In vitro effects of different 8-methoxypsoralen treatment protocols for extracorporeal photopheresis on mononuclear cells

• Main Authors: Holger Budde, Ulrike Berntsch, Joachim Riggert, Tobias J. Legler
• Format: Article
• Language: English
• Published: Termedia Publishing House 2017-05-01
• Series: Central European Journal of Immunology
• Subjects: <i>apoptosis; regulatory T cells (Tregs); photopheresis</i>
• Online Access: https://www.termedia.pl/-In-vitro-effects-of-different-8-methoxypsoralen-treatment-protocols-for-extracorporeal-photopheresis-on-mononuclear-cells,10,29840,1,1.html

Extracorporeal photopheresis (ECP) is an important second-line therapy for graft- versus -host disease. A central therapeutic mechanism is the induction of immune tolerance through apoptosis in patient’s leukocytes, caused by ex vivo incubation with 8-methoxypsoralen (8-MOP) and subsequent UVA irradiation. We hypothesized that different 8-MOP incubation times and an additional 8-MOP removal step could influence the apoptosis kinetics of leukocytes in general and in particular could lead to different apoptotic levels in the leukocyte subpopulations. After 8-MOP/UVA treatment of human leukocytes, cells were cultured and the percentage of annexin V positive cells from several leukocyte subpopulations was determined. Only regulatory T cells (Tregs) were relatively resistant to 8-MOP/UVA induced apoptosis. When cells were incubated for 30 minutes with 8-MOP prior to UVA exposure, higher percentages of annexin V positive cells were detected on day 1 and day 2 after treatment. Removal of 8-MOP after UVA exposure caused no significant changes in the apoptosis kinetics during the 72 h culture period compared with unwashed cells. The results of our in vitro study indicate that it could be possible to adjust the apoptosis kinetics via modulation of the 8-MOP incubation time. In further in vivo studies it should be elucidated to which extent different apoptosis kinetics influence the therapeutic effect of ECP since steady-state apoptosis levels are probably important for establishing a long lasting immune tolerance. Furthermore we found that Tregs, according to their well-known tolerogenic function, are more resistant to apoptosis after 8-MOP/UVA treatment compared to GvHD inducing T cell populations.