At the onset of the Covid-19 pandemic, there was uncertainty over the risk of infection and Covid-19 disease outcomes in pwMS treated with B-cell depleting therapy, namely ocrelizumab. Data is emerging from various global and national registries that exposure to ocrelizumab portends a more severe course of Covid-19. The implications of ocrelizumab exposure for immunisation when a vaccine against Covid-19 becomes available remain uncertain.

In multiple sclerosis (MS), ocrelizumab is administered as a fixed 600mg dose at six monthly intervals (≈180days).

Previous research indicates that there is inter-individual variability in time to B-cell repopulation after B-cell depletion therapies.  To balance the risks of suboptimal MS treatment against the uncertain risks of ocrelizumab during the pandemic, we offered B-cell depletion monitoring with the aim of ocrelizumab re-infusion when peripheral B-cells were detected.

Prior to Covid-19, lymphocyte subsets were measured before each 6 monthly ocrelizumab treatment cycle. During the pandemic, we aimed to measure peripheral lymphocyte subsets at monthly intervals starting from the infusion due date. B-cell repopulation was defined as the first detection of CD19⁺ cell percentage of total lymphocytes >1 by flow cytometric analysis.

Our cohort consisted of 32 pwMS. Out of a total of 48 treatment cycles, 15 demonstrated B-cell repopulation with the time to B-cell re-population ranging from 160 to 321 days. Two pwMS had a CD19+ cell count >1% prior to the 6 monthly infusion due date at 160 and 176 days. Data collection is ongoing and will be presented when available.

Our data indicates that B-cell repopulation after ocrelizumab exposure demonstrates inter individual variability, as has been observed with rituximab. Monitoring of B-cell subsets prior to dosing could help identify and tailor dosing schedules to minimise risk of ocrelizumab exposure.