Somatic human cell hybrids produced by fusion of HeLa cells and diploid fibroblasts were analysed in a study designed to test the coordinate expression of transformation markers and tumorigenicity. The great majority of these hybrids displayed a finite lifespan in culture, but some of them inherited from the HeLa parent the capability to grow as permanent cell lines. Hybrids from both groups all had a plasminogen activator activity 20 to 100-fold higher and a cloning efficiency in semisolid medium 2 to 10-fold lower than the HeLa parent. Cell surface fibronectin was expressed at variable levels, albeit in a disorganized form. No correlation between the level of plasminogen activator or fibronectin content and cloning efficiency in agar was observed. Two hybrid lines, assayed for tumorigenicity in nude mice, did not produce tumors, even at inocula 20-fold greater than those at which the HeLa cells formed tumors.
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