Interleukin-2 (IL-2) is a cytokine which becomes depleted in HIV infection. In the test-tube IL-2 encourages the growth of CD4 cells. American researchers have been studying IL-2 for over three years, and in March reported some startling examples of immune system re-constitution among treated people.

The participants in the study were given infusions of 6 to 18 million units of IL-2 every 8 weeks, plus anti-retroviral therapy. The infusions last about five days and had to be done on an in-patient basis, but experiments are now being carried out with infusion methods which can be performed at home.

Six out of ten people with baseline CD4 counts above 200 enjoyed CD4 count increases of at least 50% that lasted two months after each infusion. Although participants' counts then started to drop again, they didn't fall back to their starting values, and the next infusion increased them again. In some cases CD4 counts had risen to 1000 after two years of treatment. The number of functional CD8 cells also increased.

Treatment Issues last month reported that similar responses appear to be occurring in the randomised IL-2 trial now taking place in the US and Australia.

The effects were less among 12 people with lower CD4 counts. Only two out of six people with a baseline CD4 count between 100 and 200 had a 50% increase, and none of the six people with counts below 100 seemed to benefit. IL-2 also caused sustained increases in levels of HIV in 10 out of 12 people in this group, and caused more severe side-effects.

IL-2 has unpleasant side-effects; it causes a severe flu-like illness during the infusion period, described by one recipient as "worse than the worst flu I've ever had", and trials have been slow to recruit because many otherwise healthy people find the prospect of hospitalisation every two months unacceptable. Experiments are now going on to find agents which can reduce the severity of IL-2's side effects.

A French trial sponsored by the ANRS, the French national clinical trials body, has just opened and aims to recruit 100 people. Plans for a UK trial of IL-2 plus anti-retroviral therapy are still at an early stage.

www.aegis.org