Frequently Asked Questions

Human developmental biology is an area of research focussed on trying to better understand how our bodies are formed – from just one cell to the trillions of cells that make up a human being.

We hope to better understand how typical development happens in humans and just as importantly, understand how and why development may happen differently sometimes. By improving our knowledge, eventually, we will be able to provide new treatments and interventions for a wide range of diseases such as infertility, childhood cancers, spina bifida and heart defects. In the future, our research may also have impacts on regenerative medicine. Regenerative medicine is the ability to regenerate, fix or replace tissues that are worn out due to ageing, disease or injury.

The human body is made up of hundreds of different kinds of cells. Stem cells have the potential to produce different types of cells, with specific functions (e.g. blood, skin, brain, muscle). There are different types of stem cells, including embryonic and adult stem cells.

Embryonic stem cells usually come from a very early embryo – when it is a ball of cells called a blastocyst. These stem cells are extremely versatile and can give rise to any type of cell found in the body.

Adult stem cells can be found in many different types of tissue, including the skin, liver, bone marrow, brain and muscle. These stem cells usually lie dormant until they are needed to regenerate lost or damaged tissue. Until relatively recently, researchers thought that adult stem cells could only create similar types of cells (e.g. that skin stem cells could only produce skin cells). However, in 2006 a researcher discovered that adult stem cells can be ‘convinced’ to return to an embryonic-like state and regain their ability to create many different types of cells. You can read more about this type of stem cell, called ‘induced pluripotent stem cells’ (or iPSCs) here.

Some HDBI research involves studying specific stem cells which are present in developing human organs and how they work to build that organ. For example, HDBI researchers are trying to better understand how different lung stem cells work together to build the part of the lungs that enables us to absorb oxygen - an important aspect of breathing.

In addition to studying some types of stem cells, we are also looking at processes during the formation of our organs which may not necessarily be related to stem cells, such as how the lungs and heart form – not just by looking at specific cells, but also by looking at overall changes in size and shape.

We are primarily investigating human development by directly working with human cells, instead of researching animal development and making educated guesses about how human development may be similar or different.

HDBI researchers are also producing resources that can be used by the scientific community such as data and new techniques and tools for studying how humans develop.

We are also distinct from other projects that cover aspects of human development, such as the Wellcome-funded Human Cell Atlas, because our researchers primarily use experimental, rather than observational, methods to study human cells - we are looking not just at where different cell types are found in the human body, but also at how cells ‘know’ to organise themselves into different organs, such as the brain, lungs and heart.

An embryo is created when an egg is fertilised by a sperm. The embryo becomes a fetus about 8 weeks after conception. By then, all of the major organs and body parts have begun to form and the fetus is about 3cm long, with the head making up about half of this size.

To note: doctors, nurses and midwives usually count the weeks of pregnancy from the first day of the last menstrual period, even though conception usually happens about 2 weeks later (after an egg is released by an ovary during ovulation). Developmental biologists, by contrast, count the number of weeks of development from conception (not from the date of the last menstrual period). For example, if a person is 11 weeks pregnant according to a medical professional, the fetus would technically be only 9 weeks old.

For more information about the different types of tissues we use in HDBI research and where they come from, check out our Research Tissue & Ethics page.

From previous research, we know that humans develop differently to other animals in some important ways. (For example, mice and humans both start as fertilised eggs, but mouse pregnancies last about 20 days and end up with a mouse, whereas human pregnancies last about 40 weeks and end up with a human.) This is why we study human development by using human tissues – so we can learn more about what makes us unique from other animals. Research with human embryos and fetal tissues can also be relevant to understanding and eventually treating adult human diseases, for example, cancer.

The human embryonic and fetal tissue used in our research is voluntarily donated. It falls into three main categories:

• Eggs and sperm which are used to create embryos for research on the very earliest stages of human development

• Embryos at an early stage of development that are generated for use in fertility treatment and will not be used for family building,

• Embryonic and fetal tissues that are donated after a termination of pregnancy (abortion).

The UK has a strong legal and regulatory framework for research involving these tissues, and HDBI researchers work within and respect these regulations. For example, all of our research is ethically reviewed and the tissue donors who voluntarily donate have to go through an informed consent process.

For more information about the tissues we use and where they come from, check out our Research Tissues & Ethics page.

Feelings (good or bad) arise in the cortex (the outermost layer of the brain which is associated with higher mental functioning). This brain structure is one of the last to develop in humans.

The nerves that carry sensory information from the skin and other organs are connected to the spinal cord and brain by about 8 weeks of development. Muscles are connected to nerve cells around the same time, enabling the fetus to move, swallow and make other reflex-based movements which do not need a cortex.

In order to feel pain, at a minimum, the fetus would need sensory inputs to reach the cortex. This connection is only established much later, probably not before about 20 weeks. While the exact timing of this connection is not yet known, some research groups are trying to understand this better.

