1 September 2006
Human embryonic stem cell lines are currently derived using a protocol that involves the destruction of human embryos. Last year saw reports of a novel methodology that allowed stem cell line derivation to occur but also preserved the embryo as a viable entity that could then be implanted and develop normally. This technique was utilised in mice, and is similar to pre-implantation diagnosis (PGD), which is used to screen human embryos for genetic diseases such as cystic fibrosis during IVF treatment. It involves the removal of a single blastomere from the eight cell stage embryo, leaving the embryo with full developmental potential if implanted. In PGD this single cell would then be analysed for genetic defects, but in the report by Chung et al. it was used to derive embryonic stem cell lines (see previous newsletter item).
A new publication by Klimanskaya et al., reports on the first derivation of human embryonic stem cell lines using this methodology. The research team from biotechnology company Advanced Cell Technology began with sixteen embryos that were produced during IVF treatment but were surplus to requirements. Of these embryos, six were of a high quality with little cytoplasmic fragmentation. Single blastomeres were separated from each embryo and cultured, with 58% dividing at least once. Of these, approximately half went on to form outgrowths within two days.
Within these outgrowths the researchers observed three distinct cell fates: i) cells that resembled trophoectoderm, ii) cells that initially resembled ES cells, but which then went on to differentiate, and iii) cells that behaved as ES cells and which continued to proliferate without differentiation. The researchers report that a total of two stable stem cell lines with normal karyotype were generated from the six high quality embryos. These cell lines were shown to readily differentiate into a variety of cell types when allowed to do so, and their pluripotency within an organism was confirmed by their ability in mice to form teratomas containing tissue from all three germ layers.
Although the blastomere-derived stem cells were observed to differentiate at the same rate and in the same manner as conventionally derived hES cell lines, the authors point out that further study is required to determine whether the new cell lines differ in their ability to form fully functional differentiated cell types.Comment: While this new technique appears to overcome one of the major ethical objections to the current method of creating hES cell lines - namely the destruction of the source embryos