Individual Variability of CD19 + B‐Cell Repopulation in People With Multiple Sclerosis Treated With Extended Interval Dosing of Ocrelizumab

Background and Objectives B‐cell repopulation patterns in ocrelizumab treated patients with multiple sclerosis are highly variable between individuals, but the course of B‐cell reoccurrence after subsequent doses within an individual is not yet determined. Our aim was to determine the intraindividual variability of CD19+ B‐cell repopulation after each ocrelizumab dose when using CD19+ B‐cell guided interval dosing. Methods This was a prospective cohort study, as part of the ongoing BLOOMS trial, investigating participants randomised for B‐cell guided interval dosing of ocrelizumab with ≥ 2 dosing intervals. Coefficients of variation were calculated for time from last ocrelizumab dose to first CD19+ B‐cell measurement ≥ 0.01 × 10 9 cells/L. Results Seventy‐five participants with a total of 209 B‐cell guided intervals were included. Time from last dose to first appearance of CD19+ B‐cell count ≥ 0.01 × 10 9 cells/L showed wide variability between individuals (20.6–72.1 weeks), but the median variation was 5.6% (IQR: 3.1–8.4) within an individual. This translated to a variation of 2 weeks per dosing interval on average. Discussion Time to CD19+ B‐cell repopulation after each ocrelizumab dose is individually stable. This finding could pave the way for easier and more accessible future personalised interval dosing of B‐cell depleting therapies if this stability is confirmed in long‐term treatment.