In other words, all of the embryos and almost all of the fetal tissue used in our research is collected much too early to feel any pain and cannot feel any pain at the time the research is conducted.

The fetal tissue we use in research comes from the Human Developmental Biology Resource (HDBR). They work with clinics around the UK to collect tissues from pregnancy termination (abortion) ranging from 4 to 22 weeks after fertilisation. HDBR are licensed by the Human Tissue Authority, the UK’s regulatory body for research involving human tissue.

Abortions are legal in the UK up to 24 weeks of pregnancy in most circumstances. The 24-week limit is related to the idea that after 24 weeks the fetus might in some circumstances be able to survive outside the womb (this is also known as ‘viability’). Prior to this point, the lungs, brain and other vital organs are not fully formed enough to make survival outside the womb possible. You can find more information about Britain’s abortion laws here.

Donated tissue is disposed of respectfully once the research is completed.

Very early human embryos (up to 14 days of development) are allowed to perish by means specified in each lab’s research license, such as:

- being placed in warm water

- being placed in a liquid which breaks down the outer cell membrane, preventing further development

- being placed in a liquid which preserves the embryo in its current state but stops it from ever developing further.

Later stage embryonic and fetal tissues which are obtained from pregnancy terminations are cremated or, where this is not possible, incinerated in accordance with national guidelines.

Before agreeing to donate tissue to research, donors are informed about what will happen to their tissue when the research has been completed in accordance with the requirements of the regulating authorities for this type of research in the UK: the Human Tissue Authority and the Human Fertilisation and Embryology Authority.

Scientists sometimes study animals to understand similarities and differences between human and animal development. Understanding Animal Research has more information on this type of research.

Scientists are also now able to grow very small 3-dimensional structures called ‘organoids’ in the lab using donated human stem cells. These can mimic some key features of certain organs and can be used to better understand how things work at a cellular or molecular level.

While these alternative approaches are valuable, to answer some questions such as how different cell types within an organ develop together, we still need to work directly with human embryonic and fetal tissues.

People have long been interested in what happens during pregnancy and human development. For example, ancient Egyptians mummified fetuses in some special cases and medieval Europeans regularly pictured the womb and its imagined or assumed contents in medical texts. This however was not based on scientific research, but rather religious ideas.

In 1799, a German anatomist created the first series of images which illustrated the development of human embryos. This served as a model for later biologists who hoped to create a more accurate and complete series of images illustrating early human development.

In 1914, John Hopkins University (Baltimore, USA) opened the Carnegie Department of Embryology which collected thousands of human embryos through a network of gynaecologists over several decades. In order to obtain very early embryos from the first ~2 weeks after fertilisation, in the 1930’s and 40’s, the Carnegie Department worked with researchers at Harvard Medical School to collect Fallopian tubes and uteruses from patients who were already having hysterectomies for medical reasons. They collected these samples at specific times after menstruation and intercourse which increased the chances of finding very early embryos, before they would have been detectable by a pregnancy test. This research was ethically sensitive at the time and would almost certainly not be allowed under today’s ethical standards.

The Carnegie embryologists observed and made models of the embryos they collected and created a ‘staging system’ which actually enables today’s researchers to determine the age of an embryo based on key features (e.g. development of limbs and internal organs).

Human developmental biology today must undergo rigorous ethical review, external audits and inspections by UK regulatory authorities (such as the Human Fertilisation and Embryology Authority). And unlike the past, all tissue donors today go through a strict informed consent process.

You can watch Visible Embryos: A History of Human Development, a recorded lecture from 2021 with Professor Nick Hopwood for more information.

The digital exhibition Making Embryos Visible also has more information about the history of images of human embryos.

There are two main pieces of legislation which affect HDBI research in the UK:

• The Human Tissue Act (2004) which created the Human Tissue Authority

• The Human Fertilisation and Embryology Act (1990, amended in 2008) which created the Human Fertilisation and Embryology Authority

The Human Tissue Authority (HTA) was set up in 2005 to regulate organisations that remove, store and use human tissue for research, medical treatment, medical training and other purposes. This was done in response to a series of events in the 1990s which revealed that hospital staff were sometimes removing and retaining human organs and tissues without consent.

HTA regulation also applies to tissues that come from pregnancy terminations (abortions). Because of the HTA, we have confidence that all donors have provided informed consent for us to use their tissues in our research.

The Human Fertilisation and Embryology Authority (HFEA) was set up in 1991 to regulate fertility treatment and research using human embryos and gametes (eggs and sperm). This was done in response to public concerns about the implications of assisted reproductive technology (such as in vitro fertilisation, or IVF).

HFEA regulation applies to eggs and sperm which are used to create embryos for research as well as embryos that were created for fertility treatment which won’t be used for family building.

HDBI researchers have a variety of motivations, beliefs and perspectives, and any two researchers are likely to have some views that overlap and some views that are different. Such diversity of opinion is enriching to the research environment and welcomed.

