Regulatory T cells and extracorporeal photochemotherapy: correlation with clinical response and decreased frequency of proinflammatory T cells.

Background. Immune mechanisms of extracorporeal photochernotherapy (ECP) in refractory/resistant graft-versus-host disease (GvHD) are complex. We have previously analyzed the role of CD4(+)CD25(+)Foxp3(+) regulatory T cells (T-regs). Methods. In the current study, we have enlarged the size of the population (n=27; chronic GvHD=18, acute GvHD=9) for a median follow-up of 24 months. T-regs were monitored for CD4, CD25, glucocorticoid-induced tumor necrosis factor receptor (GITR), CD62L, CCR7, Foxp3, and STAT-5. Immune analysis by interleukin (IL)-17 Elispot was carried out on circulating T-helper CD4(+) cells secreting IL-17, a subset of T cells considered relevant in the pathogenesis of GvHD. Results. We confirm that ECP is accompanied by a significant increase of CD4(+)CD25(+)Foxp3(+)GITR(+)CD62L(+)CCR7(+) T-regs. Sorted T-regs show augmented phosphorylation of STAT-5. Only ECP-responding patients demonstrate a raise of circulating T-regs, being mostly affected by chronic GvHD. Moreover, this phenomenon corresponds to a diminished secretion of IL-17. Discussion. In conclusion, our study shows that T-regs represent important immune mediators of the clinical benefits of ECP in patients affected by GvHD.