Cord blood CD4⁺CD25⁺ cells are a distinct population. Representative 2-color FACS plots of PBMCs, CBMCs, and purified CD4⁺CD25⁺ cells from both adult and cord blood sources. (A) Examination of cord blood reveals a distinct population of CD4⁺ and CD25⁺ cells. There is a wide separation of the CD25⁺ cells from the CD25^- cells. (B) Examination of peripheral blood reveals CD4⁺CD25⁺ cells constitute 1% to 2% of PBMCs. There are many CD25^dim cells (arrow). (C) CD25⁺ cells purified from cord blood by direct anti-CD25 microbeads are a more pure population. (D) CD25⁺ cells purified from adult blood by direct anti-CD25 microbeads. Representative of 10 donors and 10 cell purification experiments.