Original research

Rapid generation of an anthrax immunotherapeutic from goats using a novel non-toxic muramyl dipeptide adjuvant

Cassandra D Kelly^1,2 , Chris O'Loughlin³ , Frank B Gelder³ , Johnny W Peterson⁴ , Laurie E Sower⁴ and Nick M Cirino^1,2

¹Wadsworth Center, New York State Department of Health, Biodefense Laboratory, Albany, NY, USA

²SUNY at Albany, School of Public Health, Department of Biomedical Sciences, Albany, NY, USA

³Virionyx Corporation Ltd, Auckland, NZ, USA

⁴The University of Texas Medical Branch, Galveston, TX, USA

author email corresponding author email

Journal of Immune Based Therapies and Vaccines 2007, 5:11doi:10.1186/1476-8518-5-11

Published:	22 October 2007

Abstract

Background

There is a clear need for vaccines and therapeutics for potential biological weapons of mass destruction and emerging diseases. Anthrax, caused by the bacterium Bacillus anthracis, has been used as both a biological warfare agent and bioterrorist weapon previously. Although antibiotic therapy is effective in the early stages of anthrax infection, it does not have any effect once exposed individuals become symptomatic due to B. anthracis exotoxin accumulation. The bipartite exotoxins are the major contributing factors to the morbidity and mortality observed in acute anthrax infections.

Methods

Using recombinant B. anthracis protective antigen (PA83), covalently coupled to a novel non-toxic muramyl dipeptide (NT-MDP) derivative we hyper-immunized goats three times over the course of 14 weeks. Goats were plasmapheresed and the IgG fraction (not affinity purified) and F(ab')₂ derivatives were characterized in vitro and in vivo for protection against lethal toxin mediated intoxication.

Results

Anti-PA83 IgG conferred 100% protection at 7.5 μg in a cell toxin neutralization assay. Mice exposed to 5 LD₅₀ of Bacillus anthracis Ames spores by intranares inoculation demonstrated 60% survival 14 d post-infection when administered a single bolus dose (32 mg/kg body weight) of anti-PA83 IgG at 24 h post spore challenge. Anti-PA83 F(ab')₂ fragments retained similar neutralization and protection levels both in vitro and in vivo.

Conclusion

The protection afforded by these GMP-grade caprine immunotherapeutics post-exposure in the pilot murine model suggests they could be used effectively to treat post-exposure, symptomatic human anthrax patients following a bioterrorism event. These results also indicate that recombinant PA83 coupled to NT-MDP is a potent inducer of neutralizing antibodies and suggest it would be a promising vaccine candidate for anthrax. The ease of production, ease of covalent attachment, and immunostimulatory activity of the NT-MDP indicate it would be a superior adjuvant to alum or other traditional adjuvants in vaccine formulations.