Short-term tissue culture of two nonsecretory human myelomas. A morphological and functional study.

Bone marrow cells from two patients without detectable monoclonal immunoglobulin (Ig) in serum and urine but with the clinical picture of plasma cell myeloma were cultivated in vitro. Immunofluorescence studies of cultured living and fixed bone marrow cells showed no signs of Ig production in one of the cases, whereas in the other case cytoplasmic kappa chains were detected, which, however, were not expressed at the surface of living cells. Cells from the later patient were also subjected to kinetic, ultrastructural, and functional studies in vitro. The fraction of myeloma cells incorporating tritiated thymidine in vitro decreased gradually during prolonged culture, indicating a continuous cell death. The morphological characterization revealed many similarities between this nonsecretory myeloma and classical myeloma, although the frequency of cells with cisternae of endoplasmic reticulum distended by a granular material was unusually high, as was the frequency of "flaming" myeloma cells. "Flaming" cells were not labeled by tritiated thymidine, suggesting that they are nonproliferative end cells. Studies of the Ig synthesis by gel diffusion analyses of supernatant and cell lysates from [14C]leucine-labeled cultures agreed with the immunofluorescence studies that the myeloma cells were nonsecretory.