Who discovered stem cells is a question worthy of exploration. While Robert Hooke first discovered the concept of cells themselves, the discovery of stem cells is usually credited to Drs. James Till & Ernset McCulloch.
For several hundred years, researchers have known that the human body is comprised of trillions of tiny structures. Known as cells, these structures can only be seen at a microscopic level. These cells come in hundreds of variations – 200, to be exact – and serve multitudinous functions within the human body.
These functions include pumping blood, digesting food, and ridding our bodies of toxins and waste products, among others.
In this article:
- Cells and Stem Cells
- A Brief History of Cell Study
- Further Development of Cell Research
- The History of Stem Cell Research
- Stem Cell Research Today
- Who Discovered Stem Cells Exactly?
- Learning to Isolate Stem Cells
- When Were Stem Cells Discovered?
- What Types of Stem Cells Exist?
- History of Treating Diseases with Stem Cells
- Cloning as Part of Stem Cell History
Who Discovered Stem Cells?
Answering the question of who discovered stem cells requires a review of the past several hundred years. Let’s dive right in.
The question of discovery becomes more difficult to answer when you divide it into two queries: who discovered cells and who discovered stem cells? Both questions factor into the history of stem cell research, which will comprise the bulk of this article. In discussing this topic, it is also necessary to consider when stem cells were discovered, what that meant for medicine at the time, and what it means today.
Whether you simply wish to learn more about the fascinating field of regenerative medicine and how it got its start, or if you’re interested on a personal level because of an illness or injury, this subject is a critical one. Perhaps it’s the most critical in the medical field, today.
A Brief History of Cell Study
Cell research first arose in the mid-17th century. That was when medical science developed a wealth of new tools with which to study cells. However, it did not really take off until the 19th century. Soon enough, medical science came to rely heavily on cell research to help it counteract and cure diseases, heal injuries, and understand the body in ever-greater depth.
The microscope is fundamental to the study of stem cells. It was invented by either Hans Lippershey or Hans and Zacharias Janssen. The former filed the patent, but if history is any indicator, that means very little in that heady heyday of scientific invention. In any case, someone invented the compound microscope. It uses successive lenses to magnify the specimen so that the human eye can perceive structures of diminutive size.
Robert Hooke gets credit for “discovering” the cell as the building block of the human body. In 1665 (other sources say 1655), he used a microscope to examine cork. He found that it was made up of tiny structures that reminded him of “cellula,” the rooms in which monks live in monasteries. Thus, the name cell arose and remains to this day. These cells were dead, but in 1674, Anton van Leeuwenhoek viewed living algae cells under a microscope.
The human understanding of cells quickly grew. Science now knows that the smallest component of life that can exist is a cell. It contains organelles, analogous to organs in the body, which perform specialized functions. Nevertheless, any of these organelles on their own cannot survive and, therefore, are not technically forms of life.
Further Development of Cell Research
Scientists soon learned that cells are highly differentiated and can only perform specific functions. For instance, muscle cells are made to lengthen and contract. It helps people perform the motions we take for granted: sitting, standing, running, writing, and so forth. On the other hand, blood cells float freely through veins. Neurons perform the extra-specialized task of carrying impulses from one place to another and therefore delivering information throughout the body.
Throughout the last several centuries, scientists have also discovered that cells:
- Give birth to other cells via division (called mitosis)
- Contain a complete set of genetic information (DNA) in the nucleus
- Die at appropriate times to reduce the chances of an old cell copying bad genetic information, which can lead to cancer and other diseases
- Cannot give rise to other types of specialized cells
Scientists also understood by the 19th century that people originally come from the merging of an egg and a sperm. This merger creates a single-celled organism that eventually becomes a person. This pointed to a quandary: How could one cell become so many different types of cells, with all their specialized functions?
The path to stem cell research had appeared, and many notable researchers soon followed it.
The History of Stem Cell Research
The term “stem cell” makes its first appearance in the scientific annals by way of Ernst Haeckel in 1868. The German biologist used the term to describe the above-mentioned phenomenon of a fertilized egg becoming a fully functioning adult organism. He also used the term – which he referred to as a Stammzelle – to refer to the ancestor cell of all living things. However, this meaning has become obsolete today.
In 1886, William Sedgwick applied the term to the growing parts of plants, which only regenerate at certain points of the organism.
Various scientists (discussed below) discovered several facts about stem cells. These details include where they’re commonly found, what uses they have, as well as which cells in the human body can generate other cells and which cannot. For obvious reasons, the first place they looked to understand stem cells was in the mammalian uterus. That’s because it’s the site where one stem cell becomes many fully differentiated cells. The study of this process helped illuminate when undifferentiated cells become differentiated and what types of stem cells exist (also discussed below).
