MDSC were isolated from splenocytes by positive selection with FITC anti-Ly6C, PE anti-Ly6G, or PE anti-Gr1 using anti-FITC or anti-PE microbeads (Miltenyi Biotec), as described (12 , 14 (link)). DC were isolated by CD11c immunomagnetic bead selection and γ-irradiated (20 Gy). T cell proliferation was assessed at 72 h by [3H] TdR incorporation or CFSE dilution (Invitrogen).