背景资料:Lymphocyte activation gene 3 (LAG-3; CD223) plays an important role in negatively regulating T cell proliferation, function and homeostasis. It is required for maximal natural and induced regulatory T cell (Treg) function. LAG-3 is closely related to the T cell co-receptor CD4 and binds to MHC class II molecules but with a significantly higher affinity than CD4.