A KINETIC-ANALYSIS OF THE EFFECTS OF INTERLEUKIN-2 DIPHTHERIA-TOXIN FUSION PROTEIN UPON ACTIVATED T-CELLS

The interleukin-2 diphtheria toxin-related fusion protein (IL-2 toxin) inhibits protein and DNA synthesis IN rIL-2 (IO-10 M) stimulated T lymphoblasts in a dosedependent fashion. However, prior to target cell death very low concentrations of rIL-2 and IL-2 toxin synergistically stimulate [3H] thymidine incorporation despite inhibition of [14C] leucine uptake. A sequential analysis of [3H] thymidine incorporation shows that high IL-2 toxin concentration (10-9-10-7 M) stimulates DNA synthesis at 18 hr of culture and inhibits [3H] thymidine uptake after 24 hr, while low concentrations of IL-2 toxin (10-12-1 0 -10 M) exhibits stimulatory effects only after 24 hr of culture. Anti-Tac a monoclonal antibody directed against the p55 chain of the high affinity IL-2 receptor (IL-2R) blocks the stimulatory effects of highdose IL-2 toxin, thereby proving that these effects are mediated through the IL-2 domain of the fusion protein.At 7 hr following interaction with IL-2R receptor (IL-2R)+ T cells, IL-2 toxin-treated cells evidence augmented transcription of the heat shock protein gene, an effect indistinguishable from those mediated by rIL-2. We conclude that interaction of IL-2 toxin with IL-2R+T cells initially mimicks the stimulatory effects of IL-2 upon gene transcription and DNA synthesis yet concomitant inhibition of protein synthesis is evident. © 1990 by Williams and Wilkins.