The analysis of malignancy by cell fusion. I. Hybrids between tumour cells and L cell derivatives.

A wide range of different kinds of malignant cell were fused with certain derivatives of the L cell line and the ability of the resulting hybrid cells to grow progressively in vivo was examined. In all cases the highly malignant character of the tumour cells was suppressed by fusion with the L cell derivatives, whether or not these had metabolic defects that facilitated selection of the hybrid cells. So long as the hybrid cells retained the complete chromosome complements of the two parent cells, their ability to grow progressively in vivo was very limited, for tumours composed of such unreduced hybrids were not found. However, when they lost certain specific, but as yet unidentified, chromosomes, the hybrid cells regained the ability to grow progressively in vivo and gave rise to a tumour. These findings thus indicated that the L cell derivatives contributed something to the hybrid that suppressed the malignancy of the tumour cell, and that this contribution was lost when certain specific chromosomes were eliminated.