Every tissue in the human body, from the lining of your gut to the neurons in your brain, traces its origin back to stem cells.
These are the cells that build us during development, repair us after injury, and maintain the tissues we depend on throughout life. Understanding what stem cells are, how they differ from one another, and what they make possible in research is fundamental to modern biology and medicine.
This guide covers the essentials: what stem cells are, the main types, where they come from, and how they are used in research today.
What Are Stem Cells?
Stem cells are unspecialized cells with two defining abilities: self-renewal and differentiation.
Self-renewal means a stem cell can divide and produce more stem cells indefinitely. Differentiation means it can develop into specialized cell types such as muscle cells, neurons, blood cells, or liver cells, depending on the signals it receives.
No other type of cell in the body shares both of these properties. A red blood cell cannot replicate itself. A neuron cannot become a heart cell. Stem cells can do both, and that is what makes them so scientifically significant.
They are found in virtually every tissue of the body, residing in specialized microenvironments called stem cell niches. These niches regulate when stem cells divide, what they become, and how many new cells a tissue produces.
Types of Stem Cells
Stem cells are classified in two ways: by their potency, meaning how many cell types they can produce, and by their source or origin.
Classification by Potency
Potency describes how many different cell types a stem cell can generate.
Totipotent cells are the most versatile of all. A fertilized egg and the cells produced in the first few divisions are totipotent, meaning they can develop into any cell type in the body and the placental tissue that supports the embryo.
Pluripotent cells can generate any cell type in the body but cannot form placental tissue. Embryonic stem cells and induced pluripotent stem cells (iPSCs) are pluripotent. This is the potency level that draws the most attention in research and therapy.
Multipotent cells can produce several related cell types but not all. Hematopoietic stem cells in bone marrow are multipotent: they can generate all types of blood cells, including red blood cells, white blood cells, and platelets, but not neurons or heart cells.
Oligopotent cells can differentiate into a limited number of closely related types. Lymphoid and myeloid progenitor cells are examples.
Unipotent cells produce only one cell type. Muscle stem cells, for instance, generate only muscle cells. Their self-renewal ability still makes them stem cells.
Embryonic Stem Cells
Embryonic stem cells (ESCs) are derived from the inner cell mass of a blastocyst, a 3 to 5 day old embryo.
They are pluripotent, can be maintained in culture indefinitely, and have the capacity to differentiate into any somatic cell type. These properties made them the gold standard of stem cell research for decades.
The main limitation is ethical. Harvesting embryonic stem cells requires destruction of the embryo, which raises significant moral and legal concerns in many countries. Research using ESCs is tightly regulated and varies considerably between jurisdictions.
Scientifically, ESCs remain the benchmark against which other pluripotent stem cells are compared.
Adult Stem Cells
Yes, adult tissues contain stem cells, though they are more limited in their differentiation capacity than embryonic stem cells.
Adult stem cells, also called somatic or tissue stem cells, are found in small numbers in most organs and tissues. Their primary job is maintaining and repairing the tissue they reside in.
The most clinically well-established example is the hematopoietic stem cell (HSC), found in bone marrow. HSCs generate the entire blood and immune system and have been used in bone marrow transplants for decades to treat leukemia, lymphoma, and other blood disorders.
Other examples include mesenchymal stem cells, which can generate bone, cartilage, and fat tissue, and neural stem cells, which give rise to neurons and glial cells in the brain.
Adult stem cells are easier to work with ethically than ESCs, but they are harder to isolate in large numbers and more limited in what cell types they can produce.
Induced Pluripotent Stem Cells
iPSCs are adult cells that have been reprogrammed back into a pluripotent state in the laboratory.
The technique was first demonstrated by Shinya Yamanaka in 2006 using a set of four transcription factors, OCT4, SOX2, KLF4, and c-MYC, introduced into mouse fibroblasts. He received the Nobel Prize in Physiology or Medicine in 2012 for this discovery.
Because iPSCs can be generated from a patient's own cells, they avoid the immune rejection issues associated with embryonic stem cells. They also sidestep the ethical concerns of using embryos.
iPSCs are now used extensively across research, drug development, and early-stage clinical applications. For a deeper look at how they work and how they are made, see our full guide on what iPSC cells are and how they are used in research.
Mesenchymal Stem Cells
Mesenchymal stem cells (MSCs) are multipotent stromal cells originally identified in bone marrow.
They can differentiate into osteoblasts (bone cells), chondrocytes (cartilage cells), and adipocytes (fat cells), and have been isolated from a wide range of tissue sources including adipose tissue, umbilical cord, and dental pulp.
MSCs are widely used in research because of their relative ease of isolation, their immunomodulatory properties, and their potential in regenerative medicine applications.
They are also the most commonly used cell type in clinical stem cell trials globally, primarily for orthopedic and cardiovascular conditions, though results have been variable and many programs remain investigational.
Perinatal Stem Cells
Perinatal stem cells are found in amniotic fluid, placental tissue, and umbilical cord blood, and are collected at or around birth.
They occupy an intermediate position between embryonic and adult stem cells in terms of potency. Cord blood is already used clinically as a source of hematopoietic stem cells for transplant, particularly in pediatric blood disorders where a matched adult donor is not available.
Research into amniotic and placental stem cells is ongoing, with particular interest in their immunological properties and potential for treating inflammatory and degenerative conditions.
Where Do Stem Cells Come From?
The source determines the stem cell type and its research or therapeutic applications.
Bone marrow is the most established source of hematopoietic and mesenchymal stem cells and has been used in clinical transplantation for decades.
