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Arms supply. Plasma from vaccinated volunteers may provide an experimental anthrax treatment.

Borrowed Immunity for Anthrax

The U.S. government wants to have something more effective than antibiotics on hand should anthrax terrorists strike again. Now investigators at the Centers for Disease Control and Prevention (CDC) and other federal agencies want to give future victims an experimental therapy designed to confer instant immunity: blood plasma from military personnel vaccinated against anthrax.

Of the 11 bioterrorism victims who came down with inhalation anthrax last fall, five died despite the powerful antibiotics they were given. Antibiotics can fail, researchers say, because Bacillus anthracis churns out a toxin that continues to wreak havoc even after the bacteria have been killed. Blood plasma from vaccinees contains a variety of antibodies that researchers hope may eliminate the toxin. In a later stage, CDC plans to use not the plasma itself, but antibodies purified from it.

The approach, called passive immunotherapy, has a long history: Plasma from vaccinated horses was the only available anthrax treatment in the preantibiotic era, and it's still used in Russia and China. Unfortunately, none of the reports about its efficacy in humans meets modern scientific standards, says anthrax researcher Arthur Friedlander of the U.S. Army Medical Research Institute of Infectious Diseases (USAMRIID). Given this paucity of data, the proposed treatment would be given only to failing patients who didn't improve on antibiotics alone, says CDC anthrax researcher Bradley Perkins.

The proposal has passed CDC's internal ethics board and could be sent for approval as early as this week to the Food and Drug Administration (FDA), says Perkins. Whether it will pass is uncertain; the plasma was collected before the anthrax attacks with scientific experiments in mind, not for use in humans, and the way it was collected and stored may raise eyebrows at the FDA.

Meanwhile, CDC, the National Institutes of Health, and USAMRIID plan to conduct further animal experiments to determine whether the therapy will work and how much plasma would be needed. The investigators also want to collect a second, larger batch of plasma from vaccinated volunteers. But it would be a fairly modest amount, says Perkins: "Most [investigators] are not willing to stockpile this material in any serious quantity without much better data about its efficacy in animals."

Related sites
CDC's anthrax site
Anthrax as a Biological Weapon: Consensus statement