Pluripotency is the ability of a single cell to become almost any cell type in the body, from a neuron to a heart muscle fiber to a liver cell. It is the defining trait of certain stem cells found in early embryos and, since 2006, of lab-made cells called induced pluripotent stem cells (iPSCs). The concept sits at the center of regenerative medicine, drug development, and some of the most ambitious efforts in biology to grow replacement tissues and even model whole embryos outside the body. Understanding what pluripotency actually means, how it works at the molecular level, and where it stands in clinical practice requires a closer look than the shorthand “stem cells can become anything” usually provides.
What Pluripotency Is and What It Is Not
In the earliest moments after fertilization, cells are totipotent: a single cell from the two-cell or four-cell stage can generate an entire organism, including the placenta and other supporting tissues. That capacity narrows quickly. By the time the embryo reaches the blastocyst stage, the inner cluster of cells (the epiblast) is pluripotent rather than totipotent. These cells can give rise to virtually every tissue in the body but can no longer form extraembryonic structures like the placenta.1Cell Press. Pluripotency Explained: From Stem Cells to Medicine That distinction matters for medicine: pluripotent cells are the starting material for therapies, but they cannot on their own build a full pregnancy.
Below pluripotency on the ladder sit multipotent cells, which can become several related cell types within one tissue family (blood stem cells, for instance, produce red cells, white cells, and platelets but not neurons). Adult tissues are stocked with these narrower stem cells. Pluripotent cells are special because they sit one rung below the top, retaining the broadest useful flexibility without the ethical and practical complications of totipotency.
Two Flavors of Pluripotency
Not all pluripotent cells behave the same way. Researchers distinguish between a “naive” state, which resembles the inner cell mass of a pre-implantation embryo, and a “primed” state, which corresponds to the slightly later post-implantation epiblast. Both states can produce all three germ layers (the developmental origins of every organ), but naive cells have a broader functional repertoire. One clear test of this difference: naive cells can integrate into a host blastocyst and contribute to a chimeric animal, while primed cells cannot.2PubMed Central. Epigenetic differences between naïve and primed pluripotent stem cells
The distinction is not just academic. When researchers culture human embryonic stem cells under standard conditions, those cells tend to settle into a primed-like state. Capturing true naive human pluripotency in a dish took years of additional work and has opened new avenues for studying the earliest decisions an embryo makes. The culture conditions, growth factors, and even the stiffness of the surface cells sit on all push them toward one state or the other.
How Cells Keep Their Options Open
A pluripotent cell contains the same DNA as a skin cell or a liver cell, so what keeps it uncommitted? The answer lies largely in how genes are packaged. In embryonic stem cells, researchers discovered an unusual pattern called “bivalent domains,” regions of DNA that carry both an activating chemical mark and a repressing chemical mark at the same time. These opposing signals keep developmental genes silent but ready to flip on at a moment’s notice.3Cell. A Bivalent Chromatin Structure Marks Key Developmental Genes in Embryonic Stem Cells Roughly three-quarters of the repressive regions in embryonic stem cells also contained the activating mark, meaning the genome is densely loaded with these poised switches. When a cell receives the right developmental signal, one mark wins out and the gene either turns on or stays off permanently, locking in a cell fate.
This poised state is maintained by a network of transcription factors, with three proteins at the hub: OCT4, SOX2, and NANOG. They activate each other and a web of downstream genes that collectively say “stay pluripotent.” Disrupt any one of them and the cell begins to differentiate. The physical environment matters too: the stiffness and geometry of the material surrounding cells can tip them toward staying flexible or committing to a lineage.4PubMed Central. Control of stem cell fate by physical interactions with the extracellular matrix Research on tunable lab-grown scaffolds has shown that substrate stiffness alone can either promote or suppress the transition from a stem-like state toward a more specialized identity.5PubMed. Mechanotransduction of human pluripotent stem cells cultivated on tunable cell-derived extracellular matrix
The Two Paths to Pluripotent Cell Lines
The first human embryonic stem cell (ESC) lines were reported in 1998, derived from donated blastocysts left over from fertility treatments. Those cell lines maintained their pluripotent character through months of culture, expressing markers characteristic of primate embryonic stem cells and retaining the ability to form tissues from all three germ layers, including gut lining, bone, muscle, and neural tissue.6PubMed. Embryonic stem cell lines derived from human blastocysts This was transformative for research but immediately raised ethical objections, because creating the lines required the destruction of human embryos.
