LONDON, Oct. 17 (Xinhua) -- Scientists have claimed that two new vaccine therapies have finally produced protective immune responses against prions in mice, and that such therapies could be further developed to work in humans or livestock.

    The vaccines, developed by scientists at the University of Rochester Medical Center in New York and the New York University School of Medicine respectively, rely on training the immune system to make defensive antibody molecules and have treated infectious prions in mice, raising hopes of a cure for deadly "madcow disease" in humans, according to New Scientist Tuesday on its website.

    Rochester University scientists engineered a harmless virus to carry genetic code for antibodies that bind to prion proteins and injected the modified virus into the brains of mice, and these experimental mice and their control counterparts then received injections of infectious mouse prion proteins into their bellies.

    The prions traveled to the animals' brains where they caused other proteins to misfold and form deadly, toxic clumps in the nervous system. The control mice died from these toxic effects within about 200 days but mice given the vaccine injections survived, on average, about 30 percent longer, dying after approximately 260 days, according to the scientists.

    This is the first time that a virus-based vaccine has successfully slowed the progression of prion disease, leading scientist Howard Federoff claimed, adding the antibodies most likely work by binding to infectious prions, preventing them from forming toxic clumps.

    The scientists believe that this vaccine approach might work to treat people who have Creutzfeldt-Jakob disease (CJD), a currently incurable human form of prion disease, related to mad cow disease or known as bovine spongiform encephalopathy (BSE).

    Meanwhile, New York University researchers, focusing on a different approach which creates an intense immune reaction in the gut and aims to treat the disease there and prevent its transmission, removed the harmful genes usually found in Salmonella bacteria and insert ones for the production of prion protein. These microbes invade the gut and cause special "dendritic" immune cells there to become highly active.

    When dendritic cells in this active state encounter prion proteins, they stimulate the immune system to produce antibodies against them, the researchers said, adding in recent experiments, 30 percent of mice that received oral doses of these prion-loaded bacteria appeared completely immune to prion infection and these mice survived about 600 days after exposure to infectious prions.

    The vaccine slowed the progression of prion disease in the remaining 70 percent of the experimental mice, allowing them to live longer than control mice, which did not receive the vaccine and died within about 200 days following infection, Fernando Goni at the New York University School of Medicine said.

    Goni said the ultimate aim is an easily ingestible vaccine that could be given to livestock, such as cows, to protect them against BSE. Enditem