Does the bone marrow stroma protect myeloma cell lines against rATG-induced apoptosis?
The bone marrow microenvironment may protect myeloma cells from proapoptotic signals, either via secreted factors such as interleukin-6 (IL-6), or by direct cell contact.27 Thus, we next tested whether the presence of bone marrow stroma provided any protection against rATG-induced apoptosis. First, myeloma cell lines were incubated with 250 µg/mL rATG in the presence or absence of varying concentrations of IL-6 (Figure 2B). No difference in the efficacy of rATG-induced apoptosis was observed. Next, myeloma cell lines were cultured in transwell plates so that they were exposed to stromal-cell-secreted factors (SS), or in direct contact with primary bone marrow stromal cultures (SC; Figure 2B). We found several patterns of stromal-cell effect on apoptosis. NCI-H929 cells had reduced apoptosis in rATG when cultured in contact (SC) with stroma, but this effect was lost when cultured in transwell plates. In contrast, MC-CAR and U266 cells had modest reductions in apoptotic sensitivity with
