HIV triggers immune system 'amnesia' to smallpox

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HIV wreaks havoc with previous immunisations.
HIV wreaks havoc with previous immunisations.

HIV infection causes a loss of immunity to smallpox, even in people who were vaccinated as kids and are taking antiretroviral drugs to restore their immune system, a new study finds.

Such "HIV-associated immune amnesia" could explain why people with HIV who are on antiretroviral therapy still have shorter lives on average than people without HIV, according to the researchers.

No recent exposure

The new study included 100 HIV-positive and HIV-negative women who were vaccinated against smallpox in their youth. Their blood was exposed to the vaccinia virus, which is used in the smallpox vaccine, in order to assess T-cell and antibody responses.

Smallpox was chosen because the last known US case was in 1949, so participants couldn't have had recent exposure to the virus, which would have triggered new immune responses.

Normally, a person vaccinated against smallpox has CD4 T-cells that remember the virus and respond in large numbers when the person is exposed to it again. But the immune systems of HIV-positive women on antiretroviral therapy had a limited response to the vaccinia virus.

Antiretroviral therapy works by boosting CD4 T-cell counts in people with HIV. These findings suggest that while antiretroviral therapy may increase total T-cell counts, it can't recover virus-specific T-cells created by childhood vaccinations, said study leader Mark Slifka. He's a professor of molecular microbiology and immunology at Oregon Health and Science University School of Medicine, in Portland.

Other recent studies

The study was recently published in the Journal of Infectious Diseases.

The researchers now plan to evaluate whether the loss of smallpox immunity also occurs in HIV-infected men, and if people with HIV also lose immune memory to other diseases.

Other recent studies found that the immune systems of children who contracted measles similarly "forgot" their immunity against other illnesses, such as the flu.

Image credit: iStock

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