Laquinimod is a novel oral drug that is currently being evaluated for the treatment of relapsing-remitting multiple sclerosis (RRMS). Although the mode of action of laquinimod remains to be fully elucidated, current knowledge indicates that laquinimod exerts beneficial activities both on the peripheral immune system and within the central nervous system (CNS). The immunomodulatory properties have been deciphered primarily from studies of laquinimod in the animal model of multiple sclerosis, experimental autoimmune encephalomyelitis (EAE). Data indicate that laquinimod has a primary effect on innate immunity. Laquinimod modulates the function of various myeloid antigen presenting cell populations, which then downregulate proinflammatory T cell responses. Further, data also indicate that laquinimod acts directly on resident cells within the CNS to reduce demyelination and axonal damage. Results from clinical trials that tested laquinimod in RRMS demonstrated that it reduced relapse rate and the mean cumulative number of active lesions, and had a more marked reduction in disability progression than relapse rate. Laquinimod treatment was associated with an excellent safety and tolerability profile. These data indicate that laquinimod will offer a valuable new treatment option for RRMS patients.

Reliable biomarkers corresponding to disease progression or therapeutic responsiveness in multiple sclerosis (MS) have not been yet identified. We previously reported that low expression of the antiproliferative gene TOB1 in CD4⁺ T cells of individuals presenting with an initial central nervous system (CNS) demyelinating event (a clinically isolated syndrome), correlated with high risk for progression to MS. We report that experimental autoimmune encephalomyelitis (EAE) in Tob1⁻/ ⁻ mice was associated with augmented CNS inflammation, increased infiltrating CD4⁺ and CD8⁺ T cell counts, and increased myelin-reactive Th1 and Th17 cells, with reduced numbers of regulatory T cells. Reconstitution of Rag1⁻/ ⁻mice with Tob1⁻/⁻ CD4⁺ T cells recapitulated the aggressive EAE phenotype observed in Tob1⁻/⁻ mice. Furthermore, severe spontaneous EAE was observed when Tob1⁻/⁻ mice were crossed to myelin oligodendrocyte glycoprotein–specific T cell receptor transgenic (2D2) mice. Collectively, our results reveal a critical role for Tob1 in adaptive T cell immune responses that drive development of EAE, thus providing support for the development of Tob1 as a biomarker for demyelinating disease activity.

Objective

To evaluate the influence of oral laquinimod, a candidate multiple sclerosis (MS) treatment, on induction of T follicular helper cells, development of meningeal B cell aggregates, and clinical disease in a spontaneous B cell-dependent MS model.

Methods

Experimental autoimmune encephalomyelitis (EAE) was induced in C57BL/6 mice by immunization with recombinant myelin oligodendrocyte glycoprotein (rMOG) protein. Spontaneous EAE was evaluated in C57BL/6 MOG p35-55-specific T cell receptor transgenic (2D2) × MOG-specific immunoglobulin (Ig)H-chain knock-in (IgH^MOG-ki [Th]) mice. Laquinimod was administered orally. T cell and B cell populations were examined by flow cytometry and immunohistochemistry.

Results

Oral laquinimod treatment (1) reduced CD11c⁺CD4⁺ dendritic cells, (2) inhibited expansion of PD-1⁺CXCR5⁺BCL6⁺ T follicular helper and interleukin (IL)-21-producing activated CD4⁺CD44⁺ T cells, (3) suppressed B cell CD40 expression, (4) diminished formation of Fas⁺GL7⁺ germinal center B cells, and (5) inhibited development of MOG-specific IgG. Laquinimod treatment not only prevented rMOG-induced EAE, but also inhibited development of spontaneous EAE and the formation of meningeal B cell aggregates. Disability progression was prevented when laquinimod treatment was initiated after mice developed paralysis. Treatment of spontaneous EAE with laquinimod was also associated with increases in CD4⁺CD25^hiFoxp3⁺ and CD4⁺CD25⁺IL-10⁺ regulatory T cells.

Conclusions

Our observations that laquinimod modulates myelin antigen-specific B cell immune responses and suppresses both development of meningeal B cell aggregates and disability progression in spontaneous EAE should provide insight regarding the potential application of laquinimod to MS treatment. Results of this investigation demonstrate how the 2D2 × Th spontaneous EAE model can be used successfully for preclinical evaluation of a candidate MS treatment.

