In a significant advance for reproductive medicine, scientists have for the first time successfully converted human skin cells into egg-like cells capable of being fertilized and developing into early-stage embryos. The research, led by a team at Oregon Health & Science University (OHSU), provides a powerful new proof-of-concept for creating functional human gametes in the laboratory, potentially opening new avenues for treating infertility and understanding human development.
This achievement overcomes a fundamental biological barrier, demonstrating that ordinary adult body cells can be reprogrammed to mimic the specialized process of meiosis, where reproductive cells halve their genetic material. While the scientists and outside experts caution that the technology is years, possibly decades, away from any clinical application, the work represents a critical step forward. The breakthrough hinges on a novel laboratory method that coaxes a skin cell’s full set of chromosomes to divide in a way that mirrors the natural formation of an egg, a feat that could one day transform the treatment of infertility for those unable to produce their own eggs.
A New Method for Halving Chromosomes
The core challenge in creating eggs from non-reproductive cells lies in genetics. A typical human body cell, such as a skin cell, is diploid, containing 46 chromosomes arranged in 23 pairs. In contrast, an egg or sperm cell is haploid, containing only a single set of 23 chromosomes. During fertilization, a haploid egg and a haploid sperm combine to restore the full complement of 46 chromosomes in the resulting embryo. Forcing a skin cell to discard half of its genetic material in a controlled way has been a major obstacle.
Somatic Cell Nuclear Transfer
To achieve this, the OHSU team, led by biologist Shoukhrat Mitalipov, employed a technique known as somatic cell nuclear transfer (SCNT). This process, famously used to create Dolly the sheep in 1996, involves removing the nucleus from a healthy donor egg and replacing it with the nucleus of a somatic cell—in this case, a skin cell. The researchers collected skin cells from female donors and carefully transferred their nuclei, which contained the full 46 chromosomes, into donor eggs that had been enucleated.
Inducing ‘Mitomeiosis’
Once the skin cell nucleus was inside the donor egg, the primary innovation came into play. The team developed a new process they have termed “mitomeiosis” to induce the cell to reduce its chromosome number. They chemically activated the reconstructed egg, prompting it to behave as if it were undergoing meiosis, the special type of cell division that produces gametes. This activation successfully persuaded the transplanted nucleus to undergo the specific kind of division required, discarding half of its chromosomes and resulting in an egg-like cell, or oocyte, with the necessary 23 chromosomes for fertilization.
From a Lab-Grown Oocyte to Blastocyst
The researchers successfully produced 82 functional oocytes using this novel reprogramming method. To test their viability, the team proceeded with in vitro fertilization, injecting the lab-made eggs with donated sperm. The subsequent development was monitored closely to determine if these cells could function like natural eggs and support the initial stages of embryonic growth.
Observing Early Development
Following fertilization, a small but significant fraction of the oocytes began to develop. The scientists reported that around nine percent of the fertilized eggs successfully grew into blastocysts, the stage of development that occurs around five to six days after fertilization, by day six. A blastocyst is a cluster of dividing cells that represents the earliest form of an embryo, and reaching this stage is a key benchmark in assisted reproductive technology. For ethical reasons and due to the preliminary nature of the research, no embryos were cultured beyond this point or considered for implantation.
Hurdles on the Path to Clinical Use
Despite the groundbreaking nature of the findings, the researchers have been clear that the technique is far from being ready for clinical use. The primary concern is the high frequency of genetic errors observed in the resulting embryos. The process of artificially inducing chromosome reduction is not yet perfected, and many of the blastocysts that did develop showed significant chromosomal abnormalities. These errors would likely lead to developmental failure, miscarriage, or severe genetic disorders, making the current method unsafe for human reproduction.
The overall success rate also remains very low. While producing 82 oocytes was a major achievement, the fact that only nine percent reached the blastocyst stage highlights the inefficiency of the process. Senior author Shoukhrat Mitalipov and other experts in the field have stated that it could take a decade or more of additional research to refine the technique, improve its safety and efficiency, and fully understand the health of any resulting embryos. Significant work is needed to ensure the method is reliable and does not introduce harmful genetic or epigenetic changes.
The Broader Scientific and Ethical Context
This research provides a vital “proof of concept” that could reshape the landscape of reproductive medicine. Experts not involved in the study praised the work for its ingenuity. Roger Sturmey, a professor of reproductive medicine at the University of Hull, called it an “insightful piece of research” that demonstrates the remarkable plasticity of adult cells. Similarly, Ying Cheong, a professor at the University of Southampton, hailed the study as an “exciting” breakthrough that could one day transform the understanding and treatment of infertility.
Alternative Approaches
The OHSU team’s SCNT-based method is not the only avenue being explored for creating lab-grown gametes. Another prominent strategy involves reprogramming skin cells into induced pluripotent stem cells (iPSCs). These iPSCs, which have the potential to develop into any type of cell in the body, could then be coaxed into becoming eggs or sperm. Researchers in Japan recently announced progress in creating mice with two biological fathers using a similar stem-cell-based approach. It is still too early to know which method will ultimately prove more successful or safer for human application.
Future Considerations
As this science advances, it will prompt important societal conversations. Experts have stressed the need for robust governance and public dialogue to address the ethical implications of creating human embryos from reprogrammed skin cells. While the primary beneficiaries would be women who cannot produce their own eggs, the technique also opens the theoretical possibility that the skin cells used could come from anyone, raising complex questions about genetic parentage. For now, the research provides a new and powerful tool for studying human reproduction, fertilization, and the causes of miscarriage, offering a glimmer of hope for future therapies.
