Small portion of human CD4⁺ memory T cells can be converted to Foxp3⁺ T cells <i>in</i><i>vitro</i>.

<p>(A) CD4⁺ naive (Tn) and memory (Tm) T cells were sorted and activated with plate-bound anti-CD3 (5 μg/ml) and soluble anti-CD28 (1 μg/ml) in the presence or absence of TGF-β (5 ng/ml) and IL-2 (100 UI/ml). Foxp3 expression was analysed by flow cytometry at different time points as indicated. (B) The average percentages of Foxp3 expression in CD4⁺ naive and memory T cells on day 5 after TGF-β and IL-2 induction. (C) and (E) Flow cytometric analysis of CTLA-4 (extracellular and total), PD-1, and PD-L1 expression in total, freshly sorted, naive (Tn) or memory (Tm) CD4⁺ T cells. (D) and (F) Sorted CD4⁺ naive (Tn) or memory (Tm) T cells were activated for 5 days as described above, and the total population was analysed using flow cytometry for the expression of CTLA-4 (extracellular and total), PD-1, and PD-L1.