CD19 B cell repopulation after ocrelizumab, alemtuzumab and cladribine: Implications for SARS-CoV-2 vaccinations in multiple sclerosis

Background CD20 depletion is a highly-effective treatment for relapsing multiple sclerosis that maintains B cells at low levels through six monthly dosing of 600mg ocrelizumab. This dosing schedule is associated with inhibition of seroconversion following SARS-CoV-2 vaccination, in contrast to the high levels of seroconversion following treatment with alemtuzumab and cladribine tablets. A number of emerging reports suggest that repopulation of 1-3% B cells facilitates seroconversion after CD20-depletion. The frequency of this occurring following repeated ocrelizumab treatment, after other DMT, and after treatment cessation is largely unknown. Methods Relapse data, lymphocyte and CD19 B cell numbers were extracted from phase II ocrelizumab extension study ( NCT00676715 ) data supplied by the manufacturer via the Vivli Inc, trial data-request portal. Repopulation data of oral cladribine from the phase III CLARITY study ( NCT00213135 ) was supplied by the European Medicines Agency; and the alemtuzumab phase III CARE-MS I ( NCT00530348 ) and CARE-MS II ( NCT00548405 ) trial data were supplied by the manufacturer via the clinicalstudydatarequest.com portal. Results Only 3-5% of people with MS exhibit 1% B cells at 6 months after the last infusion following 3-4 cycles of ocrelizumab, compared to 50-55% at 9 months, and 85-90% at 12 months. During this time relapses occurred at consistent disease breakthrough rates compared to people during standard therapy. In contrast most people (90-100%) exhibited more than 1% B cells during treatment with either cladribine or alemtuzumab. Conclusions Few people repopulate peripheral B cells with standard ocrelizumab dosing, however an extending the dosing interval by 3-6 months may allow many more people to potentially seroconvert in the relative absence of excess relapse-activity. Most people demonstrate B cell repletion within 3 months of the last treatment of alemtuzumab and cladribine. This may help protect against severe COVID-19.