GSI decreases shedding of BCMA from myeloma cell lines and primary samples. (A) Surface BCMA staining of MM.1R after 24-hour incubation with increasing concentrations of RO4929097. (B) Fold change in surface BCMA on myeloma cell lines after 24-hour incubation with increasing concentrations of RO4929097. (C) Concentration of sBCMA in supernatant of cell lines cultured in increasing concentrations of RO4929097 for 24 hours as measured by ELISA. (D) Fold change of surface BCMA expression on myeloma cell lines cultured in 1 μM RO4929097 at various time points (hours) and after RO4929097 was washed out and cells were cultured in media without GSI (left and right panel, respectively). (E-F) Representative staining (E) and fold increase of BCMA (F) on CD138⁺ primary myeloma cells (n = 7) after 4-hour incubation with increasing amounts of RO4929097. (G) Fold change in surface BCMA on myeloma cell lines after 24-hour incubation with increasing concentrations of LY3039478. (H-I) Representative staining (H) and fold increase of BCMA (I) on CD138⁺ primary myeloma cells (n = 7) after 4-hour incubation with increasing amounts of LY3039478. Primary cells and cell lines were cultured at 0.5 × 10⁶ cells per milliliter. Fold change in BCMA is defined as treated (MFI_BCMA)/control (MFI_BCMA) and isotype corrected for primary samples. Data in panels A through D and G are representative of 3 independent experiments. *P < .05, **P < .01, as determined by repeated measures 1-way ANOVA with the Tukey posttest.