Paoletti L C, Wessels M R, Michon F, DiFabio J, Jennings H J, Kasper D L
Channing Laboratory, Brigham and Women's Hospital, Boston, Massachusetts.
Infect Immun. 1992 Oct;60(10):4009-14. doi: 10.1128/iai.60.10.4009-4014.1992.
Group B streptococci (GBS) are the most common cause of bacterial sepsis and meningitis in neonates in the United States. Although the capsular polysaccharide of GBS is an important virulence factor, it is variably immunogenic in humans. In this report, we have increased the immunogenicity of GBS type II polysaccharide by coupling it to tetanus toxoid (TT). Like other GBS capsular polysaccharides, the type II polysaccharide has side chains terminating in sialic acid. Controlled periodate oxidation of native II polysaccharide resulted in the conversion of 7% of sialic acid residues to an analog of sialic acid, 5-acetamido-3,5-dideoxy-D-galactosyloctulosonic acid. TT was conjugated to free aldehyde groups created on the oxidized sialic acid residues by reductive amination. Serum from rabbits vaccinated with type II-TT conjugate (II-TT) vaccine contained antibodies specific to type II polysaccharide as well as to TT, whereas rabbits vaccinated with uncoupled native type II polysaccharide failed to produce a type-specific antibody response. Antibodies elicited by II-TT vaccine were serotype specific and mediated phagocytosis and killing in vitro of type II GBS by human peripheral blood leukocytes. Serum from rabbits vaccinated with II-TT vaccine provided 100% protection in a mouse model of GBS type II infection. Antibodies induced by II-TT vaccine were specific for the native but not desialylated type II polysaccharide, suggesting that an important antigenic epitope of II-TT vaccine was dependent on the presence of sialic acid. Therefore, the coupling strategy which selectively modified a portion of the sialic acid residues of types II polysaccharide before coupling the polysaccharide to TT preserved the epitope essential to protective immunity and enhanced the immunogenicity of the polysaccharide.
B组链球菌（GBS）是美国新生儿细菌性败血症和脑膜炎的最常见病因。尽管GBS的荚膜多糖是一种重要的毒力因子，但它在人类中的免疫原性存在差异。在本报告中，我们通过将GBS II型多糖与破伤风类毒素（TT）偶联，提高了其免疫原性。与其他GBS荚膜多糖一样，II型多糖具有以唾液酸结尾的侧链。对天然II型多糖进行可控的高碘酸盐氧化，导致7%的唾液酸残基转化为唾液酸类似物5-乙酰氨基-3,5-二脱氧-D-半乳糖基辛糖醛酸。通过还原胺化反应，TT与氧化唾液酸残基上产生的游离醛基偶联。用II-TT偶联物（II-TT）疫苗免疫的兔血清中含有针对II型多糖以及TT的特异性抗体，而用未偶联的天然II型多糖免疫的兔未能产生型特异性抗体反应。II-TT疫苗引发的抗体具有血清型特异性，并介导人外周血白细胞在体外对II型GBS的吞噬和杀伤作用。在II型GBS感染的小鼠模型中，用II-TT疫苗免疫的兔血清提供了100%的保护作用。II-TT疫苗诱导的抗体对天然而非去唾液酸化的II型多糖具有特异性，这表明II-TT疫苗的一个重要抗原表位依赖于唾液酸的存在。因此，在将多糖与TT偶联之前选择性修饰II型多糖一部分唾液酸残基的偶联策略保留了保护性免疫所必需的表位，并增强了多糖的免疫原性。
