Enhanced tumorigenicity of cloned UV-regressor tumor lines following selected in vivo and in vitro manipulations.

Passage of cloned ultraviolet (UV) radiation-induced fibrosarcomas with regressor phenotype through 500-rad-irradiated syngeneic mice resulted in their conversion to transplantable progressor tumors. A similar conversion in tumorigenic phenotype (regressor leads to progressor) was found to be inducible in vitro by coculturing a cloned regressor tumor with normal splenocytes, but not with splenocytes from tumor-immune or UV-irradiated animals. Recloning of regressor and converted progressor tumor lines yielded regressor and progressor phenotype subclones, respectively, suggesting a degree of stability in their growth phenotype. Although all of the cloned progressor tumors tested were found to be cross-reactive with related regressor tumor lines, suggesting that related clones share a similar tumor-specific transplantation antigen, the progressor clones appeared to be less immunogenic than the regressor clones. Potential mechanisms that influence this conversion in tumorigenic phenotype are discussed.