Image: BRYAN CHRISTIE
Despite the fact that in recent years scientists have devised many drugs capable of stalling the onset of AIDS, the demand for an effective vaccine against the human immunodeficiency virus (HIV), which causes the disease, has only grown. In regions of the world where HIV infection is spreading most quickly, the spate of new treatments are typically too expensive to help the people affected. Hopeful news comes from researchers at Beth Israel Deaconess Medical Center today, though, by way of a paper published in the journal Science. Norman Letvin and his colleagues describe a vaccine that prevented monkeys infected with a particularly deadly strain of HIV from becoming sick.
To create their new vaccine, the researchers borrowed a trick from tumor immunology, adding to DNA from the virus' core a fusion protein of interleukin-2 and part of immunoglobulin G (IgG). The first spike is a chemical messenger famous for its ability to activate killer CD8+ T cells--the very same immune cells that can target and destroy CD4+ T helper cells infected with HIV. And the IgG mixer helps to prolong the powers of interleukin-2. The idea behind this "vaccine-plus" design was to boost levels of the killer immune cells high enough that they keep levels of viral particles low enough to prevent illness and limit the chance of transmission.
In tests in rhesus monkeys, it seems to have worked. Among eight animals who received the new vaccine, all showed significantly increased killer T cell responses. And when they were subsequently infected with a combination of pathogenic HIV and SIV (the simian version of the virus), none became sick. After 140 days, all eight animals had high levels of both CD4+ and CD8+ T cells, nearly undetectable levels of the virus and no signs of clinical AIDS. By comparison, monkeys who received the viral DNA alone, without the double fusion protein punch, fared less well. And four of eight animals who did not receive any vaccine died of AIDS during the same time period.
"We haven't made a vaccine that will prevent AIDS virus infections in humans," Letvin says. "However, the findings in this study suggest that a vaccine might slow disease progression after an infection has occurred and decrease the likelihood of an infected individual transmitting the virus. This could have important ramifications for the AIDS epidemic."