Peripheral blood can be mobilized to release hematopoietic stem cells using growth factors such as G-CSF, allowing collection by apheresis without surgical bone marrow harvest.
Adipose tissue is an abundant and accessible source of mesenchymal stem cells, now widely used in research protocols where large MSC numbers are needed.
Umbilical cord blood is collected after birth and stored in cord blood banks. It is an established source of hematopoietic stem cells used in transplantation.
Embryos from in vitro fertilization provide embryonic stem cells, but only with informed donor consent and under regulatory oversight.
Reprogrammed adult cells produce iPSCs, the most flexible and ethically uncomplicated source of pluripotent cells available today.
AstralCell's stem and progenitor cell collection includes a broad range of human stem cell types sourced from multiple tissues, with full authentication and quality documentation to support research workflows.
Research Uses of Stem Cells
Stem cells have moved from a theoretical concept to a practical tool across several areas of biomedical research. The main applications are outlined below.
Disease Modeling
Yes, stem cells are now one of the primary tools researchers use to model human disease in the laboratory.
Patient-derived iPSCs can be differentiated into the specific cell types affected by a disease, generating neurons for Parkinson's research, cardiomyocytes for cardiac disease models, or hepatocytes for liver disease studies, all carrying the patient's exact genetic background.
This produces models that reflect the biology of individual patients rather than averages, which is particularly important for studying rare genetic diseases and for developing personalized therapeutic approaches.
Drug Discovery and Toxicity Testing
Yes, stem cell-derived cells are increasingly accepted as a platform for early-stage drug testing.
iPSC-derived cardiomyocytes are now used to screen compounds for cardiac toxicity before clinical trials. This is one of the most validated applications of stem cells in pharmaceutical development, and regulatory bodies have begun accepting iPSC-based safety data in certain drug submission contexts.
Stem cell-derived hepatocytes provide human liver toxicity data that is more predictive than rodent hepatocyte models for many compound classes.
Regenerative Medicine
Stem cells are the foundation of regenerative medicine, which aims to replace or repair damaged tissues using cells rather than synthetic materials or donor organs.
The most established clinical application is hematopoietic stem cell transplantation for blood disorders and certain cancers. Bone marrow and cord blood transplants are performed routinely worldwide.
Beyond this, clinical programs are underway or in development using stem cell-derived products for Parkinson's disease, macular degeneration, type 1 diabetes, heart failure, and spinal cord injury.
Immunotherapy Research
Stem cells are increasingly central to the development of next-generation cell therapies in oncology.
iPSC-derived T cells and NK cells are being developed as off-the-shelf allogeneic alternatives to patient-derived CAR-T therapies. Because iPSCs can be expanded indefinitely before differentiation, they offer a scalable manufacturing solution that autologous approaches cannot easily match.
AstralCell's blood and immune cell collection includes primary immune cells and established lines used across immunotherapy and cell therapy research programs.
Understanding Development and Basic Biology
Stem cells provide a window into how the human body develops that no other system can replicate.
By differentiating stem cells through defined stages, researchers can observe in real time how cell fate decisions are made, how signaling pathways regulate tissue formation, and what goes wrong in developmental disorders.
Organoids, three-dimensional structures grown from stem cells that partially mimic the architecture of organs like the kidney, gut, liver, and brain, have opened entirely new possibilities for studying human biology in ways that animal models often cannot replicate.
Key Considerations When Working with Stem Cells
A few practical points apply to virtually any stem cell research workflow.
Authentication is essential, especially for iPSC lines. Confirm pluripotency marker expression (SSEA-4, TRA-1-60, OCT4, NANOG), verify a normal karyotype, and test for mycoplasma before beginning experiments.
Passage number matters. Extended culture can introduce genetic changes and alter differentiation behavior. Use authenticated low-passage stocks and monitor lines regularly.
Differentiation protocols are specific. The signals required to generate neurons differ from those needed to produce cardiomyocytes or hepatocytes. Use validated, published protocols and confirm cell identity with lineage-specific markers after differentiation.
Ethical and regulatory compliance is non-negotiable for embryonic stem cells. Know the legal framework in your country before sourcing or working with ESC lines.
Frequently Asked Questions
What are stem cells? Stem cells are unspecialized cells with the ability to self-renew and differentiate into specialized cell types throughout the body.
What are the main types of stem cells? The main types are embryonic stem cells, adult stem cells, induced pluripotent stem cells (iPSCs), mesenchymal stem cells, and perinatal stem cells from cord blood and amniotic fluid.
What is the difference between embryonic and adult stem cells? Embryonic stem cells are pluripotent and can become any cell type, while adult stem cells are more limited in potency and primarily maintain and repair the tissue in which they reside.
What are stem cells used for in research? Stem cells are used for disease modeling, drug discovery, toxicity testing, regenerative medicine, immunotherapy development, and studying human development and biology.
Can stem cells cure diseases? Yes, hematopoietic stem cell transplants already treat blood cancers and disorders, and clinical programs using stem cell-derived products are underway for Parkinson's disease, macular degeneration, and other conditions.
What is the difference between totipotent and pluripotent stem cells? Totipotent cells can form any cell type including placental tissue, while pluripotent cells can form any body cell but cannot form the placenta.
What are mesenchymal stem cells used for? MSCs are used in research on bone, cartilage, and fat tissue regeneration, and are the most commonly studied stem cell type in clinical trials for orthopedic and inflammatory conditions.
Are iPSCs the same as embryonic stem cells? No, iPSCs are reprogrammed adult cells that acquire pluripotency artificially, while embryonic stem cells are derived from embryos; they share many properties but are not identical.