The ocrelizumab phase II extension trial suggests the potential to improve the risk:benefit balance in multiple sclerosis

Objective: Ocrelizumab inhibits relapsing multiple sclerosis when administered every six months. Based on potential similar memory B cell depletion mechanisms with cladribine and alemtuzumab, we hypothesised that CD20-depletion of B cells by ocrelizumab may exhibit a duration of response exceeding the current licenced treatment interval. Methods: Internet-located information from regulatory submissions and meeting reports relating to the unpublished open-label, phase II ocrelizumab extension trial (NCT00676715) were reviewed. This followed people (54-55/arm) with MS, who switched from placebo or interferon-beta to ocrelizumab for three 600mg treatment cycles (week 24, 48, 72) or people treated with ocrelizumab for four 600mg treatment cycles (week 0-72), followed by an 18 month treatment-free period. Results: CD19+ B cells were rapidly depleted within 2 weeks and slow CD19+ B cell repopulation began about 6 months after the last infusion with median-repletion of over 15 months. The reduced annualized relapse rate during the published efficacy study appeared to be maintained in the extension study and there were no new T1 gadolinium-enhancing or T2 lesions detected in the treatment-free period. Importantly, within these extension cohorts, there appeared to be fewer adverse events and infections events. Conclusions: Ocrelizumab appears to induce durable relapsing disease inhibition, within 3 treatment cycles Therefore, it may be possible to reduce the frequency of dosing to maintain efficacy, whilst limiting infection and other risks associated with continuous immunosuppression. Further studies are now clearly required to determine whether this data is robust, as few people seemed to complete the study.