JNJ-64407564 can bind and deplete primary MM patient BM CD138⁺ cells. Frozen BM MNCs were incubated with various concentrations of JNJ-64407564 (0-532 nM) with or without exogenous healthy T cells to measure target binding and killing. Dose-dependent binding of JNJ-64407564 (black circles) and GPRC5DxNull (blue square) to target cells (top). NullxCD3 (red triangle) failed to show any binding. Dose-dependent plasma-cell depletion (middle). BM MNCs were incubated for 48 hours with exogenous healthy T cells at a 1:1 E/T ratio in the presence of JNJ-64407564 and depletion measured as remaining CD138⁺ and BCMA⁺ cells. JNJ-64407564-mediated T-cell activation was measured by flow cytometry by gating T cells using CD3 surface marker and CD25 activation marker (bottom). Percent CD25⁺ T-cell values were plotted on the y-axis. JNJ-64407564 (circles) was able to activate T cells efficiently when incubated with GPRC5D⁺ cells, but not GPRC5D⁻ cells, while control antibodies GPRC5DxNull (triangle) and NullxCD3 (square) had no effect.