Understanding Pluripotent Stem Cells: Biology, Potential, and Challenges

by Lorenzo Gentile

Introduction

Stem cells are a very important and interesting part of our body, they are capable of dividing and differentiating along different pathways, following the needs of the organism. In simple terms, the actions a stem cell can do are:  

• Self-renewal: it is a process where the stem cell divides in two identical cells, retaining the ability to differentiate in other type of cells. It is important to maintain a certain amount of stem cells in the organism, so that they don’t run out; 

• Differentiation: it is a process where the stem cell divides in two specialised cells (such as neurons, muscle fibres, etc…). 

The stem cells can divide symmetrically (dividing in two new stem cells or two specialised cells) or asymmetrically (producing one stem cell and one differentiated cell). However, in order to do so, they must receive a certain type of signal. The morphogens are special signaling molecules that control the differentiation of stem cells based on their concentration. The morphogens gradients result in different genes being expressed. 

There are different types of stem cells:

• Totipotent: can produce every tissue in the body, they exist only in the early stage of an embryo (they may form a complete organism);

• Pluripotent: similar to totipotent cells, but they cannot produce a whole organism;

• Multipotent: only forms a limited type of cells, they occur both in the development of an embryo and in the adult-stage of an organism (bone marrow, skin);

• Unipotent: only form one type of cell.

Each type of stem cell has a specific potential and role in development and tissue maintenance. The pluripotent cells are the one scientists are studying and researching the most for their versatility and therapeutic potential. 

Origin

Embryonic stem cells (ESCs) are derived from the inner cell mass of the blastocyst. They are naturally pluripotent and have been widely studied since the 1990s. Their ability to generate almost any cell type makes them an invaluable tool in developmental biology and regenerative medicine.

Induced pluripotent stem cells (iPSCs), discovered in 2006 by Shinya Yamanaka, are adult cells reprogrammed to a pluripotent state using specific transcription factors. iPSCs provide the same versatility as ESCs, without the ethical concerns associated with using embryos, and allow for patient-specific cell therapies.

Molecular Mechanism

The conversion of somatic cells, such as skin fibroblasts and B lymphocytes, into pluripotent stem cells can be done through careful manipulations of the genetic code. Basically, scientists are now able to transform isolated somatic cells into iPSCs through reprogramming factors. It was initially thought that the genome of a mature cell was locked in a somatic state and unable to revert into a fully embryonic stem cell or (ESC)-like state. However, there have been scientists that succeeded in doing so. For example, Sir John B. Gurdon created a fully functional frog tadpole with an unfertilised egg and the nucleus of an epithelial cell. Further, Keith Campbell, Ian Wilmut and colleagues cloned a sheep with the nuclear transfer technique. These findings concluded that differentiated cells still retain the genetic memory that is important for an organism's development and that oocytes contain factors that can reprogram the mature cells' nuclei. The conservation of the genome during development serves as a basis of principle for nuclear process. It was hypothesised that the factors that play important roles in the maintenance of ESC identity also play an essential role in the induction of pluripotency in somatic cells. 

Takahashi and Yamanaka were the first scientists to validate that the pluripotent cell could be induced from the adult fibroblasts by introducing four transcription factors: octamer-binding transcription factor ¾ (Oct3/4), SRY (sex determining region Y)-box2 (Sox2), Krüppel-like factor 4 (Klf4), and cellular-Myelocytomatosis (c-Myc). Yamanaka studies explained that ectopic (manipulated) expression of cellular transcription factor done by retroviral vector (engineered viruses used to transport genetic material into target cells) in fibroblasts was sufficient to reverse a somatic cell into a pluripotent-like state. 

Later on, a lot of other groups of scientists tried to replicate Yamanaka’s work through different pathways, also searching a better way to adapt them for regenerative medicine. 

