Growth in vitro of tumour cell x fibroblast hybrids in which malignancy is suppressed.

We have studied the growth in vitro of a lymphoma x fibroblast hybrid and several melanoma x fibroblast hybrids in which malignancy is suppressed. The parental cells, the hybrids, and malignant segregants derived from the hybrids were analysed for serum requirement, cloning efficiency in soft agarose, density-dependent inhibition of growth, and secretion of plasminogen-activating enzyme. One malignant segregant from the lymphoma x fibroblast cross was found by a number of criteria to have a more highly 'transformed' phenotype than the hybrid from which it was derived. However, in the case of the melanoma x fibroblast crosses, none of the parameters examined could be correlated in a direct way with malignancy.