At present it is necessary to destroy embryos ex utero to obtain human embryonic stem (hES) cells, but a study in mice suggests that ES cells might be generated using a single-cell biopsy technique similar to that used for preimplantation genetic diagnosis (PGD). This will not interfere with the developmental potential of the embryo. Overnight growth of a single blastomere could yield cells that may be used for both genetic testing and stem cell production without altering the clinical outcome.
The investigators carried out ten experiments which, collectively, showed that hES cells can be derived from single blastomeres. Starting with unused embryos produced by in vitro fertilization, 19 ES-cell-like outgrowths and two stable hES cell lines were obtained. A majority of isolated blastomeres divided at least once, and about half formed vesicles or clumps that produced outgrowths within 2 days. The cells remained able to form derivatives of all three embryonic germ layers (primitive endoderm, mesoderm, ectoderm) in vitro and also in teratomas. Among the outcomes observed over several days were three that are typical when ES cells are derived from human embryos. Cells resembling trophectoderm dominated some cultures. Secondly, cells that initially resembled ES cells differentiated within cultures. Finally, ES-cell-like cells continued to proliferate without differentiating. Some hES cell lines proliferated without differentiating for longer than 8 months. Both karyotypes and the expression of markers of pluripotency were normal.
The ability to create new stem cell lines without destroying embryos addresses the ethical concerns shared by many interested individuals. Potentially, matched tissues can be generated for children and siblings born from transferred PGD embryos. Further studies will be needed to learn whether blastomere-derived hES cell lines resemble conventional hES cell lines in their ability to form functional differentiated cell types. The investigators recommend that, until safety issues are resolved, this procedure be used only in the context of PGD.