ICOS and Alzheimer disease: ICOS+ Tregs preferentially produce IL‐10, whereas ICOS– Tregs use TGF‐β.37 Indeed, ICOS is believed to be part of a switch mechanism for IL‐10 production in Tregs.39 Here, we found impaired production of IL‐10 in the main immunosuppressive Treg population, that is, ICOS+ Tregs in AD patients, despite similar levels of cells with demethylated FOXP3i1. 35, 63 These results can be explained by the observation of increased ICOS+ Treg cell death after ex vivo restimulation.