Toxicity of subcutaneously administered recombinant human interleukin-2 in rats

Recombinant human interleukin-2 (rIL-2) was administered subcutaneously to rats at doses of 0.3-10 mg/kg/day in a range-finding study and 0.03-0.3 mg/kg/day in a 4-week toxicity study. Treatment-related effects were assessed by hematology, clinical chemistry, anti-rIL-2 antibody production, and gross and histopathologic evaluations. Doses of 1 mg/kg/day or above were not tolerated, resulting in death or moribund termination by Day 7. Slight decreases in red blood cell counts (including hematocrit and hemoglobin) were observed at >/= 0.1 mg/kg/day. White blood cells counts increased in a dose-dependent manner; increases were primarily due to increases in lymphocytes and eosinophils. Hepatic abnormalities, including increases in aspartate aminotransferase and bilirubin, were noted at 0.3 mg/kg/day. Histologic findings were evident primarily in the spleen, liver, lung, and injection sites, with dose-related increases in inflammatory cell foci/infiltrates noted in these sites. Findings in the liver also included biliary hyperplasia, hepatocellular degeneration, necrosis, vascular mural thickening in the portal triads, and fibrosis. Red and white pulp hyperplasia and capsular fibrosis occurred in the spleen. Most clinical and histopathologic findings were reversible within 4 weeks after termination of treatment. Anti-rIL-2 antibodies were detected beginning on Day 19 and were still present on Day 56. The pharmacological and toxicological effects associated with subcutaneous administration of rIL-2 are comparable to those reported after intravenous administration, indicating that subcutaneous dosing may be an alternative to the current clinical iv regimens.