A blastoid is a laboratory-created structure from stem cells that closely resembles an early human embryo, specifically a blastocyst. This model allows researchers to study the initial stages of human development. While the term “blastoid” also refers to an extinct class of marine fossils, this article focuses on the stem cell-derived biological structures, which are a recent advancement in developmental biology.
The Creation of a Blastoid
Blastoids are generated from pluripotent stem cells. Scientists guide these cells to self-organize by providing specific chemical signals and culturing them in a three-dimensional environment. This process induces stem cells to form components seen in a natural blastocyst.
This includes an inner cell mass-like region, which would eventually form the embryo, and a trophectoderm-like outer layer that contributes to the placenta. A fluid-filled cavity, similar to the blastocoel, also forms within the structure. This self-assembly allows researchers to produce these models in large numbers for study.
Distinguishing Blastoids from Natural Blastocysts
Blastoids share several similarities with natural blastocysts, including their spherical morphology, size, and distinct cell lineages. Single-cell transcriptomic analysis reveals that about 97% of cells in blastoids align with the gene expression profiles of blastocyst-stage cells.
Despite these resemblances, blastoids are not identical to natural blastocysts. They often exhibit organizational flaws, such as incorrect cell numbers or cell type proportions, and their transcriptomic profiles differ from actual embryos. Blastoids do not possess the capacity to develop into a viable fetus. This functional difference means they are considered embryo models rather than embryos.
The Role of Blastoids in Scientific Research
Blastoids serve as a tool for investigating the earliest stages of human development, a period often referred to as a “black box” due to its inaccessibility. They allow scientists to study events occurring shortly after fertilization and before implantation into the uterus, including how different cell types emerge and organize to form the initial embryonic structure.
Researchers use blastoids to explore the underlying causes of infertility and early miscarriages, which often stem from issues during this pre-implantation phase. The models help identify developmental errors or genetic factors that lead to pregnancy loss. Blastoids also provide a controlled environment for testing the effects of drugs, toxins, or environmental factors on early embryonic development, assessing potential risks to pregnancy. Their ability to be generated in large numbers makes them suitable for high-throughput screening, accelerating the discovery of new insights into human reproduction and developmental disorders.
Ethical and Regulatory Frameworks
Research involving human embryos has traditionally been guided by the “14-day rule,” which limits in vitro culture to 14 days post-fertilization or until the primitive streak appears. This guideline addresses ethical considerations surrounding the moral status of developing human life. Blastoids challenge this framework because they are derived from stem cells rather than fertilization, blurring the lines of what constitutes an “embryo.”
An ongoing debate exists among scientists, ethicists, and policymakers regarding the moral status of these stem cell-based models. Some argue that because blastoids currently lack the potential to develop into a fetus, they should not be subject to the same strict regulations as natural embryos. Others suggest their structural and genetic similarities warrant careful oversight. The International Society for Stem Cell Research (ISSCR) updated its guidelines in 2021 to address stem cell-based embryo models, recommending specialized scientific and ethical review processes for such studies, especially when modeling integrated embryonic development. These guidelines emphasize that local laws and public support should also inform regulatory decisions.