The TGF‐b/SOX4 axis and ROS‐driven autophagy co‐mediate CD39 expression in regulatory T‐cells

The ectonucleotidase CD39 on human regulatory T‐cells (Treg) is an important immune regulator which is dysregulated in autoimmune diseases and cancer immunosuppression. We here define that CD39 expression on Treg is independent of the Treg‐specific transcription factors FOXP3 and HELIOS and promoted by canonical TGF‐b‐ and mTOR‐signaling. Furthermore, the TGF‐b mediated upregulation of CD39 is counteracted by reactive oxygen species (ROS)‐driven autophagy. In line, CD39(+) peripheral blood Treg constitute a distinct lineage with low autophagic flux and absent ROS production. Patients with rare genetic defects in autophagy show supraphysiological levels of CD39(+) Treg, validating our observations in vivo. These biological processes rely on a distinct transcriptional program with CD39(+) Treg expressing low levels of two genes with putative involvement in autophagy, NEFL and PLAC8. Furthermore, the TGF‐b downstream transcription factor SOX4 is selectively upregulated in CD39(+) Treg. Overexpression of SOX4 in Treg strongly increases CD39 expression, while Crispr/Cas9‐mediated knockout of SOX4 in Treg has the opposing effect. Thus, we identify a crucial role of SOX4 in immune regulation and provide new insights involving the interplay of tolerogenic cues and autophagy in Treg.