(a) Percentages of CD4+CD39+CD25+ Treg in the peripheral circulation of HNSCC patients who are NED after CRT. The elevated Treg frequency in patients was independent of the time period elapsed between the last treatment and phlebotomy for this study. (b) In HNSCC patients treated with SRG alone, the Treg frequency was increased shortly after treatment but later appeared to normalize. (c) percentages of total CD4+ T cells were persistently decreased in CRT-treated patients. In a, b and c, the solid line represents the mean Treg (3.2%) or CD4+ T cell (42%) frequency established for NC, and the dotted lines show ± 1 SD of the mean. (d) Isolated CD4+CD39+ and CD4+CD39neg T cells obtained from 4 different NC were incubated in the presence of physiological concentrations of cisplatin for 48h. At the cisplatin concentration of 3ug/mL, the increase in frequency of ANXV+ cells was greater (p<0.03) among CD4+CD39neg Tconv than among CD4+CD39+ Treg.