Other leukemia-associated factors released into the extracellular space and present in the CSF include soluble L-selectin (sL-selectin) [29], interleukin-2 receptor-α (sIL2-Rα) [30], the chemokine CXCL13 [41], interleukin 7 receptor (IL7R) [31], the chemokine receptor CCR7 [42], monocyte chemotactic protein (CCL2), vascular endothelial growth factor 1 and 2 (VEGF 1 and 2) [32], and osteopontin [33]. Here, IL7R is linked to leukemia.