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2539 Background: CD40 is expressed on B-cells, monocytes, dendritic cells, other normal tissues and tumors. Previous studies showed that CD40 stimulation enhances antigen presentation, breaks tolerance, bypasses T-cell help, and induces apoptosis in CD40 pos tumor cells. We report the in vitro activity and primate pharmacokinetics of a human anti-CD40 agonist antibody, CP-870,893, currently in clinical trials for the treatment of cancer. Methods: CP-870,893 was identified as a CD40 agonist antibody by screening lead molecules generated through the Abgenix Xenomouse® platform. Agonist activity was determined using upregulation of B-cell and monocytes derived dendritic cell surface markers, as well as dendritic cell IL-12 induction. BIAcore and equilibrium binding were utilized to determine affinity, and competition studies with CD40L were conducted on BIAcore. CP-870,893 was administered to cynomolgus monkeys i.v. at various doses, serum antibody levels were evaluated over time in an ELISA assay, and B-cell markers were monitored by FACS. Results: CP-870,893 (IgG2, kappa) binds CD40 with sub-nanomolar affinity, and does not block binding of CD40L. When human whole blood is incubated with CP-870,893, upregulation of key surface molecules involved in antigen presentation (MHC Class II, CD80, CD86, CD23 and ICAM-1) is observed with an EC50 of 5–50 ng/ml. Human monocytes derived dendritic cells, when stimulated with CP-870,893, upregulate activation markers (MHC Class II, CD80 and CD83) with an EC50 of 100–300 ng/ml, and secrete high levels of IL-12p40. In the presence of a second stimulus, such as LPS, human dendritic cells also secreted bioactive IL12-p70 when stimulated with CP-870,893 (EC50 ∼ 150 ng/ml). In addition, a CD40 positive human B-cell tumor line, when stimulated with CP-870,893, becomes susceptible to killing by human CTLs. In cynomolgus monkey studies, the clearance of CP-870,893 decreased with increasing dose. Circulating B-cell numbers decreased, and surface molecules were upregulated on B-cells. Conclusions: These data support the potential utility of CP-870,893 as an immune enhancing agent in cancer immunotherapy, by activating antigen presenting cells, and by enhancing the immunogenicity of CD40 positive tumor cells. Table: see text
Bedian et al. (Tue,) studied this question.