It is a generally accepted fact that childhood immunization against a particular disease provides protection against it in adulthood. However, a new study suggests that patients with HIV lose their immunity for smallpox despite receiving the vaccination against the disease in their childhood.
According to the study by the Oregon Health & Science University, the immune system of women afflicted with HIV undergoes what is called HIV-associated immune amnesia. In simple words, the immune system of HIV+ women 'forgets' immunity against smallpox. Researchers speculate that this 'forgetfulness' of the immune system may serve as the reason for people with HIV having a shorter lifespan than HIV-negative in spite of being under antiretroviral treatment.
Comparing T-cell and antibody responses
A T-cell is a form of lymphocyte or white blood cell (WBC) that plays an important role in the immune system of the body. An antibody is a blood protein that aids the immune system in eliminating pathogens such as viruses or bacteria. The scientists compared the response of these two entities in 50 pairs of HIV+ and HIV- women—100 women in total—who had received vaccination against smallpox as children.
The reason why smallpox was chosen for the study was that the last known case of smallpox in the US was reported in 1949. Therefore, the subjects could not have been exposed to the virus recently. Such exposure would have activated new T-cell and antibody responses in them.
Antiretroviral therapy does not protect against smallpox
As an accepted rule, CD4 T-cells or T helper cells—a type of T-cell associated with adaptation of the immune system to a particular pathogen—in vaccinated individuals—are expected to remember the smallpox virus and counter it by mobilizing in large numbers. Studies have shown that CD4 T-cells aimed at the elimination of smallpox virus are present in the body for a period of nearly 75 years after vaccination.
Despite being on antiretroviral therapy, the immune systems of women with HIV showed a restricted response when their blood interacted with the Vaccina virus—the pathogen used in the smallpox vaccine. This led the researchers to conclude that while antiretroviral therapy boosts the count of CD4 T-cells in HIV+ women in general, it may not be able to recover CD4 T-cells that are specific to smallpox virus created due to vaccination in childhood.
So what is the next step in this research? The authors intend to ascertain whether the immune systems of men with HIV also develop amnesia towards diseases vaccinated against.