title: Blocking both signal 1 and signal 2 of T-cell activation prevents apoptosis of alloreactive T cells and induction of peripheral allograft tolerance.
abstract: The alloimmune response against fully MHC-mismatched allografts, compared with immune responses to nominal antigens, entails an unusually large clonal size of alloreactive T cells. Thus, induction of peripheral allograft tolerance established in the absence of immune system ablation and reconstitution is a challenging task in transplantation. Here, we determined whether a reduction in the mass of alloreactive T cells due to apoptosis is an essential initial step for induction of stable allograft tolerance with non-lymphoablative therapy. Blocking both CD28-B7 and CD40-CD40 ligand interactions (co-stimulation blockade) inhibited proliferation of alloreactive T cells in vivo while allowing cell cycle-dependent T-cell apoptosis of proliferating T cells, with permanent engraftment of cardiac allografts but not skin allografts. Treatment with rapamycin plus co-stimulation blockade resulted in massive apoptosis of alloreactive T cells and produced stable skin allograft tolerance, a very stringent test of allograft tolerance. In contrast, treatment with cyclosporine A and co-stimulation blockade abolished T-cell proliferation and apoptosis, as well as the induction of stable allograft tolerance. Our data indicate that induction of T-cell apoptosis and peripheral allograft tolerance is prevented by blocking both signal 1 and signal 2 of T-cell activation.
authors.affiliation: Department of Medicine, Harvard Medical School, Division of Immunology, Beth Israel Deaconess Medical Center, Boston, Massachusetts 02215, USA.
authors.forename: Y
authors.initials: Y
authors.lastname: Li
authors.forename: X C
authors.initials: XC
authors.lastname: Li
authors.forename: X X
authors.initials: XX
authors.lastname: Zheng
authors.forename: A D
authors.initials: AD
authors.lastname: Wells
authors.forename: L A
authors.initials: LA
authors.lastname: Turka
authors.forename: T B
authors.initials: TB
authors.lastname: Strom
mesh_terms: D000222:Adaptation, Physiological / Q000276:immunology; D000818:Animals; D017209:Apoptosis / Q000276:immunology*; D002455:Cell Division / Q000276:immunology; D006085:Graft Survival / Q000276:immunology*; D008213:Lymphocyte Activation; D051379:Mice; D008815:Mice, Inbred Strains; D015398:Signal Transduction; D013601:T-Lymphocytes / Q000166:cytology / Q000276:immunology*