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Biomedical subjects

L A Turka

Publications and source records attributed to L A Turka.

At least 37 records · Page 2Linked to original sources
PubMed1999

The role of CD80, CD86, and CTLA4 in alloimmune responses and the induction of long-term allograft survival.

Blocking the interaction of the CD28 costimulatory receptor with its ligands, CD80 and CD86, inhibits in vivo immune responses, such as allograft rejection, and in some instances induces tolerance. Previously, we found that CTLA4Ig, which blocks the CD28/CTLA-4 (CD152) ligands CD80 and CD86, can be used to induce transplantation tolerance to vascularized allografts. Recent data suggest that an intact CD152-negative signaling pathway is essential for induction of tolerance to nominal Ags. Here, we show that blockade of CD152 using an anti-CD152 mAb at the time of transplantation prevents the induction of long-term allograft survival by agents that target CD80 and CD86. In contrast, CD152 signals are not required for the maintenance of established graft survival. We also report for the first time that blockade of CD86 alone can induce long-term graft survival. This requires that anti-CD86 mAb is given on the day of transplantation and also depends upon an intact CD152 pathway. This result, plus experiments using CD80-deficient mice, suggests a dominant role for CD80 molecules on donor cells as the relevant ligand for CD152. We additionally find that blockade of CD152 at the time of transplantation does not interfere with the effectiveness of anti-CD154 mAbs, suggesting distinct mechanisms for inhibition of graft rejection by blocking the CD28 vs CD154 pathways.

Abatacept↗
PubMed1999

Generation of protective immunity against an immunogenic carcinoma requires CD40/CD40L and B7/CD28 interactions but not CD4(+) T cells.

Interactions between CD40 and CD40L play a central role in the regulation of both humoral and cellular immunity. Recently, interactions between these molecules have also been implicated in the generation of protective cell-mediated tumor immunity. We have generated a tumor model in which a well-understood and clearly immunostimulatory antigen, influenza hemagglutinin has been transfected into the BALB/c-derived, MHC-class-I-positive, B7-deficient murine mammary carcinoma, MT901. In this model, expression of the influenza hemagglutinin antigen does not alter tumorigenicity in naïve but serves as a tumor-rejection target in immunized mice. T-cell-depletion experiments indicate that successful tumor protection can occur following immunization in mice depleted of CD4(+) but not CD8(+) T cells, suggesting that tumor protection is largely CD8-mediated and CD4-independent. Interestingly, despite the ability of tumor protection to be generated in the absence of CD4(+) T cells, effective immunization was clearly dependent on CD40/CD40L as well as CD28/B7 interactions.

Abatacept↗
PubMed1999

Functional characterization of soluble and membrane-bound forms of vaccinia virus complement control protein (VCP).

Vaccinia virus secretes a 35 kD protein, vaccinia virus complement control protein (VCP), that inhibits the classical and alternative pathways of complement at several points, indicating that it may be a viral analogue of human complement receptor type 1 (CR1; CD35). Structurally, however, CR1 is composed of 30 short consensus repeats (SCRs), whereas VCP consists entirely of four SCRs. We have begun a structure-function analysis of VCP to define the minimum number of SCRs necessary for function, the functional differences between VCP and CR1, and the potential therapeutic roles for VCP. We addressed these questions by creating and characterizing recombinant soluble and membrane-bound forms of VCP. We have determined that (1) VCP requires all four SCRs to bind C3b, (2) whereas CR1 binds C3b and iC3b, VCP binds C3b but not iC3b, and (3) although normally secreted, if expressed on the membrane of mammalian cells, VCP effectively protects the cells from complement-mediated lysis. Thus, VCP appears to be a compact and unique complement regulatory protein with the ability to inhibit both arms of the complement cascade, but lacking affinity for iC3b. By releasing rather than capturing iC3b-bearing complexes following inactivation of C3b, VCP may 'recycle' its active site locally among infected cells, and thereby enable the virus to evade more efficiently host immune and inflammatory responses. The unique function, compact structure, and capacity of VCP to protect mammalian cells from complement-mediated attack, suggests that it could be used both to better understand the structure-function relationship of complement regulatory proteins, in general, and also to rationally design and develop novel therapeutic agents.

Animals↗
PubMed1999

Tissue-specific consequences of the anti-adenoviral immune response: implications for cardiac transplants.

The immune response to adenoviral vectors can induce inflammation and loss of transgene expression in transfected tissues. This would limit the use of adenovirus-mediated gene transfer in disease states in which long-term gene expression is required. While studying the effect of the anti-adenoviral immune response in transplantation, we found that transgene expression persisted in cardiac isografts transfected with an adenovirus encoding beta-galactosidase. Transfected grafts remained free of inflammation, despite the presence of an immune response to the vector. Thus, adenovirus-mediated gene transfer may have therapeutic value in cardiac transplantation and heart diseases. Furthermore, immunological limitations of adenoviral vectors for gene therapy are not universal for all tissue types.

