iPSCs: Transforming Biomedicine Over Two Decades

Two decades after researcher Shinya Yamanaka’s historic discovery of induced pluripotent stem cells (iPSCs), cellular reprogramming has become one of the greatest revolutions in contemporary biomedicine. By successfully bringing specialized adult cells back to an embryo-like state of pluripotency, this technology has opened up promising new avenues in regenerative medicine and disease modeling, while also offering an ethically acceptable alternative that avoids the destruction of human embryos while enabling the development of personalized autologous transplants.

It has been two decades since Japanese researcher Shinya Yamanaka and his collaborator Kazutoshi Takahashi published their discovery of induced pluripotent stem cells (iPSCs) in Cell.^[^1] These are cells derived from differentiated somatic cells—obtained from adult tissues of mice, humans, or other organisms—through an experimental cell reprogramming process that reverses their differentiated state and returns them to a state similar to that of pluripotent embryonic stem cells (ESCs).

This finding was not accidental, but the result of research aimed at understanding the pluripotency of ESCs and the molecular mechanisms underlying cell reprogramming and differentiation, i.e., their conversion into the cells of the different tissues that make up an organism as complex as a mammal. Yamanaka sought to investigate the genes that determine the pluripotency of mouse ESCs and how to reactivate them towards differentiated cells. Now, 20 years later, he has just published an article describing the details of that discovery, stating that “What began as an unexpected observation in Kyoto quickly transformed stem cell biology and regenerative medicine worldwide”.

The term “unexpected” refers to the rapid identification of the key genes whose activation by transcription factors determines cell fate during the transition towards a specialized cell type. In 2006, Yamanaka’s team published their study on the generation of pluripotent cells (similar to embryonic cells), which they achieved by inducing the expression of only four of the 24 candidate genes tested in differentiated skin cells (mouse fibroblasts). The four genes, which have come to be known as the Yamanaka factors, are: Oct4, Sox2, Klf4 and c-Myc (OSKM).^[1] The introduction of these genes into mouse fibroblasts cultured in vitro using genetic engineering techniques resulted, in some assays, in the emergence of cells that could only grow in culture if their differentiation was reversed, returning them to an ESC-like state. At its core, this discovery lay in elucidating the genetic and molecular determinants of cell fate.

The study was based on the premise that embryonic cells retain the same identity and genetic information in the adult state, preserving even the capacity to be reactivated or deactivated. Gene activity is expressed through transcription, i.e., the synthesis of proteins that will then determine cellular function. This depends on the physiological and molecular states of the DNA of the genes at their specific locations on the chromosomes, i.e., on epigenetic factors. For a gene to be activated, its DNA must be “open” and accessible to transcription factors. Conversely, genes whose DNA is tightly packed will not be expressed. These differ in each tissue and/or time of development. Yamanaka’s team studied the molecular factors that establish, maintain, and modify cell identities, which forms the foundation of developmental biology. The idea of how differential gene activity determines cell specialization was based on the knowledge that, in multicellular organisms, all cells—regardless of how different their functions may be—retain the same genetic information as the zygote from which they originate, and therefore retain the potential ability to construct a complete organism given the proper conditions. This had already been demonstrated in the 1960s by the English researcher John Gurdon (1933-2025), through experiments that consisted of transplanting a somatic cell nucleus from the intestinal epithelium of Xenopus laevis tadpoles—thus derived from differentiated adult cells—into unfertilized eggs of the same species whose nuclei had previously been removed. This resulted in the development of individuals genetically identical to the nuclear donor (i.e., clones). This method, known as nuclear transplantation, was later used by the British embryologist Ian Wilmut (1944-2023) to obtain Dolly the sheep, the first mammalian clone.

Given the presence of orthologous genes (genes with the same function) in the human genome, scientists were able to achieve the same outcome using human fibroblast cultures within just one year.^[2] The dedifferentiated cells generated using the Yamanaka factors came to be known as “induced pluripotent stem cells” (iPSCs). The low efficiency in obtaining these cells gradually improved as scientists developed a deeper understanding of the physiological state of the cells and gained control over the molecular factors that determine the accessibility of the transcription factors, on which the expression of the genes involved in pluripotency depends. This allowed them to elucidate the factors governing cell reprogramming and plasticity that influence cellular aging.

