Graft-versus-host disease (GvHD) is still one of the major complications following allogeneic stem cell transplantation (SCT) triggered by alloreactive donor T cells. Whereas murine data have clearly shown the beneficial effects of regulatory T cells (Tregs) on the development of GvHD, data from the human system are rare mainly due to low cell numbers of circulating or organ-infiltrating Tregs in lymphopenic patients. Here, we present a comparative analysis of Tregs from patients with and without acute/ chronic GvHD designed as a dynamical approach studying the whole genome profile over the first 6 months after SCT. For this purpose, blood samples were collected monthly for FACS-based isolation of CD4+CD25highCD127low/- Tregs. The Treg transcriptome showed a high stability in the first half year representing the most sensitive time window for tolerance induction. However, the comparison of the Treg transcriptome from patients with and without GvHD uncovered regulated gene transcripts that point to a reduced suppressive function of Tregs with diminished migration capacity to the target organs likely contributing to the development of GvHD. These findings highlight the critical role of human Tregs in the pathophysiology of GvHD and identify novel targets for the manipulation of Tregs to optimize cellular immune intervention strategies.