Recombinant Protective Antigen (rPA) Anthrax Vaccine – Product Candidate

• Disease Overview
• Prevalence and Current Treatment
• Product Candidate Description
• Announcements

Disease Overview

Bacillus anthracis are naturally occurring, spore-forming bacteria found in soil throughout the world. B. anthracis spores can withstand extreme heat, cold and drought for long periods without nutrients or air. Anthrax infections occur if the spores enter the body through one of three possible routes: 1) a cut, abrasion or open sore (cutaneous anthrax), 2) ingestion of the spores (gastrointestinal anthrax), or 3) inhalation of the spores (inhalational anthrax). Once inside the body, the spores germinate into bacteria that then multiply. B. anthracis bacteria secrete three proteins, protective antigen (PA), lethal factor (LF), and edema factor (EF). Individually these proteins are non-toxic, but they can become highly toxic if allowed to be combined in a binary fashion (PA + LF or PA + EF) on the surface of human or animal cells.

Cutaneous anthrax, although rare in the United States, is the most common type of naturally acquired anthrax. Cutaneous anthrax typically occurs through contact with contaminated animals and animal products. The fatality rate for untreated cases of cutaneous anthrax is estimated to be approximately 20%.

Inhalational anthrax is the most lethal form of anthrax, and consequently aerosolized anthrax spores are the most likely method to be used in a potential anthrax bioterrorism attack. Inhalational anthrax has been reported to occur from one to
43 days after exposure to aerosolized spores. Initial symptoms of inhalational anthrax are non-specific and may include sore throat, mild fever, cough, achiness or weakness, lasting up to a few days. After a brief period of improvement, the release of anthrax toxins may cause an abrupt deterioration of the infected person, with the sudden onset of symptoms including fever, shock and respiratory failure. Hemorrhagic meningitis is common. Death often occurs within 24 hours of the onset of advanced respiratory complications. The fatality rate for inhalational anthrax is estimated to be between 45% and 90%, depending on whether aggressive, early treatment is provided.

Prevalence and Current Treatment

The only FDA-licensed product for pre-exposure prophylaxis of anthrax is BioThrax^® (Anthrax Vaccine Adsorbed). The only FDA-licensed products for post-exposure treatment of anthrax are antibiotics. Currently, there are no licensed vaccines for post-exposure prophylaxis against anthrax.

In February 2008, the U.S. Department of Health and Human Services (HHS) issued a request for proposal (RFP) seeking 25 million doses of recombinant protective antigen (rPA)-based anthrax vaccine to be used in a post-exposure prophylaxis (PEP) scenario in a declared emergency under an Emergency Use Authorization (EUA). Awards under this RFP are anticipated in the first half of 2009.

Product Candidate Description

Emergent’s rPA vaccine candidate is based on a recombinant form of the protective antigen protein and is designed to induce antibodies that neutralize anthrax toxins. It is a reformulated and potentially more stable form of the rPA 102 vaccine originally developed at the U.S. Army Medical Research Institute of Infectious Diseases (USAMRIID). We believe that our rPA vaccine candidate is well positioned to be a leading candidate for an award under the RFP issued by HHS in 2008 for the procurement of 25 million doses of an rPA vaccine for the Strategic National Stockpile (SNS) for use in a declared emergency under an EUA. Emergent’s rPA has been the subject of two research and development grants totaling approximately $100 million from the National Institute of Allergy and Infectious Diseases (NIAID).

Announcements