Interleukin-2 is an important regulatory cytokine of the immune system, with potent effects on T cells, B cells, and natural killer cells. In vitro, interleukin-2 can induce the proliferation and differentiation of peripheral-blood mononuclear cells from patients infected with the human immunodeficiency virus (HIV).

We treated 25 HIV-infected patients with interleukin-2 administered as a continuous infusion at a dosage of 6 to 18 million IU per day for 5 days every 8 weeks during a period of 7 to 25 months. All patients also received at least one approved antiviral agent. Immunologic and virologic variables were monitored monthly.

In 6 of 10 patients with base-line CD4 counts higher than 200 per cubic millimeter, interleukin-2 therapy was associated with at least a 50 percent increase in the number of CD4 cells. Changes ranged from -81 to +2211 cells per cubic millimeter. Interleukin-2 therapy resulted in a decline in the percentage of CD8 lymphocytes expressing HLA-DR and an increase in the percentage of CD4 lymphocytes that were positive for the p55 chain of the interleukin-2 receptor. Four patients had a transient but consistent increase in the plasma HIV RNA level at the end of each infusion. In the remaining 15 patients, who had CD4 counts of 200 or fewer cells per cubic millimeter, interleukin-2 therapy was associated with increased viral activation, few immunologic improvements, and substantial toxic effects.

Intermittent courses of interleukin-2 can improve some of the immunologic abnormalities associated with HIV infection in patients with more than 200 CD4 cells per cubic millimeter.