NfL was included as a secondary outcome if available. Follow-up values under treatment were assessed at the earliest time point available, but not before 3 months after treatment start. In total, follow-up values were available for 55 patients (ocrelizumab n = 23, natalizumab n = 30) after a mean time to follow-up of 9.9 months. For 30 patients (ocrelizumab n = 17, natalizumab n = 13), both baseline and follow-up values were available (mean time to follow-up = 8.8 months). NfL values were assessed from the patient’s sera using a standardized protocol described in detail previously.25 (link) NfL levels were determined in duplicates by single molecule array with an SiMoA HD-1 (Quanterix, Billerica, MA, USA) using the Nf-Light Advantage Kits (Quanterix) according to the manufacturer’s instructions. All coefficients of variation (CVs) of the two replicates were below 20%, resulting in a mean intra-assay CV of 6.8%. Low and high controls, consisting of recombinant human NfL antigen, were included in each sample run to monitor plate-to-plate variation (low: mean = 3.0 pg/ml, inter-assay CV = 4.0%; high: mean = 132.1 pg/ml, inter-assay CV = 6.9%). The NfL measurements were performed blinded and without information on clinical data.