Updated publication reference for PubMed record(s): 28993769. Regulatory T cells (Tregs) suppress other immune cells and are indispensable for human health, yet the molecular mechanisms of suppression remain incompletely understood. Tregs can suppress proliferation and cytokine production of CD4+CD25- conventional T cells (Tcons). We previously demonstrated that human Tregs rapidly suppress T cell receptor (TCR)-induced calcium, NFAT and NF-κB pathways in Tcons, leading to inhibition of effector cytokine transcription (Schmidt A et al., Science Signaling 2011 Dec 20;4(204):ra90. doi: 10.1126/scisignal.2002179). Due to the short time period required to induce suppression, it is probable that Tregs alter protein modifications, such as (de)phosphorylations, in suppressed Tcons to cause this inhibition of particular TCR signaling events, while de novo production of repressor proteins seems unlikely. Thus, in order to identify causative factors which initiate rapid Treg-mediated suppression of Tcons, we compared phosphoproteomes of 5 minutes TCR-stimulated responder Tcons re-isolated from cocultures with primary human Tregs with those from control cocultures (Tcons cocultured with other Tcons). In addition, we measured the basal state of the phosphoproteome in unstimulated Tcon of the same donors. In total, we provide phosphoproteomics data of primary human CD4+CD25- T cells from three human healthy donors each for (i) unstimulated Tcons, (ii) 5 minutes TCR-stimulated Tcons, (iii) 5 minutes TCR-stimulated and Treg-suppressed Tcons.