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Interleukin-2 (IL-2, Proleukin) and Immune Function

January 2003

IL-2 is an immune-based therapy that results in dramatic increases in CD4 cell counts when used in conjunction with anti-HIV therapy. Although IL-2 has been discussed in previous issues of PI Perspective, new information warrants a further look at the product.

The value of the large CD4 cell count increases realized with the use of IL-2 therapy remains unknown. Two large studies are underway to see if IL-2 use among people with HIV prolongs life and improves quality of life. A small study, conducted by the AIDS Clinical Trials Group (ACTG 328), sought to assess immune function in IL-2 treated people who had CD4 cell counts between 50 and 300 at study entry.

ACTG 328 included people who had never taken either protease inhibitors or 3TC (lamivudine, Epivir). All volunteers received indinavir (Crixivan), 3TC and another NARTI drug (like AZT, d4T, etc.). After 11 weeks of anti-HIV therapy, those who achieved viral load suppression to below 5,000 received intravenous IL-2 (high dose, cycled), IL-2 administered by injection under the skin (high dose, cycled) or no IL-2, in addition to continued anti-HIV therapy. Results from this study showed that IL-2 is able to bolster CD4 cell counts above what is observed with anti-HIV therapy alone.

In an attempt to glean information about the function of CD4 cells, a substudy of ACTG 328 evaluated responses to HIV-1 Immunogen (Remune), tetanus, hepatitis A and hepatitis B vaccines. More people in the anti-HIV therapy alone group demonstrated skin test reactivity to the Remune vaccine than those receiving IL-2 (60 percent vs. 20 percent). Antibody responses to Remune were similar between both groups, however. There was no apparent difference in antibody responses induced by hepatitis A vaccination between those receiving IL-2 compared to those who did not. While there were no statistically significant differences in hepatitis A vaccine responses, there was a trend toward slightly better responses among those receiving anti-HIV therapy alone.

Researchers note that this is a very small study and it's quite possible that a few very stellar responders in the anti-HIV therapy alone group could be driving trends in favor of this group and thus masking the activity of IL-2. In other studies, IL-2 therapy has shown to promote more pronounced and sustained responses to various vaccinations. At best, the results of this study suggest that the function of CD4 cell increases resulting from IL-2 therapy remain unknown. It is clear, in this study, that responses were not notably better among IL-2 users. Rather, trends favored the anti-HIV therapy alone group. More research is needed to understand the discrepancy between this observation and contrary observations from other studies.

As we went to press, Chiron Corporation, the company that is developing IL-2, has announced the closure of its large study of IL-2, called SILCAAT. The company states the reason for the study closure is a "business decision." Project Inform and other advocacy groups have strongly protested this action by the company. Non-Chiron scientists involved with the study are struggling to find a way to continue this important research, which external safety monitors state is proceeding as planned and should continue. Chiron says that those currently receiving IL-2 in the study are guaranteed to continue receiving the drug for a minimum of one year. As this story evolves, more information will be available. For more information about IL-2, call the Project Inform hotline.

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