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What are embryonic stem cells? Narrated by Dr. Janet Rossant

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Since their first discovery, embryonic stem (ES) cells have been the focus of intense research and public scrutiny. Derived from discarded 5-day old embryos (typically obtained from patients undergoing in vitro fertilization), this type of stem cell possesses the ability to create any tissue in the human body and replicate indefinitely in culture conditions.

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Explore Stem Cells Find out about stem cells and stem cell research

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Classroom activity

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Education Resources and activities for educational settings

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overview of policies in different countries

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StemGen | International Database on the Legal and Socio-Ethical Aspects on StemGen Research

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International Database on the Legal and Socio-Ethical Issues in Stem Cell Research

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Do we still need research on human embryonic stem cells

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Do we still need research on human embryonic stem cells

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By: Austin Smith and Clare Blackburn

Can induced pluripotent stem (iPS) cells replace human embryonic stem (hES) cells? One day this may be the case, but for the foreseeable future, side-by-side research on both types of stem cell is needed.

Facts at-a-glance

Pluripotent stem cells are not all the same - mouse ES cells and human ES cells are not equivalent

Mouse ES cells are more consistent, easier to grow, and easier to differentiate

Clinical grade human embryonic stem cell lines already exist

How to make a few specialised cell types from human pluripotent stem cells

iPS cells will be an important tool for drug development

Use of iPS cells in the clinic will require much more research and understanding

Human pluripotent stem cells equivalent to mouse ES cells may be isolated in the next few years

How to establish the identity and safety of human iPS cells

How to direct specialization of pluripotent stem cells into many different adult cell types

How to ensure the cells do not undergo unpredictable genetic changes when grown long-term

There are three key reasons for continuing to study human ES cells:

1. Safety and function
ES cells are essentially normal human embryo cells, whereas iPS cells are created by reprogramming adult cells using molecular engineering. These laboratory manipulations have not yet been perfected and can produce abnormal, potentially unsafe cells. iPS cells are definitely promising tools to investigate disease mechanisms and develop new drugs in the laboratory, but many more careful studies are needed to determine whether they will be safe to inject into people. New technologies are also required to produce fully functional adult cells from iPS cells. Human ES cells therefore provide an essential standard for iPS cell safety and differentiation.

2. Ready for the clinic
Cells that will be transplanted into people must be prepared in a strictly controlled environment to ensure they are not contaminated and are of high quality and purity. Several clinical grade hES cell lines have been developed and are already approved for use in clinical trials. Reaching this point on the road to the clinic is the result of years of research and development. Currently, no iPS cells are approved for clinical use because of the gene manipulation procedures required for their production. It will take time to overcome this hurdle and develop clinic-ready iPS cell lines.
3. The missing human pluripotent stem cell
Currently, different human ES and iPS cell lines show a great deal of variability and inconsistency. Mouse ES cells however can be grown under very standardised conditions, with minimum variability.

Mouse and human ES cells are not equivalent; human ES cells appear to represent cells at a more advanced stage of embryonic development, when they have already begun to specialise. Scientists think that it may be possible to isolate a new type of human pluripotent stem cell that is equivalent to mouse ES cells. These new cells - shown above as 'stage 1 pluripotent stem cells' and often referred to as 'ground state stem cells' - are predicted to have very consistent properties that will allow reliable differentiation into all types of specialised adult cell. Researchers worldwide are currently investigating how to isolate and grow these human ground state cells.

This has three important implications:

Finding out how to obtain and grow human ground state pluripotent stem cell requires experiments to modify current human ES cells, and also derivation of new human pluripotent/ES cells using alternative techniques recently developed for mouse ES cells. Only through these experiments can the best possible methods for obtaining human pluripotent stem cells be determined.

Once obtained, human ground state stem cell lines are likely to replace existing human ES cell lines in medical research and clinical applications.

Ground state human ES cells will provide an accurate reference for iPS cells which will allow them to be standardised, overcoming one of the major barriers to their use by industry and to regulatory approval for their use in clinical applications.

Further information
References
References to scientific research publications are listed in the downloadable pdf below. Journal subscriptions may be required to access the listed references.

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Do we still need research on human embryonic stem cells?

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By: Austin Smith and Clare Blackburn Can induced pluripotent stem (iPS) cells replace human embryonic stem (hES) cells? One day this may be the case, but for the foreseeable future, side-by-side research on both types of stem cell is needed. Facts at-a-glance We know:

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the sources of human embryonic stem cells

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Origins, ethics and embryos: the sources of human embryonic stem cells | Eurostemcell

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Some people oppose using human embryonic stem cells under any circumstances. However, the use of cell lines that already exist is the most widely accepted source of stem cells. This acceptance is based on the argument that what's done is done.

