(Patients 11C12) Early after starting ATZ, patients presented upcoming or ongoing disease activity paralleled by sNfL increase. activity. Even patient-reported relapse-suspicious symptoms, which have not been confirmed because relapses were accompanied by sNfL, increase, proposing sNfL assessment RPR-260243 as a marker for relapse activity. sNfL started to increase earliest 5 months before, peaked at clinical onset, and recovered within 4C5 months. sNfL presented at higher levels in active patients requiring ATZ retreatment compared with responder patients. During 2 documented pregnancies, sNfL was at a low level, whereas a postpartum transient sNfL increase was seen without any indicators of activity. Conclusions This study applied a long-term high-frequency sNfL assessment in an ATZ-treated cohort, allowing a holistic profiling on the individual level and highlighted that sNfL can eminently complement the individual clinical and MRI monitoring in clinical practice. Alemtuzumab (ATZ; Lemtrada, RPR-260243 Sanofi) is usually a humanized monoclonal antibody and represents one of the most effective treatments for active relapsing-remitting MS.1,2 ATZ might produce a durable therapeutic response as a consequence of a permanent rebalancing of the immune system.3 It has introduced the immune reconstitution therapy as a new therapeutic induction therapy-like concept in MS.4 The definition of clinical response profiles after ATZ dosing is crucial to the identification of patients who need retreatment or switching to other therapy. Until now, primarily clinical characteristics such as relapse activity, disability, and repeated MRI analysis have been used to define response profiles to MS treatment.5,6 However, this approach has several limitations because even high-frequency clinical and MRI assessment is not sensitive enough to detect all neuroinflammatory and neurodegenerative activity, and additional biomarkers are needed to complement clinical- and MRI-derived information.7 In particular, reliable quantification and longitudinal follow-up evaluation of neuroaxonal damage would be important for assessing MS disease activity, monitoring treatment response, facilitating treatment development, and determining RPR-260243 prognosis. The neurofilament proteins that represent one of the main cytoskeletal constitutes in neurons show promise in this context because their levels rise upon neuroaxonal damage not only in the CSF but also in blood, indicating neuroaxonal injury impartial of causal pathways.8,C10 Different studies presented that neurofilament light chain (NfL) is increased in the CSF of patients with clinically isolated syndrome and MS and correlates with MRI activity, disability, and relapse activity.11,C16 Third-generation (electrochemiluminescence) and particularly fourth-generation (single-molecule array [SIMOA]) assays enable the reliable measurement of neurofilaments throughout the range of concentrations found in blood samples. Previous studies suggest serum (s)NfL as a potential predictive marker for MS disease outcome.13,17,C19 Nevertheless data and studies are missing that clarify how sNfL measurements develop over time, at relapse, or remission and whether sNfL level may be able to predict treatment response. In this study, we analyzed individual long-term series of sNfL levels in patients with highly active relapsing-remitting MS after immune reconstitution treatment SCA27 with ATZ using high-frequency sNfL assessment over a long observational period of up to 102 months. By this approach, we aim to observe sNfL changes in the MS disease course and stratify the potential to predict disease activity vs remission and treatment response in patients with MS in clinical practice. Methods Patients, collection of clinical data, and blood sampling In this pilot study, we included 15 patients with relapsing-remitting MS with clinical- and MRI-confirmed highly active disease course (figures 1C5, table). All patients were treated based on a standardized infusion scheme as described and used in CARE-MS 1 and 2 clinical trials20,C22: During the first infusion course, 12 mg ATZ was infused for 5 consecutive days. During the second course, 12 months later, ATZ was administered for 3 consecutive days. Serum samples were obtained before the first ATZ infusion (baseline, month 0) and then monthly during follow-up for.