Lymphocyte Subtypes in Relapsing Remitting Multiple Sclerosis (RRMS) Patients Treated with Dimethylfumarate (DMF) (P3.063)

Objective: To investigate the effect of DMF on lymphocyte subtypes in RRMS patients with and without Background: Recent data suggest that lymphopenia is more prevalent than reported in clinical trials in RRMS patients taking DMF, with potential life-threating complications. Lymphocyte subtypes have not been well studied in this population. Methods: Cross-sectional observational study comparing lymphocyte subtypes by flow cytometry in RRMS patients treated with DMF. Patients were divided in 2 groups: G1- lymphocytes u003c1.2, G2 - lymphocytes ≥ 1.2. Absolute cell counts were used for subtype analyses. Results: We had 59 patients, 35 in G1, 24 in G2, mean age 49, 71.2[percnt] females. Patients were treated with DMF for 20-month average. Age, sex, treatment duration and baseline mean WBC were not significantly different between groups. Prior interferon therapy was more frequent in G1 (p=0.02) and although normal, mean baseline lymphocyte count was lower in this group (p=0.04). During evaluation, mean lymphocyte count in G1 was 0.8±0.2 and 1.6 ±0.3 in G2, without significant decrease in mean WBC. B cell (p=0.04), T cell, CD4 and CD8 (pu003c0.0001) mean counts were significantly decreased in G1, while the helper/suppressor (H/S) ratio was increased (p=0.03). Natural killer percentage was not different between groups. Adjusting for age, disease duration and prior interferon exposure, a positive correlation was noted between absolute lymphocyte count and B cells (p=0.005), T cells, CD4 and CD8 (pu003c0.0001) mean counts. A negative correlation was observed between lymphocyte count and H/S ratio (p=0.02), mostly driven by low CD8 counts; this association did not persist in the adjusted model. Conclusions: Most lymphocyte subtypes were significantly reduced in RRMS patients with DMF-induced lymphopenia, with more dramatic reduction in CD8 counts. Lower normal baseline lymphocyte counts and pre-DMF interferon use were predictors for lymphopenia. These findings may have implications in this population’s immunologic competence. Disclosure: Dr. Ganguly has nothing to disclose. Dr. Camac has nothing to disclose. Dr. Dionne has nothing to disclose. Dr. Chaves has nothing to disclose.