• Viola Hähnel, Andreas-Michael Brosig, Martin Ehrenschwender, Ralph Burkhardt, Robert Offner, and Norbert Ahrens.
• Institute for Clinical Chemistry and Laboratory Medicine, Transfusion Medicine, University Hospital Regensburg, Regensburg, Germany.
• Transfusion. 2021 Oct 1; 61 (10): 2991-2999.

BackgroundExtracorporeal photopheresis (ECP), an apheresis-based therapy for various immunological diseases, works mainly by inducing apoptosis in lymphocytes. Several factors influence the efficacy of ECP with the photosensitizer 8-methoxypsoralen (8-MOP) and ultraviolet light A (UVA). This study aimed to optimize treatment by varying the 8-MOP starting concentration and the cell suspension medium.Materials And MethodsAll patients (n = 13) included in this study received photopheresis as medically indicated. Cells collected with a Spectra Optia apheresis system were suspended in plasma or physiological saline (NaCl) and incubated with 200 ng/ml versus 340 ng/ml photosensitizer before UVA irradiation (Macogenic G2 or UVA PIT system). Lymphocyte apoptosis and caspase activity were analyzed by flow cytometry and fluorimetry, and residual 8-methoxypsoralen concentrations by liquid chromatography-mass spectrometry.ResultsRaising the 8-MOP starting concentration significantly increased lymphocyte apoptosis, with values of 22% versus 35% (plasma) and 28%-46% (NaCl) at 24 h post-ECP and 37% versus 86% (plasma) and 74% versus 97% (NaCl) at 48 h for 200 ng/ml versus 340 ng/ml. Pre-transfusion residual 8-MOP levels were 168 ng/ml (plasma) and 162 ng/ml (NaCl) versus 290 ng/ml (plasma) and 266 ng/ml (NaCl) for the lower versus higher dose, respectively.DiscussionHence, 8-MOP concentration influences the efficacy of photopheresis as lymphocyte apoptosis rates were significantly higher with the higher starting concentration and with NaCl versus plasma. This indicates that increased 8-MOP starting doses and saline as additional suspension medium could help in improving ECP's efficacy.© 2021 The Authors. Transfusion published by Wiley Periodicals LLC on behalf of AABB.

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