Extracorporeal photopheresis affects interleukin (IL)-10 and IL-12 production by monocytes in patients with chronic graft-versus-host disease

Background Chronic graft-versus-host disease (cGVHD) is a major complication of allogeneic bone marrow transplantation. Extracorporeal photopheresis (ECP) has recently been introduced as an alternative treatment for cases of cGVHD refractory to conventional immunosuppressive treatment, but its mechanism of action is not yet clear. Objectives To investigate in seven patients with cGVHD the effects of ECP on resistance of monocytes to apoptosis and on monocyte cytokine production. Methods We designed an in vitro model that could mimic the potential in vivo effect of reinfusion of peripheral blood mononuclear cells treated by ECP. The model was based on coculture of ECP-treated lymphocytes with untreated monocytes from the same patient. Results ECP did not accelerate spontaneous apoptosis of monocytes. However, ECP-treated monocytes produced increased amounts of interleukin (IL)-12. In contrast, IL-12 production by monocytes did not increase in cocultures, but IL-10 production was upregulated. Conclusions These results suggest that reinfusion of large numbers of autologous apoptotic lymphocytes is significant for the therapeutic outcome of ECP through upregulation of IL-10, which is an immunosuppressive cytokine.