Effect of ocrelizumab on leptomeningeal inflammation and humoral response to Epstein-Barr virus in multiple sclerosis. A pilot study

Background: Ocrelizumab is an effective treatment for relapsing and primary-progressive multiple sclerosis (MS). However, the effect of ocrelizumab on leptomeningeal (LM) inflammation is unknown. Objective: To investigate whether ocrelizumab reduces LM inflammation by reducing the exposure to Epstein-Barr virus (EBV)-infected B cells in relapsing-remitting (RR) MS. Methods: This was a Phase IV, prospective, open-label, single-center, observational, longitudinal pilot study of RRMS patients who started treatment with ocrelizumab (NCT03025269). Clinical, MRI and EBV-antibodies outcomes at baseline, 12- and 24-month of the study were evaluated. The MRI outcomes included T2, T1 and T1-contrast enhancing (CE) lesion counts and volumes, LM CE count, and percentage brain volume changes. Results: 27 RRMS patients started ocrelizumab and 24 remained on the treatment for whole duration of the study. Most patients remained stable (74.1%) or improved (18.5%) in their disability status. At baseline, 42.3% of patients showed LM CE lesions. The majority of patients remained stable in their LM CE status over the follow-up (72.7%). A significant decrease in percentage volume loss of cortex (p=0.009), GM (p=0.01) and thalamus (p=0.038) was detected, while T1-LV increased (p=0.02). A significant decrease of EBNA-1 IgG (p=0.013) was evidenced. An infusion-related allergic reaction led to discontinuation of the medication in one patient at first dose. Conclusions: Treatment with ocrelizumab was safe and clinically effective. Brain volume loss and accumulation of T1-LV occurred. While ocrelizumab decreased humoral response to EBV possibly by reducing B cells, it did not reduce LM inflammation.