CXCR4 and B-cell chronic lymphocytic leukemia: Low expression levels of CXCR4 were previously (Burger, Burger & Kipps, 1999; Okkenhaug & Burger, 2016) seen in the proliferating CLL cells in bone marrow and lymph nodes, while the circulating CLL cells were found to express high levels of CXCR4.