title: Ex vivo expansion of human Tregs by rabbit ATG is dependent on intact STAT3-signaling in CD4⁺ T cells and requires the presence of monocytes.
abstract: The addition of low, nondepleting doses of rabbit antithymocyte globulin (ATG) to human peripheral blood mononuclear cells has been shown to expand functional CD4(+) CD25(+) FoxP3(+) regulatory T cells (Tregs) in vitro. This report is the first to elucidate the exact cellular mechanisms of ATG-mediated Treg expansion. CD4(+) T cells require monocytes, but not other antigen presenting cell subsets, to be present in coculture to expand Tregs. However, T cells do not require direct cell-cell contact with monocytes, suggesting the importance of soluble factors. Moreover, ATG initially "reprograms" CD4(+) T cells, but not monocytes, and induces STAT3 and STAT5 signaling in CD4(+) cells. These reprogrammed CD4(+) T cells subsequently secrete GM-CSF and IL-10 only in case of intact STAT3 signaling, which in turn promote the generation of tolerogenic CD14(+) CD11c(+) dendritic cells characterized by enhanced IL-10 and decreased IL-12 production. Treg expansion following ATG treatment is accompanied by enhanced gene expression of both GM-CSF and Bcl-2, but not TGF-β, in peripheral blood mononuclear cells. These results demonstrate that ex vivo expansion of human Tregs by ATG is due to its ability to reprogram CD4(+) T cells in a STAT3-dependent but TGF-β-independent manner, leading to the generation of monocyte-derived dendritic cells with a tolerogenic cytokine profile.
authors.affiliation: Transplantation Research Center, Brigham and Women's Hospital and Children's Hospital Boston, Harvard Medical School, Boston, MA, USA.
authors.forename: O
authors.initials: O
authors.lastname: Boenisch
authors.forename: M
authors.initials: M
authors.lastname: Lopez
authors.forename: W
authors.initials: W
authors.lastname: Elyaman
authors.forename: C N
authors.initials: CN
authors.lastname: Magee
authors.forename: U
authors.initials: U
authors.lastname: Ahmad
authors.forename: N
authors.initials: N
authors.lastname: Najafian
mesh_terms: D000818:Animals; D000961:Antilymphocyte Serum / Q000494:pharmacology*; D015496:CD4-Positive T-Lymphocytes / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D049109:Cell Proliferation / Q000187:drug effects*; D002478:Cells, Cultured; D016207:Cytokines / Q000235:genetics / Q000378:metabolism; D003713:Dendritic Cells / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D005434:Flow Cytometry; D016178:Granulocyte-Macrophage Colony-Stimulating Factor / Q000235:genetics / Q000378:metabolism; D006801:Humans; D007166:Immunosuppressive Agents / Q000494:pharmacology*; D007963:Leukocytes, Mononuclear / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D009000:Monocytes / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics; D011817:Rabbits; D060888:Real-Time Polymerase Chain Reaction; D050796:STAT3 Transcription Factor / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects; D050378:T-Lymphocytes, Regulatory / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D016212:Transforming Growth Factor beta / Q000235:genetics / Q000378:metabolism
chemical_list: D000961:Antilymphocyte Serum; D016207:Cytokines; D007166:Immunosuppressive Agents; D012333:RNA, Messenger; D050796:STAT3 Transcription Factor; D016212:Transforming Growth Factor beta; D016178:Granulocyte-Macrophage Colony-Stimulating Factor