P1338: vascularized bone marrow-on-chip to study vascular aberration in hematopoietic diseases

Topic: 23. Hematopoiesis, stem cells and microenvironment Background: The bone marrow (BM) is the main physiological site for adult hematopoiesis. BM niche is a complex tissue composed of different cell populations interconnected by a network of matrix proteins and vessels. Endothelial cells (ECs) lining the vessels actively participates in normal hematopoiesis and are dramatically remodeled in diseases affecting the bone (Stucker et al., 2020). We have observed a thorough remodeling of the vascular tree in the BM upon acute myeloid leukemia (AML) development by using mouse models of the disease and patient-derived xenografts, pointing towards the existence of an active crosstalk between the two compartments contributing to disease pathogenesis (Gomes AL, 2021; Passaro et al., 2017; Passaro, 2021). Aims: Being able to model the cross-talk between leukemia and the vascular BM niche in a humanized system is a key path toward the development of novel clinical strategies. Moreover, studying the vascular microenvironment in a flexible in vitro system that can be easily manipulated can progress our understanding of the fundamental mechanisms underlying its implication in disease (Bessy et al., 2021). Methods: We propose the generation of an all-in-one vascularized BM-on-chip (vBM-on-chip) with fully controlled cell deposition. We performed two-photon laser ablation to pattern a vascular tree in ECM hydrogel embedded in a PDMS chip in close proximity with bone-like structures. This chip connected with a microfluidics system can recapitulate the native BM vascular flow, with human ECs lining capillary-size vessels and associated with pericytes. Results: Our system is able to recapitulate the BM heterogeneity in terms of size, morphology and functional parameters (e.g., blood flow, permeability). Mathematical modelling allows the prediction of areas of flow perturbation favouring cell adhesion. Functionally, these vessels can sustain normal hematopoietic stem cell adhesion and maintenance in a quiescent or active state over time, as well as inducing multiple fate differentiation. This system is currently used as a target discovery platform to study AML patient-derived cell interaction with the vascular niche, monitor leukemia-driven vascular aberration over time and interfere with candidate targets to hamper AML-niche pathologic cross-talk. Summary/Conclusion: Our approach allows the generation of a fully humanized BM vascular niche unit in a microscopy friendly environment to follow in real time the local vascular environment for normal and malignant hematopoiesis with multimodal microscopy and molecular approaches, in order to develop targeted therapy that can normalize the vessels in BM diseases and promote better therapeutic success in patients.Keywords: Acute myeloid leukemia, Endothelial cell, Bone marrow microenvironment, Angiogenesis