Human myeloma in vitro colony growth

Human myeloma stem cells were examined by their capacity to form colonies in culture. Cells separated from bone marrow of 15 patients with multiple myeloma were cultured in semi-solid methylcellulose with conditioned medium obtained from cultured T lymphocytes stimulated by phytohemagglutinin. The number of colonies consisting of more than 20 cells was counted after 10 days of culture. The colonies formed consisted mostly of lymphoplasmacytoid or plasma cells, and the immunoglobulin in the cytoplasm of cells from colonies was identical to that found in cells used for culture. The number of colonies formed was proportional to the number of cells plated. These results suggested that the cells in the colonies were derived from the myeloma cells originally used. The proportion of myeloma stem cells in the proliferative state was examined in 12 patients by the suicide method using [3H]-TdR and the results were between 21 and 75 %, the mean value being approximately 40 %. The irradiation sensitivity of myeloma stem cells was examined by the 60Co-γ-irradiation method. The mean Do value in 7 cases was 116 rads and the mean extrapolation number was 2.0. An inverse relationship was observed between the Do value and the proportion of cells in the S phase. (author)