Shear Stress and Microbubble-Mediated Modulation of Endothelial Cell Immunobiology

Cellular immunotherapy remains hindered in the context of solid tumors due to the immunosuppressive microenvironment, in which key endothelial cell adhesion molecules (CAM) are suppressed. Microbubble-mediated focused ultrasound is being explored for targeted immunotherapy and can exert local shear stress upon neighboring endothelial cells. However, fluid and microbubble-induced shear modulation of endothelial immunobiology is not well understood. Herein, the influence of both types of shear stress on human endothelial vein (HUVEC) and brain endothelial (HBEC-5i) CAM expression and secretion of over 90 cytokines using acoustically coupled microscopy is examined. Fluid flow results in time-dependent modulation of CAM expression, where ICAM-1 peaked at 4 h (1.98-fold, p < 0.001, HUVEC) and 24 h (1.56-fold, p < 0.001, HBEC-5i). While some chemokines are significantly enhanced (up to 16.2-fold; p < 0.001) from both endothelial cell types (e.g., IL-8, MCP-1, MCP-3), others are differentially expressed (e.g., CCL5, CXCL-16, SDF-1). Under ultrasound, ICAM-1 expression at 4 h increased (≈1.4-fold, p < 0.01) and resulted in significant large-magnitude (p < 0.05) differential expression of 20 cytokines, most of which have immune-activating function and within a subset of those induced by shear-flow. Microbubble-mediated ultrasound regulates ICAM-1 expression and the human endothelial secretome toward an immune cell recruitment paradigm, and thus may reinforce solid tumor cellular immunotherapy efforts.