Protection against inhalation anthrax by immunization with Salmonella enterica serovar Typhi Ty21a stably producing protective antigen of Bacillus anthracis

Abstract

The national blueprint for biodefense concluded that the United States is underprepared for biological threats. The licensed anthrax vaccine absorbed vaccine, BioThrax, requires administration of at least 3–5 intramuscular doses. The anthrax vaccine absorbed vaccine consists of complex cell-free culture filtrates of a toxigenic Bacillus anthracis strain and causes tenderness at the injection site and significant adverse events. We integrated a codon-optimized, protective antigen gene of B. anthracis (plus extracellular secretion machinery), into the chromosome of the licensed, oral, live-attenuated typhoid fever vaccineTy21a to form Ty21a-PA-01 and demonstrated excellent expression of the gene encoding protective antigen. We produced the vaccine in a 10-L fermenter; foam-dried and vialed it, and characterized the dried product. The vaccine retained ~50% viability for 20 months at ambient temperature. Sera from animals immunized by the intraperitoneal route had high levels of anti-protective antigen antibodies by enzyme-linked immunosorbent assay and anthrax lethal toxin-neutralizing activity. Immunized mice were fully protected against intranasal challenge with ~5 LD50 of B. anthracis Sterne spores, and 70% (7/10) of vaccinated rabbits were protected against aerosol challenge with 200 LD50 of B. anthracis Ames spores. There was a significant correlation between protection and antibody levels determined by enzyme-linked immunosorbent assay and toxin-neutralizing activity. These data provide the foundation for achievement of our ultimate goal, which is to develop an oral anthrax vaccine that is stable at ambient temperatures and induces the rapid onset of durable, high-level protection after a 1-week immunization regimen.

Zoonoses under our noses

“…Such approaches are using reverse vaccinology, subunit vaccines and conjugate vaccines (e.g. the Salmonella -Ty21a-PA-01 anthrax toxin conjugate vaccine, glycoconjugate vaccines for brucellosis and tularaemia, and epitope-selected subunit vaccines for Q fever [35], [49], [61], [78]). These minimise safety risks (such as potential animal toxicity of the anthrax Sterne strain vaccine) and enable more effective herd surveillance methods.…”

“…The prospect of room-temperature-stable vaccines (e.g. anthrax toxin-conjugate vaccine [35]) offers advantages for public health and veterinary preparedness, as well as outbreak and bio-terrorism management.…”

“…In addition to this, a live attenuated Salmonella spp. expressing the anthrax antigen Ty21a-PA-01 is currently being developed [35]. This aims to achieve a human vaccine that is stable at room temperature, and can be administered orally over a much-reduced immunisation period (approximately seven days compared to 18 months with AVA).…”

Disrupting vaccine logistics

“…No licensed vaccine yet meets this standard, although Vivotif, the orally administered vaccine against typhoid fever, formulated as enteric-coated capsules, is probably closest. Several candidate vaccines in early-stage development employ ‘new’ methods of thermostabilization such as spray drying and foam drying 6 that may yet yield licensed products stable at ambient temperatures. At the other end of the scale, the chimeric antigen receptor T-cell (CAR-T) products Kymriah and Yescarta and the malaria vaccine Sanaria®PfSPZ Vaccine, now entering phase 3 trials, contain cryopreserved live eukaryotic cells that are stabilized by cryopreservation and are stored and transported at < −150°C using liquid nitrogen vapour phase (LNVP) as the refrigerant.…”

Development of Enzyme Linked Immunosorbent Assay for humoral immuneresponse and infection monitoring of anthrax

“…Subunit vaccines or attenuated vaccines applied against anthrax disease increase the immune systems' antibody against the PA. Therefore, the cornerstone of a vaccine showing its protection and efficacy in curbing the disease is the power of antibody applied against the PA (Sim et al, 2017). {Sim, 2017 Testing the potency of anthrax vaccine entails us-ing a virulent strain of B. anthracis so that the real immunization of the vaccine would be determined (Moazeni et al, 2007).…”