An IL-2/Ig fusion protein influences CD4(+) T lymphocytes in naive and simian immunodeficiency virus-infected rhesus monkeys

The T cell-stimulatory cytokine interleukin 2 (IL-2) is being evaluated as a therapeutic in the clinical settings of HIV infection and cancer. However , the clinical utility of IL-2 may be mitigated by its short in vivo half-l ife, toxic effects, and high production costs. We show here that an IL-2/Ig fusion protein possesses IL-2 immunostimulatory activity in vitro and a lo ng in vivo half-life. IL-2/Ig treatment of healthy rhesus monkeys induced s ignificant increases in CD4(+) T lymphocyte counts and expression of CD25 b y these cells. Short courses of IL-2/Ig treatment of simian immunodeficienc y virus (SIV)-infected rhesus monkeys in conjunction with antiretroviral dr ugs resulted in increased CD25 expression on T lymphocytes, and transient i ncreases in CD4(+) T lymphocyte counts. Plasma viremia did not increase in these treated animals. Treatment of healthy or SIV-infected rhesus monkeys with a plasmid encoding the IL-2/Ig protein did not affect CD4(+) T lymphoc ytes. These results demonstrate that IL-2/Ig has potential utility as an im munostimulatory therapeutic.