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Embryonic stem cell research: an ethical dilemma

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Embryonic stem cell research: an ethical dilemma

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EuroStemcell fact sheet

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The moral status of the embryo is a controversial and complex issue. The main viewpoints are outlined below.

1. The embryo has full moral status from fertilization onwards
Either the embryo is viewed as a person whilst it is still an embryo, or it is seen as a potential person. The criteria for 'personhood' are notoriously unclear; different people define what makes a person in different ways.

Arguments for this view Arguments against this view

Development from a fertilized egg into to baby is a continuous process and any attempt to pinpoint when personhood begins is arbitrary. A human embryo is a human being in the embryonic stage, just as an infant is a human being in the infant stage. Although an embryo does not currently have the characteristics of a person, it will become a person and should be given the respect and dignity of a person.

An early embryo that has not yet been implanted into the uterus does not have the psychological, emotional or physical properties that we associate with being a person. It therefore does not have any interests to be protected and we can use it for the benefit of patients (who ARE persons).

The embryo cannot develop into a child without being transferred to a woman's uterus. It needs external help to develop. Even then, the probability that embryos used for in vitro fertilization will develop into full-term successful births is low. Something that could potentially become a person should not be treated as if it actually were a person. A candidate for president is a potential president, but he or she does not have the rights of a president and should not be treated as a president.

2. There is a cut-off point at 14 days after fertilization
Some people argue that a human embryo deserves special protection from around day 14 after fertilization because:

After 14 days the embryo can no longer split to form twins. Before this point, the embryo could still be split to become two or more babies, or it might fail to develop at all.

Before day 14, the embryo has no central nervous system and therefore no senses. If we can take organs from patients who have been declared brain dead and use them for transplants, then we can also use hundred-cell embryos that have no nervous system.

Fertilization is itself a process, not a 'moment'. An embryo in the earliest stages is not clearly defined as an individual.

3. The embryo has increasing status as it develops
An embryo deserves some protection from the moment the sperm fertilizes the egg, and its moral status increases as it becomes more human-like.

Arguments for this view Arguments against this view

There are several stages of development that could be given increasing moral status:

We protect a person's life and interests not because they are valuable from the point of view of the universe, but because they are important to the person concerned. Whatever moral status the human embryo has for us, the life that it lives has a value to the embryo itself.

If we judge the moral status of the embryo from its age, then we are making arbitrary decisions about who is human. For example, even if we say formation of the nervous system marks the start of personhood, we still would not say a patient who has lost nerve cells in a stroke has become less human. (But there is a difference between losing some nerve cells and losing the complete nervous system - or never having had a nervous system).

If we are not sure whether a fertilized egg should be considered a human being, then we should not destroy it. A hunter does not shoot if he is not sure whether his target is a deer or a man.

1. Implantation of the embryo into the uterus wall around six days after fertilization.
2. Appearance of the primitive streak - the beginnings of the nervous system - at around 14 days.
3. The phase when the baby could survive if born prematurely.
4. Birth.

If a life is lost, we tend to feel differently about it depending on the stage of the lost life. A fertilized egg before implantation in the uterus could be granted a lesser degree of respect than a human fetus or a born baby.

More than half of all fertilized eggs are lost due to natural causes. If the natural process involves such loss, then using some embryos in stem cell research should not worry us either.

4. The embryo has no moral status at all
An embryo is organic material with a status no different from other body parts.

Arguments for this view Arguments against this view

Fertilized human eggs are just parts of other people's bodies until they have developed enough to survive independently. The only respect due to blastocysts is the respect that should be shown to other people's property. If we destroy a blastocyst before implantation into the uterus we do not harm it because it has no beliefs, desires, expectations, aims or purposes to be harmed.

By taking embryonic stem cells out of an early embryo, we prevent the embryo from developing in its normal way. This means it is prevented from becoming what it was programmed to become - a human being.

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Embryonic Stem Cell Research: An Ethical Dilemma

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The moral status of the embryo is a controversial and complex issue. The main viewpoints are outlined below. 1. The embryo has full moral status from fertilization onwards Either the embryo is viewed as a person whilst it is still an embryo, or it is seen as a potential person.

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article by bioethicist Kristina Hug

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Therapeutic perspectives vs moral status

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Therapeutic perspectives vs moral status

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article by bioethicist Kristina Hug