Background Costimulatory molecule pair CD40-CD40L plays a central role not only in immune cell interactions but also in immune-non immune cell activation. Targeting this pathway has generated great interest but early attempts to target CD40L failed mainly due to thrombotic complications observed in the clinic. In addition, developing a potent truly antagonistic CD40 antibody has proven to be challenging.

Objectives Here we describe the preclinical characterization of BI 655064, an anti-human CD40 mAb that is being developed for the treatment of autoimmune disorders. BI 655064 is engineered as a human IgG1 molecule with a mutated Fc region to abrogate effector function.

Methods Binding of BI 655064 to CD40 expressed on primary B cells was measured by flow cytometry. The ability of BI 655064 to block CD40L-induced B cell proliferation in vitro was measured by tritium uptake, while blockade of endothelial and DC activation was measured by inhibition of cytokine release. A subcutaneous PK/PD study in the cynomolgus monkey was performed to establish correlations between BI 655064 exposure, target coverage using a receptor occupancy assay and pharmacodynamic effects using an ex vivo CD54-induction assay. In vivo blockade of B cell function was also tested in a human-peripheral blood lymphocyte (huPBL) induced SCID mouse model of graft-versus-host disease (GvHD) and in cynomolgus monkeys immunized with keyhole limpet hemocyanin (KLH).

Results In human whole blood, BI 655064 binds to CD40 on B cells (EC₉₀ of 6.85 nM ±0.74). Blockade of CD40L-induced B cell proliferation was observed at an average IC₅₀ of 0.4 nM. Inhibition of CD40L mediated cytokine release was observed in DCs (IC₅₀=0.25 nM and 0.59 nM for TNFα and IL12/23p40, respectively) and to verify effects beyond immune cells, BI655064 was tested in CD40L stimulated endothelial cell cultures. Binding of BI 655064 to human platelets did not induce or augment platelet activation as determined by in vitro induction of CD62P. In the PK/PD study, cynomolgus monkeys dosed with greater than 1 mg/kg of BI 655064 exhibited complete blockade of ex vivo CD54 upregulation corresponding to full CD40 target coverage on B cells. In vivo, BI 655064 demonstrated clear effects on B cell function in the GvHD model where both human IgM and IgG responses were completely abrogated. As part of a repeat dose tolerability study, BI 655064 given to cynomolgus monkeys prior to immunization with KLH resulted in inhibition of KLH-specific IgM and IgG antibody responses. At doses of 5 mg/kg and above, germinal center size was decreased microscopically in Peyer's patches, lymph nodes, spleens and tonsils in treated monkeys. Evaluation of platelet function in cynomolgus monkeys dosed with BI 655064 did not reveal any effects on ex vivo platelet activation or aggregation.

Conclusions BI 655064 is a humanized antagonistic anti-CD40 mAb which is to be tested in human clinical trials for autoimmune disorders to establish safety and efficacy. BI 655064 demonstrated relevant pharmacologic in vitro and in vivo activity, blocking CD40-related functions at clinical dosing levels of >1 mg/kg in animal models.

Disclosure of Interest K. Ralph Employee of: Boehringer Ingelheim Pharmaceuticals, A. Nicoletti Employee of: Boehringer Ingelheim Pharmaceuticals, E. Musvasva Employee of: Boehringer Ingelheim Pharmaceuticals, S. Cannan Employee of: Boehringer Ingelheim Pharmaceuticals, S. VanTongeren Employee of: Boehringer Ingelheim Pharmaceuticals, D. Blanset Employee of: Boehringer Ingelheim Pharmaceuticals, S. Brodeur Employee of: Boehringer Ingelheim Pharmaceuticals, J. Ahlberg Employee of: Boehringer Ingelheim Pharmaceuticals, H. Li Employee of: Boehringer Ingelheim Pharmaceuticals, S. Fogal Employee of: Boehringer Ingelheim Pharmaceuticals, S. Desai Employee of: Boehringer Ingelheim Pharmaceuticals, K. O'Shea Employee of: Boehringer Ingelheim Pharmaceuticals, R. Kroe-Barrett Employee of: Boehringer Ingelheim Pharmaceuticals, E. Mainolfi Employee of: Boehringer Ingelheim Pharmaceuticals, G. Nabozny: None declared, H. Wu Employee of: Boehringer Ingelheim Pharmaceuticals, G. Hansen Employee of: Boehringer Ingelheim Pharmaceuticals, K. Canada Employee of: Boehringer Ingelheim Pharmaceuticals, S. Singh Employee of: Boehringer Ingelheim Pharmaceuticals, X. Zhu Employee of: Boehringer Ingelheim Pharmaceuticals, M. Ramanujam Employee of: Boehringer Ingelheim Pharmaceuticals, C. Grimaldi Employee of: Boehringer Ingelheim Pharmaceuticals