Israeli Scientists Create Synthetic Human Embryo Models

In September 2023, a research team led by Professor Jacob Hanna at Israel's Weizmann Institute of Science announced a significant scientific advancement: the creation of complete human embryo models from stem cells, cultivated in the laboratory without the use of eggs, sperm, or a womb. These synthetic embryos were grown outside the womb up to day 14, exhibiting all the structures and compartments characteristic of this developmental stage, including the placenta, yolk sac, chorionic sac, and other external tissues essential for dynamic and adequate growth.

The team utilized pluripotent stem cells, which have the potential to differentiate into various cell types. Some of these cells were derived from adult skin cells that had been reverted to a "naïve" state, corresponding to day seven of natural human embryonic development—the point at which an embryo implants into the womb. The researchers divided these cells into three groups: one intended to develop into the embryo itself, and the other two treated with chemicals to differentiate into tissues necessary to sustain the embryo, such as the placenta and yolk sac. Under optimized conditions, about one percent of these cell mixtures self-organized into complete embryo-like structures.

These synthetic embryo models closely mimic the development of a real human embryo, particularly the emergence of its fine architecture. Professor Hanna emphasized the importance of the first month of embryonic development, stating, "The drama is in the first month. The remaining eight months of pregnancy are mainly lots of growth. But that first month is still largely a black box."

The models offer an ethical and accessible way to study early human development, potentially advancing research in infertility, drug testing, and tissue transplantation. They may help reveal the causes of many birth defects and types of infertility, lead to new technologies for growing transplant tissues and organs, and provide a means to study the effects of exposure to drugs or other substances on fetal development.

The creation of human embryo models without the use of eggs, sperm, or a womb raises significant ethical questions. Traditionally, a 14-day limit for embryo cultivation is enforced in many countries based on ethical and developmental milestones, such as the formation of the primitive streak. The development of these models challenges existing regulations and prompts a reevaluation of ethical guidelines in embryonic research.

The ability to create embryo-like structures from stem cells without fertilization also blurs the lines between natural and synthetic life forms, leading to debates about the moral and legal status of these models. As Professor Hanna noted, "An embryo is self-driven by definition; we don’t need to tell it what to do—we must only unleash its internally encoded potential."

Professor Jacob (Yaqub) Hanna is a prominent figure in stem cell biology and synthetic embryology. He leads an interdisciplinary group at the Weizmann Institute's Department of Molecular Genetics, focusing on understanding embryonic stem cell biology, early development, and advancing human stem cell-based disease modeling. His research encompasses cellular reprogramming, pluripotency maintenance, and the development of synthetic embryo models.

The Weizmann Institute of Science, located in Rehovot, Israel, is a leading multidisciplinary research institution. It is renowned for its contributions to various scientific fields, including molecular genetics, where Professor Hanna's lab is based.

This groundbreaking research opens new avenues for understanding early human development and addressing medical challenges. However, it also necessitates careful ethical consideration and regulatory oversight to navigate the complex implications of creating human embryo models in the laboratory.