A serum-free culture method for myeloma progenitors in vitro: proliferative and immunophenotypic characteristics

Methods for forming multiple myeloma (MM) colonies are difficult because nonproliferative, but viable, plasma cells can survive for several weeks in culture and because MM cells tend to clump readily, forming pseudo-colonies. The present study describes a method for growing pure myeloma colonies in serum-free conditions in which genuine myeloma growth is unequivocally demonstrated. Growth was observed in 17 of 32 MM bone marrow samples. After a delay of 3-5 weeks, during which most cells died, Ig light-chain-restricted colonies emerged, expanded for approximately 3 weeks, and then showed no evidence of further proliferation. Cell doubling time was 8-10 days, and a significant number of cells in all cultures expressed Ki-67, having earlier lacked this nuclear proliferation antigen. In addition, colony formation was abrogated by irradiation, and two of eight cultures were successfully replated in 0.8% methylcellulose. Phenotypic analysis revealed a mixed population of plasma cells (RFD6+) and B-lymphocytes (CD19+, CAL-LA-), and cells were consistently Epstein-Barr virus negative. Culture of myeloma bone marrow by this serum-free method will allow appraisal of the role of various recombinant growth factors.