Growth factors in the tumorigenicity of a brain tumor cell line.

We studied a virally induced canine gliosarcoma brain tumor cell line capable of producing brain tumors in vivo following intracerebral inoculation of the cells into the brains of adult mongrel dogs. Cloned populations from this cell line differed in their ability to produce brain tumors in vivo. In vitro transforming growth factor-beta secretion by each clone correlated with in vivo tumorigenicity. Mitogenic activity like that produced with platelet-derived growth factor was also secreted by each clone and correlated with in vivo tumorigenicity. Epidermal growth factor and transforming growth factor-alpha production was not detected in any of the clones of canine gliosarcoma cells. Although only some of the brain tumor cell clones were able to produce tumors in immunologically normal dogs, brain tumors were produced in all dogs pretreated with cyclosporin and in all "nude" mice, suggesting that tumor immunology plays an important role in this brain tumor model. In vitro cloning efficiency of each brain tumor cell clone also correlated with in vivo tumorigenicity. We postulate that transforming growth factor-beta may both stimulate brain tumor cell growth and inhibit host antitumor immune surveillance.