Cumulative effect of E:T ratio (tumor burden), sBCMA levels, and TCE dose intensity on anti-BCMA TCE efficacy. (A-C) The TCE cytotoxicity assay dose-response curve. OPM2 or OPM2_BCMA^high target cell viability 48 hours after coculture with healthy donor PBMCs at the indicated E:T ratios with elranatmab (A-B) or talquetamab (C). PBMCs and TCE were mixed with sBCMA before adding the target MM cells. Raw values for the triplicate experiments of cell viability measurement and calculated P values are indicated in supplemental Tables 5-7. (D) Scatter plot representing levels of sBCMA measured from the culture media of OPM2 or OPM2_BCMA^high cells after 48 and 96 hours. At time 0, the cells were seeded at 1 × 10⁵ cells per mL with or without GSI at a dose of 200 nM. The supernatant was collected at the respective time points and the sBCMA levels analyzed by enzyme-linked immunosorbent assay. Raw values for the triplicate experiments and the calculated P values are indicated in supplemental Table 8. (E) Flow histogram representing surface BCMA levels on OPM2 or OPM2_BCMA^high cells treated with GSI at 200 nM at time 0. (F) Dot plot representing the ratio of sBCMA (ng/mL) to membrane BCMA (mBCMA) MFI levels at 48- and 96-hour time point. (G) Illustration of the experimental protocol. Target MM cells were resuspended in fresh media at 1 × 10⁵ cells per mL with or without GSI at time 0 and cultured alone for 48 hours to allow the accumulation of sBCMA in the media. At 48-hour mark, PBMCs and TCE were spiked into the wells and cocultured for an additional 48 hours, after which target cell viability was assessed by flow cytometry. Figure created with BioRender.com. (H) The TCE cytotoxicity assay with or without GSI. The target cell viability was assessed by flow cytometry. Raw values for the triplicate experiments of cell viability measurement and the calculated P values are indicated in supplemental Table 9. ∗∗∗P ≤ .001; ∗∗∗∗P ≤ .0001.