FUT4 and teratocarcinoma: At the same time, I had extended our studies of the teratocarcinoma cell lines by single cell cloning of one line, 2102Ep, and found that these clones all formed pure ECs in xenografts in nude mice.[35] Further, I discovered that if they were maintained at high cell density, the cells retained a morphology typical of EC cells, namely tightly packed with high nuclear to cytoplasmic ratios, and also expressed SSEA3, but not SSEA1.