One of the major challenges in the successful clinical translation of cell-based therapy is the inefficient delivery or targeting of systemically infused cells to desired sites3,4. Consequently, there is a constant search for approaches to improve cell homing, and specifically cell rolling, as a strategy to improve cell therapy. Cell rolling on blood vessels is a key step in the cell homing cascade, classically defined for leukocytes that are recruited to disease sites5. This step is governed by specific interactions between endothelial selectins, i.e. P-and E-selectin (P-and E-sel), and their counter ligands on the surface of leukocytes5,6. Better understanding and improved efficiency of cell homing, and specifically the rolling step, are of great importance in the quest for new platforms to improve cell-based therapy. To date this has been achieved by using parallel plate flow chambers (PPFCs), comprising two flat plates with a gasket between them, with an inflow and outflow port located on the upper plate, through which a cell suspension is perfused by using a syringe pump7,8 ,9. The surface of the bottom plate can be coated with a relevant cell monolayer/substrates and the interaction between perfused cells and the surface under shear flow is then explored7. However, PPFC is a low throughput, reagent-consuming, and fairly tedious method, with bubble formation, leakage, and poorly controlled flow presenting major drawbacks.
An alternative technique to the traditional PPFC is a multi-well plate microfluidic system, permitting higher throughput performance of cellular assays (up to 10 times higher than PPFCs) under accurate, computer-controlled shear flow, with low reagent consumption1,10. Cell rolling experiments are performed inside the microfluidic channels, which can be coated with cell monolayers or engineered substrates and imaged using a microscope, with rolling properties readily analyzed using a suitable software. In this study, we demonstrate the capabilities of this multi-well plate microfluidic system by studying the rolling properties of human promyelocytic leukemia (HL-60) cells on different surfaces. HL-60 rolling on substrates like P-and E-sel, as well as on cell monolayers expressing different rolling receptors, was analyzed. In addition, antibody (Ab) blocking was used to demonstrate direct involvement of specific selectins in mediating the rolling movement of HL-60 on those surfaces. Rolling experiments were performed with increased throughput, under stable shear flow, with minimal reagent/cell consumption, allowing efficient analysis of key rolling parameters such as rolling velocity, number of rolling cells, and rolling path properties.