The Novel ADCC-Optimized Human CD54 (ICAM-1) Antibody MSH-TP15e Has Potent Anti-Myeloma Activity

Background: Monoclonal antibodies directed against various target antigens have proven efficacy in cancer therapy including hematological malignancies. Recently, daratumumab and elotuzumab became the first antibodies approved for the treatment of multiple myeloma (MM). Due to the substantial number of patients still in need for long-term disease control, the investigation of additional target structures and potent molecule formats for antibody-based therapy of MM remains important.

Methods: Human synthetic single-chain fragment variable (scFv) phage display libraries were subjected to a cellular screening approach. The MSH-TP15 clone was selected based on its binding to various MM cell lines and patient-derived CD138-positive malignant plasma cells. Intercellular adhesion molecule-1 (ICAM-1/CD54), known to be important for the interaction of malignant plasma cells with the bone marrow microenvironment, was identified as target antigen. Based on the scFv sequence, fully human IgG1 antibody variants with selected mutations in the Fc domain were constructed to generate wild-type, antibody-dependent cell-mediated cytotoxicity (ADCC)-optimized and Fc-knockout variants. First, these variants were analyzed for their capacity to kill MM cells in vitro. Apoptosis induction and growth inhibition were tested by flow cytometry and in MTS proliferation assays. ADCC and complement-dependent cytotoxicity were investigated in chromium-release assays using human serum, peripheral blood mononuclear cells or purified NK cells of healthy donors. In vivoefficacy of an ADCC-optimized variant was analyzed in the INA-6 myeloma xenograft model.

Results: The MSH-TP15 antibodies target an epitope on the N-terminal part of the extracellular domain of human ICAM-1/CD54. The antibody variants showed no anti-proliferative effects on patient-derived bone marrow stromal cells, nor directly induced apoptosis or inhibited proliferation of myeloma cells. While complement-dependent cytotoxic activity was generally absent, the Fc-engineered antibody variant MSH-TP15e significantly triggered ADCC against various MM cell lines and freshly isolated patient myeloma cells. The recruitment of human NK cells was crucial for the cytotoxic effects observed in vitro. Importantly, an ADCC-optimized variant completely prevented tumor engraftment in the INA-6 xenograft model.

Conclusions: The novel ADCC-optimized fully human antibody MSH-TP15e directed against ICAM-1/CD54 exerts potent anti-myeloma activity in vitro and in vivo. Therefore, it has promising characteristics and will be further evaluated for MM immunotherapy.