To determine whether myeloma cells induce CD84 and PD-L1 expression on their microenvironment, healthy donor–derived PB CD14+ cells were incubated alone or in the presence of 3 different human MM cell lines, MM.1S, U266, and KMS11, which do not express CD84 (Supplemental Figure 1, C and D), and PD-L1 and CD84 surface protein levels were analyzed after 48 hours. This evidence concerns the gene CD84 and plasma cell myeloma.