3d multicellular spheroid for the study of human hematopoietic stem cells: Synergistic effect between oxygen levels, mesenchymal stromal cells and endothelial cells

Introduction: The human bone marrow microenvironment is composed of biological, chemical and physical factors that act in a synergistic way to modulate hematopoietic stem cell biology, such as mesenchymal stromal cells (MSCs), endothelial cells (ECs) and low oxygen levels; however, it is difficult to mimic this human microenvironment in vitro. Methods: In this work, we developed 3D multicellular spheroid (3D-MS) for the study of human hematopoietic stem cells (HSCs) with some components of perivascular niche. HSCs were isolated from umbilical cord blood, MSCs were isolated from human bone marrow and a microvasculature EC line (CC-2811, Lonza®) was used. For the formation of a 3D structure, a magnetic levitation culture system was used. Cultures were maintained in 21%, 3% and 1% O₂ for 15 days. Culture volume, sphericity index and cell viability were determined. Also, human HSC proliferation, phenotype and production of reactive oxygen species were evaluated. Results: After 15 days, 3D-MS exhibited viability greater than 80%. Histology results showed structures without necrotic centers, and higher cellular proliferation with 3% O₂. An increase in the expression of the CD34 antigen and other hematopoietic antigens were observed to 1% O₂ with MSCs plus ECs and low ROS levels. Conclusion: These findings suggest that 3D-MS formed by MSCs, ECs and HSCs exposed to low concentrations of oxygen (1–3% O₂) modulate human HSC behavior and mimics some features of the perivascular niche, which could reduce the use of animal models and deepen the relationship between the microenvironment of HSC and human hematological diseases development.