HIV could hide for 60 years

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US researchers now believe that it may be impossible to eradicate HIV from

some individuals, following experiments which suggest that HIV could persist in

latent form in some memory CD4 cells for up to 60 years.

Glossary

CD4 cells

The primary white blood cells of the immune system, which signal to other immune system cells how and when to fight infections. HIV preferentially infects and destroys CD4 cells, which are also known as CD4+ T cells or T helper cells.

primary infection

In HIV, usually defined as the first six months of infection.

eradication

The total elimination of a pathogen, such as a virus, from the body. Eradication can also refer to the complete elimination of a disease from the world.

reservoir

The ‘HIV reservoir’ is a group of cells that are infected with HIV but have not produced new HIV (latent stage of infection) for many months or years. Latent HIV reservoirs are established during the earliest stage of HIV infection. Although antiretroviral therapy can reduce the level of HIV in the blood to an undetectable level, latent reservoirs of HIV continue to survive (a phenomenon called residual inflammation). Latently infected cells may be reawakened to begin actively reproducing HIV virions if antiretroviral therapy is stopped. 

detectable viral load

When viral load is detectable, this indicates that HIV is replicating in the body. If the person is taking HIV treatment but their viral load is detectable, the treatment is not working properly. There may still be a risk of HIV transmission to sexual partners.

Writing in the May 1999 edition of Nature Medicine, Robert Siliciano and

colleagues reported on the decay rate of the reservoir of resting CD4+ cells.

The decay rate is the time taken for half the cells to die. By isolating HIV

from resting CD4+ cells taken from 35 people on HAART and correlating the HIV

burden with the length of time on therapy, the researchers were able to estimate

how long it takes for resting CD4 cells infected with HIV to die off. HIV levels

were tested up to seven times during a mean follow-up period of 14 months to

assess the decay rate.

Statistical analysis suggests that it could take anywhere between 21 and 73

years for the reservoir to disappear completely. However, there were wide

variations between individuals in decay rates observed, and no clear correlation

between the stage of infection at which treatment commenced and the decay rate.

Several patients who started treatment in the early stages of primary infection

had detectable latently infected CD4 cells and minimal evidence of decay during

the follow-up period.

These findings call into question the view that commencing treatment during

primary infection holds the best hope of eventual HIV eradication, a position

first advocated by Dr David Ho at the 1996 Vancouver International AIDS

Conference.

Reference:

Finzi D, Siliciano RF et al. Latent infection of CD4+ T cells provides a

mechanism for lifelong persistence of HIV-1, even in patients on effective

combination therapy. Nature Medicine 5 (5): 512-517, 1999.

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