3D <i>In Vitro</i> Models of the Bone Marrow Niche.

Abstract

The bone marrow niche is a specialized microenvironment sustaining a hematopoietic stem cell (HSC) pool and regulating the production of mature blood cells. Its exact composition and mechanisms remain incompletely defined, mainly due to the lack of <i>in vitro</i> models that accurately reproduce its physiological three-dimensional (3D) architecture and cellular crosstalk. Two-dimensional cultures fail to sustain HSC quiescence and stemness, while advanced 3D systems can reproduce key structural and mechanism cues of the niche. In this review, we first describe physiological cellular, stromal, and matrix components of the bone marrow niche, highlighting their coordinated regulation of HSC maintenance, proliferation, and mobilization. We then critically examine current approaches for 3D <i>in vitro</i> bone marrow models, including scaffold-based methods, decellularized models, spheroid and organoid systems, 3D bioprinting applications, and organ-on-chip technologies, discussing their advances, limitations, and potential disease modeling in this field. Finally, we outline how these technologies could deepen our understanding of hematopoiesis mechanisms, clonal evolution, and niche-mediated drug resistance. We also highlight the pros and cons of each methodology and future directions toward standardized protocols, integrating tissue components, and the use of human cells to enhance reproducibility and clinical relevance. Advances like bone marrow-on-a-chip, computational models, and patient-specific systems will help bridge the gap between <i>in vitro</i> and <i>in vivo</i> studies, enabling drug testing, stem cell expansion, and gene editing strategies, including chimeric antigen receptor expression. Bone marrow models have evolved from simple 2D cultures to advanced 3D and organ-on-a-chip systems, significantly improving our understanding of hematopoiesis and accelerating new therapies.