Characterization of naturally occurring CD4+CD25+ regulatory T cells in rhesus monkeys

BACKGROUND. Translational research in a relevant preclinical model is recommended before Treg-inducing protocols can be implemented in humans. We have characterized rhesus monkey CD25 cells phenotypically and functionally. METHODS. The phenotype of CD4CD25 cells was determined by FACS, focusing on established markers of mouse and human Treg cells. Percentages of cells positive for CD45RA, CD62L, and intracellular CTLA-4 and FOXP3 were compared between CD4CD25 and CD4CD25 cells. CD25 cells stimulated with anti-CD3, ConA, and/or allogeneic peripheral blood mononuclear cells were mixed with freshly isolated CD25 cells. The suppressive activity of the CD25 cells in vitro was assessed using several experimental conditions. RESULTS. Rhesus monkey CD4CD25 cells expressed high intracellular levels of CTLA-4 and FOXP3, whereas expression was negligible in CD4CD25 cells. The CD25 population was mostly CD45RA, indicative of a memory phenotype. The CD25 cells were anergic, because they showed low proliferative responses, no interleukin-2 production, and some interferon-γ and interleukin-10 production. Proliferation of CD4CD25 cells stimulated by anti-CD3 or allogeneic cells was decreased when CD4CD25 cells were added at a 1:1 ratio. In addition, we found that CD25 cells inhibited the interleukin-2 and interferon-γ production by anti-CD3-stimulated CD25 cells in a dose-dependent fashion, through a cell-cell contact-dependent mechanism. CONCLUSIONS. Rhesus monkey CD4CD25 cells have similar phenotypic and functional characteristics as natural Tregs in humans. These findings allow testing of Treg expansion and induction protocols in a relevant preclinical model, the rhesus monkey.

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