Since the first vaccine, for smallpox, was developed more than 200 years ago, immunization has proven to be a powerful weapon in the fight against infectious disease. Today, NIDA-supported researchers are using modern molecular biology to create vaccines against another deadly disease—addiction to drugs such as cocaine, nicotine, phencyclidine (PCP), and methamphetamine.

Immunization against drugs provides a different sort of protection than do the shots routinely given to prevent measles, hepatitis, and the flu. Those vaccines stimulate the immune system to produce antibodies that destroy or deactivate viruses or bacteria. Anti-drug vaccines also stimulate the immune system to produce antibodies, but these antibodies do not destroy drug molecules. Instead, they attach to drug molecules, forming a compound molecule that is too big to cross the blood-brain barrier easily. By slowing drugs' entry into the brain, the vaccines reduce or prevent the euphoria that promotes addiction. The higher the level of antibodies in the body, the more effective the vaccine in preventing euphoria.

Preliminary research on anti-drug vaccines is encouraging. NicVAX is a nicotine vaccine being developed, with NIDA support, by Nabi Biopharmaceuticals of Rockville, Maryland. In early studies, antibody levels rose with vaccine dose, and smokers receiving the vaccine did not smoke more to compensate for the reduced nicotine levels. In a 12-month trial, 16 percent of the NicVAX recipients quit smoking and remained abstinent, compared with 6 percent of recipients of an inactive substance.

In tests of TA-CD, a cocaine vaccine produced by Bermuda-based Celtic Pharma, investigators found that cocaine-dependent users who received high doses produced more antibodies against the drug than did those who were given less. High-dose recipients were also more likely to abstain from cocaine during the 12-week study.

To counter methamphetamine and PCP, researchers are exploring an approach called passive immunization. Injections of antibodies specifically targeted to these drugs quickly reduced the drug concentrations in the brains of laboratory animals. If this approach proves to be safe and effective for people, it could be a lifesaving treatment for overdose. Periodic antibody injections might also serve as a treatment for addiction to these and other drugs.

As drug vaccines emerge, researchers will need to learn the most effective ways to use them, perhaps combining them with behavioral therapy. Just as protection against infectious illness often requires "booster shots," drug vaccines will probably need to be administered more than once to have a long-term effect.

Volume 22, Number 2 (September 2008)