Suppressive properties of human CD4+CD25+ regulatory T cells are dependent on CTLA-4 expression.

It has been demonstrated that T cells with regulatory properties are present within the peripheral blood CD4+CD25+ T cell compartment. Here, we describe an original method to purify human CD4+CD25+CD152+ T lymphocytes as living cells by forcing the exportation of CTLA-4 molecules stored in intracellular vesicules at the cell surface. By doing so, we demonstrate that CD4+CD25+ T cells contain a smaller and more homogeneous population enriched in cells with in vitro regulatory activity. Moreover, we show that this enrichment in regulatory T cells is associated with an increased expression of Foxp3 and that CD4+CD25+CD152+ T lymphocytes display a much stronger suppressive activity in controlling in vitro proliferation of alloantigen-specific T cells than CD4+CD25+CD152– T lymphocytes purified in parallel. Lastly, by purifying such cells expressing CTLA-4, we demonstrate that indeed CTLA-4 is involved in CD4+CD25+CD152+ T cell regulatory activity, while suppressive cytokines are not.