Can scientists grow an accurate biological stand-in for a human embryo? Not yet—but a new benchmarking tool shows some lab-grown models are getting closer than others.
The study, published in Cell Systems, examined how four widely used blastoid-generation protocols reproduce the cell types and developmental processes seen in natural human embryos. Blastoids, embryo models derived from stem cells, offer researchers a way to study the biology underlying fertility, pregnancy success and early human development without relying on donated embryos—these stem-cell-derived structures are research models, not actual human embryos, and current models cannot develop into one. But whether a model merely looks like an embryo under a microscope is a different question from whether it behaves like one biologically.
Researchers took than 14,000 single-cell transcriptomes from human embryos spanning key stages of development and combined and harmonized them into a reference map of how cells normally differentiate and organize themselves in the days immediately before and after implantation.
This reference was then compared against the four blastoid protocols, examining their molecular identities, developmental timing, lineage structure and other biological characteristics rather than simple visual resemblance. Some models reproduced all three major cell lineages of a natural human blastocyst relatively well, while others failed to accurately represent certain cell types or contained large numbers of cells that couldn't be confidently matched to any known embryonic state. No single model perfectly replicated a natural human blastocyst.
“Human embryo models have enormous potential for studying the earliest days of an embryo's development, but there has been no consistent way to assess how accurately these reflect real human development,” said Pengyi Yang, fellow at the University of Sydney and unit head of computational systems biology at the Children's Medical Research Institute. “Our framework allows researchers to compare these models against a detailed biological reference and determine which cell types and developmental processes are faithfully reproduced, and which are not.”
The researchers have made their reference datasets and benchmarking tools publicly available, allowing scientists worldwide to test new embryo models against the same standard. They hope this roadmap will let future models be refined more quickly and evaluated more rigorously, keeping scientific claims grounded in what the models can actually support.
Data from University of Sydney