This means that embryo stem cells are by far the most valuable in terms of providing information about how cell specialization occurs, and are, perhaps, the only ones with potential for developing cell-replacement therapies. If eventually there turn out to be pragmatic reasons for using foetal or adult stem cells rather than embryonic cells in cell therapies and other developments, it will be studies on embryonic stem cells that provide the crucial information. Research on stem cells from human embryos does not mean that embryos are produced for the purposes of research. The sort of stem cells used by researchers are those that exist in a hollow ball of cells called a blastocyst that forms around 5-6 days after fertilisation. These are produced solely for reproductive purposes, but inevitably more are produced than are used in the treatment.
Blastocysts can develop further only if implanted in a woman's uterus.
With informed consent from the couple, blastocysts that are no longer needed for implantation and which otherwise would be destroyed, can be a source of stem cells. These procedures are tightly regulated under the Human Fertilisation and Embryo Authority, a statutory body. Research on stem cells from human embryos may be a transitional step in the development of other stem cell technologies. Use of embryonic stem cells in research does not mean that there will be an on-going requirement for more and more embryos as a source of cells. Cultured embryonic stem cells could also be used to provide some tissues for therapies that are currently derived from aborted foetuses.