Tuesday, September 6, 2016

Foxp3+ Tregs control CD8 T cells, but not CD4 T cells, by IL-2 deprivation

This week Nature Immunology published another interesting study from Rudensky's lab done in collaboration with Jason Fontenot (who apparently moved from Biogen to Juno Therapeutics). So, if you are a fan of Tregs, below is my short scientific overview of that paper.

This study tries to answer what role IL-2 signaling plays in already established Foxp3+ Tregs. For such study mice with germline deficiency in IL-2 signaling cascade would have been impractical since IL-2's effect on thymocytes and etc. Instead, the authors went to already well established path of using mice lacking "molecule of interest" specifically in Tregs. In this case several Foxp3-cre mice were used, such as: l2rbfl/flFoxp3Cre, Il2rafl/flFoxp3Cre, Stat5afl/flStat5bfl/flFoxp3Cre, Rosa26Stat5bCAIl2rbfl/flFoxp3Cre and Rosa26Stat5bCAIl2rafl/flFoxp3Cre, Rosa26Stat5bCAFoxp3Cre–ERT2. All these gene-modified mice allows specific targeting of Foxp3+ Tregs.

Unsurprisingly, mice lacking IL-2Rβ or IL-2Rα or STAT5 signaling specifically in Tregs developed autoimmunity.

Surprisingly, however, while constitutive expression of STAT5 in Tregs lacking IL-2 signaling receptors (IL-2Rβ or IL-2Rα) could rescue mice from "CD4 effector phenotype" and early death, these mice still developed immunopathology later due to massive expansion of CD8 effector/memory cells, suggesting that sensing of IL-2 by Tregs, so called "IL-2 sink", was necessary to specifically control CD8 T cells, but not CD4 T cells.

In summary, this study suggests that Tregs are using distinct mechanisms to control CD4 and CD8 T cells. It kind of makes sense because MHC class-II restricted CD4+ Tregs cannot interact the same way with MHC class-I restricted CD8+ T cells as they could with conventional MHC class-II restricted conventional CD4+ T cells.

David Usharauli

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