The second path arrived in 2006, when Shinya Yamanaka’s lab showed that ordinary mouse skin cells (fibroblasts) could be reprogrammed into a pluripotent state by introducing just four transcription factors: Oct3/4, Sox2, Klf4, and c-Myc.7PubMed. Induction of pluripotent stem cells from mouse embryonic and adult fibroblast cultures by defined factors These induced pluripotent stem cells, or iPSCs, looked and behaved like embryonic stem cells, expressing the same marker genes and growing the same way.8PubMed Central. A decade of transcription factor-mediated reprogramming to pluripotency The discovery was awarded a Nobel Prize in 2012 and effectively sidestepped the embryo debate by offering a way to create patient-matched pluripotent cells from a blood draw or skin biopsy.
Early iPSC methods used retroviruses to shuttle the four factors into cells, which raised safety concerns because the viral DNA could integrate into the genome and potentially activate cancer genes. Since then, researchers have developed “footprint-free” alternatives. RNA-based reprogramming, for instance, uses synthetic messenger RNA or self-replicating RNA to deliver the same factors temporarily, producing iPSCs with no lasting genomic alterations.9PubMed Central. Generation of iPSCs by Nonintegrative RNA-Based Reprogramming Techniques: Benefits of Self-Replicating RNA versus Synthetic mRNA These safer methods have been essential for moving iPSC technology toward the clinic.
Turning Pluripotent Cells into Treatments
Making a pluripotent cell is only the first step. To be medically useful, those cells need to be coaxed into a specific type, say, dopamine-producing neurons for Parkinson’s disease or retinal pigment cells for macular degeneration. This process, called directed differentiation, typically involves exposing the cells to a carefully timed sequence of growth factors and signaling molecules that mimic what happens during normal embryonic development.10PubMed Central. Directed Differentiation of Pluripotent Stem Cells by Transcription Factors
Several clinical trials are now testing these derived cells in patients. For Parkinson’s disease, at least four first-in-human trials have launched in the United States, Europe, and Japan, all using dopamine neuron precursors grown from pluripotent stem cells and transplanted into the brain to replace the neurons that die as the disease progresses.11Stem Cells. Advancing Parkinson’s disease treatment: cell replacement therapy with neurons derived from pluripotent stem cells One such product, called STEM-PD, is a cryopreserved, off-the-shelf dopaminergic progenitor derived from human pluripotent stem cells, currently being evaluated in a phase 1/2 trial with 12-month safety data already reported.12Nature Medicine. Human embryonic stem cell-derived dopaminergic cells for Parkinson’s disease: a phase 1/2 open-label trial
In ophthalmology, the landmark came in Japan, where a patient with age-related macular degeneration received a transplant of retinal pigment epithelial cells derived from her own iPSCs, making it the first clinical use of autologous iPSC-derived tissue.13PubMed. Autologous Induced Stem-Cell-Derived Retinal Cells for Macular Degeneration Follow-up analysis of the transplanted cells confirmed they maintained appropriate molecular characteristics.14PubMed Central. Base-Resolution Methylome of Retinal Pigment Epithelial Cells Used in the First Trial of Human Induced Pluripotent Stem Cell-Based Autologous Transplantation The trial demonstrated feasibility more than cure, but it proved that the entire pipeline, from a patient’s skin cells to iPSCs to specialized retinal cells and back into the same patient, could work in practice.
