Yan Ming, Roehrl Michael H, Basar Emre, Wang Julia Y
Channing Laboratory, Department of Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, MA 02115, United States.
Vaccine. 2008 Feb 13;26(7):947-55. doi: 10.1016/j.vaccine.2007.11.087. Epub 2007 Dec 26.
Protective antigen (PA) is a central component of anthrax toxin and a major antigen in anthrax vaccines. However, the use of native PA as a vaccine is not optimal. If administered to people who have been freshly exposed to anthrax, PA may actually aid in anthrax toxin formation and thus may pose a serious safety concern for postexposure vaccination applications. A non-functional PA mutant may be a much safer alternative. To identify an improved anthrax vaccine antigen, we examined four non-functional mutants of PA, each being impaired in a critical step of the cellular intoxication pathway of PA. These mutants were Rec(-) (unable to bind PA-receptors), SSSR (resistant to activation by furin), Oligo(-) (unable to form oligomers), and DNI (Dominant Negative Inhibitory, unable to form endosomal transmembrane pores). When tested in mice and after three doses of immunization, all four mutants were highly potent in eliciting PA-specific, toxin-neutralizing antibodies, with immunogenicity increasing in the order of PA<Rec(-)<SSSR<Oligo(-)<DNI. While the differences between Rec(-) or SSSR and PA were small and not statistically significant, DNI and Oligo(-) were significantly more immunogenic than wild-type PA. One year after immunization and compared with PA-immunized mice, DNI-immunized mice maintained significantly higher levels of anti-PA IgG with correspondingly higher titers of toxin-neutralizing activity. In contrast, Oligo(-)-immunized mice had high levels of anti-PA IgG but lower titers of toxin-neutralizing activity, suggesting that Oligo(-) mutation sites may overlap with critical protective epitopes of PA. Our study demonstrates that PA-based vaccines could be improved both in terms of safety and efficacy by strategic mutations that not only render PA non-functional but also simultaneously enhance its immunogenic potency. Recombinant PA mutants, particularly DNI, hold great promise as better and safer antigens than wild-type PA for use in postexposure vaccination.
保护性抗原（PA）是炭疽毒素的核心成分，也是炭疽疫苗中的主要抗原。然而，使用天然PA作为疫苗并非最佳选择。如果给刚接触过炭疽的人接种，PA实际上可能有助于炭疽毒素的形成，因此可能给暴露后疫苗接种带来严重的安全隐患。一种无功能的PA突变体可能是更安全的替代品。为了鉴定一种改良的炭疽疫苗抗原，我们检测了PA的四种无功能突变体，每种突变体在PA细胞中毒途径的关键步骤中受损。这些突变体分别是Rec(-)（无法结合PA受体）、SSSR（对弗林蛋白酶激活具有抗性）、Oligo(-)（无法形成寡聚体）和DNI（显性负抑制，无法形成内体跨膜孔）。在小鼠中进行测试并经过三剂免疫后，所有四种突变体在诱导PA特异性、毒素中和抗体方面都具有高效力，免疫原性按PA<Rec(-)<SSSR<Oligo(-)<DNI的顺序递增。虽然Rec(-)或SSSR与PA之间的差异较小且无统计学意义，但DNI和Oligo(-)的免疫原性明显高于野生型PA。免疫一年后，与接种PA的小鼠相比，接种DNI的小鼠维持了显著更高水平的抗PA IgG以及相应更高滴度的毒素中和活性。相比之下，接种Oligo(-)的小鼠具有高水平的抗PA IgG，但毒素中和活性滴度较低，这表明Oligo(-)突变位点可能与PA的关键保护性表位重叠。我们的研究表明，通过策略性突变不仅可以使PA失去功能，还能同时增强其免疫原效力，基于PA的疫苗在安全性和有效性方面都可以得到改善。重组PA突变体，特别是DNI，作为比野生型PA更好、更安全的抗原用于暴露后疫苗接种具有很大潜力。
