ACKR3 and plasma cell myeloma: The small-molecule CXCR4 selective antagonist AMD3100, a once promising anti-HIV drug, currently approved for clinical use for lymphoma and multiple myeloma (for a review see [38]), has also been shown to be an allosteric ACKR3 agonist at high concentrations [39] activating βarrestin recruitment and increasing CXCL12 binding to ACKR3.