Early disappearance of murine plasmocytoma stem cells in long-term bone marrow culture.

Long-term bone marrow culture (LTBMC) was evaluated as a purging procedure in the murine plasmocytoma MOPC-315s system. MOPC-315s cells injected in Balb-c mice rapidly proliferate both in marrow and spleen, where macroscopic tumor colonies develop. A linear relationship between the number of injected cells and spleen colonies was observed, consistent with the presence of 1 clonogenic myeloma stem cell out of 1800 cells. In vitro, MOPC-315s cells are easily identifiable as rosette-forming cells (RFC+) with trinitrophenil acid (TNP) coated sheep red blood cells. When bone marrow (BM) cells containing 20-40% RFC+ were seeded in LTBMC, RFC+ rapidly decreased and were no longer detectable by day 14 of culture. Clonal Ig gene rearrangement was evident at time 0, but it was no more detectable later on. In addition, cells taken at days 14 and 21 of culture were no more tumorigenic when injected in vivo. The results suggest the efficacy of the LTBMC for the in vitro elimination of myeloma cells, including the neoplastic stem cells.