These cells attack virus-infected cells, making it harder for the virus to spread and cause disease, at least for the short term, says study coauthor Norman L. Letvin, an immunologist at Harvard Medical School in Boston. HIV overwhelms the body's defenses by invading and destroying immune system sentinels called CD4 T cells. The virus mutates rapidly and hides in the body, making it hard for the immune system to eradicate. Sidestepping antibodies and focusing on killer T cells seemed like a practical alternative, Letvin says. To strengthen the vaccine, the researchers added either two naturally occurring mammalian proteins called interleukin-2 and immunoglobulin G or the DNA that encodes those proteins.
T cells become specific killers when presented with protein cues.
Once programmed to seek a particular protein, these cells work like bloodhounds on a trail, sniffing out and latching onto anything displaying that molecule. Primed by the proteins encoded by the AIDS vaccine, killer T cells attacked virus-infected CD4 T cells. Meanwhile, the interleukin-2 induced rapid proliferation of the killer T cells. This strongly suggests that killer T cells were responsible for suppressing AIDS in the monkeys, he says. The researchers gave eight monkeys a series of injections of the new vaccine over 9 months.