Cytos Biotechnology of Zurich is enrolling obese volunteers in the first human trial of a vaccine designed to trigger antibodies to ghrelin, a human peptide, or hormone, that stimulates the appetite.

In the combined phase I/II clinical trial of the vaccine CYT009-GhrQb, the volunteers, who must live in Switzerland and have a body mass index of between 30 and 35, will receive monthly shots for six months.

A control group will receive placebo injections, and all will be counseled on diet and exercise.

"The vaccination aims to induce antibodies against ghrelin that will bind the ghrelin in the blood system, so it does not get to the brain and cannot induce a feeling of hunger," according to Claudine Blaser, a spokesperson for Cytos Biotechnology.

Levels of ghrelin, a chemical messenger identified in 1999, increase before a meal and decrease after eating. The peptide also seems to play a role in long-term weight regulation. After weight loss occurs, blood levels of ghrelin rise dramatically, which may explain why so many dieters quickly regain the pounds they managed to lose.

Preclinical experiments in mice showed that vaccination with CYT009-GhrQb induced high levels of ghrelin-specific antibodies. In mice given a high-fat diet, the weight gain was found to be up to 15 percent lower after vaccination.