Adenoviridae↗
PubMed1999

Blocking both signal 1 and signal 2 of T-cell activation prevents apoptosis of alloreactive T cells and induction of peripheral allograft tolerance.

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.

Adaptation, Physiological↗
PubMed1999

Requirement for T-cell apoptosis in the induction of peripheral transplantation tolerance.

The mechanisms of allograft tolerance have been classified as deletion, anergy, ignorance and suppression/regulation. Deletion has been implicated in central tolerance, whereas peripheral tolerance has generally been ascribed to clonal anergy and/or active immunoregulatory states. Here, we used two distinct systems to assess the requirement for T-cell deletion in peripheral tolerance induction. In mice transgenic for Bcl-xL, T cells were resistant to passive cell death through cytokine withdrawal, whereas T cells from interleukin-2-deficient mice did not undergo activation-induced cell death. Using either agents that block co-stimulatory pathways or the immunosuppressive drug rapamycin, which we have shown here blocks the proliferative component of interleukin-2 signaling but does not inhibit priming for activation-induced cell death, we found that mice with defective passive or active T-cell apoptotic pathways were resistant to induction of transplantation tolerance. Thus, deletion of activated T cells through activation-induced cell death or growth factor withdrawal seems necessary to achieve peripheral tolerance across major histocompatibility complex barriers.

Abatacept↗
PubMed1999

T cell costimulatory blockade: new therapies for transplant rejection.

Optimal T cell responses occur when T cells receive both antigen-specific signals through the T cell receptor and non-antigen-specific costimulatory signals through accessory cell surface molecules. The best understood costimulatory receptor is CD28. Signals through the T cell receptor and CD28 cooperatively induce cytokine gene expression and promote T cell proliferation and survival. Negative signals delivered through a related cell surface receptor, cytotoxic T lymphocyte antigen (CTLA-4), act to terminate immune responses and are required for normal immune homeostasis. This article reviews T cell costimulation, including the CD28/CTLA-4 system and other potential costimulatory pathways (such as CD40/CD154), the role of these pathways in normal immune responses, and the potential for the inhibition of these pathways to induce transplantation tolerance.

Animals↗
PubMed1999

Blocking costimulatory signals to induce transplantation tolerance and prevent autoimmune disease.

Similar cellular and molecular mechanisms are responsible for the pathogenesis of transplant rejection and autoimmunity. Recent advances in the studies of lymphocyte activation have shown a requirement for two distinct signals for full activation and development of effector function. The first signal is antigen itself; the second is a nonspecific costimulatory signal, the best example of which is delivered through the CD28 receptor. We and others have shown that blockade of this costimulatory signal can be used as part of strategy to prevent or treat transplant rejection and autoimmune disorders in animal models. This paper will review these findings and discuss their implications for clinical use.

Abatacept↗
PubMed1998

Utility of adenoviral-mediated Fas ligand gene transfer to modulate islet allograft survival.

BACKGROUND: 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. METHODS: 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. RESULTS: 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. CONCLUSION: 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.

Adenoviridae↗
PubMed1998

What's new in transplant immunology: problems and prospects.

In the past 40 years, transplantation has moved from an experimental form of therapy used almost exclusively for renal failure to an accepted treatment for end-stage kidney disease, heart disease, liver disease, lung disease, and diabetes mellitus. Tissue transplantation for conditions from thermal injury to Parkinson disease is being investigated. The primary barrier in transplantation medicine is the immunologic reaction of the recipient to donor organs and tissues. Currently available drugs permit excellent short-term graft survival but have not led to reliable long-term survival. Recent advances in the understanding of this immune response have suggested new approaches to induction of immunologic tolerance and reduction of late graft losses. Because of the excellent short-term success of current agents, integration of these new approaches into clinical trials is challenging and raises important questions about the design of such trials.

Graft Survival↗
PubMed1998

Individual T cells hold unexpected clues to the nature of anergy and memory.

The primary interest of our laboratory is understanding how the signals that a T cell receives influence its behavior during an immune response. Recently, we have focused our attention on the examination of T cell responses at an individual cell level. This article outlines our approach, presents our initial findings, and discusses the implications of these findings relative to our current models of T cell activation.

Animals↗
PubMed1998

Adenoviral transduction of melanoma cells with B7-1: antitumor immunity and immunosuppressive factors.

