TNF-related apoptosis. inducing ligand (TRAIL) is a TNF family member capable of inducing apoptosis. Death receptor 5(DR 51 is a key receptor of TRAIL and plays an important role in TRAIL-induced apoptosis. To prepare monoclonal antibodies (mAbs) against DR5, cDNA encoding soluble DR5(sDR5)was firstly amplified by revere transcriptase. polymerase chain reaction (RT-PCR) with specific primers, and then inserted into a prokaryotic expression vector pET-30a. The recombinant plasmid Was expressed in Escherichia coil strain BL21(DE3), and sDR5 was purified by nickel affinity chromatography. As an antigen. sDR5 Was used to immunize mice. Hybridomas secreting antibodies against sDR5 were identified. One positive clone Was selected to produce antibody, WD1. ELISA and immunofluorescence demonstrated that WD1 could bind recombinant sDR5 and membrane bound DR5 (mDR5)on Jurkat and Molt-4 cells. ATPLite assays showed that Jurkat and Molt-4 cells were sensitive to the antibody in a dose dependent manner. The Annexin V/PI assays and Giemsas staining both showed that WD1 could induce Jurkat cell apoptosis efficiently. Transient transfection of 293T cells and indirect immunofluorescence assay demonstrated that mAb(WD1)couldnt cross. react with DR4.Our findings indicated that the novel antibody, WD1 could act as a direct agonist, bind DR5 characteristically, and initiate efficient apoptotic signaling and tumor regression. Thus, WD1 would be a leading candidate for potential cancer therapeutics. Cellular & Molecular Immunology. 2008;5(1):55-60.