Liu, et al.. Umbilical Cord Mesenchymal Stem Cells Inhibit the Differentiation of Circulating T Follicular Helper Cells in Patients with Primary Sjögren's Syndrome Through the Secretion of Indoleamine 2,3-dioxygenase. Oxford University Press (OUP), Aug. 2014, doi:10.1093/rheumatology/keu316.