Interleukin-2 fusion protein (DAB389IL-2) selectively targets activated human peripheral blood and lamina propria lymphocytes.

Activated mucosal T lymphocytes correlate with the intestinal inflammation of inflammatory bowel disease. Activated T cells elaborate interferon-gamma (IFN-gamma) and express high-affinity interleukin-2 (IL-2) receptors. The IL-2/diphtheria toxin fusion protein (DAB389IL-2) has been shown to specifically kill high affinity IL-2 receptor-bearing cells. We tested whether DAB389IL-2 could specifically target activated lamina propria lymphocytes. Lymphocytes were activated in vitro with phytohemagglutinin and IL-2 for 24-48 hr. Toxin efficacy was determined by the [14C]leucine incorporation, IFN-gamma ELISA, and flow cytometry. DAB389IL-2 (10(-11) M) inhibited protein synthesis by 80% in activated lamina propria lymphocytes. This inhibition was blocked by coculture of either excess IL-2 or a nonfunctional IL-2 diphtheria toxin mutant protein. DAB389IL-2 (10(-12) M) also significantly reduced the numbers of activated helper T cells and IFN-gamma levels in 24-hr cultures. DAB389IL-2 specifically targets activated IL-2 receptor-positive lamina propria lymphocytes and is a potential new therapeutic agent for patients with active inflammatory bowel disease.