A hallmark of HIV infection is the progressive loss of CD4+ T cells (a key type of white blood cell) and the subsequent decline in the infected person’s ability to fend off disease. NIH clinical investigators pioneered the experimental use of IL-2 in HIV therapy to help boost the immune systems of people with HIV infection. Produced naturally by T cells, IL-2 is a powerful immune system regulator. While its use in HIV therapy is experimental and can be associated with various side effects, IL-2 is licensed to treat certain cancers.
NIH researchers have long observed that in responsive patients, intermittent cycles of IL-2 therapy lead to substantial increases in the number of circulating CD4+ cells. The mechanisms driving this increase as well as its potential clinical significance, however, have remained unclear, note the scientists.
Using two relatively new techniques for labeling cells, the team demonstrated that IL-2 therapy can lead to greatly increased numbers of new CD4+ cells. “More remarkable than the proliferation of these cells was how long they lived,?says Dr. Kovacs. The average lifespan of CD4+ cells in healthy individuals as measured with this technique is about four weeks, according to Dr. Kovacs. In contrast, the average lifespan of CD4+ cells in 15 HIV-positive volunteers who had received three or more courses of IL-2 was 37.6 weeks, about nine times longer.
In the first set of experiments, inve