Background: Experimental data have suggested that adoptive transfer of
CD4+CD25+Foxp3+ regulatory T cells (Tregs), capable of controlling immune
responses to specifi c auto- or alloantigens, could be used as a therapeutic strategy to
promote specifi c tolerance in T-cell mediated diseases and in organ transplantation
(Tx). However, before advocating the application of immunotherapy with Tregs in
Tx, we need to improve our understanding of their in vivo homeostasis, traffi cking
pattern and effector function in response to alloantigens.
Methods : Donor-antigen specifi c murine Tregs were generated and characterized
in vitro following our described protocols. Using an adoptive transfer and skin
allotransplantation model, we have analyzed the in vivo expansion and homing of
fl uorescent-labeled effector T cells (Teff) and Tregs, at different time-points after
Tx, using fl ow-cytometry as well as fl uorescence microscopy techniques.
Results: Tregs expressed CD62L, CCR7 and CD103 allowing their homing into
lymphoid and non-lymphoid tissues (gut, skin) after intravenous injection. While
hyporesponsive to TCR stimulation in vitro, transferred Tregs survived, migrated to
secondary lymphoid organs and preferentially expanded within the allograft draining
lymph nodes. Furthermore, Foxp3+ cells could be detected inside the allograft as early
as day 3-5 after Tx. At a much later time-point (day 60 after Tx), graft-infi ltrating
Foxp3+ cells were also detectable in tolerant recipients. When transferred alone,
CD4+CD25- Teff cells expanded within secondary lymphoid organs and infi ltrated
the allograft by day 3-5 after Tx. The co-transfer of Tregs limited the expansion of
alloreactive Teff cells as well as their recruitment into the allograft. The promotion
of graft survival observed in the presence of Tregs was in part mediated by the
inhibition of the production of effector cytokines by CD4+CD25- T cells.
Conclusion: Taken together, our results suggest that the suppression of allograft
rejection and the induction of Tx tolerance are in part dependant on the alloantigendriven
homing and expansion of Tregs. Thus, the appropriate localization of Tregs
may be critical for their suppressive function in vivo.