Hi guys, thank you very much for reading my question. To study the phenotype of MDSCs in the tumor microenvironment, I resected the mouse tumor (subcutaneous xenograft), cut it into small pieces, digested it into single cell suspension with collagenase II and IV, removed the dead cells using Dead Cell Removal Kit (Miltenyi, 130-090-101), and isolated PMN-MDSC and M-MDSC using the Miltenyi MDSC Isolation Kit (130-094-538) according to the manufacturer's protocol. The viability of cells was pretty good as revealed by Trypan Blue staining during and after the magnetic sorting. But it seems that the purity of the sorted MDSC was very poor, as shown in the FACS results below. Do anyone know what is the problem and how can I optimize the protocol? Thanks very much!