Sensitivity of myeloma cell lines to HB-EGF. XG-1 and XG-6 cells were IL-6 starved for 3 hours and cultured in RPMI 1640 culture medium and 5% FCS with either 5 pg/mL IL-6, or 5 pg/mL IL-6 and 1 μg/mL HB-EGF, or 500 pg/mL IL-6, or 500 pg/mL IL-6 and 1 μg/mL HB-EGF (with or without 10 μg/mL B-E8 anti–IL-6 MoAb). Cells were cultured for 6 days and were pulsed for 12 hours with tritiated thymidine at the end of the culture. Data are means ± SDs of the tritiated thymidine incorporation determined on sixplicate culture wells and are those from one experiment representative of 4.