A Fully Human Antagonist Anti-CD40 Antibody Triggers Significant Antitumor Activity Against Human Multiple Myeloma.

We previously demonstrated that CHIR-12.12, a fully human anti-CD40 mAb (IgG₁) generated in XenoMouse^Ò mice (Abgenix, Inc), blocks CD40/CD40 ligand (CD40L) interactions and has more potent anti-lymphoma activity than Rituximab both in vivo and in vitro (abstract #2386, ASH, San Diego, Dec. 2003). In this study, we assess the efficacy of CHIR-12.12 against human multiple myeloma (MM) using CD40-expressing MM cell lines and purified CD138⁺ patient cells. CHIR-12.12 binds to purified CD138⁺ MM cells in >80% (10/12) of patient samples, as measured by flow cytometry: the mean fluorescence intensity (MFI) range was 1 to 20 for CHIR-12.12 vs 0.2–0.9 for control human IgG₁. We next examined the antagonist activity of CHIR-12.12 in MM cells. CHIR-12.12 blocked CD40L-mediated proliferation of CD40-expressing MM lines and purified CD138⁺ patient cells from 2 MM patients in a dose-response manner. In contrast, CHIR-12.12 alone did not alter constitutive MM cell proliferation. Immunoblotting analysis demonstrated that PI3-K/AKT, NF-kB, and ERK activation induced by hCD40L in the 12BM MM cell line was significantly inhibited by CHIR-12.12 (5 μg/ml). Adhesion of MM cells to bone marrow stromal cells (BMSCs) confers growth and survival benefit for tumor cells. Since CD40 activation, either by stimulatory mouse anti-CD40 mAb G28.5 or formaldehyde-fixed CHO cells expressing hCD40L, induces MM cell adhesion to fibronectin (FN) or BMSCs, we next asked whether antagonist CHI12.12 abrogates this process. CHIR-12.12 inhibited CD40L-induced adhesion of MM cell lines to FN in a dose dependent manner (0.001-10 μg/ml), whereas control human IgG did not. Moreover, CHIR-12.12 (1 μg/ml) blocked hCD40L-induced adhesion of freshly isolated patient MM cells to BMSCs. Adhesion of MM cells to BMSCs induces IL-6 secretion, an important growth and survival cytokine for MM cells, and treatment of MM cells with hCD40L further augmented adhesion-induced IL-6 secretion. Conversely, pretreatment of CD40-expressing MM cell lines with CHIR-12.12 significantly decreased IL-6 secretion triggered by coculture of MM cells with BMSCs. We next examined whether CHIR-12.12 stimulates antibody-dependent cellular cytotoxicity (ADCC) against CD40-expressing MM cells. Human peripheral blood mononuclear cells and purified NK cells (CD56⁺CD3⁻) were used as effector cells. CHIR-12.12 triggered MM cell lysis in a dose dependent manner, as measured in CD40-expressing MM cell lines. The maximum specific lysis of 20–70 % was achieved at 10 μg/ml concentration of CHIR-12.12. CHIR-12.12 mediated lysis was specific to CD40-expressing MM cells, as CHIR-12.12 did not induce ADCC against CD40-negative MM cells. Importantly, CHIR-12.12 induced ADCC against CD138⁺ cells isolated from 2 MM patients.

These results provide preclinical rationale for clinical evaluation of CHIR-12.12 with the goal of improving patient outcome in MM.