Human iPSC-derived bone marrow organoid mimics human bone marrow structure. (A) Wide-field picture of a mature human bone marrow organoid in culture on day 21. (B) Hematoxylin and eosin (H&E) staining of bone marrow organoid cultured on day 21 demonstrates the presence of hematopoietic cells within the sinusoids. (C) Representative pictures of TEM reveal diverse cell types within bone marrow organoids cultured on day 21. (D) 3D whole-mount imaging of human bone marrow organoids cultured on day 21 (left) with the cell surface rendered via Imaris (right). Organoids were immunostained for CD45⁺ hematopoietic cells and CD271⁺ mesenchymal stromal cells, with biotinylated UEA1 highlighting the endothelial cells. (E) 3D imaging reveals erythroblasts, stained for CD235a, encapsulated within UEA1-positive sinusoidal vessels (left). The cell surface rendering picture is on the right. (F) Comparison of confocal images between organoid-derived erythroblasts (day 21 culture) and those obtained from a human bone marrow core biopsy.