In short, reprogramming requires two processes: the first to erase the cellular specialty; and the second to achieve pluripotency. According to advances by Yamanaka’s team, this transformation occurs through interconnected waves of epigenetic DNA remodeling, transcriptional and metabolic reorganization, and changes in cellular structure. Expression of the Yamanaka OSKM factors initiates a slow, complex process of chromatin opening, establishing a pluripotent genome that is poised for rapid differentiation into multiple lineages.^[3]

In the 20 years since iPSC technology was developed, significant advances have been made in the parallel experimental fields of molecular and cellular biology, which have contributed to improving experimental methods and our understanding of all aspects involved in cell reprogramming and differentiation. Thus, techniques have been applied to introduce the Yamanaka factors, based on effective vectors such as episomal plasmids, adenoviruses, synthetic mRNA, etc. Advances in transcriptomics, proteomics, and metabolomics have also contributed, along with a range of technologies that allow scientists to analyze the physiological states and trajectory of cells and, in particular, to analyze gene expression and chromatin conformational changes. Similarly, observation methods and artificial intelligence (AI)-assisted analysis have helped improve our knowledge of cell lineage trajectories and other aspects of their specialization.^[4]

Medical applications and ethical aspects of iPSCs

The hope that cellular reprogramming could provide a cure for degenerative diseases was one of the reasons the Karolinska Institutet of the Royal Swedish Academy of Sciences decided to award the 2012 Nobel Prize in Physiology or Medicine to researchers John Gurdon and Shinya Yamanaka. The citation from the Nobel committee stated that John Gurdon discovered in 1962 that the specialization of cells is reversible, and that more than 40 years later, Shinya Yamanaka described how intact mature cells could be reprogrammed to become pluripotent stem cells.

The high expectations generated by iPSCs in medicine are mainly due to their potential application in regenerative medicine as an alternative to—or at least alongside—ESCs, which are derived from human embryos.

A particularly important ethical consideration is the possibility of genetically reprogramming adult cells and converting them into stem cells, equivalent to embryonic cells, without requiring the destruction of human lives during their earliest stage of development. Furthermore, since iPSCs can be generated from a patient’s own tissues, it should be possible to transplant them autologously, i.e., back into the same person from whom they were derived, without triggering an immune rejection response.

Following the extraordinary breakthrough in genetic reprogramming by Yamanaka’s group, many researchers expressed their intention to abandon the use of ESCs in regenerative medicine and redirect their research towards this clearly more ethical and promising approach. Nevertheless, since their discovery two decades ago, considerable effort has been made to address various technical aspects to improve cell culture yields, optimize the kinetics of reprogramming, reduce residual epigenetic memory, overcome obstacles related to safety, reproducibility, and the maintenance of genomic integrity, prevent tumor formation, and avoid immune rejection as a result of having to use iPSCs from other individuals due to their slow growth, in addition to other safety and efficiency challenges.

The path to clinical applications has been slow. From the beginning, the same researchers continued to investigate until they succeeded in deprogramming human fibroblasts, eliminating the c-Myc gene without compromising results^[5]; they also managed to increase the proportion of iPSCs and improve the yield of the technique to achieve rapid growth of the patient’s own iPSCs for use in autologous transplantation. In addition, other experiments have shown that iPSCs induce negligible immune responses, comparable to those observed with ESCs.^[6]

Beyond their use in regenerative medicine, specialized applications of iPSCs include the development of models to investigate disease mechanisms and drug responses, as well as their use in obtaining organoids for research and organ modeling for transplantation.

Since their discovery, the interest in and use of iPSCs has grown, as evidenced by the number of projects listed in the clinicaltrials.org database. As of the end of August 2026, there are 262 studies underway worldwide investigating the application of this technology for biomedical purposes, including the treatment of cardiac lesions, various forms of blindness, degenerative diseases, etc. According to Yamanaka, early clinical trials for age-related macular degeneration and Parkinson’s disease have demonstrated the feasibility and safety of iPSC-derived grafts in autologous transplantation.^[3] Many of these trials seek to develop protocols for clinical applications and, at the same time, include among their objectives technical improvements to improve cell culture yields, optimize the kinetics of reprogramming, reduce so-called residual epigenetic memory, ensure the genetic and epigenetic stability of cells, and control the risk of abnormal cell proliferation and tumor formation. Further studies have also been necessary to investigate possible immune responses and confirm the reproducibility of the procedures. Issues related to large-scale production, standardization of procedures, and quality control also need to be resolved. In addition, the high cost of some of the technologies involved may limit widespread access to these therapies.

Interest in the clinical applications of iPSCs continues to raise ethical concerns, particularly those related to their use in personalized medicine. The use of cultures in terms of confidentiality, informed consent, privacy, and maintenance of data related to the origin of iPSCs warrants particular attention. Similarly, given the high cost of these technologies, significant progress is expected in reducing the costs associated with the use of iPSCs, thereby enabling their more affordable and widespread application.