Tregs In Graft-Versus-Host Disease: A Task Force In Trouble?.

Abstract 3748

Graft-versus-host disease (GvHD) remains the major clinical complication in hematopoietic stem cell transplantation (SCT) resulting in severe morbidity and significant mortality. This alloreactive immune response is mainly induced by donor T cells transplanted with the graft. Regulatory T cells (Tregs) play an essential role in the induction and maintenance of peripheral tolerance. In addition, data from murine models have shown that Tregs can prevent GvHD while preserving the graft-versus-leukemia effect. In order to functionally and dynamically characterize human Tregs after allogeneic SCT, we analyzed CD4⁺CD25^highCD127^dim T cells isolated from the peripheral blood of more than 80 patients with hematological malignancies every 30 days over half a year following SCT.

Patients were divided into the following clinical groups: (A) no signs of acute or chronic GvHD, (B) acute GvHD, (C) chronic GvHD and (D) acute GvHD passed into chronic GvHD. Human peripheral blood lymphocytes were separated by Ficoll gradient and CD4⁺CD14⁻CD25^highCD127^dim T cells were isolated by MoFlow cell sorting. Isolated RNA was pooled and microarray analysis was performed by using Affymetrix HG_U133_Plus2.0 Arrays. Results were verified by using quantitative realtime RT-PCR. Additionally, Tregs were phenotypically analyzed by FACS.

We monitored a continous but slower recovery of Tregs in GvHD within the first 6 months following PBSCT. Manifestation of acute and chronic GvHD correlated with significantly reduced frequencies of peripheral Tregs in the first month after PBSCT compared to patients without GvHD. Microarray data revealed a high stability of the Treg transcriptome in the first half year representing the most sensitive time window for tolerance induction. Moreover, comparison of the Treg gene expression profiles from patients with and without GvHD point to a reduced suppressive function of Tregs with diminished migration capacity to the target organs likely contributing to the development of GvHD.

Our findings corroborate the impact of human Tregs in the pathophysiology of GvHD and identify novel targets for the manipulation of Tregs to optimize strategies for prophylaxis and treatment of life-threatening GvHD.