New way of obtaining embryonic stem cells that avoids contamination by other types of cells

Jun 20 2005

Scientists in the USA have discovered a new way of obtaining embryonic stem cells that avoids contamination by other types of cells and reduces the numbers of embryos needed to create embryonic stem cell lines.

Dr Takumi Takeuchi told the 21st annual conference of the European Society of Human Reproduction and Embryology today (Monday 20 June) that if he and his colleagues could replicate the research, which had been carried out in mice, in humans, it would make it easier to collect embryonic stem cells (ESCs) and could make it possible to establish ESC banks. This would enable researchers to have easy access to ESCs to develop better treatments for patients suffering from a range of diseases, as well as for research on fertility.

Until now, embryonic stem cells have been collected from embryos that have developed to the blastocyst stage. In humans this occurs at about day five of development. Before the ESHRE conference began, lead author, Dr Ameeta Bahia, a senior andrologist who works with Professor Gianpiero Palermo at the Center for Reproductive Medicine and Infertility, Weill Medical College of Cornell University, New York, explained: "Blastocysts are composed of two components: an external one, defined as the trophoblast of about 55 cells that will form the placenta, and a polar mass of about 20 cells, defined as the inner cell mass (ICM) that will generate the embryo and from which we obtain the stem cells. In order to obtain ESCs from the blastocyst, we first have to isolate the ICM from the trophoblast. However, this often results in contamination of ESC cultures by trophoblastic or endodermal cells. Moreover, barely 50% of human fertilised eggs reach the blastocyst stage after being cultured in the laboratory. Therefore, the possibility of harvesting ESCs at an earlier stage of embryo development is enticing."

Dr Bahia took 46 individual cells (blastomeres) from six two-day mouse embryos, which were composed of eight cells. The blastomeres were cultured in the laboratory, and 43 of them started to divide and grow. After about two days, 22 of them started to form ICM-like structures. From these, Dr Bahia managed to establish one ESC line. From a control group of 51 blastocysts, she obtained nine ESC lines.

Dr Takeuchi, also from the Center for Reproductive Medicine and Infertility, told the conference: "This showed that it was possible to isolate and culture blastomeres that were capable of developing into any type of cell, including stem cells, from early stage embryos. The efficiency was comparable to the yield from intact blastocysts. Although the percentage is similar between the two groups, the eight-cell approach wasted only five embryos, while 42 blastocysts (or embryos), made up of about 75 cells each, were lost in the other group. Therefore, if we could replicate the technique in humans it would reduce the wastage of precious material.

"We plan to reproduce this experiment with human embryos. The procedures could be performed on single blastomeres, extracted from embryos during preimplantation genetic diagnosis (PGD) and which are destined to be transferred into women patients as part of assisted reproduction.

"Although this research is still at an early stage, it represents a great opportunity to isolate ESCs from poor quality embryos at an early stage of development, thereby reducing embryo wastage, and it also introduces the possibility of ESC banking."

In mice almost all the fertilised eggs (zygotes) divide and about 90% of these reach the blastocyst stage. In humans, on the other hand, 70-80% of the zygotes divide until day three (eight-cell stage) and only about 50% reach the blastocyst stage. Dr Bahia said: "This raises the possibility that it may be easier to culture human blastomeres, isolated from an early stage embryo, instead of waiting for the blastocyst to develop."

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