The Humanized Anti-CD40 Monoclonal Antibody SGN-40 Targets Hodgkin's Disease Cells through Multiple Mechanisms.

Abstract

CD40 is a member of the TNF receptor superfamily expressed by multiple lineages within the hematopoietic system that carries out essential functions in the maturation of antigen-presenting cells, cross-priming of cytotoxic T cells, initiation of T cell-dependent antibody responses, and Ig class-switching. CD40 is widely expressed by lymphoid malignancies including B-cell precursor acute lymphoblastic leukemia (B-ALL), non-Hodgkin's lymphoma (NHL), Hodgkin's disease (HD), and multiple myeloma (MM). SGN-40, a humanized version of the murine anti-CD40 monoclonal antibody S2C6, mediates antibody-dependent cellular cytotoxicity (ADCC) against both NHL and MM cells, directly induces apoptosis in NHL lines, and inhibits the proliferative response of MM cells toward autocrine IL-6 through down-modulation of the IL-6 receptor. Based on these activities, SGN-40 is currently in phase I clinical trials for relapsed and/or refractory MM and NHL. In this study, we examined the expression of CD40 on primary tumors isolated from 93 independent patients with HD. Seventy nine of these 93 cases (85%) demonstrated expression of CD40 by both the Reed-Sternberg cells as well as the infiltrating mononuclear cells. In a 1+ to 3+ scoring system, 35% of cases showed intense 3+ staining, 24% were positive (2+), and 26% were weakly positive (1+). Flow cytometry revealed that 8 of 9 HD cell lines expressed surface CD40, with receptor numbers ranging from 2,000 to > 370,000. SGN-40 induced CD40-positive HD cell lysis through ADCC in a dose-dependent manner, with IC50 values < 10 ng/mL. Fc-dependent effector function of SGN-40 was further exemplified by its ability to enhance macrophage mediated antibody-dependent cellular phagocytosis (ADCP). Specific ADCP against CD40-positive target cells was detected when SGN-40 was present at concentrations > 10 ng/mL. Furthermore, direct anti-proliferation signaling by SGN-40 in HD cells was also observed. In the L-1236 cell line, SGN-40 at doses ≥ 100 ng/ml reduced DNA synthesis to 25% of the untreated cells as measured by 3H-thymidine incorporation assays. Taken together, these data suggest that HD may be a suitable therapeutic target for SGN-40.