An Fc-Engineered CD133 Antibody for Induction of NK Cell Reactivity Against Cancer Cells

CD133 is expressed in various types of solid tumors where it predicts an unfavourable clinical outcome (e.g. Linuma et al., J Clin Oncol. 2011). Moreover, CD133 has been shown to be preferentially expressed by cancer stem cells (CSC), as e.g. demonstrated by its usability to enrich CSCs containing populations within cancer cell preparations (e.g. Zeppernick et al., Nature 2008). As CSC display marked resistance to chemo- and radiation therapy, great efforts are presently made to develop immunotherapeutic approaches to specifically target CSC without harming healthy tissue. We here report on the preclinical characterization of a monoclonal antibody (mAb) directed towards CD133 for induction of NK cell reactivity against cancer cells. Two different anti-CD133 antibody clones (W6B3 and 293C3) were used to study expression levels of CD133 in different cell lines derived from solid tumors (A172 and U87MG, glioblastoma; CaCo-2, Colo-205, HCT-8, HT-29 and SW48, colorectal cancer; MDA-MB-231, MDA-MB-468 and BT474, breast cancer; WERI-Rb1, retinoblastoma). CD133 was recognized by W6B3 and 293C3 in 4 and 5 out of the 11 cell lines, respectively. The latter mAb was then chosen for the development of chimeric mAbs with either a wildtype human Fc part (293C3-WT) or a variant containing amino acid exchanges (S239D/I332E) to enhance its affinity to the activating Fc receptor CD16 (293C3-SDIE) and thereby its capacity to mediate antibody dependent cellular cytotoxicity (ADCC), an important antibody property that largely contributes to the clinical success of antitumor mAbs. After confirming the binding specificity of both 293C3-WT and 293C3-SDIE we employed cytotoxicity assays to comparatively analyze their ability to induce NK cell ADCC against different solid tumor cell lines. In all cases, profound induction of tumor cell lysis upon application of 293C3-SDIE was observed, and the therapeutic effect of the Fc-optimized mAb clearly exceeded that of its counterpart containing a wild type Fc part. Notably, colony forming unit assays did not reveal any toxicity of 293C3-SDIE at the level of committed hematopoietic progenitor cells. Thus, treatment with 293C3-SDIE constitutes a promising novel strategy for immunotherapy of cancer, in particular considering its ability to preferentially target CSC which is presently under study.