Gunnar Sigfús Björnsson, Hildur Sigurgrímsdóttir, Sólrún Melkorka Maggadóttir, Berglind Ósk Einarsdóttir, Ólafur Árni Sveinsson, Haukur Hjaltason, Sigurveig Þóra Sigurðardóttir, Björn Rúnar Lúðvíksson and Siggeir Fannar Brynjólfsson
Introduction: Rituximab, a chimeric anti-CD20 monoclonal antibody, has been used to treat MS patients in Iceland for over a decade. However, long-term effect of rituximab on the leukocyte population has not yet been elucidated. We investigated whether a long-term effect of rituximab on the leukocyte population in Icelandic MS patients was present and evaluated whether the effect is dose dependent (1000mg vs 500mg).
Methods: Retrospective analysis of flow cytometric data from 349 patients visiting the neurological ward at The National University Hospital of Iceland from 2012 to 2023 for rituximab treatment. Differential counts and classification of leukocytes were analysed.
Results: No difference in efficacy of B-cell depletion was detected in patients treated with 500mg compared to 1000mg of rituximab. Efficacy of the treatment was neither age nor sex dependent. The persistence of depletion was stable for both doses for 300 days. However, long-term use of rituximab led to an increase in T-cell count (p=0,0015) in patients receiving 3-8 doses of rituximab (1.5-8 years of treatment). The increase occurred in both CD4+ (p=0,0028) and CD8+ (p=<0,0001) T-cells and led to a decrease in the CD4/CD8 ratio (p=0,004). Conclusion: Since no difference in B-cell depletion was detected between the two patient groups, 1000mg might be an excessive dose. However, the clinical implications of long-term treatment of rituximab and its effect on the T-cell pool needs to be explored further. Based on this data a personalized dosing regimen might have therapeutic and financial advantages that should be explored further.
