Written by: Renee Hein

Editors: Liz Tidwell, Ryan Schildcrout, Maddie Barron

Human embryonic stem cells (ESCs) have made quite the name for themselves throughout  history, and they continue to be a buzz-worthy topic in modern society. On the one hand, ESCs serve as valuable tools for scientists studying unique aspects of human development, such as how cells create a functioning organ and why disruptions in this process can cause disease or defects. On the other hand, there are ethical concerns surrounding the use of ESCs in research, which largely center on destroying what some consider to be a potential human life. To form an opinion on the matter, however, it’s first important to understand the facts about where ESCs come from.

What is the difference between an embryo and ESCs?

A few days after an egg is fertilized, a cluster of cells, called the inner cell mass, forms within the embryo. These are the ESCs, which later in development give rise to each part of the body. Embryonic stem cells are not embryos, but they come from embryos. This distinction is critical because it determines what has the ability to make a new life and what doesn’t. To form a new human body, ESCs need the support from the trophoblast (Figure 1). The trophoblast encloses the ESCs and eventually becomes a large part of the placenta, which is responsible for providing oxygen and nutrients to a developing baby.

Figure 1: Illustration by Zoe Yeoh

Ultimately, ESCs make our bodies and the trophoblast makes the placenta, which allows our bodies to form. Together, these two form an embryo. This means that, by themselves, ESCs are insufficient to produce a human life.

Where do human embryonic stem cells used in research come from?

In the United States, ESCs used in government-funded research originate from embryos created for family building purposes. These embryos are produced by in vitro fertilization (IVF), which is the process of inseminating an egg outside of a living organism and implanting the resulting embryo(s) into the uterus of a living organism for further growth.

Individuals may choose to use IVF for family building for a host of reasons and frequently do so in response to infertility challenges. During the IVF process, a surplus of embryos are made. One reason for the extra embryos is to increase the chance that at least one embryo will be viable for implantation in the uterus. A second reason is that if individuals decide they would like to conceive another child down the road, the embryos can be frozen in their current state and used later. Lastly, people with a high likelihood of conceiving a child with a harmful or potentially life-threatening genetic mutation can screen embryos for those that lack the disease-causing mutation.

Embryos are stored at incredibly cold temperatures through a process called cryopreservation and are still viable for IVF after multiple years. When individuals complete the IVF process, many of their unused embryos are stored this way. Frequently, even if individuals choose to use some of their frozen embryos for family building, there are additional embryos left after the IVF process.

One option is to donate the embryos to other couples who want to conceive. Alternatively, these embryos can be donated to harvest ESCs for research, only if the individuals who sought IVF give informed consent and the embryos are de-identified. If the embryos are not donated for adoption or for ESC harvest for research, they will be discarded.

In summary, embryos used to harvest ESCs in the United States are used only under the following circumstances:

  1. The embryo was originally created for family building
  2. The embryo is not suitable for implantation or is in excess
  3. Would be discarded if not donated to scientific purposes
  4. Were given consent by the donors

Is embryonic stem cell research ethical?

Are embryos, which have the potential to form human life, destroyed during the process of harvesting ESCs? Yes.

Can a human life be built from ESCs without support from the rest of the embryo? No.

Would the embryos that are destroyed to harvest ESCs ever be used to build a human life? No.

Given these facts about what ESCs are and how they travel from embryo to research lab, the resistance to ESC use in research may not be justified. Embryos donated for research are given a purpose in advancing our understanding about human development and disease when they would otherwise be discarded.

What do you think?

For additional reading, check out these resources:

  1. Saving and using IVF embryos
  2. Opinion on the death of an embryo
  3. More ethical considerations for embryonic stem cell harvest
  4. ISSCR guidelines for stem cell research
  5. Legal issues in embryo cryopreservation

Renee Hein is a Cell and Developmental Biology Ph.D. candidate in the Spence lab. Her research aims to better understand how stem cells form functional tissues during human development and regeneration. Renee has had a long-standing interest in science education and communication. For a break from all things science-related, she enjoys cooking, rock climbing, and spending time in the wilderness.

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