DT-mediated Treg depletion increased CD11b+Gr-1hi MDSC in B16-bearing and naïve aged mice. (A–D) Young and aged mice challenged with B16 cells and treated as in Fig. 1. A, Prevalence and, B, numbers of spleen CD11b+Gr-1hi phenotypic MDSC in young versus aged naïve (No tumor) or tumor-bearing mice treated with PBS or DT. C, Spleen CD11b+Gr-1hi MDSC suppression at 1:1 Effector:MDSC ratio. D, Negative correlation between splenic CD11+Gr-1hi MDSCs and Foxp3+CD4+ splenic Tregs in aged but not in young tumor-bearing mice. E, Spleen CD11b+Gr-1hi cell numbers in young and aged B16-bearing Foxp3DTR mice treated with PBS or diphtheria toxin (Dipht. Tox). F, Spleen CD11b+Gr-1hi cell numbers in young and aged naïve Foxp3DTR mice treated with PBS or diphtheria toxin (Dipht. Tox). G, Spleen CD11b+Gr-1hi cell numbers in young or aged C57BL/6 mice challenged with MC-38 carcinoma and treated with PBS, DT, anti-Gr-1 or DT+anti-Gr-1.