Description:
<jats:title>Abstract</jats:title>
<jats:p>Human natural regulatory CD4+ T cells comprise 5–10% of peripheral CD4+T cells. They constitutively express the IL-2Rα−chain (CD25) and the nuclear transcription Foxp3. These cells are heterogeneous and contain discrete subsets with distinct phenotypes and functions. Studies in mice report that LAG-3 has a complex role in T cell homeostasis and is expressed in CD4+CD25+ T regulatory cells. In this study, we explored the expression of LAG-3 in human CD4+ T cells and found that LAG-3 identifies a discrete subset of CD4+CD25highFoxp3+ T cells. This CD4+CD25highFoxp3+LAG-3+ population is preferentially expanded in the PBMCs of patients with cancer, in lymphocytes of tumor-invaded lymph nodes and in lymphocytes infiltrating visceral metastasis. Ex vivo analysis showed that CD4+CD25highFoxp3+LAG-3+ T cells are functionally active cells that release the immunosuppressive cytokines IL-10 and TGF-β1, but not IL-2. An in vitro suppression assay using CD4+CD25highLAG-3+ T cells sorted from in vitro expanded CD4+CD25high regulatory T cells showed that this subset of cells is endowed with potent suppressor activity that requires cell-to-cell contact. Our data show that LAG-3 defines an active CD4+CD25highFoxp3+ regulatory T cell subset whose frequency is enhanced in the PBMCs of patients with cancer and is expanded at tumor sites.</jats:p>