Only Follow-Up of Memory B Cells Helps Monitor Rituximab Administration to Patients with Neuromyelitis Optica Spectrum Disorders

INTRODUCTION: Neuromyelitis optica spectrum disorders (NMOSD) are identified as a spectrum of inflammatory demyelinating disorders involving the brain, spinal cord and optic nerves. These disorders require early diagnosis and highly active immunosuppressive treatment. Rituximab (RTX) has demonstrated efficacy in limiting relapse in NMOSD when using several administration schedules. We questioned if the CD19+ CD27+ memory B cell count was a more reliable marker to monitor RTX administration than the RTX plasma level and CD19+ B cell count. METHODS: We analyzed 125 blood samples from 17 NMOSD patients treated with RTX and also measured the level of anti-aquaporine-4 antibodies (anti-AQP-4 Abs), human anti-chimeric antibodies to the murine fragment of RTX (HACA-RTX Abs), and the RTX concentration. RESULTS: The mean follow-up time of the cohort was 7.4 (2–16) years. All patients improved with a mean EDSS going from 4 (1–8.5) to 2.7 (1–5.5). The mean interval between RTX infusions was 9.6 months with identification of prolonged responders. Total CD19+ B cell detection with the routine technique did not correlate to re-emergence of CD19+ CD27+ memory B cells. The RTX residual concentration did not correlate with the CD19+ CD27+ memory B cell count or with anti-RTX antibody production. CONCLUSION: In contrast to total CD19+ cell, detected with the routine technique, CD19+ CD27+ memory B cells are a reliable marker for biological relapse and allow a decrease in the frequency of infusions.