Intravital imaging uncovers remodelling of humanised bone marrow-like niches

The bone marrow haematopoietic niche is composed of a diverse array of cell types and extracellular matrix components that together support healthy haematopoiesis. However, live imaging of the bone marrow microenvironment is hampered by tissue accessibility limitations. Using intravital imaging through a titanium imaging window, we investigated the dynamics of human haematopoietic cells and mesenchymal stromal cells within an ectopically implanted humanised scaffold in an immunodeficient murine host. These cell populations expand and differentiate over time, accompanied by progressive remodelling of the scaffold. We observe migration of murine endothelial cells into the scaffold, leading to the formation of a vascular network during the initial development of the humanised niche. Subsequently, the dense collagen matrix that makes up the implanted niche is altered and larger gaps form in regions populated by mesenchymal stroma cells. Collectively, our findings demonstrate dynamic remodelling of the extracellular milieu that supports haematopoietic cell development and establish a platform for longitudinal, in vivo investigation of these processes. Altogether, we describe a novel model that aligns with the 3R guiding principles and enables real-time assessment of bone marrow cell dynamics in vivo. Summary statementRatcliffe and Mian et al. image in vivo dynamics of a bone marrow haematopoietic niche model.