Tr1 Cells 

How they are generated

Tr1 cells are obtained by repetitive stimulation in vitro with IL10. IL-10 is required for the differentation of Tr1 cells, but is not sufficient when T cells are activated in the absence of professional APCs. In vitro manipulation with immunosuppressive drugs and anti-IL-4 and anti-IL12 antibodies has facilitated the expansion of Tr1 cells that exclusively secrete IL-10. 

Whether Tr1 cells and CD4+CD25+ Tregs are T cell subsets, which are totally different form each other, or are the same cells but which differ in their differentiation activation stage remains unkown. 

In the human, lymphoid DCs have been shown to polarize naive CD4+ or CD8+ T cells toward IL-10 production when infected by viruses that result in high levels of IFNalpha production and low levels of IL-12. Importantly, the IL-10 producing CD8-T cells display regulatory activity in vitro. 

Treatment of myeloid DCs with IFNalpha results in a population of APCS that induce IL10 producing cells. Alternatively, it has been shown that  results in a population of IL-10 producing T cells with suppressive properties. It is possible that any compound that prevents or alters the maturation of DCs may promote the generation of Tr cells specific for the antigens presented by the modulated DCs. Much evidence indicates that priming with DCs treate with compounds such as vitamin D3 and/ dexamethasone, which reduce or alter DC maturation results in reduced T cell resposnes and in some cases differentiation into Tr cells. 

A Th1 mediated colitis develops in SCID mice after transfer of CD45RBhigh CD4+ T cells. This colitis is prevented by cotransfer of a CD45RBlow subset. The phenotype of this CD45RBlow CD4+ is similar to Tr-1 cells in that they can produce IL-10 but not IL-4 and inhibit T cell activaiton in vitor and in vivo. It is likely that this subset represents the in vivo counterpart of in vitro derived Tr1 cells. IL-10 was an essential mediator of the function of thee T regs in that cotransfer of CD45RBlow CD4+ cells from IL-10 -/- mice fialed to protect mice from colitis. Treatment with an anti-murine IL-10 receptor monoclonal antibody also abrogated inhibition of colitis m ediated by WT CD45RBlow CD4+ cells.

Phenotype

T cells, from ovalbumin (OVA) T-cell receptor (TCR)-transgenic mice, cultured with OVA and IL-10 result in the generation of T cell clones with a unique cytokine profile distinct from that of Th0, Th1 or Th2 cells. These Tr1 cells produce IL-10 and IL-5 with or without TGF-?, but with little or no IL-2, IL-4, or IFNy production, and proliferate poorly following polyclonal TCR mediated activation. Tr1 clones with a similar phenotype have also been generated by repetitive stimulation of murine TCR transgenic CD4+ T cells with their cognate peptide plus IL-10. 

IL-10 may mediate its function via DCs because IL-10 prevents the maturation of DCs and stimulation of T cells with immature DCs leads to the development of T cells with regulatory activity. 

In the resting state, Tr1 cell clones epxress a large repertoire of chemokine receptors, including those previously associated with the Th1 phenotype, such as CXCR3 and CCR5 or the Th2 phenotpye, such as CCR3, CCR4 and CCR8. Interestingly, Tr1, but not Th1 and Th2 cell clones express CCR7. 

Functional Characteristics: 

Functional studies on Tr1 cells suggest that these cells have immunosuppressive properties and prevent the development of Th1-mediated autoimmune diseases. However, Tr1 and other Tr cell populations also suppress immune responses to pathogens, tumors and alloantigens. Co-culture of naive CD4+T cells and human Tr1 clones in the presence of allogenic antigen presenting cells (APCs) results in the suppression of proliferative responses. Similarly, Tr1 clones specific for filamentous haemaggultinin (FHA) from Bordetella pertussis suppress proliferation and cytokine production by a Th1 clone against an unrelated antigen, influenza virus haemagglutinin (HA). In both cases, the suppressive effects of Tr1 cell clones are reversed by neutralizing IL-10, suggesting that, regardless of their antigen specifities, Tr1 cell suppression is a bystander effect mediated through the production of IL-10.

The supressive effects of Tr1 cell clones on CD4+ T cells are reversed by neutralising anti-TGFB and/or anti-IL-10 mAbs.