We show that infection of mice with the chronic gastrointestinal helminth Heligmosomoides polygyrus drives rapid polyclonal expansion of Foxp3+Helios+CD4+ thymic (t)Tregs in the lamina propria and mesenteric lymph nodes while Foxp3+Helios−CD4+ peripheral (p)Treg expand more slowly. The gene discussed is FOXP3; the disease is infection.