Development of a highly efficacious vaccinia-based dual vaccine against smallpox and anthrax, two important bioterror entities

Abstract

Bioterrorism poses a daunting challenge to global security and public health in the 21st century. Variola major virus, the etiological agent of smallpox, and Bacillus anthracis, the bacterial pathogen responsible for anthrax, remain at the apex of potential pathogens that could be used in a bioterror attack to inflict mass casualties. Although licensed vaccines are available for both smallpox and anthrax, because of inadequacies associated with each of these vaccines, serious concerns remain as to the deployability of these vaccines, especially in the aftermath of a bioterror attack involving these pathogens. We have developed a single vaccine (Wyeth/IL-15/PA) using the licensed Wyeth smallpox vaccine strain that is efficacious against both smallpox and anthrax due to the integration of immune-enhancing cytokine IL-15 and the protective antigen (PA) of B. anthracis into the Wyeth vaccinia virus. Integration of IL-15 renders Wyeth vaccinia avirulent in immunodeficient mice and enhances anti-vaccinia immune responses. Wyeth/IL-15/PA conferred sterile protection against a lethal challenge of B. anthracis Ames strain spores in rabbits. A single dose of Wyeth/IL-15/PA protected 33% of the vaccinated A/J mice against a lethal spore challenge 72 h later whereas a single dose of licensed anthrax vaccine protected only 10%. Our dual vaccine Wyeth/IL-15/PA remedies the inadequacies associated with the licensed vaccines, and the inherent ability of Wyeth vaccinia virus to be lyophilized without loss of potency makes it cold-chain independent, thus simplifying the logistics of storage, stockpiling, and field delivery in the event of a bioterror attack involving smallpox or anthrax.biodefense | IL-15 | bioterrorism

Protective-antigen (PA) based anthrax vaccines confer protection against inhalation anthrax by precluding the establishment of a systemic infection

“…[6][7][8] Recently we reported that a cohort of rabbits immunized with a vaccinia-based PA vaccine created by the integration of the pag gene and an immune enhancing cytokine IL-15 into the genome of licensed smallpox vaccine (Wyeth/IL-15/PA), conferred sterile protection against an inhalation challenge exceeding 200 LD 50 of fully virulent Ames strain (A0462; pXO1 + pXO2 + ) spores. 9 The absence of bacteremia was also observed in the positive comparator group vaccinated with AVA suggesting perhaps PA based vaccines protect vaccinated subjects from inhalation anthrax by aborting the early events of the establishment of B. anthracis infection in the respiratory tract. 9 To explore this intriguing possibility in depth, first we examined the daily body temperature fluctuations in the rabbits that were subjected to the inhalation spore challenge as progressively rising body temperature is a consistent clinical manifestation in rabbits infected with B. anthracis via the inhalation route and parallels bacterial growth and toxin release.…”

“…9 The absence of bacteremia was also observed in the positive comparator group vaccinated with AVA suggesting perhaps PA based vaccines protect vaccinated subjects from inhalation anthrax by aborting the early events of the establishment of B. anthracis infection in the respiratory tract. 9 To explore this intriguing possibility in depth, first we examined the daily body temperature fluctuations in the rabbits that were subjected to the inhalation spore challenge as progressively rising body temperature is a consistent clinical manifestation in rabbits infected with B. anthracis via the inhalation route and parallels bacterial growth and toxin release. 10 The mean body temperature of the three groups of rabbits were similar prior to the inhalation spore challenge, for example, 24 h before the spore challenge, the mean body temperature of the Wyeth/IL-15/PA group was 102.14°F (SD 0.62), whereas the AVA group and the control group displayed a mean body temperature of 102.07°F (SD 0.58) and 102.80°F (SD 0.34) respectively.…”

“…Both of these rabbits had serum anti-PA IgG tites of 20,000 just prior to the inhalation spore challenge, whereas the mean serum anti-PA IgG titers for the Wyeth/IL-15/PA and AVA groups were 515,600 ± 192,300 (SD) and 275,600 ± 165,500 (SD) respectively as reported previously. 9 In addition, we did not detect any TNA antibodies in rabbits #35 and #43 prior to the spore challenge. assay (TNA) are dispensable for this early protective immune response.…”

“…With LC16M8/IL-15/PA vaccine, the in vivo expression of the PA takes place in an inflammatory milieu in the presence of co-expressed proinflammatory cytokine IL-15 that dictates the anti-PA immune response in the vaccinated mice. Moreover, the PA polypeptide expressed in eukaryotic cells is glycosylated 9,13,14 and could potentially influence the immune responses generated by LC16M8/IL-15/PA as well. When we assessed the subclass specificities of anti-PA IgG, the aluminum salt-adjuvanted protein vaccines elicited a predominantly Th2-biased IgG1 response compared with a lower IgG1 response elicited by LC16M8/IL-15/ PA ( Fig.…”

“…Moreover, all animals in the control group also had high bacterial counts in their blood as we reported previously. 9 We also included two rabbits (#35 and #43) that were immunized with a sub-optimal dose of a vaccine derived from a non-replicating MVA vaccinia virus (MVA/IL-15/PA). Both of these rabbits had serum anti-PA IgG tites of 20,000 just prior to the inhalation spore challenge, whereas the mean serum anti-PA IgG titers for the Wyeth/IL-15/PA and AVA groups were 515,600 ± 192,300 (SD) and 275,600 ± 165,500 (SD) respectively as reported previously.…”