Natalizumab saturation: biomarker for individual treatment holiday after natalizumab withdrawal?

Background More and more patients with multiple sclerosis (MS) switch from natalizumab to fingolimod because of the risk of progressive multifocal leukoencephalopathy. The duration of the treatment holiday is still under debate referring to a possible recurrence of disease activity. Aim of the study The aim of this study was to evaluate the prognostic value of natalizumab saturation on T cells for the recurrence of clinical and radiological disease activity. Methods Cell surface‐bound natalizumab saturation (in%) of CD8+ and CD4+ T cells from five patients with MS was determined before initiation of fingolimod by flow cytometry and related to clinical and MRI outcome during a 6‐month follow‐up. Results In two patients with either clinical or radiological disease activity, the natalizumab saturation on CD8+ and CD4+ T cells was