GENETIC CONSTRUCTION AND CHARACTERIZATION OF THE DIPHTHERIA TOXIN-RELATED INTERLEUKIN-15 FUSION PROTEIN DAB(389) SIL-15

A gene fusion encoding DAB(389) sIL-15 was constructed in which the ca talytic and transmembrane domains of native diphtheria toxin (DAB(389) ) are genetically linked to the N-terminus of simian interleukin 15 (s IL-15), It was demonstrated that the cytotoxic action of DAB(389) sIL- 15 is mediated through the IL-15 receptor, Since toxicity may be block ed with chloroquine, it was concluded that following binding to the IL -15 receptor, the fusion toxin is internalized by receptor-mediated en docytosis and must pass through an acidic compartment in order to faci litate the delivery of the catalytic domain to the cytosol of target c ells. As a non-toxic control, the ADP-ribosyltransferase defective mut ant DA(E149S)B-389 sIL-15 was constructed, It was demonstrated that bo th sIL-15 and DA(E149S)B-389 sIL-15 stimulate protein and DNA synthesi s in IL-15 receptor-positive CTLL-2 cells in vitro.