Dynamic expression of Id3 defines the stepwise differentiation of tissue-resident regulatory T cells

Foxp3 + regulatory T (T R ) cells are phenotypically and functionally diverse, and broadly distributed in lymphoid and non-lymphoid tissues. However, the pathways guiding the differentiation of tissue-resident T R populations have not been well defined. By regulating E-protein function, Id3 controls the differentiation of CD8 + effector T cells and is essential for T R maintenance and function. We show that dynamic expression of Id3 helps define three distinct T R populations, Id3 + CD62L hi CD44 lo central (c)T R, Id3 + CD62L lo CD44 hi effector (e)T R and Id3 - eT R . Adoptive transfer experiments and transcriptome analyses support a stepwise model of differentiation from Id3 + cT R to Id3 + eT R to Id3 - eT R . Furthermore, Id3 - eT R have high expression of functional inhibitory markers and a transcriptional signature of tissue-resident T R . Accordingl Id3 - eT R are highly enriched in non-lymphoid organs, but virtually absent from blood and lymph Thus, we propose that tissue-resident T R develop in a multi-step process associated with Id3 downregulation.