Selective depletion of FOXP3(high) cells by Fas-Fas-L-induced apoptosis occurs in CD4(+)CD25(+)-enriched populations during repeated expansion.

Background Aims: Expansion of anti-CD25 bead-isolated human Tregs culture has paradoxically resulted in reduced suppressive activity, but the mechanism(s) responsible for these observations are poorly defined.

Methods: Magnetic-bead isolated human CD25(+) cells were expanded with anti-CD3/CD28 beads and high doses of rhIL-2. Detection of Fas and Fas ligand (Fas-L) expression, activation of Caspase 8, cell proliferation and cytokine production was evaluated by multi-color fluorescence-activated cell sorting analysis.