Stromal cell effects on clonal growth of tumors.

Clonal growth of tumor cell lines originating from a variety of solid tumors was studied. The seeding efficiency of these tumors in methylcellulose medium was in the range of 0.036 to 0.177. Stromal cell lines from mouse bone marrow as well as primary stromal cells from human bone marrow stimulated the growth of HCT and oat human carcinoma cells 32-fold and 25-fold, respectively. In contrast, these stromal cells inhibited the in vitro cloning of human and mouse sarcoma cell lines. Both activities of the stromal cells diffused through agar layers and operated across species barriers. Despite the diffusable nature of the factors involved, no biologic activity was observed in concentrated conditioned media prepared in the presence or absence of serum. Human foreskin fibroblasts tested under identical conditions, could neither stimulate nor inhibit the clonal growth of tumors. This preferential growth of tumor cells in the presence of tissue specific stroma may be used as an in vitro model for the study of the role of stromal cells in tumor cell spread.