FUT4 and teratocarcinoma: From my previous work, I had some experience relevant to their interests as they had recently described a monoclonal antibody that recognized a mouse preimplantation stage‐specific antigen (SSEA1), also expressed on the immunizing F9 EC cells.[5] Moreover, with the developing use of mouse teratocarcinomas as models for early mouse embryos, as described by Papaioannou in this issue,[6] Barbara and Davor had been exploring the possibility of using cell lines from human germ cell tumors, which include teratocarcinomas, as tools for studying human embryogenesis.