Extracorporeal photopheresis efficiently impairs the proinflammatory capacity of human 6-sulfo LacNAc dendritic cells.

Background. Extracorporeal photopheresis (ECP) emerged as a promising treatment modality for steroid-refractory graft-versus-host disease (GVHD), which represents a major complication of allogeneic hematopoietic stem-cell transplantation. Dendritic cells (DCs) display an extraordinary capacity to induce T-cell responses and play a crucial role in the initiation and maintainance of GVHD. This study evaluated the direct impact of ECP on the proinflammatory capacity of 6-sulfo LacNAc (slan) DCs, representing a major subpopulation of human blood DCs. Methods. SlanDCs were isolated from ECP-treated or untreated blood of healthy donors or GVHD patients by immunomagnetic isolation. The maturation of slanDC was determined by flow cytometry. Cytokine production of slanDCs was measured by enzyme-linked immunosorbent assay. SlanDC-mediated T-cell proliferation was evaluated by H-3-thymidine incorporation. SIanDC-mediated T-cell programming was determined by flow cytometry. Results. ECP efficiently impairs the spontaneous maturation and secretion of proinflammatory tumor necrosis factor-a, interleukin-1 beta, and interleukin-12 by slanDCs. Furthermore, ECP markedly inhibits slanDC-induced proliferation of CD4(+) and CD8(+) T cells and polarization of naive CD4(+) T lymphocytes into Th1 cells. Conclusions. These novel findings indicate that ECP efficiently impairs the proinflammatory capacity of slanDCs, which may represent an important mechanism for the therapeutic efficiency of ECP in GVHD.