Starting in the early 1900s, scientific research papers started turning up very specific evidence for stem cells. These papers included proof that blood cells “stemmed” from a single, undifferentiated parent cell and that tumors contain undifferentiated cells related to bone and other tissues. They also discussed the conversion of differentiated cells into undifferentiated ones.
Stem Cell Research Today
Today, stem cell research is a backbone of regenerative medicine. Stem cells have a huge array of promising possibilities. Some of which we have already realized and others we can only dream, for now.
For instance, physicians can use stem cells to replace unhealthy bone marrow and blood cells in diseases such as leukemia and Hodgkin’s lymphoma. Stem cells also show promise in rebuilding ordinarily finite resources, such as cartilage, that break down in joints. This obviates the need for invasive surgeries and foreign tissue or substances in the body.
Scientists posit a future in which stem cells can completely rebuild a severed limb, replace a damaged part of the brain, or build a heart from scratch, customized to the individual. This would not only represent a miraculous breakthrough in medicine, but it would also reduce the need to rely on donor tissue. For now, stem cell treatments still come with a raft of issues, such as graft-versus-host disease and difficulty finding a match.
Who Discovered Stem Cells, Really?
So, who discovered stem cells then?
This is a matter of some debate. That’s especially because the honor of having made arguably the most important medical discovery of the 20th century is one that many countries covet. Fact is, many scientists contributed to the modern understanding of stem cells and the rich use of the term today.
In 1905, Artur Pappenheim created an illustration of stem cells that anyone familiar with their pattern and function would recognize today. It shows the originating cell sitting in the middle, with the increasingly specialized cells fanned out around it. The illustration not only demonstrates the one master cell but the fact that it gives rise to other cells that are themselves master cells for further specialization as well.
In 1909, Russian Alexander Maximow proposed a theory that all blood cells come from a single ancestor cell, an idea we now know is true. Blood cells arise from hematopoietic stem cells, capable of making everything from red blood cells that carry oxygen to white blood cells that fight off pathogens and toxins, keeping the body free of damaging substances.
In 1936, the American Florence Sabin stated in no uncertain terms that the various types of white blood cells of rabbits all originated in a master cell. They also report that there exist stem cells in the marrow. They further stated that radiation can damage them, that damaged cells can lead to anemia, and that certain types of white blood cell look almost like lymphocytes, but not quite. This last observation indicates a less specialized nature and therefore the ability to specialize further.
In 1953, American researcher Leroy Stevens discovered that testicular tumors in mice contained a wealth of different undifferentiated cells, including those that lead to bone, hair, and more.
E. Donnall Thomas
In 1957, E. Donnall Thomas performed a successful bone marrow transplant. This won him a Nobel Prize. Bone marrow transplants become a standard procedure for both adults and children. Physicians still use them today to respond to a variety of cancers.
James Till and Ernest McCulloch
In 1963, Canadian doctors Drs. James Till and Ernest McCulloch published a paper demonstrating that master blood cells in mice differentiated into distinct lines: the erythrocytic, granulocytic, and megakaryocytic series. This proved that stem cells exist (although interestingly, the scientists never used the term, which was by then well established), and identifying how they differentiated was indeed a huge step forward.
However, given the preexisting nature of the term “stem cell” and the pioneering work conducted by Dr. Sabin, these two scientists probably can’t take full credit for the discovery. All that despite the fact that there exist many in Canada who would disagree. Whatever the case, these last two represent the last possibility for who actually “discovered” stem cells. Future discoveries would relate to what they were and how they were used, but not to their existence in general.
In 1968, American doctor Robert Good performed the first successful bone marrow transplant on a child with an immune deficiency, using donor cells from his sister. The child grew to adulthood and lived a healthy life.
Who Discovered MSCs
Mesenchymal stem cells (MSCs) are a specific type of stem cell that can differentiate into a variety of cell types, including osteoblasts, chondrocytes, myocytes, adipocytes, and other cell types.
In 1924, the Russian-born researchers Alexander Maximow used histology to identify a type of precursor cell within the mesenchyme that could differentiate into a variety of blood cell types. While the term mesenchymal stem cell (MSC) did not yet exist, this is the earliest known reference to MSCs.
The discovery of mesenchymal stem cells (MSCs) is usually credited to A.J. Friedenstein and his team, who identified them in bone marrow in 1976.
Dr. Arnold Caplan is also known as the “Father of MSCs” for his role in discovering the characteristics of mesenchymal stem cells, honing the technology to isolate them, and learning to effectively grow them in culture. Dr. Caplan now calls these cells by their acronym “MSCs”, because he believes they are pericytes that become MSCs in response to injury or inflammation.
