13价肺炎链球菌结合疫苗中的6A和6B诱导对新发现血清型6C和6D的交叉保护抗体

PCV13 （13-valent pneumococcal conjugate vaccine） containing capsular polysaccharides of Streptococcus pneumoniae serotypes 6A and 6B confers cross-protection against newly discovered serotypes 6C and 6D

目的血清型6C和6D是近些年新发现的肺炎链球菌血清型。本研究的目的是考察肺炎链球菌13价结合疫苗PCV13（1、3、4、5、6A、6B、7F、9V、14、18C、19A、19F和23F）里的6A和6B能否诱导对新血清型6C和6D的交叉保护抗体，以及它们对交叉保护抗体的贡献。方法PCV13、6A和6B荚膜多糖分别与CRM197的结合物PCV6A和PCV6B分别于第0天、第14天和第28天以等剂量肌肉注射免疫新西兰兔。免疫前和第35天采血分离血清。采用世界卫生组织（WHO）推荐的定量酶联免疫吸附试验（ELISA）检测兔血清中针对6A、6B、6C和6D荚膜多糖的抗体浓度，并采用WHO肺炎链球菌血清学参考实验室的调理吞噬试验（OPA）检测兔血清抗体针对6A、6B、6C和6D的杀菌功能。结果PCV13能够诱导兔产生针对6A和6B荚膜多糖的抗体，该抗体不仅能够与6C和6D荚膜多糖产生交叉反应，而且能够识别靶细菌6A、6B、6C和6D并激活补体，在激活补体的调理下，靶细菌被分化的HL60细胞吞噬，它们对靶细菌6A、6B、6C的杀菌滴度大致相当，但略高于对6D。PCV6A能够诱导兔产生针对6A荚膜多糖的抗体，该抗体能够与6B、6C和6D荚膜多糖产生交叉反应，它对靶细菌6A、6B和6C的调理吞噬滴度高于对6D。PCV6B能够诱导兔产生针对6B荚膜多糖的抗体，该抗体能够与6A、6C和6D荚膜多糖产生交叉反应，它对靶细菌6A、6B和6C的调理吞噬滴度高于对6D。PCV13、PCV6A和PCV6B免疫后针对6A、6B、6C和6D的荚膜多糖特异性抗体浓度和杀菌滴度均较免疫前有显著性升高（P〈0.01）。结论PCV13能够诱导兔产生针对6A和6B的抗体，它们不仅能够与6C和6D的荚膜多糖产生交叉反应，而且能够交叉保护6C和6D。PCV13中的6A和6B均对产生6C和6D的交叉保护抗体有贡献，其中对6C的贡献多于对6D。

ObjectiveTo investigate whether capsular polysaccharides of Streptococcus pneumoniae serotypes 6A and 6B contained in 13-valent pneumococcal conjugate vaccine （PCV13） could induce cross-protective antibodies against newly discovered serotypes 6C and 6D and the differences between them.MethodsNew Zealand rabbits were radomly divided into three groups and respectively muscularly administrated with three doses of PCV13, PCV6A and PCV6B on days 0, 14 and 28. PCV6A and PCV6B were conjugates of capsular polysaccharides of serotypes 6A and 6B chemically coupled with diphtheria toxin mutant CRM197. Serum samples were collected on days 0 and 35. Enzyme-linked immunosorbent assay （ELISA） recommended by World Health Organization （WHO） was used to quantitatively measure serotype-specific antibodies to capsular polysaccharides of serotypes 6A, 6B, 6C and 6D. Opsonophagocytosis assay （OPA） of WHO pneumococcal serology reference laboratory was used to determine antibody functional activities targeting serotypes 6A, 6B, 6C and 6D.ResultsImmunization rabbits with PCV13 induced the secretion of antibodies to capsular polysaccharides of serotypes 6A and 6B. These antibodies were able to not only cross-react with capsular polysaccharides of serotypes 6C and 6D but also recognize and bind to target Streptococcus pneumoniae serotypes 6A, 6B, 6C and 6D, resulting in the activation of complements and further phagocytosis of target bacteria by differentiated HL60 cells. Bactericidal titers were largely even among these serotypes except for serotype 6D which was slightly lower. PCV6A could induce antibody against capsular polysaccharide of serotype 6A, which was able to cross-react with capsular polysaccharides of serotypes 6B, 6C and 6D and showed higher bactericidal titers to serotypes 6A, 6B and 6C over serotype 6D. PCV6B could induce antibody against capsular polysaccharide of serotype 6B, which was able to cross-react with capsular polysaccharides of serotypes 6A, 6C and 6D and showed higher bactericidal titers to serotypes 6A, 6B and 6C over serotype 6D. Antibody concentrations and bactericidal titers specific to serotypes 6A, 6B, 6C and 6D were significantly increased following immunization with PCV13, PCV6A or PCV6B （P〈0.01）.ConclusionPCV13 containing pneumococcal serotypes 6A and 6B induced antibodies against capsular polysaccharides of serotypes 6A and 6B in New Zealand rabbits, which were able to cross-react with capsular polysaccharides of serotypes 6C and 6D and provide cross-protection to bacteria of serotypes 6C and 6D. Both serotypes of 6A and 6B contained in PCV13 contributed to the induction of cross-protective antibodies, especially to serotype 6C.