Bridging the gap in embryogenesis research: North Bornean orangutan-derived blastoids as models for human development

Understanding early primate embryogenesis remains limited by ethical and technical constraints. To address this, we established a stem cell-based embryo model from the North Bornean orangutan ( Pongo pygmaeus pygmaeus ). Using integration-free induced pluripotent stem cells (iPSCs), we generated blastoids that self-organized into structures resembling human blastocysts in morphology, lineage composition, and transcriptomic identity. Initial aggregation of primed iPSCs produced blastoids with organized lineage segregation. We enhanced this approach by combining isogenic iPSCs maintained under different culture conditions at optimized ratios, generating "bi-blastoids" with high formation efficiency, balanced lineage specification, and dimensions matching human blastocysts. Single-cell RNA sequencing revealed epiblast-, trophectoderm-, and hypoblast-like populations with transcriptomic profiles closely resembling human E6-7 blastocysts. Comparative analysis demonstrated that orangutan blastoids exhibited stronger transcriptional fidelity to human embryos than existing macaque models, establishing their unique value for developmental studies. Functional validation confirmed that orangutan blastoids could generate embryonic stem cell-like and trophectoderm stem cell-like lines, recapitulate trophoblast differentiation and secrete chorionic gonadotropin. However, primitive endoderm/hypoblast-like cells failed to form a distinct compartment, mirroring limitations observed across other primate models. This orangutan blastoid system provides a less ethically restrictive platform for studying human-relevant embryogenesis while maintaining high developmental fidelity. Beyond developmental insights into primate development, this model may inform future reproductive interventions for critically endangered great apes as conservation technologies advance.