Figure 5. Blocking CD84 induces T cell–mediated killing of human MM cells.

(A and B) PB CD14⁺ cells (A) or T cells (B) from a healthy donor were cultured alone or with MM.1S MM cell line cells at a ratio of 1:2, in the presence or absence of the anti-CD84-inhibitory (B4) or control antibodies. After 48 hours, PD-L1 (A) or PD-1(B) cell surface levels were determined by flow cytometry (n = 3). Representative plots are shown. (C) Purified PBMCs from healthy donors were treated with IgG or B4 antibodies. After 24 hours, the cells were cocultured with GFP⁺ MM.1S at a ratio of 6:1 for 16 hours. The percentage of 7AAD staining on GFP⁺ MM.1S cells was determined by flow cytometry. Representative histograms are shown (n = 3). (D–I) Primary MM BM aspirates were treated with B4 or IgG2a antibodies. After 48 hours, the percentage of MM cells (D, left graph) and annexin V staining (D, right graph), as well as PD-L1 expression (E), were determined by flow cytometry. Representative histograms, showing the percent of annexin V⁺ cells or B4-treated cells, are shown (n = 4–6). (F–I) M-MDSCs (F and G), and G-MDSCs (H and I) were incubated with control or B4 antibodies. Percentage of cells (F and H) and PD-L1 expression (G and I) following treatment were determined by FACS. Representative plots or histograms are shown (n = 4–5). (J and K) The percentage of CTLA-4, LAG-3, and PD-1 on CD4⁺ (J) and CD8⁺ (K) T cells from whole MM BM aspirates treated with B4 or IgG2a control antibodies was analyzed using flow cytometry. Representative histograms are shown (n = 5–7). *P < 0.05, **P < 0.01, ****P < 0.0001, with unpaired or paired t test for pairwise comparisons.