Fc-engineering significantly improves the recruitment of immune effector cells by anti-ICAM-1 antibody MSH-TP15 for myeloma therapy.

Despite several therapeutic advances, patients with multiple myeloma (MM) require additional treatment options since no curative therapy exists yet. In search of a novel therapeutic antibody, we previously applied phage display with myeloma cell screening and developed TP15, a scFv targeting intercellular adhesion molecule 1 (ICAM-1/CD54). To more precisely evaluate the antibody's modes of action, fully human IgG1 antibody variants were generated bearing wild-type (MSH-TP15) or mutated Fc to either enhance (MSH-TP15 Fc-eng.) or prevent (MSH-TP15 Fc k.o.) Fc gamma receptor binding. Especially MSH-TP15 Fc-eng. induced potent antibody-dependent cell-mediated cytotoxicity (ADCC) against malignant plasma cells by efficiently recruiting NK cells and engaged macrophages for antibody-dependent cellular phagocytosis (ADCP) of tumor cells. Binding studies with truncated ICAM-1 demonstrated MSH-TP15 binding to ICAM-1 domain 1-2. Importantly, MSH-TP15 and MSH-TP15 Fc-eng. both prevented myeloma cell engraftment and significantly prolonged survival of mice in an intraperitoneal xenograft model. In the subcutaneous model MSH-TP15 Fc-eng. was superior to MSH-TP15, whereas MSH-TP15 Fc k.o. was not effective in both models - reflecting the importance of Fc-dependent mechanisms of action also in vivo. The efficient recruitment of immune cells and the potent anti-tumor activity of the Fc-engineered MSH-TP15 antibody hold significant potential for myeloma immunotherapy.

A novel Fc-engineered human ICAM-1/CD54 antibody with potent anti-myeloma activity developed by cellular panning of phage display libraries.

To identify antibodies suitable for multiple myeloma (MM) immunotherapy, a cellular screening approach was developed using plasma cell lines JK-6L and INA-6 and human synthetic single-chain fragment variable (scFv) phage libraries. Isolated phage antibodies were screened for myeloma cell surface reactivity. Due to its binding characteristics, phage PIII-15 was selected to generate the scFv-Fc fusion protein TP15-Fc with an Fc domain optimized for FcγRIIIa binding. Various MM cell lines and patient-derived CD138-positive malignant plasma cells, but not granulocytes, B or T lymphocytes from healthy donors were recognized by TP15-Fc. Human intercellular adhesion molecule-1 (ICAM-1/CD54) was identified as target antigen by using transfected Chinese hamster ovary (CHO) cells. Of note, no cross-reactivity of TP15-Fc with mouse ICAM-1 transfected cells was detected. TP15-Fc was capable to induce antibody-dependent cell-mediated cytotoxicity (ADCC) against different human plasma cell lines and patients' myeloma cells with peripheral blood mononuclear cells (PBMC) and purified NK cells. Importantly, TP15-Fc showed potent in vivo efficacy and completely prevented growth of human INA-6.Tu1 plasma cells in a xenograft SCID/beige mouse model. Thus, the novel ADCC-optimized TP15-Fc exerts potent anti-myeloma activity and has promising characteristics to be further evaluated for MM immunotherapy.