Separation of human CD4+CD39+ T cells by magnetic beads reveals two phenotypically and functionally different subsets

ObjectiveThe ectonucleotidase CD39 is an enzyme involved in adenosine production. Its surface expression on human regulatory T cells (Treg) allows for their flow-cytometry-based isolation from peripheral blood. To further develop and improve this method on a scale supporting translational studies, we introduced capture of CD39+ Treg on magnetic immunobeads.MethodsPeripheral blood mononuclear cells (PBMC) obtained from healthy donors were used for negative selection of CD4+ T cells on AutoMACS using antibodies (Abs) specific for all lineage+ cells. CD4+CD39+ Treg were captured by biotin-conjugated anti-CD39 Abs and anti-biotin Ab-coated magnetic beads. Isolated CD4+CD39+ T cells were phenotyped by flow cytometry for Treg-associated markers: CD39, CD73, FOXP3, CD25, CTLA-4, CCR4, CD45RO and CD121a or for the absence of CD127 and CD49d. CFSE-based proliferation assays and ATP hydrolysis were used to measure Treg functions.ResultsThe purity, recovery and viability of the separated CD4+CD39+ T cells were satisfactory. The isolated CD4+CD39+ T cell population consisted of FOXP3+CD25+ T cells which hydrolyzed exogenous ATP and suppressed autologous CD4+ T cell proliferation and of FOXP3negCD25neg T cells without suppressor function. The same two subsets were detectable by flow cytometry in normal PBMC, gating on CD4+CD39+, CD4+CD127neg, CD4+CD49dneg or CD4+CD25high Treg.ConclusionCD4+CD39+ Treg capture on immunobeads led to a discovery of two CD39+ subsets. Similar to CD39+ Treg in the peripheral blood, half of these cells are CD25+FOXP3+ active suppressor cells, while the other half are CD25negFOXP3neg and do not mediate suppression.