In the homing of B cell progenitor ALL cells to the BM, CXCL12-mediated activation of p38MAPK was required [51], and those with high CXCR4 expression had more significant liver or spleen infiltration than those with low CXCR4 expression in pediatric B-ALL patients [46]. Here, CXCL12 is linked to acute lymphoblastic leukemia.