Dimethyl Fumarate Treatment Shifts The Immune Environment Toward An Anti-Inflammatory Cell Profile While Maintaining Protective Humoral Immunity

Background: Delayed-release dimethyl fumarate (DMF) demonstrates sustained efficacy and safety for relapsing forms of MS. Absolute lymphocyte count (ALC) is reduced initially, then stabilizes on treatment. Objective: PROCLAIM, a 96-week, prospective, open-label, phase 3b study, assessed lymphocyte subsets and immunoglobulin (Ig) levels during 48 and 96 weeks (W) of DMF treatment. Methods: Patients received 240 mg DMF BID. Endpoints: lymphocyte subset count changes (primary); Ig isotypes and ALC changes (secondary); adverse events and relationship between ALC changes and ARR/EDSS (exploratory); and neurofilament assessment (ad hoc). Results: Of 218 patients enrolled, 158 (72%) completed the study. Median ALC decreased 39% from baseline to W96 (BL-W96), stabilizing above the lower limit of normal (baseline: 1.82 x 10(9)/L; W48: 1.06 x 10(9)/L; W96: 1.05 x 10(9)/L). CD4 (+) and CD8 (+) T cells correlated highly with ALC from BL-W96 (p < 0.001). Relative to total T cells, naive CD4 (+) and CD8 (+) T cells increased, whereas CD4 (+) and CD8 (+) central and effector memory T cells decreased. Total IgA, IgG, IgM, and IgG1-4 subclass levels remained stable. Adverse event rates were similar across ALC subgroups. ARR, EDSS, and neurofilament were not correlated with ALCs. Conclusion: Lymphocyte decreases with DMF were maintained over treatment, yet immunoglobulins remained stable. No increase in infection incidence was observed in patients with or without lymphopenia. Support: Biogen