Disease Modeling and Drug Screening
Not every use of pluripotent cells involves putting them into a patient. One of the fastest-growing applications is creating “disease in a dish” models. Researchers take skin or blood cells from a person with a genetic disease, reprogram them into iPSCs, and then differentiate those iPSCs into the cell type affected by the disease. The resulting cells carry the patient’s own mutations and can be studied to understand what goes wrong at the molecular level.15PubMed Central. Induced Pluripotent Stem Cells in Drug Discovery and Neurodegenerative Disease Modelling
This approach has been particularly valuable for neurological diseases, where getting living human neurons to study has historically been almost impossible. iPSC-derived neurons from patients with Alzheimer’s, Parkinson’s, or ALS give researchers a way to test potential drugs on the exact cell type that degenerates, in a genetic background that reflects real patient variation. Disease-specific iPSC models have already been used to screen multiple drug candidates, confirming the practical utility of these platforms.16Nature Reviews Molecular Cell Biology. Pluripotent stem cells in disease modelling and drug discovery
Organoids and Miniature Organs
When pluripotent stem cells are grown in three-dimensional culture rather than flat dishes, they do something remarkable: they begin to self-organize into structures that resemble miniature organs, called organoids. These tiny tissue clusters spontaneously break their initial symmetry and undergo pattern formation and shape changes that echo what happens in a developing embryo.17PubMed. Engineering Stem Cell Self-organization to Build Better Organoids
The complexity that organoids can achieve keeps growing. Researchers have generated heart organoids from human pluripotent stem cells that form two distinct chamber-like regions, with a thick muscular wall in one compartment and a layer of surface cells covering the other, mimicking early cardiac architecture.18Nature Communications. A patterned human primitive heart organoid model generated by pluripotent stem cell self-organization Others have built neuromusculoskeletal organoids containing nerve, muscle, and skeletal tissue all co-developing within a single structure, with motor neurons extending projections into the muscle regions.19Cell Stem Cell. Generation of human neuromusculoskeletal organoids These multi-tissue organoids are particularly exciting because many diseases involve interactions between cell types that simpler models miss entirely.
The Teratoma Problem
The same versatility that makes pluripotent cells medically promising also makes them dangerous. If even a small number of undifferentiated cells survive in a transplant preparation, they can form teratomas: tumors that contain a chaotic mix of tissues (teeth, hair, bone, gut lining) growing where they do not belong. Eliminating every last pluripotent cell before transplantation is therefore a critical safety requirement.
One strategy is a built-in kill switch: engineering pluripotent cells with a “suicide gene” that is active only in the undifferentiated state, so that adding a trigger drug destroys any remaining stem cells without harming the differentiated product. Research has tested an inducible version of a cell-death enzyme for this purpose. The approach worked but had limitations, including some off-target toxicity to nearby blood-forming cells.20PubMed Central. Evaluation and Control of Teratoma Risk in Hematology A potentially cleaner alternative targets survivin, a protein that pluripotent cells depend on for survival but that differentiated cells can do without. Small-molecule survivin inhibitors like quercetin and YM155 selectively killed undifferentiated stem cells while leaving dopamine neurons and smooth muscle cells unharmed, and treatment fully prevented teratoma formation in mice.21PubMed Central. Inhibition of pluripotent stem cell-derived teratoma formation by small molecules The fact that a simple compound like quercetin, found in onions and apples, can act as a selective stem-cell poison is one of those surprises the field did not see coming.
Partial Reprogramming and Aging
If the four Yamanaka factors can rewind a cell all the way back to pluripotency, what happens if you only turn them on briefly? This is the premise behind partial reprogramming: giving cells a short pulse of reprogramming activity to reverse some hallmarks of aging without erasing their identity as, say, a muscle cell or a liver cell.22PubMed Central. Partial cellular reprogramming: A deep dive into an emerging rejuvenation technology
In one striking experiment, mice with a premature-aging condition received cyclic pulses of the four reprogramming factors, two days on followed by five days off. After many cycles, the treated mice lived about a third longer than untreated controls and showed signs of cellular rejuvenation, including reduced oxidative stress in mitochondria and restored levels of a key chromatin mark associated with youth, all without obvious weight loss or other harmful side effects.23Nature Communications. The long and winding road of reprogramming-induced rejuvenation Whether those results translate to normal aging in humans remains a wide-open question, but the commercial interest is intense, with several well-funded startups pursuing the approach.
When Cancer Borrows the Pluripotency Playbook
The transcription factors that maintain pluripotency in stem cells sometimes show up in tumors. OCT4, SOX2, and NANOG, the same core trio that keeps embryonic stem cells in their undifferentiated state, are also expressed in cancer cells with stem-like properties, sometimes called cancer stem-like cells.24PubMed Central. Pluripotency transcription factors and cancer stem cells: small genes make a big difference These cells appear to drive tumor self-renewal and resistance to treatment, borrowing from the same molecular toolkit that embryos use for growth.
