Quantitative Proteomics Reveals Specialized Wiring of Signaling Pathways that Protects Human Regulatory T Cell Identity - 2 populations in vitro

Regulatory CD4+ T cells (Tregs) are functionally distinct from conventional CD4+ T cells (Tconvs). To understand Treg identity, we compared by proteomics and transcriptomics human naïve (n) and effector (e)Tregs, Tconvs and transitional FOXP3+ cells. Only 12% of 422 differentially expressed proteins was identified as such at the mRNA level, demonstrating the importance of direct proteome measurement. Fifty-one proteins discriminated Tregs from Tconvs. This common Treg protein signature indicates altered signaling by TCR-, TNF receptor-, NFB-, PI3 kinase/mTOR-, NFAT- and STAT pathways, and unique cell biological and metabolic features. Another protein signature uniquely identified eTregs and revealed active cell division, apoptosis sensitivity and suppression of NFB- and STAT signaling. eTreg fate appears consolidated by FOXP3 outnumbering its partner transcription factors. These features explain why eTregs cannot produce inflammatory cytokines, whereas transitional FOXP3+ cells can. Collectively, our data reveal that Treg identity is defined and protected by uniquely “wired” signaling pathways.