CXCR4 and plasma cell myeloma: For this assay, we used MM.1S (multiple myeloma) and U937 (acute myeloid leukemia) cells with high endogenous CXCR4 expression (S1 Table in S1 File, S1 Fig in S2 File) [58], which showed a robust migration response to CXCL12 with a sub-nanomolar EC50 values (S2a, S2b Fig in S2 File).