title: Contribution of regulatory T cells and effector T cell deletion in tolerance induction by costimulation blockade.
abstract: Blocking of costimulatory signals for T cell activation leads to tolerance in several transplantation models, but the underlying mechanisms are incompletely understood. We analyzed the involvement of regulatory T cells (Treg) and deletion of alloreactive cells in the induction and maintenance of tolerance after costimulation blockade in a mouse model of graft-vs-host reaction. Injection of splenocytes from the C57BL/6 parent strain into a sublethally irradiated F(1) offspring (C57BL/6 x C3H) induced a GVHR characterized by severe pancytopenia. Treatment with anti-CD40L mAb and CTLA4-Ig every 3 days during 3 wk after splenocyte injection prevented disease development and induced a long-lasting state of stable mixed chimerism (>120 days). In parallel, host-specific tolerance was achieved as demonstrated by lack of host-directed alloreactivity of donor-type T cells in vitro and in vivo. Chimerism and tolerance were also obtained after CD25(+) cell-depleted splenocyte transfer, showing that CD25(+) natural Treg are not essential for tolerance induction. We further show that costimulation blockade results in enhanced Treg cell activity at early time points (days 6-30) after splenocyte transfer. This was demonstrated by the presence of a high percentage of Foxp3(+) cells among donor CD4(+) cells in the spleen of treated animals, and our finding that isolated donor-type T cells at an early time point (day 30) after splenocyte transfer displayed suppressive capacity in vitro. At later time points (>30 days after splenocyte transfer), clonal deletion of host-reactive T cells was found to be a major mechanism responsible for tolerance.
authors.affiliation: Division of Clinical Immunology, University Hospital, Catholic University of Leuven, Leuven, Belgium.
authors.forename: Bert
authors.initials: B
authors.lastname: Verbinnen
authors.forename: An D
authors.initials: AD
authors.lastname: Billiau
authors.forename: Jan
authors.initials: J
authors.lastname: Vermeiren
authors.forename: Georgina
authors.initials: G
authors.lastname: Galicia
authors.forename: Dominique M A
authors.initials: DM
authors.lastname: Bullens
authors.forename: Louis
authors.initials: L
authors.lastname: Boon
authors.forename: Pascal
authors.initials: P
authors.lastname: Cadot
authors.forename: Greet
authors.initials: G
authors.lastname: Hens
authors.forename: Christiane
authors.initials: C
authors.lastname: Dewolf-Peeters
authors.forename: Stefaan W
authors.initials: SW
authors.lastname: Van Gool
authors.forename: Jan L
authors.initials: JL
authors.lastname: Ceuppens
mesh_terms: D019264:Adoptive Transfer; D000818:Animals; D018122:B7-1 Antigen / Q000276:immunology / Q000378:metabolism; D051940:B7-2 Antigen / Q000276:immunology / Q000378:metabolism; D018106:CD28 Antigens / Q000276:immunology / Q000378:metabolism; D019013:CD40 Antigens / Q000276:immunology / Q000378:metabolism; D023201:CD40 Ligand / Q000276:immunology / Q000378:metabolism; D005260:Female; D051858:Forkhead Transcription Factors / Q000276:immunology / Q000378:metabolism; D006086:Graft vs Host Disease / Q000276:immunology* / Q000378:metabolism; D008213:Lymphocyte Activation; D051379:Mice; D008809:Mice, Inbred C3H; D008810:Mice, Inbred C57BL; D013602:T-Lymphocytes, Cytotoxic / Q000276:immunology* / Q000378:metabolism; D050378:T-Lymphocytes, Regulatory / Q000276:immunology* / Q000378:metabolism; D018183:Transplantation Chimera / Q000276:immunology; D023001:Transplantation Tolerance
chemical_list: D018122:B7-1 Antigen; D051940:B7-2 Antigen; D018106:CD28 Antigens; D019013:CD40 Antigens; D051858:Forkhead Transcription Factors; C498833:Foxp3 protein, mouse; D023201:CD40 Ligand