Abstract
CD40, a transmembrane glycoprotein belonging to the tumor necrosis factor receptor family, is an attractive target for cancers of lymphoid origin since it is expressed on most mature B-cell malignancies, some early B-cell acute lymphocytic leukemias, and multiple myeloma. Finding efficient therapies for multiple myeloma (MM), chronic lymphocytic leukemia (CLL) and rituximab-refractory Non-Hodgkin Lymphoma (NHL) represents an unmet need. Several anti-CD40 antibodies, both agonistic and antagonistic, have demonstrated objective responses in early clinical NHL trials and thus validated this antigen as a target for lymphoproliferative diseases. Here we present the characterization of a novel Fc-engineered and humanized anti-CD40 antibody, XmAb®5485, that was generated using our XmAb antibody engineering technology. This antibody is highly cytotoxic against lymphoma, leukemia and multiple myeloma cell lines as well as primary cancer cells. XmAb5485 is characterized by: i) increased affinity for Fc gamma receptors (FcgR), ii) improved effector function, and iii) significantly increased antitumor potency. We investigated several direct and indirect (Fc-mediated) mechanisms of antibody-mediated cytotoxicity in vitro. The potency (EC50) of XmAb5485 in antibody-dependent cell-mediated cytotoxicity (ADCC) increased up to 150-fold relative to the native non Fc-engineered version (anti-CD40 IgG1) of the antibody in a screen of Burkitt’s lymphoma [BL], CLL and MM-derived cell lines. In the same cell lines, ADCC potency and maximal efficacy (% lysis) of XmAb5485 were also superior to that of rituximab: 74- and 1.3-fold higher in CLL, 12.5- and 1.4-fold higher in BL, and 190- and 1.9-fold higher in MM. In a MM cell line with low density of CD40 expression (~3500 per cell) XmAb5485 facilitated efficient ADCC whereas anti-CD40 IgG1 was virtually ineffective. Furthermore, using a BL cell line (Ramos) XmAb5485 displayed antibody-dependent cellular phagocytosis (ADCP) with potency and efficacy increased relative to rituximab (15- and 1.6-fold) and anti-CD40 IgG1 (5- and 1.2-fold). XmAb5485 also exhibited anti-proliferative apoptotic activity that was similar to that of rituximab. Ex vivo, XmAb5485 mediated potent ADCC of multiple primary patient-derived CLL, MCL, and plasma cell leukemia (PCL, an aggressive form of MM) cells, with substantially increased potency and efficacy relative to rituximab; in contrast, anti-CD40 IgG1 displayed minimal or no activity in these primary tumor cells. In vivo, in an established large (210–350 mm3) sc Ramos tumor xenograft model, 6 mg/kg XmAb5485 cured 80% of mice of detectable tumors and displayed statistically significant superiority over anti-CD40 IgG1. In contrast, only 7% of animals in the rituximab cohort were cured. In summary, our data suggest that XmAb5485, an anti-CD40 Fc variant antibody engineered for increased effector function, is a promising next-generation immunotherapeutic for leukemias, lymphomas, and multiple myeloma.
SET oncoprotein overexpression in B-cell chronic lymphocytic leukemia and non-Hodgkin lymphoma: a predictor of aggressive disease and a new treatment target
