DAB389IL-2 is an interleukin-2 receptor (IL-2R) specific fusion protein produced by recombinant DNA techniques by expression of a fusion gene in E. coli. The fusion gene consists of nucleotide sequences for the enzymatically active and membrane translocation domains of diphtheria toxin together with sequences for human interleukin-2 (IL-2). DAB389IL2 is specifically cytotoxic for cells bearing high-affinity IL-2R. The purspose of this study is to explore an in vivo dose-response relationship between administration of DAB389IL-2 and cell death in susceptible immune cells. Once the kinetics of activated T-cell death and re-population are established, this information may be used to help determine dose levels and treatment intervals for actual clinical use. This protocol is intended to establish proof-of-concept for the assays and methods used to measure these parameters. These assays have the potential to determine a dose-response relationship between different dosing schedules of DAB389IL-2 and the cytotoxicity and repopulation of specific T-lymphocyte subsets may provide a potential basis for the selection of dosing intervals and frequencies.