Optimal retreatment schedule of rituximab for neuromyelitis optica spectrum disorder: A systematic review

Several studies have shown the efficacy of rituximab (RTX) in preventing relapses in patients suffering from Neuromyelitis Optica spectrum disorder (NMSOD) and have explored different therapeutic schemes. Given the extreme inter-individual variability of the disease course, there is the need to identify biomarkers to tailor the retreatment schedule and dosage. This review aimed to identify the most useful biomarker to guide reinfusion and, in turn, the optimal retreatment schedule of RTX for NMSOD.The literature search was conducted in the Web of Science, Scopus and Pubmed electronic databases. We limited document type to articles written in English and published up to 28 February 2022. Inclusion criteria were: (i) Patients affected by NMSOD and treated with RTX, (ii) followed up for at least one year and for whom Annualized Relapse rate (ARR) was collected over a period of at least 12 months before and after therapy initiation and (iii) induction protocols consisting of 375 mg / m2 / week for four weeks or 1000 mg infused once or twice two weeks apart. Collected information was: first authors' name, publication year, study design, sample size, sex, age, percentage of patients positive for antibodies to aquaporin 4 (AQP4-IgG), maintenance regimen, primary outcome, mean ARR pre-therapy and mean ARR post-therapy initiation, percentage of relapse-free patients. The primary outcome that we considered was the ARR reduction. Further, we considered the number of relapses that occurred when B cells and memory B cells were under the chosen threshold and the percentage of relapse-free patients when available.Among 31 potentially eligible studies, 9 fulfilled the inclusion criteria. ARR reduction was not comparable between studies. The studies that monitored CD19+ and CD27+ cell kinetics showed a higher number of relapses when CD19+ lymphocyte count was below the threshold compared to the number of relapses that occurred when CD27+ cell count was below the threshold. Further, a higher percentage of patients achieved the relapse-free condition with a reinfusion schedule when CD27+ reached 0, 05% of peripheral blood mononuclear cells (PBMCs) compared to the reinfusion when CD19+ reached 0, 1% of PBMCs.To date, the optimal retreatment schedule for RTX in NMOSD has not yet been determined. However, the presented findings suggest that CD27+ B cells might be a reliable biomarker to guide retreatment in AQP4-IgG positive patients, at least in the first six months from the infusion. Further effort is needed to identify those factors influencing anti-CD20 therapy effectiveness to tailor dosage and treatment schedule to achieve the most favourable risk/benefit ratio.