Survival of myeloma cell lines in serum-free culture medium. (A) HMCLs were starved for 2 hours and cultured for 4 days without cytokine in the Syn H serum-free culture medium. The cell concentration at the start of the culture was 2 × 105 cells/mL for all HMCLs. Results are the mean luminescent signals of a luciferase assay in 3 independent experiments 2 hours and 4 days after culture start. The mean value is significantly different from that obtained at 2 hours using a Student t test for pairs (*P ≤ .05). (B) CD45 protein expression was determined by flow cytometry using murine anti-CD45RO, anti-CD45RA, and anti-CD45RB mAbs in the 3 autonomously surviving HMCLs and 5 nonautonomously surviving ones. The fluorescence intensity was set up to get a mean fluorescence intensity between 3 and 5 with isotype-matched control antibodies. Results are the percentage of positive cells and in parentheses, the mean fluorescence intensity of positive cells. These data are from 1 experiment representative of 3. (C) XG-5, XG-7, and XG-20 HMCLs were starved for 2 hours and cultured for 4 days without inhibitor (control) or with the anti–IL-6 mAb (10 μg/mL) or the IGF-1R inhibitor (1 μM) or the pan-ErbB kinase inhibitor (1 μM) or the anti-HGF mAb (25 μg/mL) or BCMA-Fc (10 μg/mL) in the Syn H culture medium. The cell concentration at the start of the culture was 105 cells/mL. Results are the mean percentages (± SD) of the luminescent signal of each group compared with that of the control group in 3 independent experiments. The mean value was significantly different from that obtained with the control group using a Student t test for pairs (*P ≤ .05).
