Neoplastic embryoid bodies of embryonal carcinoma C44 as a source of blastocele-like fluid

There is a cytotoxic activity in blastocele fluid that kills embryonal carcinoma cells with trophectodermal potential but spares those with embryonic potential. This activity is present when programmed cell death occurs in the inner cell mass (ICM), and the ICM loses its trophectodermal potential. Because of the paucity of blastocele fluid, cystic embryoid bodies of embryonal carcinoma C44 were examined ultrastructurally and in tissue culture to determine if they corresponded to late blastocysts and if their fluid corresponded to blastocele fluid. No trophectoderm was demonstrated in the embryoid bodies, but embryonal carcinoma and endoderm were present, leading to the conclusion that the embryonal carcinoma corresponded to late ICM that had expressed endodermal potential. As a result the cyst fluid might have contained the toxic activity of blastocele fluid. The cyst fluid of C44 embryoid bodies did contain a soluble, low-molecular-weight, cytotoxic activity that preferentially killed embryonal carcinoma cells with trophectodermal potential while sparing those with embryonic potential. Enough of this fluid was available to determine the chemical nature of this toxic activity.