Who Discovered iPS Cells?
Induced pluripotent stem cells (also called iPSCs or iPS cells) are differentiated cells that are reprogrammed back into an embryonic-like state. Derived from skin or blood cells, iPS cells are not controversial, because they are made from adult cells. As pluripotent stem cells, they can give rise to nearly all of the tissues that form the human body.
The discovery of iPS cells is widely credited to Dr. Shinya Yamanaka of Kyoto University.
In August 2006, Dr. Yamanaka and his team generated iPS cells from adult mouse fibroblasts for the first time. By 2007, iPS cells were concurrently generated from human cells by Dr. Yamanaka’s team, as well as by a research team at the University of Wisconsin led by James Thomson. Thomson’s team published their findings in Science in a 2007 article titled “Induced Pluripotent Stem Cell Lines Derived from Human Somatic Cells.”
In 2012, Shinya Yamanaka was awarded the Nobel Prize in Physiology or Medicine for the discovery that mature cells can be reprogrammed to become pluripotent.
Who Discovered Embryonic Stem Cells (ESCs)?
Embryonic stem cells are cells that can give rise to all of the tissues types that form the human body. These stem cells are supporting research into new drugs, being explored for disease reversal, and being utilized to create healthy new tissue to heal injuries.
Martin Evans of Cardiff University, UK, then at the University of Cambridge, was the first researcher to isolate embryonic stem cells from mice in 1981. 26 years later in 2007, he was awarded the Nobel Prize in Medicine for his ground-breaking discoveries concerning embryonic stem cells and DNA recombination.
It took until 1998 for researchers to isolate embryonic stem cells from humans. It was first achieved by Dr. James Thomson of the University of Wisconsin in Madison. Dr. John Gearhart of Johns Hopkins University in Baltimore also achieved the feat the same year.
Learning to Isolate Stem Cells
By the 1970s, scientists generally understood how stem cells worked to populate differentiated cells in the body. However, they hadn’t yet developed the technology to isolate and use them. From the 70’s through today, scientists have been developing increasingly specific technology to help them extract stem cells from mice, other animals, and then humans.
These cells showed promise for treating a huge array of immunodeficiency diseases, cancers, congenital disorders, and more.
Having closely examined the major players that helped discover stem cells, the question that naturally arises next is about when their discovery took place. Now, that is a difficult question to answer.
When Were Stem Cells Discovered?
While this is a matter of some debate, the credit for discovering stem cells usually goes to James Till and Ernest McCulloch. Of course, numerous other researchers contributed as well, including Ernst Haeckel, Artur Pappenheim
When considering the question “When were stem cells discovered?”, it’s important to understand what exactly constitutes the true discovery of stem cells. Some argue that the first scientist to identify the fertilized egg as a stem cell – Ernst Haeckel – deserves the honor, since he was the one to note, rightly, that this foundational cell eventually became all the others. However, his understanding of this phenomenon was not fully fleshed out.
If one counts the understanding that stem cells differentiate into ever more specialized cells, then the winner is Artur Pappenheim in 1905, whose prescient chart hasn’t changed much in more than a century. However, most people give final credit to the Canadian team, James Till and Ernest McCulloch, owing to their stunning achievement in actually isolating different stem cell lines.
At the end of the day, it’s probably not possible to pin down one single “discovery” of such a huge medical niche. The sum combination of knowledge needed to understand as much as we know about stem cells is huge. It’s also attributable to a number of different men and women. This will almost certainly highlight new stars in the decades and centuries to come as well.
For now, a more useful pursuit is to understand why types of stem cells exist and what they mean for the industry today and in future.
What Types of Stem Cells Exist?
No history of stem cell research is complete without an explanation of what types of stem cells exist, where they’re found, and what functions they perform in the fetus, juvenile, and adult body. As discussed, stem cells exist at different levels of specialization. Some can do anything – literally. Meanwhile, others have vast potential to develop into different tissue types, but can’t do so to a limitless extent.
Stem Cell Categories
The main categories of stem cells include:
- Multipotent Stem Cells: Alexander Maximow was correct in his theory that blood cells all come from a single source cell, the hematopoietic stem cell. This is a multipotent stem cell that can turn into any type of blood cell. Note the emphasis on blood; it cannot turn into a muscle or heart cell, for instance. Multipotent stem cells demonstrate a lot of possibilities still, however, because physicians can use them to regrow damaged areas of the body using their tissue-specific properties.
