In addition to these and studies presented here, ASKP1240-related thrombosis was not observed among 72 renal transplantation recipient monkeys treated with ASKP1240. weeks, significantly attenuated both delayed-type hypersensitivity and specific antibody formation evoked by tetanus toxoid. The Ibuprofen (Advil) immunosuppressive effect was well correlated with the CD40 receptor saturation. Thus, these results suggest that ASKP1240 is immunosuppressive but not prothromboembolic, and as such appears to be a promising therapeutic candidate for the management of solid organ transplant rejection and autoimmune diseases therapy. Keywords: CD40, costimulation, immunosuppressive therapy, mAbs Introduction The CD40 molecule is mainly expressed on antigen-presenting cells such as macrophages, and dendritic cells (DCs) as well as on B lymphocytes and appears to play an important role in immunological responses 1. Blocking the CD40CCD154 interaction has shown therapeutic effects in several experimental disease models, including organ rejection after transplantation 2, atherosclerosis 3 and autoimmune diseases 4C7. Although several humanized anti-CD154 mAbs (hu5C8, IDEC-131 and ABI793) have been developed and shown to be markedly efficacious in nonhuman primate renal allograft models 8C12, there are significant obstacles to further clinical development. In particular, in early clinical trials with hu5C8 or IDEC-131 there were thromboembolic events 13C15. The mechanism is not fully understood 16C19, but recent studies have suggested that CD154 functions to stabilize arterial thrombi in a CD40-independent manner through its integrin binding KGD (Lys-Gly-Asp) sequence 20,21. It is assumed that targeting the CD40CCD154 pathway via CD40 rather than CD154 might allow an immunosuppressive effect, while leaving the CD154Cintegrin interactions necessary to regulate thrombus stability unaltered. Several chimeric mAbs against CD40 (chi220 and ch5D12) have been developed as alternatives to anti-CD154 mAbs and were also found to be effective in renal allograft models 22C24 as well as autoimmune disease models in nonhuman primates 25. However, these mAbs were immunogenic reducing their suitability for drug development. Therefore, we generated a fully human anti-CD40 antagonistic mAb (ASKP1240) from trans-chromosome mice 26. This is an IgG4 masking antibody that shows neither antibody-dependent cell-mediated cytotoxicity (ADCC) nor complement-dependent cytotoxicity (CDC) 27. This ASKP1240 antibody was recently reported to significantly prolong kidney, liver and islet graft survival in nonhuman primates 28C31. The current study characterized this antibody with respect to its effects on soluble human CD154 (shCD154) induced cellular proliferation. In PTGFRN addition, the potential for prothromboembolic effects was assessed using human platelets and endothelial cells. Finally, the immunosuppressive activity and safety of ASKP1240 were examined in cynomolgus monkeys. Materials and Methods ASKP1240 antibody generation Fully human anti-CD40 antibodies were generated using the KM mouse? technology 26. These mice were immunized with soluble human extracellular domain CD40 protein and the splenocytes were fused with SP20 cells (ATCC, Rockville, Ibuprofen (Advil) MD). A SMART RACE cDNA Amplification Kit (Clontech Laboratories, Palo Alto, CA) was used for the cloning of the human antibody variable region. Human heavy and light chain variable sequences were subsequently cloned into IgG4 antibody expression vector. The expression vector was transfected into Chinese hamster ovary cells and the antibody ASKP1240 was expressed and purified. ADCC assay Blood samples were collected from human healthy volunteers and peripheral blood mononuclear cells (PBMCs) were isolated by density centrifugation. 51Cr-labeled Raji cells (ATCC) were incubated in triplicate with 100?g/mL indicated antibodies and PBMCs at effector-target ratio of Ibuprofen (Advil) 100:1 at 37C. After 4-h incubation, the radioactivity in the supernatants was counted. The percentage of specific lysis was calculated according Ibuprofen (Advil) to the following formula: % lysis?=?100??(ER???SR)/(MR???SR), where ER, SR and MR represent experimental, spontaneous and maximum 51Cr-release, respectively. CDC assay 51Cr-labeled Raji cells were incubated with 100?g/mL indicated antibodies and 10% normal human serum at 37C. After 2-h incubation, the radioactivity in the supernatants was counted. The percentage of specific lysis was calculated as described above. Internalization assay by flow cytometry To measure the clearance of immunocomplexes from the cell surface, Ramos cells (ATCC) were incubated with fluorescein isothiocyanate (FITC)-labeled ASKP1240 or FITC-labeled anti-CD40 agonistic mAb (clone G28.5; ATCC) in RPMI1640 supplemented with 10% fetal bovine serum (FBS) for 15?min at 4C. The stained cells were washed, and then incubated for varying durations in culture medium at 37C. At the given.