The test can detect a hidden virus that can remain in the body after standard treatment with three anti-Aids drugs, known as "triple therapy," has stopped all viral replication in the blood.
The presence of the hidden virus has limited the effectiveness of anti- Aids drugs, which can curb the disease but not cure it. Researchers at Hammersmith Hospital, west London, who developed the test, say it will enable doctors to monitor the effectiveness of drug treatments and direct them more accurately for individuals. It also brings the development of a cure a step closer.
Professor Robert Winston, the fertility pioneer and director of research and development at the hospital, said: "This is real world-class research. It is already changing the way the scientific world looks at how to monitor HIV in the body. Such a crucial finding is destined to have international repercussions and benefit the millions of people living with HIV around the world."
Patients who have taken triple therapy for a year, and in whom there is no sign of the virus on conventional tests, relapse if they stop taking the drugs, demonstrating that the virus is hiding somewhere in the body and is continuing to replicate. Although it has been eliminated from the blood, it is still present in the lymphatic system and in organs such as the brain, eyes and testicles.
Researchers led by Dr Sunil Shaunak discovered an HIV "calling card", which reveals that the virus has gone to ground in some hidden part of the body. It consists of small loops or "circles" of viral DNA, the waste products of replication, which can be found in white blood cells. By detecting and tracking the circles it is possible to show that the virus is alive and replicating in a patient taking anti-retroviral triple therapy. Treatment can then be tailored to the individual, with the aim of stopping all viral replication.
Dr Shaunak, who heads a team from the Imperial College School of Medicine, said: "The `circle test' will undoubtedly mean better treatment for patients with HIV and should help us to identify new therapies which will lead to total control of this virus within the body. The complex and toxic medications that HIV patients receive at present can now be monitored more effectively and should lead to more informed decisions about the best therapy for each patient. The new challenge now lies in understanding the nature of the reservoir in which the virus continues to grow despite anti-retroviral drugs."
His research was reported yesterday in the journal Nature Medicine. Researchers in Britain and America took blood from 63 patients who had been on anti- retroviral drugs for more than a year and whose blood appeared to be clear of HIV. Using the new test, 75 per cent of the patients were found to have viral circles. Dr Shaunak found they still had the infectious virus in their bodies.
A spokesman for the National Aids Trust said: "So far anti-Aids drugs have not succeeded in eliminating the virus from the body and this is an important step forward in identifying where in the body it is. It should help us develop new drug treatments and it may point the way to the total elimination of the virus from the body. But there is still a long way to go to achieve that goal."
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