Therapeutic Strategy for Rheumatoid Arthritis by Induction of Myeloid-Derived Suppressor Cells with High Suppressive Potential.

Combination treatment using fingolimod (FTY720), an immunomodulator, and a pathogenic antigen prevents the progression of glucose-6-phosphate isomerase (GPI)325-339-induced arthritis. In this study, we focused on myeloid-derived suppressor cells (MDSCs; CD11b+Gr-1+ cells) and investigated the effects of the combination treatment on these cells. DBA/1J mice with GPI325-339-induced arthritis were treated using FTY720 and/or GPI325-339 for five days. The expanded CD11b+Gr-1+ cell population and its inhibitory potential were examined. The percentage of CD369+CD11b+Gr-1+ cells effectively increased in the combination-treated mice. The inhibitory potential of CD369+CD11b+Gr-1+ cells was higher than that of cells not expressing CD369. Among bone marrow cells, the expression of CD369 in CD11b+Gr-1+ cells increased following stimulation with granulocyte-macrophage colony-stimulating factor, and the expression of CD11c increased accordingly. The increased CD11c expression indicated a decrease in the potential to suppress T cell proliferation based on the results of the suppression assay. The percentage of CD11c-CD369+ cells in CD11b+Gr-1+ cells that were induced by the combination treatment also increased, and these cells tended to have a higher capacity to inhibit T cell proliferation. In conclusion, the combination treatment using FTY720 and the pathogenic antigen effectively induces MDSC, which demonstrates a high potential for suppressing T cell proliferation in the lymph nodes, thereby establishing an immune-tolerant state.

Characterization of an Expanded IL-10-Producing-Suppressive T Cell Population Associated with Immune Tolerance.

An increase in the number of glucocorticoid-induced tumor necrosis factor receptor-family related gene/protein (GITR)+CD25- (or fork-head box protein 3: Foxp3-) CD4+ T cells, after treating a mouse model of arthritis with fingolimod (FTY720), and a pathogenic antigen may play a key role in the establishment of immune tolerance. In this study, we characterized a specific expanded T cell subset in this population. Mice with glucose-6-phosphate isomerase peptide (GPI325-339)-induced arthritis were treated with FTY720 (1 mg/kg, per os) and GPI325-339 (10 µg/mouse, intravenously) for five days, starting from the onset of symptoms. The expanded GITR+CD25- (or Foxp3-) CD4+ T cell population and its cytokine production were examined using flow cytometry. Furthermore, time-dependent changes in T-bet and/or early growth response gene 2 (Egr-2) expression in this T cell subset were examined. The density of T cell immunoreceptors with immunoglobulin (Ig) and immunoreceptor tyrosine-based inhibition motif domains (TIGIT)+CD39+ cell subset in the GITR+Foxp3-CD4+ T cell population was significantly increased only in the combined treatment group, compared to that in the untreated and single-treatment groups. In the TIGIT+CD39+GITR+Foxp3-CD4+ T cell population, T-bet+Egr-2+/T-bet+Egr-2- cell ratio increased in the latter stage of the treatment. Furthermore, this T cell subset, which corresponded to a T helper 1 (Th1) response, produced high levels of both interleukin (IL)-10 and interferon (IFN)-γ. In conclusion, expanded TIGIT+CD39+GITR+Foxp3-CD4+ T cells shifted from an effector Th1 to IL-10-producing-suppressor T cell phenotype, which may promote an immune-tolerant state.