- Pluripotent Stem Cells: These are even more useful than multipotent stem cells because they can develop into any cell in the body. However, they present a historic problem with stem cells. In decades past, researchers could only find them in human embryonic tissue. Today, however, the technology exists to reverse adult stem cells and turn them into pluripotent stem cells, avoiding the moral disputes associated with embryonic stem cells. Many parents now choose to donate umbilical cord blood as well, which is a rich source of pluripotent stem cells.
- Totipotent Stem Cells: As their name suggests, these stem cells have the total ability to transform into any type of cell needed at any point of human development. The difference between these and pluripotent stem cells is the former’s ability to also create the tissue needed to form the umbilical cord and other necessary tissues in fetal development.
- Induced Pluripotent Stem Cells: Operating under the assumption that medicine requires access to pluripotent stem cells, researchers have put a great deal of effort into reversing specialized tissue cells to create the range of possibility that exists in the human fetus. As it happens, a number of different tissue types contain cells that scientists have succeeded in reversing, from teeth and fat to muscle and blood.
Stem Cell Sources
Another way to classify stem cells is their source. Mesenchymal stem cells originate in bone marrow, while adipose-derived stem cells originate in fat tissue. Scientists have found ways to use both to form a variety of other tissues other than the tissue of origin. Stem cells also live in diverse regions across the body. These include the liver and brain as well as teeth and blood vessel lining. So there exists no end of options for where to find them.
History of Treating Diseases with Stem Cells
The historic research conducted on stem cells started in a very academic environment. Later on, it progressed naturally into the treatment of disorders rooted in the blood or bone marrow. Because hematopoietic stem cells are relatively easy to obtain, and work with and don’t need any manipulation (stem cells already exist in the blood in great quantities), it was easy to use them for transfusions and transplants.
Treating other types of disease with stem cells has proven a little more intractable. Solid tumors, for instance, don’t tend to respond as well to stem cell treatment. That has not stopped researchers from trying, however, and they continue to design and execute studies intended to use stem cells in the treatment of many types of cancer. Success in this arena would prove especially valuable in the case of metastatic cancer. In this stage of the disease, cancer has progressed past a localized point of origin. Any treatment in which stem cells could seek out all affected areas and heal them would be hailed as nothing short of revolutionary in the field. However, research is still far from that point.
Treatment of Degenerative Disorders
One of the most promising new possibilities today is the treatment of degenerative disorders, such as rheumatoid arthritis or osteoarthritis. Both conditions stem from the breakdown of tissues in the body that cannot get rebuilt. The body is born with all the cartilage it will ever have. So when it breaks down in joints, that’s it. Once it’s gone, the patient experiences the extreme discomfort or pain as bones rub against one another without any lubrication or cushioning between them.
Stem cells may change that. In a treatment that is becoming increasingly common, physicians withdraw stem cells from a patient’s blood or fat. He or she then separates them out using one of a variety of techniques. In the case of blood, for instance, doctors use an apheresis machine. This apparatus separates out hematopoietic stem cells and returns the rest of the blood to the body. They then isolate those cells, grow them in a lab if necessary, add growth factors (hormones that tell the stem cells “what to do”) and inject them back into the patient. In the case of adipose-derived stem cells, this can sometimes happen in a clinic on an outpatient basis.
Once stem cells get introduced to the affected area – a knee or elbow joint, for instance – they often exert a therapeutic effect. The mechanisms on this aren’t entirely clear. Yet researchers have found that when introduced into a damaged environment, stem cells may respond by exerting cues that can impact healing. For example, current research suggests that the power of MSCs stems from their ability to regulate the immune response and influence the human body’s own regenerative machinery.
Another factor in stem cell therapy is where the cells come from. Stem cells have a rich history of medical treatments in which the donor cells come from another patient. The same is true today.
Cloning as Part of Stem Cell History
Lastly, it’s crucial to understand the importance of cloning throughout stem cell history. Cloning essentially means to create a copy of something. While it has sci-fi movie connotations of false humans mimicking other humans, the truth is far less creepy.
Cloning simply means using stem cells to create a replica, usually just of part of the body. For instance, if a patient needed a new heart, then the best choice would be another of their own heart, right? Cloning offers up that possibility. And although growing new hearts is far in the future, the technology is mostly in place to make it possible.
Cloning also offers research possibilities. Scientists can clone part of an organ or a sample piece of tissue in a lab. They then perform experiments on it to see how the human body would respond to a new medicine, procedure, or treatment. In so doing, they could obviate the need for human trials. They can then confine experimentation, wherever possible, to cells that don’t have the ability to feel or undergo emotional stress. This, too, lies in the future, but still shows great promise for advancing the possibilities of medical science.
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