title: Single-cell analysis of the human T regulatory population uncovers functional heterogeneity and instability within FOXP3+ cells.
abstract: Natural FOXP3(+)CD4(+)CD25(High) regulatory T cells are critical in immunological self-tolerance. Their characterization in humans is hindered by the failure to discriminate these cells from activated effector T cells in inflammation. To explore the relationship between FOXP3 expression and regulatory function at the clonal level, we used a single-cell cloning strategy of CD25-expressing CD4(+) T cell subsets from healthy human donors. Our approach unveils a functional heterogeneity nested within CD4(+)CD25(High)FOXP3(+) T cells, and typically not revealed by conventional bulk assays. Whereas most cells display the canonical regulatory T (T(reg)) cell characteristics, a significant proportion of FOXP3(+) T cells is compromised in its suppressive function, despite the maintenance of other phenotypic and functional regulatory T hallmark features. In addition, these nonsuppressive FOXP3(+) T cells preferentially emerge from the CD45RO(+) memory pool, and arise as a consequence of a rapid downregulation of FOXP3 expression upon T cell reactivation. Surprisingly, these dysfunctional T(reg) cells with unstable FOXP3 expression do not manifest overt plasticity in terms of inflammatory cytokine secretion. These results open a path to an extensive study of the functional heterogeneity of CD4(+)CD25(High)FOXP3(+) T(reg) cells and warrant caution in the sole use of FOXP3 as a clinical marker for monitoring of immune regulation in humans.
authors.affiliation: Department of Microbiology and Immunology, McGill University, Montreal, Quebec H3A 2B4, Canada.
authors.forename: Eva
authors.initials: E
authors.lastname: d'Hennezel
authors.forename: Ekaterina
authors.initials: E
authors.lastname: Yurchenko
authors.forename: Evridiki
authors.initials: E
authors.lastname: Sgouroudis
authors.forename: Valérie
authors.initials: V
authors.lastname: Hay
authors.forename: Ciriaco A
authors.initials: CA
authors.lastname: Piccirillo
mesh_terms: D015703:Antigens, CD / Q000032:analysis / Q000276:immunology; D015415:Biomarkers / Q000032:analysis; D002999:Clone Cells / Q000276:immunology; D051858:Forkhead Transcription Factors / Q000032:analysis* / Q000235:genetics; D006801:Humans; D007156:Immunologic Memory / Q000276:immunology; D018836:Inflammation Mediators / Q000032:analysis; D008213:Lymphocyte Activation / Q000276:immunology; D017634:Self Tolerance / Q000276:immunology; D050378:T-Lymphocytes, Regulatory / Q000166:cytology / Q000276:immunology*
chemical_list: D015703:Antigens, CD; D015415:Biomarkers; C418974:FOXP3 protein, human; D051858:Forkhead Transcription Factors; D018836:Inflammation Mediators