Introduction: Despite novel agents in multiple myeloma (MM) a substantial number of patients is still in need of better disease control. Monoclonal antibodies provide therapeutic options in other tumor entities but in MM no antibody has been approved yet. Two antibodies currently evaluated namely Daratumumab (CD38) and Elotuzumab (CD319), are ahead and achieved phase 3 clinical trials, but other antigens on myeloma cells could also be promising targets. Here, a cell-based phage display screening strategy is presented that identified a novel intercellular adhesion molecule-1 (ICAM-1)/CD54 antibody suitable for myeloma immunotherapy.
Methods: Synthetic human single-chain fragment variable (scFv) phage display libraries were pre-absorbed with granulocytes and T lymphocytes of healthy individuals and subsequently panned with plasma cell lines INA-6 and JK-6L. Phage binding characteristics were evaluated by cellular ELISA and flow cytometry. The coding sequence of the leading candidate MSH-TP15 was used to generate scFv-Fc fusion proteins and fully human IgG1 antibodies with wild type or modified Fc domains for functional in vitro and in vivo testing.
Results: Panning of human phage display libraries with a newly established subtractive cellular screening approach resulted in phages with preferential binding to MM cells. Based on its reactivity with MM cell lines and patient-derived CD138+ malignant plasma cells from bone marrow, pleural effusion and peripheral blood, the leading candidate MSH-TP15 was selected. Notably, MSH-TP15 showed no or only marginal binding to B and T lymphocytes, NK cells, monocytes and granulocytes of healthy individuals and MM patients. Recent studies identified ICAM-1/CD54 as the antigen recognized by MSH-TP15. The antibody alone was not capable to significantly inhibit growth of plasma cell lines in vitro, however induced antibody-dependent cell-mediated cytotoxicity (ADCC), an important killing mechanism of many therapeutic antibodies. An Fc-engineered antibody variant of MSH-TP15 triggered dose-dependent ADCC against INA-6, L363, RPMI-8226, U266 and MM1.S plasma cell lines and freshly isolated tumor cells using blood mononuclear cells and NK cells of healthy donors as effector cells. In contrast, complement-dependent cytotoxicity was not induced. Importantly, in vivo studies revealed that MSH-TP15 completely prevented tumor engraftment in the INA-6 myeloma xenograft model.
Conclusions: The cell-based screening of phage display libraries led to the identification of a novel ICAM-1/CD54 antibody that is effective in antibody-mediated cellular cytotoxicity of MM cells in vitro and completely prevented myeloma tumor engraftment in vivo. The relevant mechanisms of action of MSH-TP15 will be defined with different antibody variants and in vivo models to further evaluate its potential for an antibody-based treatment approach of MM.
No relevant conflicts of interest to declare.
Asterisk with author names denotes non-ASH members.