August 6, 2008
Results from a study of IL2 (interleukin-2) garnered substantial interest from a full audience today at the International AIDS Conference in Mexico City. Though IL2 is the most studied immune based therapy, its usefulness as an adjunct for HIV therapy mostly hasn't panned out, except as an experimental drug for discreet use in a select group of people. However, these results are quite exceptional and have the potential to offer a person to take extra time before starting HIV therapy.
IL2 works with the immune system to create a stronger defense against HIV infection. In general, the theory has been to activate the immune system to produce more immune cells in order to combat and control HIV. (Some inaccurately refer to this as "boosting"). However, this hasn't worked because the activation actually causes unwanted and sometimes life-threatening side effects.
What's intriguing about how IL2 was used in this study is that the researchers used it before a person went on HIV therapy, unlike how much of IL2/HIV research has so far done. The theory here was to prevent the loss or improve the level of CD4 cells and thus defer the start of HIV therapy. Since the current Federal Guidelines recommend starting therapy at or below 350 CD4s, keeping them above that mark was the goal for the study.
The study enrolled 130 people with HIV and randomly assigned them to two groups: those on IL2 (66) and those on placebo (64). All had CD4 counts from 300-500 (average 383), and had average viral loads of 4.36 log10 cp/ml. None had signs of HIV progression. Those on IL2 received 4 cycles of it twice a day for 5 days, every 8 weeks for the first 52 weeks. After that, 2 optional cycles per year were offered but not required.
In this study, those volunteers who experienced any one of 4 different events by week 96 were taken off IL2 therapy and started on HIV therapy. These events were: a CD4 count below 300, an independent decision to start HIV therapy, the diagnosis of an AIDS-defining condition, or death. The study extended its follow-up on the volunteers to 150 weeks.
The results are quite remarkable. Through week 96, the average change in CD4 counts was +51 for the IL2 group and -64 for placebo. There was no difference between the groups in terms of vial loads. This is an important finding, as one of the fears of IL2 therapy is that it might cause HIV levels to rise. For those on IL2, CD4 count and viral load changes predicted HIV disease progression; while for those on placebo, only their CD4 count change predicted progression.
Even more remarkable was that for volunteers with lower viral loads (below 4.5 log10 cp/ml) at the start of the study, the likelihood that their HIV did not progress was 66% for those on IL2 and only 10% for those on placebo. This allowed those IL2 volunteers to delay starting HIV therapy by up to 92 weeks on average! These results are striking given the amount of time without therapy and the similar rate of adverse events between the two groups.
It should be noted here that this study used a lower dose of IL2 than has been used in other studies, like SILCAT and ESPRIT. Still, people taking IL2 reported feeling fatigue, fevers and other 'flu-like' symptoms while on IL2 therapy. While the severity of these symptoms may have been less due to the lower dose used in the study, these side effects are a major drawback for IL2.
Once a person starts his or her HIV therapy, it's a lifelong commitment. So strategies that help delay when a person actually starts are greatly encouraged. Longer time off treatment might improve one's quality of life and offset long-term side effects seen with HIV therapy. If IL2 can fill that void, then it's a step forward for those who can access the treatment. However, much more research will need to be conducted.