Modelling Lymphocyte Subset Dynamics after Ublituximab therapy in patients with Multiple Sclerosis: An Italian Prospective Study

Aurora ZanghìPaola Sofia Di Filippoclaudia rutiglianoMaria Claudia Moretticarlo avolioEMANUELE D'AMICO^*

• University of Foggia, Foggia, Italy

Background and Objectives: Ublituximab, a novel, glycoengineered anti-CD20 monoclonal antibody has recently entered clinical use for multiple sclerosis (MS). In this study we aimed to delineate the longitudinal kinetics of circulating lymphocyte subsets over the first six months following ublituximab initiation. Secondarily, we aimed to investigate whether relevant baseline demographic and clinical characteristics predicted the residual counts at day 30 after infusion of CD3⁺CD8⁺ T cells and CD19⁺ B naive cells, the two subsets that exhibited the most distinctive early kinetics. Methods: A real-world prospective study performed at the MS center of Foggia, Italy. Inclusion criteria were patients with a diagnosis of relapsing MS who started ublituximab between December 1st, 2024 and May 31st, 2025. Longitudinal trajectories were modelled with subject-specific random-intercept linear mixed-effects models. To identify determinants of early residual depletion, linear regression models were built. Results: A total cohort of 16 patients was enrolled, median age 47 (Q1-Q3 41–58), 69 % male, median EDSS 4.5, median Body Mass Index-BMI 26.9 kg/m2. Mixed-effects models showed a significant effect of time on all lymphocyte subsets. CD3+ T cells decreased by 1,577 cells/μL immediately after ublituximab infusion (p<0.001), returning to baseline from day 7 onward. CD3+CD8+ T cells dropped by approximately 400 cells/μL within the first week (day 7 = 44 cells/μL;95% CI 11–77) and stabilized from day 30. CD3+CD4+ T cells fell by 1,133 cells/μL post-infusion (p<0.001), but rebounded from day 7 and remained stable through day 180. CD19+ naive B cells remained profoundly suppressed throughout six months (all p<0.001). NK cells CD16+CD56+ NK cells showed a transient reduction of 239 cells/μL at day 0 (p=0.004), normalizing by day 7. Regression analyses at day 30 indicate no significant baseline predictors for CD3+CD8+ T or CD19+ naive B cell recovery (R²=0.48 and 0.24, all p>0.05). Infusion reactions were mild and self-limited; no adverse events occurred. Discussion: In our cohort ublituximab induced rapid, durable CD19⁺ naive B cell depletion with only transient, reversible effects on other lymphocyte subsets and preserved immunoglobulin levels. This signature extends to older and high-BMI patients, supporting ublituximab as a versatile therapeutic option across heterogeneous MS populations.