In this blog post, we’ll explore the principles and benefits of induced pluripotent stem cells (iPSCs)—which have made the reversal of time, once thought possible only in movies, a reality at the cellular level—as well as the bioethical issues surrounding them and their current potential for medical applications.
We have long understood, as a law of nature, that time that has already passed cannot be reversed. However, the movie ‘The Curious Case of Benjamin Button’, released in 2008 and introduced in South Korea in 2009, shattered the mental framework we had held. Benjamin Button, born with the appearance of an 80-year-old, actually grows younger as time goes on. This film made us reexamine our preconception that time cannot be reversed.
However, technology has now been developed that makes this dream-like scenario possible at the cellular level. Thanks to the induced pluripotent stem cell (iPS cell) technology established by Professor Shinya Yamanaka, it is now possible to reprogram already-differentiated adult cells—much like Benjamin Button in the film—restoring them to an early state and granting them pluripotency. Professor Yamanaka currently serves as the Director Emeritus and a professor at the Kyoto University iPS Cell Research Institute (CiRA), where he continues to advance research and applications in the field of iPS cells.
Professor Yamanaka focused on 24 transcription factors highly expressed in embryonic stem cells—transcription regulatory proteins that specifically bind to DNA at the transcriptional regulatory sites of specific genes to activate or suppress the transcription of those genes. He hypothesized that some of these factors would play a key role in generating “pluripotency”—the characteristic of stem cells that allows them to differentiate into any type of cell. Subsequent extensive research confirmed that four of these 24 candidate transcription factors—Oct3/4, Sox2, Klf4, and c-Myc—play a pivotal role in reprogramming existing adult cells into a state with pluripotency similar to that of embryonic stem cells. In other words, these four transcription factors were loaded onto a “bus”—a retrovirus—and sent to already differentiated adult cells, where they were dropped off at their final destination: the cell’s genome.
Once transported, the transcription factors are expressed within the cell, resetting the adult cell to an early state and enabling it to acquire “pluripotency” similar to that of embryonic stem cells. Since the induced pluripotent stem cells (iPSCs) created in this way can be further differentiated into various types of cells, they are currently being used to explore potential treatments for intractable diseases. Furthermore, iPSCs are gaining attention as a new tool in medical research because they are not limited to simply producing cells; they can also be used to investigate the causes of diseases and to evaluate the efficacy and toxicity of new drug candidates.
In South Korea, the term “stem cells” often brings to mind the concept of “bioethics” in connection with Dr. Hwang Woo-suk’s embryonic stem cell research. Since embryonic stem cells are generally derived from early-stage embryos, their use and the research process have long been the subject of bioethical controversy. In contrast, induced pluripotent stem cells (iPSCs) are created from already differentiated adult cells—not embryos—to produce cells with the same pluripotency as stem cells; therefore, they offer ethical advantages over embryonic stem cell research, which requires the direct use of embryos. Consequently, iPSCs have been regarded as an important alternative that can mitigate bioethical concerns, as they allow for the acquisition of pluripotent cells without destroying embryos.
Furthermore, since some research methods for obtaining embryonic stem cells require processes such as nuclear transfer using oocytes, various practical and ethical issues can arise during the procurement of oocytes and the research process itself. In contrast, with iPSCs, since the state of a person’s own adult cells can be reprogrammed using four transcription factors, it is possible to secure a sufficient quantity of cells based on cells obtained from the patient. This characteristic offers advantages in terms of cost and supply when securing cells needed for research and treatment. Furthermore, using iPSCs derived from a patient’s own cells offers the potential to reduce immune rejection compared to using cells from another person. However, even iPSCs derived from a patient’s own cells are not always completely safe from an immunological perspective; their immunogenicity and safety must be thoroughly evaluated, including genetic and epigenetic changes that may occur during the reprogramming and culture processes.
Induced pluripotent stem cell technology is not yet perfect. Improving reprogramming efficiency and ensuring cell quality and safety remain critical challenges, and for practical application in medicine, various risks—including tumorigenicity, genetic stability, the possibility of unwanted cells being introduced, and immune responses—must be meticulously evaluated. Nevertheless, induced pluripotent stem cell technology continues to advance steadily. For example, research has been conducted to increase the speed and efficiency of reprogramming using small-molecule compounds such as RSC133, and recently, research has continued aimed at developing next-generation iPS cells with improved cell quality and differentiation efficiency. As of 2026, induced pluripotent stem cells are no longer merely a future possibility. In Japan, in March 2026, products derived from induced pluripotent stem cells—including a myocardial cell sheet for the treatment of severe heart failure and a product for the treatment of Parkinson’s disease—received conditional and time-limited approval, marking a significant step forward as iPS cell-based therapies enter actual clinical practice. However, even these products must continue to undergo validation of their efficacy and safety following approval, and iPS cells have not yet matured into a technology capable of immediately replacing all organ transplants or reversing aging. If the technology continues to advance, it has the potential to provide new treatments that address the limitations of organ transplantation from donors and to open new avenues for treating intractable diseases associated with cells—such as cardiac or neural cells—that are difficult to regenerate after damage. Furthermore, based on the advantages of using cells derived from the patient’s own genetic material and the ability to secure the necessary cells, advancements in drug testing and disease modeling research using iPSCs could contribute to the realization of personalized medicine—finding the most suitable treatment for each individual patient. Although iPSCs do not actually turn back the clock on human life—unlike the elixir of eternal life that Emperor Qin Shi Huang dreamed of—the possibility of resetting the state of cells and differentiating them into new cell types has significantly transformed our perspective on aging and disease.
If iPS cell technology continues to improve in safety and efficiency, a new era of medicine—based on the ability to turn back cellular time—could dawn, making our lives healthier and more fulfilling.
