Recently alloactivated CD4+CD8−CD25+T regulatory cells express CD8alpha and are potent suppressor cells

Abstract

Abstract Therapy with antigen-specific CD4+CD25+ T regulatory cells (Treg) for induction of transplant tolerance is desirable, as naïve thymic Treg (tTreg) are non-antigen specific and weak suppressor cells. Naïve tTreg from DA rats cultured with fully allogeneic PVG stimulator cells and IL-2 express IFN-gamma receptor (IFNGR) and IL-12 receptor beta2 (IL-12Rb2) and are more potent alloantigen-specific regulators that we call Ts1 cells. This study examined other markers that could identify the activated alloantigen-specific Treg as a subpopulation within the CD4+CD25+Foxp3+Treg. After culture of naïve DA CD4+CD8−CD25+T cells with rIL-2 and PVG alloantigen, CD8a was expressed on 10–20% and CD8b on <5% of these cells. RT-PCR showed the CD8+ cells had increased Ifngr that characterizes Ts1 cells as well was Irf4, a transcription factor induced by TCR activation. Proliferation induced by re-culture with rIL-12 and alloantigen was greater with CD4+CD8+CD25+Treg consistent with the CD8a+ cells expressing IL-12R. In MLC, the CD8+ fraction had greater suppression than the mixed Ts1 population, whereas the CD4+CD8−CD25+T cells had less suppression. In an adoptive transfer assay, rIL-2 and alloantigen activated Treg suppress rejection at a ratio of 1:10 with naïve effector cells, whereas alloantigen and rIL-2 activated tTreg depleted of the CD8a cells did not prevent rejection. This study showed the expression of CD8alpha by rIL-2 and alloantigen activation of CD4+CD8−CD25+Foxp3+T cells was a marker of alloantigen-specific Treg and may be of use to enrich alloantigen-specific Treg.