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Plague has led to millions of deaths in history and outbreaks continue to the present day. The efficacy limitations and safety concerns of the existing killed whole cell and live-attenuated vaccines call for the development of new vaccines. In this study, we evaluated the immunogenicity and safety of a novel subunit plague vaccine, comprising native F1 antigen and recombinant V antigen. The cynomolgus macaques in low- and high-dose vaccine groups were vaccinated at weeks 0, 2, 4 and 6, at dose levels of 15 μg F1 + 15 μg rV and 30 μg F1 + 30 μg rV respectively. Specific antibodies and interferon-γ and interleukin-2 expression in lymphocytes were measured. For safety, except for the general toxicity and local irritation, we made a systematic immunotoxicity study on the vaccine including immunostimulation, autoimmunity and anaphylactic reaction. The vaccine induced high levels of serum anti-F1 and anti-rV antibodies, and caused small increases of interferon-γ and interleukin-2 in monkeys. The vaccination led to a reversible increase in the number of peripheral blood eosinophils, the increases in serum IgE level in a few animals and histopathological change of granulomas at injection sites. The vaccine had no impact on general conditions, most clinical pathology parameters, percentages of T-cell subsets, organ weights and gross pathology of treated monkeys and had passable local tolerance. The F1 + rV subunit plague vaccine can induce very strong humoral immunity and low level of cellular immunity in cynomolgus macaques and has a good safety profile.

PA (protective antigen) is a major immunogen of the vaccine against anthrax. In the present study, a new expression system, Escherichia coli strain Rosetta 2(DE3), was used for high-level expression of rPA (recombinant PA) whose gene contains 66 rare E. coli codons (9.0% of 733 total PA gene codons). The rPA-formed inclusion bodies were washed with Triton X-100 and 2 M urea and solubilized in 5 M urea, followed by a 60%-satd.-ammonium sulfate precipitation. Finally, the untagged rPA was efficiently and rapidly purified by single-step hydrophobic-interaction chromatography using Phenyl-Sepharose High Performance resin on an AKTA Purifier 10 system. The yield was approx. 13 mg of high-purity (>99%) biologically active rPA per litre of culture, which can be used for the detection of anthrax and as a potential component of a vaccine against anthrax.