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Cell Density-dependent Growth in Agar of Bone Marrow Cells from Tumor-bearing BALB/c Mice in the Absence of a Colony-stimulating Factor¹

Radiobiological Institute TNO, Lange Kleiweg 151, Rijswijk (Z.H.), The Netherlands

Bone marrow cells from BALB/c mice with myeloid leukemia, lymphosarcoma, erythroblastosis, or mammary tumor produce small clusters in semisolid agar cultures in the absence of specific colony-stimulating factor. This spontaneous growth is observed only when high cell numbers (5 x 10⁵ cells/ml) are plated. The phenomenon was encountered only when mice had an elevated number of mature or immature granulocytes in the peripheral blood. Removal of the adherent cells from the bone marrow did not abolish spontaneous growth, indicating that this colony-stimulating factor independency is not due to a high number of colony-stimulating cells in the bone marrow of cancerous mice. Feeder layers of bone marrow cells from the diseased animals had no higher colony-stimulating activity than did normal bone marrow cells. This excluded the possibility that the spontaneous growth was due to a high endogenous stimulating activity of the bone marrow from tumor-bearing mice.

¹ This investigation was supported by the Netherlands Organization for Fundamental Medical Research.

Received 7/ 1/74. Accepted 10/ 2/74.