The analysis of malignancy by cell fusion. VI. Hybrids between different tumour cells

Previous studies with a variety of transplantable mouse tumors showed that in hybrids between malignant and non malignant cells, malignancy behaved as a recessive character: the hybrid cells, so long as they retained something close to the complete parental chromosome sets, had little or no ability to grow progressively in vivo. In the experiments now described the heritable lesions determining the malignant phenotype were further explored by complementation analysis in which the various tumor cells were fused with each other. 42 clonal populations derived from 12 crosses between different kinds of tumor cells were examined. Only one cross generated hybrid cells with reduced tumorigenicity: in all other cases the hybrid cells formed were highly malignant. It thus appears that, in a wide range of different tumors, the lesions determining the malignant phenotype, although recessive, fail to complement each other.