Reliable biomarkers corresponding to disease progression or therapeutic responsiveness in multiple sclerosis (MS) have not been yet identified. We previously reported that low expression of the antiproliferative gene TOB1 in CD4⁺ T cells of individuals presenting with an initial central nervous system (CNS) demyelinating event (a clinically isolated syndrome), correlated with high risk for progression to MS. We report that experimental autoimmune encephalomyelitis (EAE) in Tob1⁻/ ⁻ mice was associated with augmented CNS inflammation, increased infiltrating CD4⁺ and CD8⁺ T cell counts, and increased myelin-reactive Th1 and Th17 cells, with reduced numbers of regulatory T cells. Reconstitution of Rag1⁻/ ⁻mice with Tob1⁻/⁻ CD4⁺ T cells recapitulated the aggressive EAE phenotype observed in Tob1⁻/⁻ mice. Furthermore, severe spontaneous EAE was observed when Tob1⁻/⁻ mice were crossed to myelin oligodendrocyte glycoprotein–specific T cell receptor transgenic (2D2) mice. Collectively, our results reveal a critical role for Tob1 in adaptive T cell immune responses that drive development of EAE, thus providing support for the development of Tob1 as a biomarker for demyelinating disease activity.

Laquinimod is a novel oral drug that is currently being evaluated for the treatment of relapsing-remitting (RR) multiple sclerosis (MS). Using the animal model for multiple sclerosis, experimental autoimmune encephalomyelitis (EAE), we examined how laquinimod promotes immune modulation. Oral laquinimod treatment reversed established RR-EAE and was associated with reduced central nervous system (CNS) inflammation, decreased Th1 and Th17 responses, and an increase in regulatory T cells (Treg). In vivo laquinimod treatment inhibited donor myelin-specific T cells from transferring EAE to naive recipient mice. In vivo laquinimod treatment altered subpopulations of myeloid antigen presenting cells (APC) that included a decrease in CD11c(+)CD11b(+)CD4(+) dendritic cells (DC) and an elevation of CD11b(hi)Gr1(hi) monocytes. CD11b(+) cells from these mice exhibited an anti-inflammatory type II phenotype characterized by reduced STAT1 phosphorylation, decreased production of IL-6, IL-12/23 and TNF, and increased IL-10. In adoptive transfer, donor type II monocytes from laquinimod-treated mice suppressed clinical and histologic disease in recipients with established EAE. As effects were observed in both APC and T cell compartments, we examined whether T cell immune modulation occurred as a direct effect of laquinimod on T cells, or as a consequence of altered APC function. Inhibition of Th1 and Th17 differentiation was observed only when type II monocytes or DC from laquinimod-treated mice were used as APC, regardless of whether myelin-specific T cells were obtained from laquinimod-treated or untreated mice. Thus, laquinimod modulates adaptive T cell immune responses via its effects on cells of the innate immune system, and may not influence T cells directly.

Dimethyl fumarate (DMF) (BG-12, Tecfidera) is a fumaric acid ester (FAE) that was advanced as a multiple sclerosis (MS) therapy largely for potential neuroprotection as it was recognized that FAEs are capable of activating the antioxidative transcription factor nuclear factor (erythroid-derived 2)-like 2 (Nrf2) pathway. However, DMF treatment in randomized controlled MS trials was associated with marked reductions in relapse rate and development of active brain MRI lesions, measures considered to reflect CNS inflammation. Here, we investigated the antiinflammatory contribution of Nrf2 in DMF treatment of the MS model, experimental autoimmune encephalomyelitis (EAE). C57BL/6 wild-type (WT) and Nrf2-deficient (Nrf2(-/-)) mice were immunized with myelin oligodendrocyte glycoprotein (MOG) peptide 35-55 (p35-55) for EAE induction and treated with oral DMF or vehicle daily. DMF protected WT and Nrf2(-/-) mice equally well from development of clinical and histologic EAE. The beneficial effect of DMF treatment in Nrf2(-/-) and WT mice was accompanied by reduced frequencies of IFN-γ and IL-17-producing CD4(+) cells and induction of antiinflammatory M2 (type II) monocytes. DMF also modulated B-cell MHC II expression and reduced the incidence of clinical disease in a B-cell-dependent model of spontaneous CNS autoimmunity. Our observations that oral DMF treatment promoted immune modulation and provided equal clinical benefit in acute EAE in Nrf2(-/-) and WT mice, suggest that the antiinflammatory activity of DMF in treatment of MS patients may occur through alternative pathways, independent of Nrf2.