Laquinimod is a novel orally administered
drug for the treatment of
relapsing remitting multiple sclerosis (RRMS). In this immunological substudy of the phase III Assessment of Oral
Laquinimod in Preventing Progression of MS (
ALLEGRO) trial, we performed an ex vivo and in vitro analysis of effects exerted by
laquinimod on peripheral blood immune cell populations from RRMS patients with a special focus on monocyte phenotype and function. Approximately 100 patients were enrolled following a standardized protocol. Half of the patients received
laquinimod and the other half received placebo. Peripheral blood samples were collected prior to commencement of
therapy and after 1, 3, 6, 12, and 24 months of continuous
therapy. Main lymphocytic and antigen presenting cell fractions were analyzed in peripheral blood mononuclear cells (PBMCs) ex vivo by flow cytometry. The proliferative response of PBMCs to
mitogen or recall
antigen was assessed in culture experiments. Untouched monocytes were sorted magnetically and cultured under pro-inflammatory conditions. PBMC analysis showed no significant differences of investigated lymphocytic and antigen presenting cell populations over time within each group, or between the two groups. However, the detailed in vitro analysis of monocytes demonstrated a lower level of CD86 expression on monocytes stimulated with LPS in
laquinimod patients beginning from the 1st month of treatment. Upon pro-inflammatory stimulation, monocytes obtained from
laquinimod treated patients tended to secrete lower levels of the proinflammatory
chemokines CCL2 or CCL5. Taken together, in this prospective study, we demonstrate immune modulation but no immunosuppressive
biological activity of
laquinimod in a large group of MS patients.