The overlap extends beyond individual genes. Signaling pathways, epigenetic patterns, and surface markers show up in both embryonic stem cells and cancer stem-like populations.25PubMed Central. Common stemness regulators of embryonic and cancer stem cells This shared biology has a practical upside: understanding how pluripotency is normally regulated could reveal vulnerabilities in cancers that co-opt those same pathways. It also serves as a cautionary reminder that the line between controlled stemness and uncontrolled growth is thinner than most people realize.
Synthetic Embryos and Ethical Boundaries
Perhaps the most boundary-pushing use of pluripotent cells is the creation of synthetic embryo-like structures, sometimes called embryoids, built entirely from stem cells without sperm, egg, or fertilization. In a landmark 2022 study, researchers started with mouse naive embryonic stem cells and coaxed them into forming structures that progressed through gastrulation, developed organ precursors, and built complex extraembryonic compartments resembling those of a natural mouse embryo at about eight and a half days of development.26Cell. Post-gastrulation synthetic embryos generated ex utero from mouse naive pluripotent stem cells The structures were not capable of developing into live pups, but the degree of organized self-assembly was startling.
Human versions of these models, often called blastoids when they mimic the blastocyst stage, are advancing rapidly and raising urgent ethical questions. A systematic review of the literature found 53 different terms being used across papers to describe these entities, reflecting a field that is moving faster than its vocabulary.27PubMed Central. Ethical, legal, regulatory, and policy issues concerning embryoids: a systematic review of the literature Major scientific bodies, including the International Society for Stem Cell Research, have proposed grading ethical oversight according to how “integrated” a model is: structures that mimic only one aspect of embryonic development face lower scrutiny, while models designed to recapitulate integrated whole-embryo development require stricter review.28Stem Cell Reports. Human embryo research, stem cell-derived embryo models and in vitro gametogenesis: Considerations leading to the revised ISSCR guidelines The regulatory conversation is complicated by the fact that many existing laws governing embryo research were written with fertilized eggs in mind and do not clearly apply to lab-built structures that never involved fertilization.29PubMed Central. The regulation of human blastoid research: A bioethical discussion of the limits of regulation
Scaling Up for the Clinic
A single patient therapy might require hundreds of millions or even billions of specialized cells. Growing that many cells reliably, safely, and affordably is a manufacturing challenge that does not get the same headlines as a breakthrough transplant but is equally important for turning pluripotent stem cell science into routine medicine. The field has made real progress on this front, developing chemically defined, animal-component-free culture media, clinical-grade cell banking protocols, and single-use bioreactors that comply with good manufacturing practice standards.30Process Biochemistry. Progress and challenges in large-scale expansion of human pluripotent stem cells
Two broad strategies are emerging. One is the autologous model: make iPSCs from each individual patient, differentiate them, and transplant them back. This avoids immune rejection but is slow and expensive because you are essentially creating a bespoke product for every person. The other is the allogeneic or “off-the-shelf” model: produce large banks of cells from selected donors whose immune profiles make rejection less likely, then distribute standardized products to many patients. The Parkinson’s trial using STEM-PD follows this allogeneic approach. Both models have trade-offs in cost, speed, immune compatibility, and quality control, and it remains unclear which will dominate different therapeutic areas.
Pluripotency Beyond Mammals
The molecular toolkit of pluripotency is not unique to cells sitting in a petri dish. Neural crest cells, a migratory population that arises during early vertebrate development and gives rise to an astonishing range of tissues including facial bone, peripheral nerves, and skin pigment cells, share key molecular features with pluripotent blastula stem cells. They express the same Yamanaka factors (Oct3/4, Klf4, Sox2, c-Myc) that define iPSCs, suggesting either that pluripotency is retained in the neural crest from earlier developmental stages or that it is reactivated as these cells emerge.31PubMed Central. The developmental and evolutionary origins of cellular pluripotency in the vertebrate neural crest This finding reshapes how biologists think about the evolutionary origins of stem cell flexibility. Rather than being an exclusive property of the earliest embryonic cells, elements of the pluripotency program appear to be recycled by the body in specific contexts, a strategy that evolution has apparently found useful across vertebrate lineages.