Importance: Sézary syndrome (SS) is a rare, leukemic type of cutaneous T-cell lymphoma (CTCL), which can be successfully controlled with extracorporeal photopheresis (ECP). Reliable biomarkers to objectively monitor the response to ECP in patients with SS are missing. Objective: We examined the quantitative and qualitative impact of ECP on natural killer (NK) cell activity in SS patients, and especially their functional ability for antibody-dependent cell-mediated cytotoxicity (ADCC). Further, we address the question if the magnitude of the effect can be associated with the treatment response to ECP in SS patients. Materials and Methods: We collected blood samples before starting therapy and after an average of 9 months of uninterrupted ECP treatment from a case-series of 13 SS patients (8 women, 5 men). This is a single-centre study. All patients were diagnosed according to EORTC-WHO criteria and gave written informed consent to the use of their material and data for research purposes. Blood from healthy volunteers was obtained anonymously from a blood bank. Number of NK cells by flow cytometry, ADCC activity by LDH release assay and flow cytometry, treatment response based on blood tumour staging. Results: NK cell numbers were reduced in SS patients compared to healthy individuals and showed a tendency of recovery after long-term ECP treatment, independent of the response to treatment. Patients with marginal increase (≤1.5 AU-fold) or lack of increase in ADCC activity failed to respond to treatment, while an increase in ADCC efficacy paralleled a positive response to ECP. Conclusions and Relevance: NK-mediated ADCC is selectively enhanced and can serve as a reliable biomarker to objectively monitor response to ECP in patients with SS.

ESDR268 - Enhancement of antibody-dependent cellular cytotoxicity is associated with treatment response to extracorporeal photopheresis in Sézary syndrome

50th Annual Meeting of the European Society for Dermatological Research. VIRTUAL MEETING