CXCL12 and acute lymphoblastic leukemia: However, when the CXCR4 antagonist AMD3100 was added, the expression of CXCR4 and CXCL12 was reduced, which showed that blocking the CXCR4/CXCL12 axis results in sensitizing the relapsed/refractory ALL cells to chemotherapeutic agents [96].