Introduction#
Many people think of iPS cells or when they hear '.' In fact, there are several kinds of stem cells, and they differ in where they come from, what cells they can become, and the purposes for which they are studied and used.
The three representative types are iPS cells (induced pluripotent stem cells), ES cells (embryonic stem cells), and somatic stem cells. This article explains the characteristics and differences of each as clearly as possible.
What is a stem cell?#
Simply put, a stem cell is a cell that has both 'the ability to multiply cells of the same kind' and 'the ability to change into other types of cells.' The latter is called . Our bodies contain many kinds of cells — cells, muscle cells, blood cells, skin cells — and it helps to picture stem cells as the 'source cells' that produce them.
Not every stem cell can become any cell, though — how far it can differentiate depends on the type.
Three broad types#
Stem cells can be broadly divided into the following three types by their properties and origins.
| Type | Produced from | Differentiation range |
|---|---|---|
| ES cell | Early embryo (fertilized egg) | Very broad |
| iPS cell | Artificially reprogrammed body cells such as skin | Very broad |
| Somatic stem cell | Present in the body after birth | Mainly specific tissues and cells |
ES cells and iPS cells are both called pluripotent stem cells and can differentiate into many cell types. Somatic stem cells, on the other hand, already exist in the body and are involved in maintaining and repairing their respective tissues.
1. What are ES cells?#
ES stands for Embryonic Stem Cell. Produced from cells of an early after fertilization, ES cells are 'pluripotent' — able to differentiate into many cell types.
They can be differentiated into many kinds of cells — nerve cells, heart muscle cells, blood cells, cells, and more — so they are used not only in regenerative medicine but also in disease research and new drug development.
Advantages of ES cells
The key feature of ES cells is their high capacity to differentiate into many cell types, so they have long been studied as a 'supply source' for lost cells.
Challenges for ES cells
However, because ES cells are made from embryos, they raise ethical issues. And for actual treatment, challenges remain, such as ensuring transplanted cells differentiate accurately into the intended cells and confirming safety.
2. What are iPS cells?#
iPS stands for Induced . Unlike ES cells, iPS cells are produced by applying specific factors to mature body cells such as skin cells, resetting the cells' state ().
In simple terms: skin cell → artificial 'reset' → → differentiation into nerve, heart muscle, blood, and other cells.
Like ES cells, iPS cells are pluripotent — that is their key feature.
Advantages of iPS cells
A major feature of iPS cells is the possibility of making them from the patient's own cells. In the future, this is expected to support regenerative medicine using a patient's own cells, 'disease models' that recreate illness, and new drug research. They also avoid the ethical issues that come with using embryos, as ES cells do.
Challenges for iPS cells
iPS cells have challenges too, such as reliably differentiating them into target cells and ensuring the safety of transplanted cells. In other words, iPS cells cannot cure everything — for each disease, efficacy and safety must be confirmed in actual treatment.
3. What are somatic stem cells?#
Somatic stem cells already exist in our bodies. They are also called adult stem cells or tissue stem cells.
Unlike ES and iPS cells, somatic stem cells cannot become every cell in the body — they can basically differentiate only into a limited range of cells related to their tissue. Representative examples are hematopoietic stem cells, neural stem cells, and mesenchymal stem cells.
Hematopoietic stem cells
Found mainly in , hematopoietic stem cells produce blood cells — red blood cells, white blood cells, and platelets — and play a vital role in continually making blood.
Neural stem cells
Neural stem cells can differentiate into cells of the nervous system, such as neurons and glial cells.
Mesenchymal stem cells
Mesenchymal stem cells (MSCs) are found in marrow, fat tissue, and elsewhere. They are known to differentiate into bone, , and fat cells, and to secrete various bioactive substances — research is advancing in regenerative medicine.
Differences between iPS, ES, and somatic stem cells#
To summarize the three types simply:
ES cells — 'pluripotent stem cells made from early embryos'
iPS cells — 'pluripotent stem cells made by artificially resetting adult body cells'
Somatic stem cells — 'stem cells that already exist in the body and take part in tissue maintenance and repair'
'Pluripotency' and 'differentiation' make the differences clear#
Two words are key to understanding stem cells: 'pluripotency' and 'differentiation.'
What is pluripotency?
Pluripotency is the ability to differentiate into many kinds of cells. ES cells and iPS cells are representative pluripotent stem cells.
What is differentiation?
Differentiation is a cell changing into a cell with a specific role — for example, an iPS cell becoming a heart muscle cell. Somatic stem cells have a relatively limited differentiation range.
Comparing the three types with an image#
It may help to picture stem cells as 'students choosing a career path.'
ES and iPS cells → can choose from many paths
Somatic stem cells → the field is largely predetermined
In other words: ES and iPS cells can become a wide range of cells, while somatic stem cells become cells related to specific tissues.
Can any stem cell be used in regenerative medicine?#
This is a very important point. 'Being a stem cell' and 'having proven treatment effects' are separate issues. There are many kinds of stem cells, each with different properties.
Even for the same type of stem cell, expected effects and safety differ depending on where the cells are collected, how they are cultured, how they are administered, and which disease they treat. Rather than assuming 'stem cells can cure disease,' it is important to check how far efficacy and safety have been confirmed in and trials for that specific treatment.
In Japan, providing regenerative medicine involves procedures and reviews under laws designed to ensure safety.
Summary#
There are many kinds of stem cells; the representative ones are ES cells, iPS cells, and somatic stem cells.
ES cells → made from early embryos → pluripotent
iPS cells → made by artificially resetting body cells → pluripotent like ES cells
Somatic stem cells → already present in the body → differentiate into specific tissues and cells
Each has its own characteristics, advantages, and challenges, and research continues across fields — not only regenerative medicine but also disease research and drug development.
Rather than judging by the word 'stem cell' alone, it is important to know which type is used, how it is expected to work, and how much has actually been scientifically confirmed — that is the key to understanding regenerative medicine.
Going deeper#
Once the basics click, the next question is whether a given stem cell is already an approved treatment or still a research subject — the same word can mean very different things.
Reading the and Safety categories next, and checking unfamiliar terms in the glossary, will sharpen how you read future material.
Common questions#
Q. How established is this topic?
A. The concepts are established, but clinical application is at different stages by disease — keep concept and treatment separate.
Q. What should I read next?
A. Move on to Evidence and Safety categories to turn the basics into judgment material.