Suppression of tumor cell growth in vitro by a bone marrow factor

A supernatant factor derived from monodispersed bone marrow cells was tested for its ability to inhibit the growth of tumor cell lines and freshly dispersed hemopoietic cells in vitro. The supernatant fluid from bone marrow cells was capable of inhibiting the mitogenic response of rat thymocytes to concanavalin A. It also was capable of inhibiting growth of HeLa cells, Sarcoma 180, EL-4, and BALB/c K3T3 tumor cell lines as measured by thymidine incorporation. The factor did not inhibit the growth of normal thymus cells, marrow cells, or WI-38-SV40, and F-46 tumor cell lines. From data derived from 51Cr release assays, the factor appears to be selectively cytoreductive. Bone marrow supernatant factor is stable to heat (100 degrees for 10 min) and trypsin digestion, but is sensitive to carboxypeptidase B digestion. Molecular weight estimation by gel filtration chromatography on a Sephadex G-75 column indicates its apparent molecular weight to be less than 12,000. Bone marrow supernatant factor appears to function across species and strain barriers.