Date Published: July 11, 2013
Publisher: Public Library of Science
Author(s): Pan Tao, Marthandan Mahalingam, Michelle L. Kirtley, Christina J. van Lier, Jian Sha, Linsey A. Yeager, Ashok K. Chopra, Venigalla B. Rao, Tomoko Kubori.
Pneumonic plague is a highly virulent infectious disease with 100% mortality rate, and its causative organism Yersinia pestis poses a serious threat for deliberate use as a bioterror agent. Currently, there is no FDA approved vaccine against plague. The polymeric bacterial capsular protein F1, a key component of the currently tested bivalent subunit vaccine consisting, in addition, of low calcium response V antigen, has high propensity to aggregate, thus affecting its purification and vaccine efficacy. We used two basic approaches, structure-based immunogen design and phage T4 nanoparticle delivery, to construct new plague vaccines that provided complete protection against pneumonic plague. The NH2-terminal β-strand of F1 was transplanted to the COOH-terminus and the sequence flanking the β-strand was duplicated to eliminate polymerization but to retain the T cell epitopes. The mutated F1 was fused to the V antigen, a key virulence factor that forms the tip of the type three secretion system (T3SS). The F1mut-V protein showed a dramatic switch in solubility, producing a completely soluble monomer. The F1mut-V was then arrayed on phage T4 nanoparticle via the small outer capsid protein, Soc. The F1mut-V monomer was robustly immunogenic and the T4-decorated F1mut-V without any adjuvant induced balanced TH1 and TH2 responses in mice. Inclusion of an oligomerization-deficient YscF, another component of the T3SS, showed a slight enhancement in the potency of F1-V vaccine, while deletion of the putative immunomodulatory sequence of the V antigen did not improve the vaccine efficacy. Both the soluble (purified F1mut-V mixed with alhydrogel) and T4 decorated F1mut-V (no adjuvant) provided 100% protection to mice and rats against pneumonic plague evoked by high doses of Y. pestis CO92. These novel platforms might lead to efficacious and easily manufacturable next generation plague vaccines.
Plague, also known as Black Death, is one of the deadliest infectious diseases known to mankind. Yersinia pestis, the etiologic agent of plague, is a Gram-negative bacterium transmitted from rodents to humans via fleas . The bite of an infected flea results in bubonic plague which can then develop into secondary pneumonic plague, resulting in person-to-person transmission of the pathogen through infectious respiratory droplets . Pneumonic plague can also be caused by direct inhalation of the aerosolized Y. pestis, leading to near 100% death of infected individuals within 3–6 days , . Due to its exceptional virulence and relative ease of cultivation, aerosolized Y. pestis poses one of the greatest threats for deliberate use as a biological weapon . Since the disease spreads rapidly, the window of time available for post-exposure therapeutics is very limited, usually 20–24 h after the appearance of symptoms . Although levofloxacin has recently been approved by the Food and Drug Administration (FDA) for all forms of plague (http://www.fda.gov/NewsEvents/Newsroom/PressAnnouncements/ucm302220.htm), prophylactic vaccination is one of the most effective means to reduce the risk of plague.
Since the deadly anthrax attacks in 2001, stockpiling of recombinant anthrax and plague vaccines to protect masses against a potential bioterror attack became a national priority. However, no plague vaccine has yet been licensed. The reasons include poor stability, insufficient immunogenicity, and/or manufacturing difficulties associated with the current formulations. New immunogen designs and vaccine platforms that could overcome some of these problems would be of great interest not only to stockpile efficacious biodefense vaccines but also to develop vaccines against a series of infectious diseases of public health importance. Here, by using structure-based immunogen design and T4 nanoparticle delivery approaches, we have engineered new and efficacious plague vaccines that could be manufactured relatively easily and provide complete protection against pneumonic plague in two rodent models.