Bad news for HIV-vaccines?

Double virus infection worries some AIDS researchers.
28 November 2002

TOM CLARKE

More than 40 million people have HIV. © GettyImages

A patient with some immunity to one strain of HIV virus has become infected with another strain¹. This could spell trouble for urgently needed HIV vaccines, warn researchers. Others think the case has little bearing on immunizing healthy people.

This alarming controversy has emerged on the eve of World AIDS day, as the United Nations announces that more than 40 million people worldwide are now infected with the virus.

The patient had been on 'stop-start' HIV therapy. Under this regimen, a patient takes anti-HIV drugs until the virus is suppressed, and then they stop. When the virus rebounds, undamaged parts of their immune system that had recovered during treatment keep the virus in check, often for months. As the virus gradually beats the immune system, they start taking the drugs again.

Several cycles into his treatment, the patient had "an extremely vigorous response to his virus", says Bruce Walker of Harvard Medical School in Boston, Massachusetts, who led the study¹. The patient then caught a second, different strain of HIV - probably from sex with another HIV-infected person - and his immune system collapsed rapidly.

This is the first case of so-called 'superinfection' in someone who had immunity to their initial infection². "We thought for a long time that if you get infected with one strain of HIV that you are well protected from another," says Walker.

There are countless strains of HIV. The hope has been that a vaccination against one would lead to immunity to the rest. The patient's second infection was caused by a closely related strain that is common in North America. "But it clearly was not something his immune system could deal with," says Walker.

Hopes for an effective HIV vaccine are far from dashed, however. "It's probably not good news," says HIV-vaccine researcher Sarah Rowland-Jones of the University of Oxford, UK, but vaccinated healthy people are likely to be very different. "Even at its best, the immune response of someone with HIV is never going to function normally," she says.

Indeed, the patient lacked cells that produce neutralizing antibodies to help destroy pathogens. "Half his immune system was missing," says Ruth Ruprecht, a vaccine researcher at the Dana-Farber Cancer Institute in Boston, Massacheusetts.

It is also possible that Walker's patient was a very rare case. It is not known how many HIV-positive people are exposed to other strains of the virus and fight them off.

There is one concrete conclusion from the study, says Anthony Fauci, director of the US National Institute of Allergy and Infectious Diseases in Bethesda, Maryland: "It is imperative that safer sex be practised during each encounter, even when both partners are HIV-infected."

1. Altfeld, M. et al. HIV-1 superinfection despite broad CD8+ T-cell responses containing replication of the primary virus. Nature, 420, 434 - 439, (2002). |Article|
2. Jost, S. et al. A patient with HIV-1 superinfection. New England Journal of Medicine, 347, 731 - 736, (2002). |Homepage|