Hybrids between F9 nullipotent teratocarcinoma and thymus cells produce multidifferentiated tumors in mice

Hybrids between F9 teratocarcinoma and mouse thymus cells (FT2 hybrids) were obtained. All of the seven FT2 hybrid clones produced tumors containing varying amounts of differentiated tissues in addition to embryonal carcinoma. This is in contrast to the F9 parental cells which gave tumors formed exclusively of embryonal carcinoma cells. Two clones produced either undifferentiated tumors or tumors that had only small foci of ectoderm and/or endoderm derivatives. The five other FT2 clones differentiated into derivatives of the three primitive germ layers. Among these five clones, two produced tumors with large amounts of differentiated tissues which resembled the well-differentiated teratocarcinoma tumors produced by pluripotent embryonal carcinoma cell lines. On the whole, 71% of the observed sections of the 26 tumors that were thoroughly examined at 0.5-mm intervals showed ectoderm derivatives, 40% mesoderm derivatives, and 46% endoderm derivatives. This result shows that hybridization with thymus cells allows expression of pluripotentiality that was blocked in F9 teratocarcinoma cells.