Acute but not chronic graft-versus-host disease is associated with a reduction of circulating CD4⁺CD25^highCD127^low/− regulatory T cells

Defects in central and peripheral tolerance are thought to contribute to life-threatening graft-versus-host disease (GvHD), a severe complication following allogeneic stem cell transplantation (SCT). Recent investigations have demonstrated regulatory T cells (Tregs) to suppress allogeneic immune reactions. Therefore, SCT patients with no or critically low numbers of Tregs may have an increased risk of GvHD. To address this hypothesis, we analyzed the recovery of CD4⁺CD25^highCD127^low/− Tregs in the peripheral blood of patients who have never developed GvHD (n = 6), patients who developed acute/chronic GvHD (n = 18), and patients who developed chronic GvHD without an earlier acute manifestation (n = 5) every 30 days for the first 6 months after peripheral blood SCT (PBSCT). The number of Tregs continuously improved in acute/chronic GvHD patients, but always remained lower than Tregs quantified in patients who never developed a GvHD. In contrast, chronic GvHD patients who did not develop acute GvHD earlier displayed significantly increased Treg cell numbers at the timepoint of chronic inflammation. These results indicate that numerically deficient Tregs following PBSCT are associated with the development of acute but not chronic GvHD.