CD11c^hiMHCII^lowDCs are the major source of myeloid-derived IL-10 in the BM of MM-relapsed mice. MM-bearing and naive (MM-free) recipients were transplanted as previously described with BM+T grafts from FoxP3-RFP × IL-10-GFP reporter donors. Recipients were sacrificed 8 weeks after SCT, BM and spleen were harvested, and cells were analyzed using flow cytometry. FACS plots are representative. (A) Gating strategy for IL-10–producing myeloid cells. (B) Expression of MHC class II (MHC II) and PD-L1 on CD11c^hiCD64⁻ DCs. (C) Frequency of MHCII^low/− DCs, cDCs and macrophages (CD64⁺CD11b⁺) within IL-10⁺ cells from the BM of MM-relapsed mice (n = 10 combined from 2 experiments). (D) Gating strategy and quantification of frequency and number of macrophages from the BM of MM-relapsed, MM-controlled, and MM-free mice and (E) F4/80 expression on BM macrophages and neutrophils (negative control) from MM-relapsed mice and (F) MHC II expression on BM macrophages from MM-relapsed, MM-controlled, and MM-free mice (n = 7-14 combined from 2 experiments). (G) Gating strategy and quantification of frequency and number and (H) histogram of MHC II expression on MHCII^low/− DCs and cDCs from the BM of MM-relapsed, MM-controlled, and MM-free mice (n = 7-14 combined from 2 experiments). (I) FLT3 (n = 4 from 1 experiment) and CD80 (n = 7 combined from 2 experiments) expression on MHCII^low/− DCs and cDCs from BM of MM-bearing mice. (J) Representative histograms of IL-10 production and geometric mean fluorescence intensity from macrophages, MHCII^low/− DCs, and cDCs from the BM of MM-relapsed, MM-controlled, and MM-free mice (n = 5-13 combined from 2 experiments). Data represent mean ± SEM. * P < .05, ** P < .01, *** P < .001 (Mann-Whitney U test). MΦ, macrophage; WBC, white blood cell.