PDF file, 78KB, Measurement of the absolute level of circulating B cells (CD20+; Panel A), T cells (CD3+; Panel B) and NK cells (CD159a+)Panel C) in blood samples collected from cynomolgus monkeys at the indicated days prior to administration (Day -2), or following intravenous administration of PBS vehicle on Day 1 (all animals received PBS vehicle on Day 1) or MGA271 on Day 8 at the indicated dose. The panels on the left for each group represent all animals (N=6) in each dosing group, while the panels on the right represent only the recovery group animals (N=2) in each dosing group.
ARTICLE ABSTRACT
Purpose: The goal of this research was to harness a monoclonal antibody (mAb) discovery platform to identify cell-surface antigens highly expressed on cancer and develop, through Fc optimization, potent mAb therapies toward these tumor-specific antigens.Experimental Design: Fifty independent mAbs targeting the cell-surface immunoregulatory B7-H3 protein were obtained through independent intact cell-based immunizations using human tissue progenitor cells, cancer cell lines, or cell lines displaying cancer stem cell properties. Binding studies revealed this natively reactive B7-H3 mAb panel to bind a range of independent B7-H3 epitopes. Immunohistochemical analyses showed that a subset displayed strong reactivity to a broad range of human cancers while exhibiting limited binding to normal human tissues. A B7-H3 mAb displaying exquisite tumor/normal differential binding was selected for humanization and incorporation of an Fc domain modified to enhance effector-mediated antitumor function via increased affinity for the activating receptor CD16A and decreased binding to the inhibitory receptor CD32B.Results: MGA271, the resulting engineered anti–B7-H3 mAb, mediates potent antibody-dependent cellular cytotoxicity against a broad range of tumor cell types. Furthermore, in human CD16A-bearing transgenic mice, MGA271 exhibited potent antitumor activity in B7-H3–expressing xenograft models of renal cell and bladder carcinoma. Toxicology studies carried out in cynomolgus monkeys revealed no significant test article-related safety findings.Conclusions: This data supports evaluation of MGA271 clinical utility in B7-H3–expressing cancer, while validating a combination of a nontarget biased approach of intact cell immunizations and immunohistochemistry to identify novel cancer antigens with Fc-based mAb engineering to enable potent antitumor activity. Clin Cancer Res; 18(14); 3834–45. ©2012 AACR.
