In vitro growth pattern of myeloma cells in liquid suspension or semi-solid culture containing interleukin-6

We examined in vitro growth pattern of myeloma cells from 21 patients with multiple myeloma either in liquid suspension or methylcellulose semi-solid culture, both in the presence of interleukin-6 (IL-6). The survival or growth of myeloma cells in liquid culture was classified into four categories. Type 1: myeloma cells survived for only 2-3 weeks in eight patients; Type 2: survival for 1-2 months in seven patients; Type 3: survival for more than 3 months without an obvious increase in cell number in three patients; and Type 4: continuous proliferation (cell line) in three patients. As the clinical stage advanced, the survival of myeloma cells became longer. All three myeloma cell lines were obtained from patients in an advanced clinical stage. Human plasma added to the liquid culture induced the survival or growth of myeloma cells better than fetal calf serum in any survival or growth type. Myeloma colonies or clusters were generated in seven of 21 patients, though myeloma colony formation was restricted to Type 4 patients. IL-6 neither prolonged the survival of myeloma cells nor promoted their growth in vitro except for Type 4 cells. Moreover, IL-6 did not increase the success rate of generating myeloma colonies in vitro. However, IL-6 did elevate the number of myeloma clusters in Types 1, 2 and 3 patients examined. These results suggest that IL-6 has a minor proliferative effect on myeloma cells in semi-solid culture but not in liquid suspension culture except for cells from patients with aggressive myeloma.