Abstract CD40 is a key molecule in the regulation of immune responses and its activity can be modulated using antibodies. In particular, agonist CD40 antibodies are highly effective in preclinical tumor models either through direct interaction with CD40-expressing lymphomas, or indirectly through the activation of an adaptive anti-tumor immune response. To date, limited clinical data have been reported with strong CD40 agonist antibodies; nonetheless it seems likely that targeting this pathway will require a balance between the benefits of immune stimulation to drive anti-tumor responses, and the damage that can result from non-specific immune cell activation. We set out to develop novel human anti-CD40 antibodies with different levels of agonist activity to identify a lead candidate for systemic application. Anti-CD40 monoclonal antibodies (mAbs) were generated by immunization of human Ig transgenic mice with recombinant and cell surface expressed human CD40. Hybridomas developed from these mice were screened using CD40 binding assays and activity on a reporter cell line engineered to express CD40 and NFêB-responsive luciferase. The variable regions of lead antibodies that displayed differential activity were cloned into vectors containing human IgG1 or IgG2 constant domains and expressed in CHO cells. These human CD40 mAbs were further characterized by analysis of binding affinity, CD40L blocking activity, B cell and dendritic cell activation, and anti-tumor activity in xenograft tumor models. We found a wide range of activities among the CD40 mAbs that is linked to epitope specificity as well as the isotype. In general, the IgG2 isotype mAbs had greater signaling activity than their IgG1 counterparts. The lead candidate mAbs are undergoing additional testing related to functional and toxicity parameters before a final candidate is nominated for clinical development. Citation Format: Laura A. Vitale, Thomas O’Neill, Jenifer Widger, Andrea Crocker, Li-Zhen He, Jeffrey Weidlick, Karuna Sundarapandiyan, James Storey, Lawrence Thomas, Joel Goldstein, Henry C. Marsh, Tibor Keler. Development and characterization of novel CD40 antibody agonists for cancer immunotherapy. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4866.