LAG-3 (CD223) molecule is preferentially expressed in human CD4+CD25+ T cells displaying suppressor activity

221 LAG-3 (CD233) molecule is expressed on activated NK cells and CD4 + and CD8 + T lymphocytes and binds MHC class II molecules with a higher affinity than CD4. Studies in mice have indicated that this molecule has a complex role in controlling T cell functions and that it is directly involved in mediating the activity of murine Treg cells. We studied the expression of CD233 in different human T cell subsets of healthy donors: We found that, although expressed also by CD25-CD4+ T cells, CD233 is strongly up-regulated in naturally occurring CD4+CD25+ T cells and its level of expression is further enhanced in in vitro stimulated CD4+CD25+ T cells. In freshly isolated CD4+CD25+ T cells CD233 is often associated to the expression of CD45RO, HLA-DR, CD71, CD122, CD62L and to the high level of CD25. Moreover, inside the naturally CD4+CD25+ T cells or in in vitro allo-activated CD4+CD25+ T cells, CD233 defined a subset of cells showing high amount of Foxp3 expression. Functional studies using CD4+CD25+CD233+ T cells sorted from in vitro activated CD4+CD25+ showed that this T cell subset displayed potent suppressor activity if compared to the CD233 negative counterpart or to the unsorted population. Stage III-IV metastatic melanoma and colorectal cancer patients did show an increased frequency of CD4+CD25+CD233+ T cells in their PBMC as compared to healthy individuals. Moreover tumor invaded lymph nodes included CD4+ CD25 brigh T cells expressing Foxp3 and CD233. Altogether, our data strongly suggest that, when used in combination with CD25, CD233 could be considered a good marker to define regulatory T cells with enhanced suppressor activity.