While circulating in the endothelium-lined hollow fiber system, (A) CLL cells experience strong shear forces and short-lived contacts with endothelial cells, resulting in their increased expression of CD5, CD62L, CXCR4, and CD49d. (B) Compared with the circulating bulk, the collected transmigrated subpopulation of CLL cells is characterized by increased expression of CD69, CD80, CD49d, CD38, and MMP9.