Evidence of the virus in the blood cells of macaques dropped 50-fold and its evidence in plasma fell 1,000-fold in the test that lasted 10 months, said researcher Wei Lu of Rene Descartes University in Paris, who led the team that studied the animals.
Unlike the preventive vaccines used to keep people and animals from catching a disease, this work deals with a therapeutic vaccine given to an infected person or animal in hopes of helping them fight the disease by increasing their immune response.
The findings, focusing on SIV - the monkey form of HIV, the AIDS virus that affects humans - were being published Monday in the online edition of the journal Nature Medicine.
"This study has opened the possibility of treating HIV infection" using immune cells that have been exposed to a weakened form of virus, Lu reported.
Nina Bhardwaj of New York University and Bruce Walker of Partners AIDS Research Center at Massachusetts General Hospital said the experiments "suggest that immunotherapy may indeed be a realistic goal."
"The apparent success of this approach is encouraging," Walker and Bhardwaj said in a commentary on the article. But they added that questions about the type of macaques used and some other aspects of the work "must temper enthusiasm until the results can be confirmed."
In the experiment, 10 macaques that had been infected with SIV were vaccinated using a type of cell called dendritic cells, which had been exposed to chemically inactivated SIV. Dendritic cells are strong producers of antigens that battle diseases invading the body.
The macaques were given five injections over two months.
While the virus was not eliminated, it was sharply reduced in seven of them as long as 10 months later.
"We are now working on an improved protocol aimed at immunologic eradication" of the virus, Lu said in an interview conducted via electronic messages.
In January, researchers at Harvard University, working on an AIDS vaccine for monkeys, reported the virus was able to overcome their vaccine by changing a single gene.
"The problem raised by Harvard researchers is a very serious one," Lu commented.
The virus did not mutate to develop immunity in the seven macaques that maintained their resistance to SIV in the French experiment, but Lu said that may have been why the three others in his experiments saw the virus progressively increase in their blood.