Laquinimod dampens IL-1ß signaling and Th17-polarizing capacity of monocytes in patients with MS.

OBJECTIVE: To assess the impact of laquinimod treatment on monocytes and to investigate the underlying immunomodulatory mechanisms in MS. METHODS: In this cross-sectional study, we performed in vivo and in vitro analyses of cluster of differentiation (CD14+) monocytes isolated from healthy donors (n = 15), untreated (n = 13), and laquinimod-treated patients with MS (n = 14). Their frequency and the expression of surface activation markers were assessed by flow cytometry and the viability by calcein staining. Cytokine concentrations in the supernatants of lipopolysaccharide (LPS)-stimulated monocytes were determined by flow cytometry. The messenger ribonucleic acid (mRNA) expression level of genes involved in cytokine expression was measured by quantitative PCR. The LPS-mediated nuclear factor kappa-light-chain-enhancer of activated B-cell (NF-κB) activation was determined by the quantification of the phosphorylation level of the p65 subunit. Laquinimod-treated monocytes were cocultured with CD4+ T cells, and the resulting cytokine production was analyzed by flow cytometry after intracellular cytokine staining. The interleukin (IL)-17A concentration of the supernatant was assessed by ELISA. RESULTS: Laquinimod did not alter the frequency or viability of circulating monocytes, but led to an upregulation of CD86 expression. LPS-stimulated monocytes of laquinimod-treated patients with MS secreted less IL-1ß following a downregulation of IL-1ß gene expression. Phosphorylation levels of the NF-κB p65 subunit were reduced after laquinimod treatment, indicating a laquinimod-associated inhibition of the NF-κB pathway. T cells primed with laquinimod-treated monocytes differentiated significantly less into IL-17A-producing T helper (Th)-17 cells. CONCLUSIONS: Our findings suggest that inhibited NF-κB signaling and downregulation of IL-1ß expression in monocytes contributes to the immunomodulatory effects of laquinimod and that the impairment of Th17 polarization might mediate its disease-modifying activity in MS.

Cladribine exerts an immunomodulatory effect on human and murine dendritic cells.

Cladribine is a purine nucleoside analog developed to treat lymphoid malignancies. Reported therapeutic benefits for the autoimmune disease multiple sclerosis indicate additional immunomodulatory effects beyond the well-characterized cytotoxic activity causing lymphopenia. Here, we demonstrate that cladribine reduces the secretion of inflammatory cytokines and chemokines by murine and human dendritic cells, the most potent antigen-presenting cells. This compound also modulates the expression of the activation markers CD86 and MHC II. Furthermore, cladribine affects the T cell priming capacity of dendritic cells, resulting in reduced induction of interferon-γ- and tumor necrosis factor-α-producing T cells and increased induction of interleukin-10-producing T cells. These effects, observed at cladribine concentrations in the therapeutically relevant range of serum steady-state concentrations for leukemia and multiple sclerosis, confirm the immunomodulatory activity of cladribine.

Modulation of dendritic cell properties by laquinimod as a mechanism for modulating multiple sclerosis.

Laquinimod is an orally administered compound that is under investigation in relapsing-remitting multiple sclerosis. To understand the mechanism by which laquinimod exerts its clinical effects, we have performed human and murine studies assessing its immunomodulatory properties. In experimental autoimmune encephalomyelitis, the therapeutic administration of laquinimod beginning during the recovery of SJL mice, prevented further relapses as expected and strongly reduced infiltration of CD4+ and CD8+ T cells in the central nervous system. We hypothesized that this beneficial effect was mediated by dendritic cells, since we and others found a modulation of different dendritic cell subsets under treatment. According to the findings on antigen-presenting cells in the murine system, we found a reduced capacity of human monocyte-derived dendritic cells treated with therapeutic concentrations of laquinimod, upon maturation with lipopolysaccharide, to induce CD4+ T cell proliferation and secretion of pro-inflammatory cytokines. Furthermore, laquinimod treatment of mature dendritic cells resulted in a decreased chemokine production by both murine and human dendritic cells, associated with a decreased monocyte chemo-attraction. In laquinimod-treated patients with multiple sclerosis we consistently found reduced chemokine and cytokine secretion by conventional CD1c+ dendritic cells upon lipopolysaccharide stimulation. Similarly to the animal model of relapsing-remitting multiple sclerosis, dendritic cell subsets were altered in patients upon laquinimod treatment, as the number of conventional CD1c+ and plasmacytoid CD303+ dendritic cells were decreased within peripheral blood mononuclear cells. Moreover, laquinimod treatment in patients with multiple sclerosis and mice modified the maturation of dendritic cells demonstrated by an upregulation of CD86 expression in vivo. Our data suggest that inhibition of the NF-κB pathway is responsible for the changes observed in dendritic cell maturation and functions. These findings indicate that laquinimod exhibits its disease-modulating activity in multiple sclerosis by downregulating immunogenicity of dendritic cell responses. We suggest that monitoring dendritic cell properties in multiple sclerosis should be implemented in future therapeutic trials.