However, in order to do so, maintaining the pluripotency of induced pluripotent stem cells (iPSCs) is also a very important aspect. It requires both internal molecular regulation and carefully controlled culture conditions. At the molecular level, pluripotency depends on key transcription factors such as OCT4, SOX2, and NANOG, which form the core regulatory network. These factors are supported by external signaling pathways, particularly FGF2 and TGF-β/Activin/Nodal, which help prevent spontaneous differentiation. Epigenetic mechanisms also play a role, keeping the cells in an undifferentiated state.

From a practical perspective, iPSCs are maintained in defined media (nutrient-rich substances), such as Essential 8 or mTeSR1, and grown on substrates like vitronectin or laminin, which support long-term adhesion and growth. Also, continuous monitoring is essential to maintain the culture alive.

Application in regenerative medicine

One of the most promising fields of research involving induced pluripotent stem cells (iPSCs) is their use in regenerative medicine. Because of their ability to differentiate into any cell type of the human body, iPSCs offer unique opportunities to replace damaged or diseased tissues. Unlike embryonic stem cells, they can be generated directly from a patient’s own somatic cells, reducing ethical concerns and lowering the risk of immune rejection. Current studies explore their potential in treating heart disease, neurodegenerative disorders, diabetes, and kidney injury, as well as in developing organoids for disease modeling and drug testing. Although challenges remain, such as ensuring safety and genomic stability, iPSCs are already reshaping the landscape of personalized therapies. Some examples of iPSCs used in regenerative medicine are:

• Cardiac Repair: iPSC-derived cardiomyocytes (iPSC-CMs) are under intensive preclinical and early clinical investigation as a therapy for myocardial injury and heart failure. Animal studies have repeatedly shown that transplantation of iPSC-CMs or engineered heart tissues can improve cardiac function, but important challenges remain. These include achieving sufficient maturation of the cells, preventing arrhythmias, and scaling manufacturing under clinical-grade conditions. Several early human studies and trial programs are underway to test safety and feasibility.

• Diabetes: Researchers have generated functional β-like cells (which create and secrete insulin) from iPSCs that respond to glucose in vitro and in animal models, for which translation efforts are now in early clinical testing. Recent reviews and trial updates report that iPSC-derived islet cell (cells that produce hormones like insulin and glucagon) approaches are feasible and can secrete insulin, but remaining hurdles include protecting grafts from immune attack (autoimmunity and alloimmunity), ensuring long-term function, and manufacturing reproducible, safe products.

• Kidney, livers and organoids: iPSC-derived organoids (self-organizing 3D tissues that recapitulate elements of organ architecture) are already mature tools for disease modelling and drug screening. Organoid technology is also being explored as a route toward regenerative applications (e.g., kidney or liver patch/implant strategies), but translation to human therapy is still at an early, experimental stage because organoids typically lack full maturation, vascularization and immune integration.

• Neurodegenerative diseases: iPSCs are being studied as a possible treatment for neurodegenerative diseases such as Parkinson’s disease, Alzheimer’s disease, and ALS. In the lab, scientists can turn iPSCs into specific types of neurons. For example, in Parkinson’s disease, iPSCs can be differentiated into dopaminergic neurons, the same cells that are lost in patients. Early clinical trials have already tested the transplantation of these cells, showing that they can survive in the brain and appear safe, although more research is needed to prove long-term benefits. In addition to transplantation, iPSC-derived neurons are very useful as disease models. By making neurons from patients’ own cells, researchers can study how the disease develops in a human context and test new drugs in vitro. This makes iPSCs an important tool not only for future therapies, but also for understanding the mechanisms of these disorders.

Conclusion

Pluripotent stem cells, and in particular induced pluripotent stem cells, represent one of the most powerful tools in modern biology and medicine. They have revolutionized our understanding of cell identity, showing that differentiated cells can be reprogrammed to an embryonic-like state. Today, iPSCs are widely used not only to explore human development and model diseases in vitro, but also as a promising source for regenerative therapies. Although important challenges remain, such as ensuring safety, functional integration, and large-scale production, the progress made in less than two decades is extraordinary. With continued advances in biotechnology, iPSCs hold the potential to transform personalised medicine and offer new hope for patients suffering from currently incurable diseases.

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