Background and Objectives Adoptive cell transfer of Treg cells is a promising approach to restore tolerance in autoimmune disease. However the various type of Tregs, their doses of injection and their in vivo-suppressive mechanism need to be precisely define to clearly establish which Tregs will be able to dampen efficiently the immune response in the various settings.
In our study, we compared the therapeutic potential of IL10-secreting Tregs: Tr1 and CD49b-induced Tregs and CD25+FoxP+ Tregs. These two Treg populations share several phenotypic markers as well as immunosuppressive properties. In the present study we perform adoptive cell transfer experiments of the various inducible Treg cells in order to compare their impact on the immune response.
Materials and Methods CD49b Treg cells were generated in naive mice following repetitive injections of immature dendritic cells (DC). Cell sorting experiments were realised to obtain 98% pure CD49b T cells and CD25+ cells. Collagen type II (bCII) specific Tr1 clones were obtained from TCR transgenic mice and expanded in vitro. Selected clones showed in vitro antigen specificity, Tr1 cytokine profile and IL10- and TGFβ-dependent suppressive activity. Several doses of CD49b or Tr1 cells were injected i.v. at day 28 in established collagen-induced arthritis. Clinical signs of arthritis were scored, as well as the in vivo impact on the proliferation of Teffector cells and the maturation of DC.
Results We defined for both Treg cell populations the most efficient dose in curative settings experiments. One single dose of 3 × 106 or 1 × 106 of Tr1 cell administration could reduce the incidence and severity of CIA. Interestingly, higher dose of 10M of Tr1 cells did not improve the disease. In the same manner, the dose of 105 CD4CD49b+ cells reverse clinical symptom with a lack of efficacy of higher doses. We demonstrated following injection of Treg cells a clear impact on the proliferation of the effector cells in vivo.
Conclusions Our results suggest that even if the Treg cells present some similarities, we need to precisely define the dose and type of Treg that will be efficient in each experimental setting. We provide also a comparative analysis of the in vivo mechanism responsible of the protection of the various subtypes of Treg cells.