Inclusion criteria.

• - The participant must have a previous diagnosis of RMS in accordance with the 2017 revised McDonald criteria.

• - The participant must have been newly prescribed to OCR treatment according to clinical practice.

• - Absence of high dose of steroid treatment for at least 4 weeks.

• - The participant must be capable of giving signed informed consent.

• - Clinical MS relapse within four-week period prior to inclusion.

• - Pregnant or nursing (lactating) women.

• - Chronic disease of the immune system, other than MS.

• - Active systemic bacterial, viral or fungal infections.

• - Allergy to OCR.

Ocrelizumab (OCR) is a humanized monoclonal anti-CD20 antibody approved by the FDA in 2017 and by the European Medicines Agency in 2018 for treatment of adult patients with Relapsing Multiple Sclerosis (RMS). In addition, having shown neuroprotective effects, OCR is the first drug ever approved for early treatment of Primary Progressive MS (PPMS). Currently, OCR is thought to mostly act via the rapid depletion of the B cells expressing CD20. Additionally, this depletion most likely causes long-lasting changes in the profile of B cells, characterized by a reduction of their pro-inflammatory phenotype, as demonstrated with other anti-CD20 antibodies. Of interest, previous studies on other anti-CD20 drugs, mainly rituximab, have shown that anti-CD20 agents also exert interesting effects on additional intracellular signaling pathways, such as those involving serine/threonine and tyrosine kinases, as well as c-myc. Considering the structural, pharmacokinetic and pharmacodynamic similarities between OCR and rituximab, it can be hypothesized that the efficacy of OCR in delaying disease progression and neuroprotection might also stem from such intracellular effects. Among the various intracellular effects elicited by rituximab through the binding with CD20, stimulation of the Protein Kinase C (PKC) pathway is of potential significance. The term PKC encompasses a family of several serine/threonine protein kinases of which the isoform β has been implicated in pathological processes, such as diabetic retinopathy, via a specific PKCβ/HuR/Vascular Endothelial Growth Factor (VEGF) pathway (Amadio et al. 2010). Notably, HuR belongs to a family of RNA-binding proteins, named ELAV, which are able to influence virtually any aspect of the post-synthesis fate of the targeted transcripts, including VEGF. VEGF is a signaling molecule involved in vital processes such as angiogenesis, endothelial proliferation and cellular response to hypoxia. The possible role of VEGF in MS pathogenesis and evolution has not been explored until recently, but mounting evidence points to the conclusion that VEGF might play a significant noxious role in the relapsing stage of MS, for instance by mediating an increase in blood-brain barrier (BBB) permeability, while playing a beneficial, neuroprotective role in the late, progressive stage of the disease. Of note, VEGF has a primary role in promoting vascular hyperpermeability, indeed via phosphorylation of endothelial tight junction proteins modulates their degradation, finally leading to BBB disruption. Further, it also regulates vessel growth and is chemotactic for monocytes and lymphocytes, promoting neuroinflammation. Of interest, a significant increase in VEGF was observed in mice in the acute phase of murine MOG-induced MS, which correlates to the clinical score, and in sera of MS patients during clinical disease relapses. Based on these considerations, it can be possible that OCR exerts an additional beneficial effect in MS therapy by modulating VEGF content. With this project, we aim to explore the effects of OCR on intracellular signaling pathways by assessing VEGF expression in Peripheral Blood Mononuclear Cells (PBMCs) of RMS patients at the beginning of OCR therapy, as well as at 6 and 12 months of ongoing treatment. In particular, ther purpose of the study is to focus on the pro-angiogenic VEGF-A 165, which seems the isoform mainly involved as mediator of inflammation and cellular immunity. Further, the PKCβ/HuR cascade will be investigated in the same conditions. Secondly, disease activity during OCR treatment will be examined at every step, and also compared with VEGF and PKC levels. The results will also possibly demonstrate a necessity of further determining the extent and significance of intracellular effects of anti-CD20 therapy in MS. This study is an observational (phase 4) , longitudinal, monocenter and single arm study, in patients with RMS who are newly prescribed with OCR as per clinical practice. The study consists of the following visits as per clinical practice:

• - Baseline/start (T0): informed consent signature, inclusion/exclusion criteria verification, demographical characteristics, clinical medical history recording, concomitant therapies, neurological history recording (MS history), number of relapses from MS onset, neurological examination, the Expanded Disability Status Scale (EDSS), the Multiple Sclerosis Severity Score (MSSS), blood sample, ocrelizumab administration.

• - T6: (after 6 months of OCR treatment) adverse events (including relapses), neurological examination, therapies changes, EDSS, MSSS, blood sample, ocrelizumab administration.

• - T12 (after 12 months* of OCR treatment), adverse events (including relapses), neurological examination, therapies changes, EDSS, MSSS, blood sample, ocrelizumab administration.