Background Adoptive transfer of regulatory T cells (Tregs) is a promising approach to restore tolerance in autoimmune diseases. However based on the heterogeneity of the Tregs, we need to precisely establish which Tregs will be able to dampen efficiently the immune response in the various settings.

We previously showed the potential of CD49b⁺ Treg cells to protect and prevent an experimental model of arthritis. Nevertheless the optimal injection dose, the phenotype and the in vivo-suppressive mechanism of these Treg cells remain unknown. In our study, we investigated and compared the therapeutic potential of CD25⁺FoxP3⁺ and induced IL10-secreting CD49b⁺ Treg cells in an experimental model of arthritis, the collagen-induced arthritis (CIA).

Materials and Methods IL-10 secreting CD49b⁺ Treg cells were generated in naïve mice following repetitive injections of immature DCs (iDCs). Treg purification was based on the negative selection of CD4 T cells isolated from spleen and liver of the iDC-vaccinated mice. Cell sorting was performed to obtain 98% pure CD49b⁺ or CD25⁺ Treg cells. Several doses of CD49b⁺ were intravenously (i.v.) injected at day 28 in established CIA. Clinical signs of arthritis were scored, as well as biological parameters such as the level of anti-bCII antibodies in sera and the cytokine profile of bCII specific T cells. Phenotypes of both Treg cells were compared as well as their suppressive activity in vitro and in vivo.

Results Several doses of CD49⁺ Treg cells were tested in curative settings experiments. The dose of 10⁵ CD49b⁺ or CD25⁺ cells reverse clinical symptoms of arthritis while interestingly, a lack of efficacy was observed after higher doses. In vitro suppressive experiments confirmed the similar efficiency of both populations and phenotype analyses of CD49b⁺ Treg cells showed expression profile of several Treg specific markers (LAP⁺, LAG⁺, CTLA-4^high). Moreover, in an OVA-specific model of inflammation, we demonstrated the high impact of the CD49b Treg cells on the proliferation of effector cells in vivo.

Conclusions Altogether, our results confirm the therapeutic potential of IL-10 secreting T cells in experimental model of arthritis in curative settings and unravel their mechanism of suppression.