Overall, we hope that our research can help us better understand human development and one day contribute to treating and preventing diseases.

We also appreciate this is a very sensitive area and we are extremely grateful to people who donate tissue to research. We are reassured by the robust regulation and strict ethical review process in this area of research. This ensures all tissue donors have given informed consent and that for some donors, giving their tissues to research is a way to have something positive come from a possibly upsetting situation.

Our research is about better understanding very basic aspects of how humans develop – this means that we’re a long way off from our research being used to create new medical treatments or preventative measures. However, a better understanding of human development is in itself useful and valuable.

Currently, one of our main goals is to pioneer new techniques for studying how humans develop before birth and to share those techniques with other researchers. These techniques include: new ways to view what is going on at a cellular level and the ability to work with and analyse tissue samples in the lab for longer periods of time.

We also expect that clues we discover about how the human body is formed before birth can influence the healthcare of the future.

Some examples of recently published research from HDBI labs include:

Cavazza et al 2021 (Herbert lab in collaboration w/Schuh lab) – researchers investigated reasons that chromosomes may not be correctly separated during the first cell divisions in a human embryo, a process which impacts healthy development.

Rayon et al 2021 (Briscoe lab) – researchers investigated which genes are turned on or off and when in the developing spinal cord of human embryos, highlighting differences and similarities between spinal cord development of humans and mice.

Alanis-Lobato et al 2021 (Niakan lab) – researchers tested genome editing techniques in the human embryo, which could inform the clinical use of genome editing for genetic diseases in the future.

In-vitro fertilisation (IVF) - where fertilisation takes place outside of the body. This procedure is useful for many people who cannot conceive naturally for a variety of reasons. IVF has been in widespread use since the birth of the first IVF baby (Louise Brown) in 1978 in the UK. Around the world, more than 8 million babies have now been born as a result of IVF. You can read more about IVF here.

Intracytoplasmic sperm injection (ICSI) - the most common and successful treatment for male infertility, which affects about half of couples who are having problems conceiving. You can read more about ICSI here.

Mitochondrial donation - a treatment that can be used to avoid passing on severe mitochondrial diseases to children. You can read more about mitochondrial donation here.

Future treatments for Parkinson’s Disease - clinical research is currently underway to investigate the possibility of treating Parkinson’s Disease (a chronic neurodegenerative disorder) by replacing patients’ unhealthy brain cells with healthy human fetal stem cells. The results so far have been mixed, and researchers are now focused on generating brain stem cells in a dish (rather than obtaining them from a fetus). This clinical research is informed by human developmental biology research.

Our research is about better understanding very basic aspects of how humans develop – this means that we’re a long way off from our research being used to develop new medical treatments or preventative measures, although we hope what we discover can contribute to healthcare in the future.

While our research may lead to new medical treatments, it may also contribute to improving existing treatments such as in vitro fertilisation and mitochondrial donation.

Diseases that could one day be impacted by our research include spina bifida, childhood cancers, heart defects, and infertility. HDBI research may also have impacts on regenerative medicine (or the ability to regenerate, fix or replace tissues that are worn out due to aging, disease or injury).

We expect the outcomes of our research will eventually be beneficial for healthcare. What we discover about how the human body forms may one day help other researchers or doctors to treat or prevent some diseases (such as childhood cancers, infertility, spina bifida and heart defects). We hope that future treatments which might be based on our research will be widely accessible to all who need and want them. Throughout our research process, we are also engaging with members of the public and checking whether they consider these kinds of outcomes to be beneficial.

Our research builds on the work of other scientists. And similarly, we expect the outcomes of our research will be beneficial to the scientific community, who will be able to build on the tools and techniques we develop to try to answer more questions about how the human body forms and to continue furthering our understanding of this extremely complex process.

Researchers often worry about their findings being misused. However, science is inherently collaborative, and therefore sharing results and research widely and publicly is key.

While there are no international laws that force all scientists to abide by the same set of principles, the scientific community does act to dissuade what is largely considered to be unethical research and to encourage ethical research. For example, in May 2021 The International Society for Stem Cell Research released new guidelines which represented an internationally recognised group of senior scientists’ consensus about what ethical research should look like.

Additionally, reputable scientific journals will not publish research which has not been through a proper ethical review process. This prevents unethical research from being credibly or widely shared within the scientific community.

Finally, throughout the HDBI research process, we are engaging with members of the public and checking whether non-scientists consider the potential outcomes of our research to be beneficial. Wherever possible, we will look for ways to communicate this public input to other researchers working in this field.

Our work is funded by Wellcome, a biomedical research charity. They fund science to solve health challenges for everyone.

Wellcome supports our aim of contributing to a better understanding of how the human body forms so that one day better treatments can be developed for many conditions such as infertility, childhood cancers, spina bifida and heart defects.