[Show abstract][Hide abstract] ABSTRACT: One of the best-defined mechanisms for the induction of apoptosis involves signaling via the cell surface molecule Fas, after binding of Fas ligand. Expression of Fas ligand is tightly regulated, being expressed primarily by T cells after activation, where it serves as a self-regulatory mechanism for immune responses. Fas ligand has also been found to be expressed constitutively at sites of immune privilege such as the testes and the anterior chamber of the eye. Recently, co-transplantation of Fas ligand-transfected myoblasts in association with islet cell allografts was shown to prolong islet allograft survival but only rarely led to indefinite graft survival. Graft rejection was associated with loss of Fas ligand on the myoblasts, suggesting that direct expression of the transgene on the islets might be more effective.
A replication-defective adenoviral construct containing murine Fas ligand (Ad/MFL) was prepared by homologous recombination. NIH 3T3 cells, rodent splenocytes, and murine islets were infected with Ad/MFL and examined in vitro for functional murine Fas ligand expression. Survival of Ad/MFL-infected islets was subsequently evaluated in vivo in both syngeneic and allogeneic islet transplantation models.
Cell lines and islet allografts transfected with Ad/MFL expressed a functional Fas ligand, capable of inducing apoptosis (confirmed by three distinct assays for DNA fragmentation) in Fas+ targets, but not in Fas- controls. Furthermore, Ad/MFL was able to modify allogeneic immune responses in vitro, as addition of this virus, but not a control adenovirus, significantly reduced proliferation in a mixed lymphocyte reaction. Surprisingly, however, transplantation of islet allografts transfected with Ad/MFL resulted in long-term allograft survival in only 1 of 30 recipients. Moreover, adenoviral-mediated Fas ligand gene transfer was complicated by transient, dose-dependent islet dysfunction, perhaps contributing to the lack of long-term engraftment.
These data suggest that adenoviral-mediated Fas ligand expression may impair normal islet function in vivo, and indicate that alternative strategies for Fas ligand transgene delivery may be required in this setting.
[Show abstract][Hide abstract] ABSTRACT: Mucosal and systemic administrations of high dose antigens induce long-lasting peripheral T cell tolerance. We and others have shown that high dose peripheral T cell tolerance is mediated by anergy or deletion and is preceded by T cell activation. Co-stimulatory molecules B7-1 (CD80)/B7-2 (CD86) and their counter-receptors CD28/CTLA-4 play pivotal roles in T cell activation and immune regulation. In the present study, we examined the roles of the B7 co-stimulation pathway in the generation of high dose peripheral T cell tolerance. We found that blocking B7:CD28/CTLA-4 interaction at the time of tolerance induction partially prevented T cell tolerance, whereas selective blockade of B7:CTLA-4 interaction completely abrogated peripheral T cell tolerance induced by either oral or i.p. antigens. These results suggest that CTLA-4-mediated feedback regulation plays a crucial role in the induction of high dose peripheral T cell tolerance.
International Immunology 05/1998; 10(4):491-8. · 3.14 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Although both B7 and its counter-receptor CD28 are expressed in the thymus, the role of B7 in thymic selection is not clear. We investigated the role of B7 in intrathymic deletion of antigen-specific T cells using a TCR transgenic model specific for antigen ovalbumin (OVA) and H-2Ad. Intraperitoneal injection of OVA induced apoptosis of thymocytes and drastic reduction of thymocyte numbers. This was significantly inhibited by co-injection of CTLA-4-Ig which blocks B7 co-stimulation. Deletion of T cells in the thymus following i.p. injection of OVA was associated with T cell pre-activation as demonstrated by T cell proliferation and cytokine production. Injection of CTLA-4-Ig blocked all these activation events and rescued thymocytes from activation-induced cell death. These results demonstrate that B7 is required for the activation-induced cell death of MHC class II-restricted thymocytes in vivo.
International Immunology 12/1997; 9(11):1663-8. · 3.14 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Although it is well established that CD40 and its ligand (CD40L) play pivotal roles in the development of humoral immunity, their roles in cell-mediated immunity and cell-mediated autoimmune diseases are not well defined. We report here that CD40:CD40L interaction is crucial for the development of experimental autoimmune encephalomyelitis (EAE), a prototype TH1-cell mediated autoimmune disease. Specific blockade of CD40L at the time of immunization markedly suppressed the incidence, mortality, day of onset, and clinical scores of EAE in (PLJ x SJL) F1 mice. Importantly, the disease suppression was not associated with anergy or deletion of autoreactive T cells but was accompanied by a drastic alteration of their cytokine profiles. The production of interferon (IFN)-gamma was markedly suppressed while that of interleukin (IL)-4 enhanced. These results suggest that CD40:CD40L interaction plays important roles in the differentiation of autoreactive TH1 versus TH2 cells in vivo, and that CD40L blockade is effective in preventing autoimmune encephalomyelitis.
Journal of Molecular Medicine 09/1997; 75(8):603-8. · 4.77 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Both rheumatoid arthritis and animal models of autoimmune arthritis are characterized by hyperactivation of synovial cells and hyperplasia of the synovial membrane. The activated synovial cells produce inflammatory cytokines and degradative enzymes that lead to destruction of cartilage and bones. Effective treatment of arthritis may require elimination of most or all activated synovial cells. The death factor Fas/Apo-1 and its ligand (FasL) play pivotal roles in maintaining self-tolerance and immune privilege. Fas is expressed constitutively in most tissues, and is dramatically upregulated at the site of inflammation. In both rheumatoid arthritis and animal models of autoimmune arthritis, high levels of Fas are expressed on activated synovial cells and infiltrating leukocytes in the inflamed joints. Unlike Fas, however, the levels of FasL expressed in the arthritic joints are extremely low, and most activated synovial cells survive despite high levels of Fas expression. To upregulate FasL expression in the arthritic joints, we have generated a recombinant replication-defective adenovirus carrying FasL gene; injection of the FasL virus into inflamed joints conferred high levels of FasL expression, induced apoptosis of synovial cells, and ameliorated collagen-induced arthritis in DBA/1 mice. The Fas-ligand virus also inhibited production of interferon-gamma by collagen-specific T cells. Coadministration of Fas-immunoglobulin fusion protein with the Fas-ligand virus prevented these effects, demonstrating the specificity of the Fas-ligand virus. Thus, FasL gene transfer at the site of inflammation effectively ameliorates autoimmune disease.
Journal of Clinical Investigation 01/1997; 100(8):1951-1957. · 12.81 Impact Factor