HIV patients who are also infected by a second, mysterious virus are less likely to develop AIDS and die of the disease, suggests a new study.
Up to six years after their initial HIV-infection, men whose blood contained the second virus 鈥� known simply as GB virus C (GBV-C) 鈥� were nearly three times less likely to die than HIV-positive men who did not have the secondary infection.
Understanding how this virus protects against AIDS and death could suggest new ways to fight HIV infections, says Jack Stapleton at the University of Iowa in Iowa City, US, one of the study鈥檚 senior authors. 鈥淲e are certainly ready to look at this virus ever more finely and probe its biology,鈥� says Stapleton. 鈥淏ut I think a lot of HIV researchers will notice this and it will be a very hot field.鈥�
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鈥淯ntil now, there have been many doubting Thomases who didn鈥檛 believe this viral antiviral effect even existed,鈥� says Roger Pomerantz of Thomas Jefferson University in Philadelphia, Pennsylvania. 鈥淭his puts an end to the debate.鈥�
Pomerantz鈥檚 team published a smaller study in 2003 that also hinted at a protective role for GBV-C in HIV infection.
Strange phenomenon
GBV-C was discovered less than ten years ago. It was initially suspected to cause liver disease because it is a close genetic relative of the hepatitis C virus. But studies of thousands of patients failed to find any link to disease in the liver or anywhere else.
鈥淎t that point, most of the world stopped studying the virus,鈥� says Stapleton. 鈥淎ll that was left were HIV researchers who were interested in its role in co-infection.鈥�
Ironically, everyone assumed the virus could only worsen HIV infection and disease. But a few researchers began reporting a strange phenomenon 鈥� in some patients, GBV-C seemed to protect patients from disease. The result was so unexpected 鈥� there was no proven precedent for one virus thwarting another in human medicine 鈥� few researchers believed the results.
This was partly because most of the reports were of small populations for which there was little background data, or because other groups found no link between the virus and AIDS progression.
Protective agent
So Stapleton and his colleagues focused on one of the best-studied groups of HIV-infected patients 鈥� the Multicenter AIDS Cohort. This group is composed of men who have sex with other men. Some of the participants have been followed since 1984 and have had blood drawn every six months. Within this group, the researchers identified 138 men whose date of HIV infection could be determined within one year and good data was available on the progress of their disease.
When they analysed the group鈥檚 blood samples for traces of GBV-C, the results were striking. Up to 18 months after HIV-infection, survival times were no different between GBV-C-infected and uninfected groups.
But after about six years, the effect of the virus was dramatic. Survival for men who were continuously infected by GBV-C was 75 per cent compared with only 39 per cent for men with no evidence of infection. But the men who faired worst were those who 鈥渓ost鈥� their GBV-C infection sometime in the first six years 鈥� only 16 per cent survived.
Those results suggest GBV-C infection is as powerful a protective agent against HIV as some genetic factors that have been linked to slow progression of AIDS. Exactly how GBV-C can accomplish this is not clear.
Stapleton says some tantalising hints will be revealed by experiments his team has conducted in which the two viruses compete for infection in a test tube. They hope to publish that data in the next few months.
Journal reference: New England Journal of Medicine (vol 350, p 981)