Previous studies in experimental models have demonstrated that the transduction of human or murine melanoma cells with the co-stimulatory B7-1 molecule induces effective antitumor immune responses. In order to develop B7-1 gene transfer as a therapeutic tool in the clinical management of melanoma, efficient means of in vivo gene transfer must be used. To this end we evaluated in vitro and in vivo immune responses associated with adenoviral transduction of murine and human melanoma cells with B7-1. Adenovirus-mediated transduction of human and murine melanoma cells with B7-1 leads to high-level transgene expression in vitro and in vivo and does not affect MHC class I and II expression. Adenovirus-delivered B7-1 induced antitumor immune responses, on the basis of observations that human melanoma cells transduced to express human B7-1 were able to co-stimulate allogeneic and autologous T cells to proliferate and that murine melanoma K1735 cells transduced to express murine B7-1 were rejected by syngeneic, immunocompetent mice. By contrast, intratumoral injection of an adenovirus encoding murine B7-1 failed to eliminate established murine melanoma (K1735) despite high-level transgene expression in tumor cells. Potent T cell inhibitory factor(s) secreted by both K1735 cells and select human melanoma cells may contribute to the failure to achieve protection in this setting. Thus, immune inhibitory melanoma-derived factors need to be taken into account when considering the clinical use of B7-1 immunotherapy.

Adenoviridae↗
PubMed1998

Antibody-induced transplant arteriosclerosis is prevented by graft expression of anti-oxidant and anti-apoptotic genes.

We investigated the pathogenesis of chronic allograft rejection in mouse cardiac allografts. Long-term survival occurred after administration of monoclonal antibody to CD4 or CD40-ligand (CD40L) plus donor cells. Both treatments induced permanent graft survival, but, in contrast to transplants in mice treated with CD4 monoclonal antibody, grafts in mice treated with CD40L monoclonal antibody lacked evidence of chronic rejection, including transplant arteriosclerosis. Freedom from chronic rejection in the group treated with CD40L monoclonal antibody correlated with vascular expression of the 'protective' genes heme oxygenase-1 (HO-1), Bcl-xL and A20. Moreover, arteriosclerosis was induced in allografts in immunoglobulin-deficient mice by antibody transfer only when the transfer was done before expression of protective genes. A direct role for protective gene expression in endothelial cells was demonstrated by in vitro experiments in which induction of HO-1 or Bcl-xL suppressed alloantibody-stimulated endothelial activation. Finally, induction of HO-1 in vivo protected allografts against chronic injury. These data show a role for protective genes in the prevention of chronic rejection, and indicate new approaches to protect grafts against development of transplant arteriosclerosis.

Animals↗
PubMed1998

Adenovirus-mediated gene transfer into cold-preserved liver allografts: survival pattern and unresponsiveness following transduction with CTLA4Ig.

The immune response of liver transplant recipients was modulated via adenovirus-mediated transduction of the cold-preserved liver with sequences encoding CTLA4Ig. Transplanted allografts demonstrated rapid transient local expression and recombinant protein production shortly after revascularization, resulting in intact liver function, indefinite survival of the recipient, and the development of donor-specific unresponsiveness. Lymphocytic infiltration of the graft was mainly of the T helper 2 (Th2) subset and was not associated with injury to primary cellular targets of the alloimmune response. These findings demonstrate a successful outcome of a feasible and potentially clinically relevant system of gene delivery of sequences encoding proteins capable of inhibiting the alloimmune response.

Abatacept↗
PubMed1998

Blunting of immune responses to adenoviral vectors in mouse liver and lung with CTLA4Ig.

Adenoviral vectors deleted of E1 are attractive vehicles for in vivo gene therapy because efficient gene transfer can be achieved. Immune responses to the vector and vector-transduced cells lead to destruction of target cells, inflammation and difficulties with vector readministration. Immune effectors have been identified as CD8+ cytotoxic T lymphocytes, which destroy vector-transduced cells, as well as B cells which secrete neutralizing antibodies and block repeated gene transfer. The central role of CD4+ T cells in the activation of both of these effector functions has focused immunosuppressive strategies towards blockade of costimulatory molecules. We describe in this study a strategy which aims to inhibit CD4+ T cell activation by transiently administering an inhibitor of the CD28/B7 pathway, ie CTLA4Lg, at the time an E1-deleted adenovirus is administered to liver or lung. In lung, CTLA4Ig treatment significantly blocked the formation of neutralizing antibodies, allowing efficient readministration of virus, whereas transgene expression was only moderately prolonged. In contrast, CTLA4Ig did not suppress neutralizing antibody formation in the context of liver gene therapy, but resulted in more stable gene expression. In vitro assays revealed suppression of T cell activation in either organ. This observation suggests that transient inhibition of the CD28/B7 pathway at the time of virus instillation can partially interfere with both arms of the immune response to adenovirus-mediated gene transfer circumventing the need for chronic immune suppression.

Abatacept↗