Macro-scale, scaffold-assisted model of the human bone marrow endosteal niche using hiPSC-vascularized osteoblastic organoids

Endosteal bone marrow (BM) niches are crucial to sustain non-steady-state hematopoiesis but are challenging to be modeled in their cellular and molecular complexity in standardized, human settings. We report a developmentally guided approach to generate a macro-scale organotypic model of BM endosteal niches (engineered vascularized osteoblastic niche [eVON]) based on human induced pluripotent stem cells and porous hydroxyapatite scaffolds. The eVON contains long-lasting vascular networks covered by pericytes and neural fibers within an osteogenic matrix. Key niche signals (CXCL12, KITLG, and vascular endothelial growth factor A [VEGFA]) are expressed in human-specific patterns. The system supports hematopoiesis in vitro and preserves hematopoietic stem and progenitor cell (HSPC) multilineage repopulation capacity in vivo. eVON perturbations at cellular (removing vasculature) and molecular (deregulating VEGF-A and CXCL12 signaling) levels enabled the investigation of the contribution of endosteal vasculature to myelopoiesis. The eVON faithfully captures phenotypic, structural, and functional features of human endosteal BM, enabling the study of pathophysiological interactions with hematopoietic cells. Overall design: Three different hiPSC lines (409B2, Wibj and WTC) are differentiated into osteogenic and vascular cells in porous hydroxyapatite scaffolds to generate a standardized and physiological model of the human bone marrow endosteal niche, termed as engineered vascularized osteoblastic niche (eVON). eVONs generated from 409B2, Wibj and WTC cells were compared at transcriptomic level through scRNA-seq.