T-regulatory (Treg) cells suppress the immune response to maintain homeostasis. There are 2 main subsets of Treg cells: FOXP3-positive Treg cells, which do not produce high levels of effector cytokines, and type 1 Treg (Tr1) cells, which are FOXP3-negative and secrete interleukin 10 (IL10). IL10 is an anti-inflammatory cytokine, so Tr1 cells might be used in treatment of inflammatory bowel diseases. We aimed to develop methods to isolate and expand human Tr1 cells and define their functions.