Researchers at Barcelona's Hospital Clinic said they were able to reduce the level of the virus in infected patients using a personalised treatment that they hope could eventually replace expensive antiretroviral drug treatment currently used to keep it at bay.

Twenty-four people with Aids took part in a clinical trial and after 24 weeks the majority had shown a "significant" decrease in their viral load, the hospital said, although it cautioned that it is still not enough as a treatment.

"This decrease was very significant is some of them but in no case did the virus become undetectable," the hospital statement said.

"However this is a very important improvement with respect to previous initiatives where with a similar vaccine there was a modest response in 30 percent of the treated patients. No therapeutic vaccine has achieved up to now the same level of response as in this study."

The vaccine was made from each person's own dendritic cells, a special type of cell that is a key regulator of the immune system. The cells were extracted and "reeducated" to attack the virus using samples of HIV also taken from individual patients.

The adjusted cells were then injected back into them in three stages, two weeks apart.

At 3,000 Euros (2,500 pounds) the new treatment is significantly less expensive than antiretrovirals which cost an estimated 8,000 Euros a year (6,800 pounds) and must be taken daily and for life.

The results of the clinical trial were announced Tuesday and published in the Journal of Infectious Diseases.

An estimated 33.3 million people worldwide have the HIV virus that causes Aids, according to the United Nations Aids agency UNAIDS.

Since the beginning of the epidemic in the 1980s, more than 60 million people have been infected with HIV and nearly 30 million have died of HIV-related causes.

Deborah Jack, Chief Executive of the National AIDS Trust, said: "This was an extremely small scale study so it's important to recognise that there is a long way to go before drawing any conclusions from this research.

"However, as HIV treatment has evolved hugely over the past ten years, we always welcome new research which sheds new light on effective treatment options for people living with HIV."

Lisa Power, Policy Director at HIV and sexual health charity Terrence Higgins Trust, said: "Therapeutic vaccines are an exciting area of research. Current drug treatment is good at keeping HIV in check, but as people with HIV now routinely live well into old age, the lifetime cost of treatment can be high. An effective therapeutic vaccine could not only be less expensive, but people living with HIV might find it easier to manage.

"This trial is a step in the right direction, but until we find a vaccine that controls the virus as well as antiretroviral treatment does, we're not there yet. This research give us a good idea of where to concentrate efforts in the future."