Although studies indicate that ICOS is not required for the induction of adaptive Foxp3+ Treg cells in vitro 47, LP Helios−Foxp3+ Treg cells failed to expand in ICOS−/− mice in response to H. polygyrus suggesting that ICOS is required for intestinal adaptive Foxp3+ Treg-cell responses during infection. Here, FOXP3 is linked to infection.