For people with high blood pressure, maintaining a healthy lifestyle and taking a daily dose of pills is essential to keeping hypertension at bay. Now scientists from the Swiss biotechnology company Cytos have created a vaccine that lowers blood pressure. They say that it may one day eliminate the need for daily medication.

"Pills have to be taken daily, and more than half of the people don't take their prescribed drugs," says Martin Bachmann, Cytos's chief scientific officer. "A vaccine could solve this issue, since it would likely only have to be injected two to three times a year."

Most antihypertensive drugs today act on a biological system that regulates blood pressure. The molecule angiotensin II plays a key role in this system, as it stimulates blood vessels to constrict, raising blood pressure. It can also produce a hormone that increases sodium and water retention, which in turn elevates blood pressure. Drugs known as receptor blockers have been designed to inhibit angiotensin II. Other drugs, called ACE inhibitors, altogether prevent the production of angiotensin II.

The new vaccine developed by Cytos also targets angiotensin II, with longer-lasting effects compared with conventional drugs. The vaccine itself is made up of virus-shaped particles covered with small receptors designed to bind with angiotensin II. When released into the bloodstream, these virus particles attract and lock onto the molecule. In response, the immune system, recognizing the virus as a foreign body, launches a defense. Antibodies attack the virus-bound angiotensin II, preventing it from constricting blood vessels and raising blood pressure.

Bachmann and his colleagues recently tested the vaccine on 72 people with mild to moderate forms of hypertension, and the team has published its results in the current issue of Lancet. In their study, the researchers randomly divided volunteers into three groups. One group received small doses of the vaccine, and another received larger doses, while the last received a placebo. The day before researchers administered the vaccine, they gave volunteers a blood-pressure monitor, which recorded readings every 15 minutes over 24 hours, providing a baseline measurement.

Volunteers returned for additional vaccinations one month and three months after the initial injection and reported any side effects via telephone. Two weeks after the last injection, the volunteers once again took home a monitor, which measured blood pressure throughout the day.

The team found that most volunteers tolerated the vaccine relatively well, albeit with minimal side effects, including flu-like symptoms and mild irritation at the site of injection. As for changes in blood-pressure levels, researchers compared monitor readings pre- and post-vaccination, and found that volunteers with a higher dose of the vaccine exhibited lower average blood pressure, with a surprising dip in the early-morning hours. Later in the day and through the night, there was little change among all volunteer groups. Bachmann says that it's unclear why the vaccine has a stronger effect in the early hours of the day, although he has some ideas.

"We hypothesize that the antibodies function like a sponge, which 'sucks up' all the generated angiotensin molecules," says Bachmann. "Since little angiotensin II is generated during the night, the sponge is 'empty' early in the morning, and therefore functions best at this time."