Avdili, A.; Auer, M.; Brislinger, D.; Kolb, D.; Moser, G.; Reinisch, A.; Hoefler, G.; Bernecker, C.; Fuchs, J.; Feichtinger, J.; Schlenke, P.; Dorn, I.

Manufacturing red blood cells (RBCs) from human induced pluripotent stem cells (iPSCs) can improve our understanding of embryonic erythropoiesis, foster innovative treatments for RBC-related diseases, and ultimately address clinical blood supply shortages. However, existing systems face low efficiency, enucleation failure, and uncertainty about the develop-mental wave of cultured RBCs. We successfully used self-organized hemanoids to improve iPSC-derived RBC generation. Based on the hypothesis that cellular interactions and 3D organization promote hematopoietic cell fate, we aimed to thoroughly characterize heman-oids. We visualized the spatiotemporal emergence of hematopoiesis by generating a CD43-GFP reporter iPSC line. Imaging and spatial transcriptomics analysis provided detailed in-sight into the hemanoid architecture, identifying stromal cells and hepatoblasts as potential erythropoiesis-supportive elements. The developmental stage mirrors extraembryonic hema-topoiesis. Given the difficulties of accessing these early stages in vivo, our system offers a platform not only for further clinical translation but also for exploring human embryonic blood wave dynamics.