Effects of a γ-secretase inhibitor on BCMA surface expression and teclistamab activity. (A) H929 and MV4-11 cells were incubated with a γ-secretase and TAPI inhibitors at various concentrations for 0 to 72 hours, and BCMA surface expression was measured by using FACS. (B) MM patient BM MNCs were incubated with a γ-secretase inhibitor, and BCMA surface expression was measured. (C) Teclistamab was incubated with H929 cells in the presence of healthy T cells with or without a γ-secretase inhibitor, and cytotoxicity and T-cell activation were measured after 48 hours.