Differential levels of MDSCs and CD40-expressing MDSCs in PBMCs from cancer patients (CP) and healthy donors (HD). (A) Representative FACS data from 4 HDs and 4 CPs. Age-matched PBMCs from HDs and CPs were stained with antibodies, and propidium iodide (PI) was added 10 minutes before FACS analysis. R1 and PI⁻ cell populations were gated, and the frequency of MDSCs (CD33⁺HLA-DR⁻ cells) is shown in the right lower quadrant. (B) CPs had significantly higher frequencies of MDSCs in PBMCs than HDs. PBMCs from HDs (n = 30) and untreated patients with metastatic breast cancer (Breast Ca, n = 9) or metastatic prostate cancer (Prostate Ca, n = 11) were evaluated. Statistical analysis was performed using an unpaired t test. (C) Higher frequency of CD40-expressing MDSCs in CPs than in HDs. Samples used in panel B were evaluated for CD40 expression on the MDSC population. The data shown in CPs were from all CPs (9 breast Ca and 11 prostate Ca). The results shown are representative of 2 experiments. Statistical analysis was performed using an unpaired t test. FSC indicates forward scatter; and SSC, side scatter.