Purpose: The mechanisms by which CD4+CD25+Foxp3+ T cells
(Tregs) regulate effector T cells in a transplantation setting and their in
vivo homeostasis still remain to be clarified. Using a mouse adoptive
transfer and skin transplantation model, we analyzed the in vivo
expansion, effector function and trafficking of effector T cells and
donor-specific Tregs, in response to an allograft.
Methods and materials: Antigen-specific Tregs were generated and
expanded in vitro by culturing freshly isolated Tregs from BALB/c
mice (H2d) with syngeneic dendritic cells pulsed with an allopeptide
(here the Kb peptide derived from the MHC class I molecule of
allogeneic H2b mice). Fluorescent-labelled CD4+CD25- naive T cells
and donor-antigen-specific Tregs were transferred alone or coinjected
into syngeneic BALB/c-Nude recipients transplanted with
allogeneic C57BL/6xBALB/c donor skin.
Results: As opposed to their in vitro hyporesponsiveness, Tregs
divided in vivo, migrated and accumulated in the allograft draining
lymph nodes (drLN) and within the graft. The co-transfer of Tregs did
not modify the early proliferation and homing of CD4+CD25- T cells
to secondary lymphoid organs. But, in the presence of Tregs, effector
T cells produced significantly less IFN- and IL-2 effector cytokines,
while higher amounts of IL-10 were detected in the spleen and drLN
of these mice. Furthermore, time-course studies showed that Tregs
were recruited into the allograft at a very early stage posttransplantation
and prevented infiltration by effector T cells.
Conclusion: Overall, our results suggest that suppression of graft
rejection involves the early recruitment of donor-specific Tregs at the
sites of antigenic challenge and that Tregs mainly regulate the effector
arm of T cell alloresponses.