CD4⁺CD25⁺ cells from umbilical cord blood of normal-term infants are phenotypically similar to those from adult peripheral blood.

(A) Cord blood mononuclear cells were isolated and stained with anti-CD4–QR, anti-CD25⁻ PE, and FITC-conjugated monoclonal antibodies as indicated (middle panel). The dot plots were gated on CD4⁺ lymphocytes as shown in the top panel. Peripheral mononuclear cells from cord blood were stained with anti-CD4–QR, anti-CD25⁻ FITC, and anti–CTLA-4–PE (thin solid lines) or isotype-matched control (thick solid lines). The histogram plot was gated on CD4⁺CD25⁺ or CD4⁺CD25⁻ lymphocytes (bottom panel). (B) Limiting dilution analyses using CD4⁺ (♦) or CD4⁺CD25⁻ (■) cells as responder cells. Serial dilutions of responder cells were cocultured with allogeneic irradiated PBMCs (5 × 10⁴) for 5 days. Control wells contained stimulator cells only.