Global & Disaster Medicine

An enhanced-delivery anthrax vaccine formulation

Weir GM, MacDonald LD, Rajagopalan R, et al. Single dose of DPX-rPA,
an enhanced-delivery anthrax vaccine formulation, protects against a
lethal _Bacillus anthracis_ spore inhalation challenge. npj Vaccines,
Anthrax is a serious biological threat caused by pulmonary exposure to
aerosolized spores of _Bacillus anthracis_. Biothrax® (anthrax
vaccine adsorbed (AVA)) is the only Food and Drug
Administration-licensed vaccine and requires 5 administrations over 12
months with annual boosting to maintain pre-exposure prophylaxis. Here
we report the evaluation of a single intramuscular injection of
recombinant _B. anthracis_-protective antigen (rPA) formulated in the
DPX delivery platform. Immune responses were compared to an alum-based
formulation in mice and rabbits. Serological analysis of anti-rPA
immunoglobulin G and toxin neutralization activity demonstrated higher
responses induced by DPX-rPA when compared to rPA in alum. DPX-rPA was
compared to AVA in rabbits and non-human primates (NHPs). In both
species, DPX-rPA generated responses after a single immunization,
whereas AVA required two immunizations. In rabbits, single injection
of DPX-rPA or two injections of AVA conferred 100% protection from
anthrax challenge. In NHPs, single-dose DPX-rPA was 100% protective
against challenge, whereas one animal in the 2-dose AVA group and all
saline administered animals succumbed to infection. DPX-rPA was
minimally reactogenic in all species tested. These data indicate that
DPX-rPA may offer improvement over AVA by reducing the doses needed
for protective immune responses and is a promising candidate as a
new-generation anthrax vaccine.

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