating the antibody quantity and quality and local and systemic B-cell population expansions in a naive model supports our understanding of how different adjuvants shape the response to the tested polysaccharidic antigens.

背景 蛋白质-多糖结合疫苗（protein-polysaccharide conjugate vaccines）依赖于T细胞依赖性免疫应答的诱导，该应答可支持生发中心（germinal center, GC）反应，从而促进抗原特异性记忆B细胞（memory B-cell, MBC）群体的扩增与高亲和力抗体应答。佐剂对蛋白质抗原的B细胞及抗体应答的影响已有充分阐释，但针对结合型多糖抗原的相关作用仍未得到广泛探索。
方法 本研究评估了5种佐剂的作用：其中4种见于已获批上市的疫苗（AS01、AS03、AS04及氢氧化铝（aluminum hydroxide, Alum）），1种处于临床评估阶段（AS37），旨在考察其对抗原特异性抗体应答以及局部/系统性B细胞应答的强度与质量的影响。将初始小鼠进行3次免疫，免疫制剂为含佐剂或无佐剂的模型糖结合疫苗，该疫苗包含与破伤风类毒素载体结合的金黄色葡萄球菌（Staphylococcus aureus, SA）荚膜多糖血清型5/8（CP5/8），以及灭活的SA HlaH35L毒素。
结果 相较于氢氧化铝佐剂或无佐剂制剂，所有含AS系列佐剂的疫苗均可提升CP5/8特异性抗体滴度与B细胞免疫水平。经2次免疫后，AS03（含α-生育酚的水包油乳剂（oil-in-water emulsion））相较于其他佐剂组及无佐剂组，可最显著地增强CP5/8特异性免疫应答。AS03可诱导产生更高水平的高亲和力抗体，该应答至少可在免疫后持续25周；同时可更显著地促进脾脏生发中心B细胞、淋巴结或脾脏中成熟记忆B细胞，以及骨髓中长寿浆细胞的群体扩增。上述效应随免疫次数增加而逐步增强，提示存在亲和力成熟过程，并凸显了载体蛋白在改善生发中心反应质量中的关键作用。尽管各佐剂均可增强HlaH35L特异性应答，但各组间未观察到显著差异，这表明本研究中佐剂对多糖抗原与蛋白质抗原的免疫调控作用存在显著差异。
结论 本研究通过初始小鼠模型，对抗体数量与质量以及局部、系统性B细胞群体扩增情况进行分析，有助于深化对不同佐剂如何调控受试多糖抗原免疫应答的理解。