Human Blastoid: A Next-Generation Model for Reproductive Medicine?

Human early embryogenesis remains unexplored due to limited access to human embryos for research purposes. Meanwhile, the number of natural early pregnancy terminations remains significant, and solving the problem requires a deep understanding of the developmental mechanisms of this period. Although assisted reproductive technologies (ART) utilize up-to-date approaches in culturing human embryos in vitro, characterization of the embryos is still based on visual evaluation and subjective assessment. In addition, embryonic development in animal models, such as rodents and cattle, correlates poorly with human embryonic development. Synthetic embryology presents a promising new approach for studying human embryos involving the creation of embryos without the use of haploid germ cells. Instead, diploid pluripotent stem cells (PSCs) in a given state of pluripotency, which is maintained under conditions of induction and/or inhibition of certain signaling pathways, are used. Synthetic embryo systems (SES) may become a successful alternative model for studying fundamental processes of human early preimplantation embryogenesis, exploring new methods of objective embryo qualification, and personalized approaches in ART. However, the question of whether SES models can be considered as full-fledged mimics of the embryo remains open. This review examines human blastocyst-like structures known as blastoids. It discusses their use as models, as well as the parameters that need to be modified to more accurately simulate the human blastocyst.