The prototype is called a therapeutic vaccine, but this is something of a misnomer, for it is not a preventive vaccine in the conventional sense, which aims at protecting people from infection.

  

Instead, it is more of a treatment, seeking to reduce levels of the human immunodeficiency virus (HIV) among individuals already infected.

  

Researchers recruited 18 Brazilian patients who were chronically infected with HIV and who were not receiving antiretroviral treatment.

  

The volunteers received a mixture of their own dendritic cells and inactivated HIV - viruses which had been killed by chemicals, and thus were not infectious - in the aim of priming their immune system.

 

Dendritic cells

  

Dendritic cells are early defensive cells that rush out to meet an intruder and destroy it with enzymes.

 

They then carry a chemical "tag", an antigen, on the surface of their cell that corresponds to the signature of the intruder. It is this tag which helps alert lymphocytes, the heavy artillery of the immune system.

  

The treatment reduced the virus
level in patients' blood by 80%

HIV, a slippery foe, is able to sidestep the dendritic cells, although how this is done is unclear.

  

The goal of the experimental treatment, using the inactivated HIV, was thus to stimulate the dendritic cells so that they recognised the virus.

  

The treatment was delivered in three injections, each a fortnight apart. There were no known side effects.

  

Four months after the first dose, the viral load - the quantity of HIV in the blood - had fallen on average by 80%.

  

Viral loads

 

A year after the jabs, eight out of the 18 patients still showed viral loads that had diminished by more than 90%.

  

Four of them had a viral load of less than 1000 particles per millilitre, "which, in theory, means they are not infective", said chief researcher Jean-Marie Andrieu, a cancer professor at the Saint-Peres Biomedical Centre in Paris, on Monday.

  

The count of CD4 lymphocytes, which are infiltrated and destroyed by the virus, initially rose after the injections, but then fell back to their baseline.

 

Antiretroviral drugs can have
toxic side effects

These results suggest that dendritic-cell therapy could be a "promising strategy" for treating people with HIV, says Andrieu's team.

  

The next step is to widen the trial so that it includes more volunteers, some of whom will not receive the treatment in order to see if it is truly as encouraging as it seems.

  

The study was published on Sunday in Nature Medicine, a journal of the Nature Publishing Group in London.

  

There are 39.4 million people with Aids or HIV around the world, according to the latest UN estimates.

  

There is no vaccine to prevent infection, nor any cure. Antiretroviral drugs keep the virus at bay, but they can have toxic side effects. If the patient stops taking them, the virus rebounds.