Abstract
Plague caused by Yersinia pestis is an ancient disease, responsible for millions of deaths in human history. Unfortunately, there is no FDA-approved vaccine available. Recombinant subunit vaccines based on two major antigens, Caf 1 (F1) and LcrV (V), have been under investigation and showed promise. However, there are two main problems associated with these vaccines. First, the Yersinia capsular protein F1 has high propensity to aggregate, particularly when expressed in heterologous systems such as Escherichia coli, thus affecting vaccine quality and efficacy. Second, the subunit vaccines do not induce adequate cell-mediated immune responses that also appear to be essential for optimal protection against plague. We have developed two basic approaches, structure-based immunogen design and phage T4 nanoparticle delivery, to construct new plague vaccines that may overcome these problems. First, by engineering F1 protein, we generated a monomeric and soluble F1V mutant (F1mutV) which has similar immunogenicity as wild-type F1V. The NH2-terminal β-strand of F1 was transplanted to the COOH-terminus and the sequence flanking the β-strand was duplicated to retain a key CD4(+) T cell epitope. Second, we generated a nanoparticle plague vaccine that can induce balanced antibody- and cell-mediated immune responses. This was done by arraying the F1mutV on phage T4 via the small outer capsid (Soc) protein which binds to T4 capsid at nanomolar affinity. Preparation of these vaccines is described in detail and we hope that these would be considered as candidates for licensing a next-generation plague vaccine.