Vaccines have been doing their part to eradicate disease since the 18th century, typically by jump-starting the immune system to fight infectious bacteria and viruses such as those that cause the flu, cholera, or tetanus. But in 1974, narcotics researcher C. Robert Schuster, then at the University of Chicago, and his colleagues published the first evidence that vaccines could rev up the immune system against a different type of target—heroin. In a twist on their typical preventive role, these vaccines stop substances from satisfying an already-addicted user's cravings.
If these vaccines eventually head to the market, they'll be welcomed by addicted people, who currently have few effective treatment options, says vaccine researcher Janda. He and his team saw a similar possibility for people struggling against obesity.
To produce their antiobesity vaccine, the researchers needed a molecule on which to focus the immune system's antibodies, like the nicotine or cocaine molecules targeted by vaccines against those addictions. But obesity is a complex phenomenon spurred by hundreds of different molecules in the body. Eventually, Janda's team settled on ghrelin, a hormone that spikes hunger, slows metabolism, encourages fat storage, and shifts food preferences toward diets rich in fat.
The scientists created molecules that mimic the structure of different forms of ghrelin. By attaching each one to a larger carrier protein, the team created three different vaccines. The researchers then vaccinated groups of rats with one of the vaccines or a placebo.
Janda's group found that rats vaccinated against either of two forms of the hormone called ghrelin 1 and ghrelin 3 gained significantly less weight and had less body fat over the next several months than did rats vaccinated with the placebo, even though all the animals ate the same amount of chow.
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