ACKR3 and neoplasm: The present experiments were performed with the human tumor cell lines, A549, DLD-1, and MDA-MB- 231, which we previously characterized for expression as well as their use of CXCR4, CXCR3, and CXCR7 in CXCL12- and CXCL11-dependent chemotaxis [6, 15] (additional file 2).