Integration of Hematopoietic and Thymus-like Niches in a Human iPSC-derived Bone Marrow Organoid

Human bone marrow generates blood cells but critically lacks the thymic environment required for T cell development. Developing an integrated in vitro platform that reconstitutes both functions simultaneously remains a major challenge in regenerative and immune medicine. We asked whether a synthetic marrow could be engineered to provide both capacities. Using human induced pluripotent stem cells, we created self-organizing bone marrow organoids (iBMOs) that faithfully reproduced native stromal and vascular structures and, remarkably, supported robust thymus-like T cell differentiation. iBMOs directed hematopoietic progenitors toward functional T and dendritic cells. When engrafted into immunodeficient mice, they autonomously sustained human erythropoiesis and de novo bone formation in vivo. Single-cell transcriptomics revealed a complex niche architecture, including a hybrid cluster co-expressing stem, endothelial, and stromal markers, key to understanding this dual functionality. This bioengineered organoid-stromal system unifies bone marrow and thymic functions in a single human-derived platform, offering a scalable source of immune cells for adoptive cell therapies and regenerative applications, as well as a versatile model for studying human hematopoiesis and immunity.