Xenogeneic interaction between human CD40L and porcine CD40 activates porcine endothelial cells through NF-κB signaling

Up-regulation of fibrinogen-like protein 2 in porcine endothelial cells by xenogeneic CD40 signal

Acute humoral xenograft rejection (AHXR), characterized by thrombin generation and endothelial cell activation, should be overcome for the success of xenotransplantation. Fibrinogen-like protein 2 (fgl2) expressed on endothelial cells can convert prothrombin to thrombin directly, which indicates that the induced fgl2 expression in activated endothelial cells can contribute to thrombosis. In xenotransplant condition, the interaction between human CD40L and porcine endothelial CD40 can activate endothelial cells. In this study, we investigated the effect of endothelial cell activation through the interaction between human CD40L and porcine CD40 on fgl2 expression and its function as a direct prothrombinase. We found that CD40 stimulation up-regulated fgl2 expression as well as its enzymatic activity in porcine endothelial cells. Moreover, functional studies using knock-down system showed that the major factor converting human prothrombin to thrombin is fgl2 protein expressed on porcine endothelial cells. Overall, this study demonstrates that fgl2 expression can be induced by xenogeneic CD40 signal on endothelial cells and contribute to thrombin generation.

Targeting and liposomal drug delivery to CD40L expressing T cells for treatment of autoimmune diseases

CD40L is considered as an important target for the treatment of autoimmune diseases. There have been many efforts devoted to the development of antibodies and other molecules to disrupt CD40/CD40L interaction for therapeutic benefits. In this study, we designed a CD40L specific peptide ligand - A25 based on CD40L crystal structure and molecular docking studies. Its binding affinity and specificity to CD40L were confirmed by Surface Plasmon Resonance (SPR) measurements. The peptide A25 was then conjugated on the surface of liposomes and shown to be able to mediate specific liposomal drug delivery to CD40L+ cells. Loaded with the cytostatic drug methotrexate (MTX), the A25 modified liposome could significantly reduce the CD40L+ cell ratios in the experimental autoimmune encephalomyelitis (EAE) mice, resulting in great improvement in clinical scores. Since CD40L+ cells are involved in the pathological development of many auto-immune diseases, A25 conjugated drug targeting systems may be useful for developing therapies that are more efficacies and with less side effects.

Costimulatory molecule CD40 is essential for myelin protein 0 peptide 106-125-induced experimental autoimmune neuritis in mice

Myelin protein 0 peptide 106-125-induced murine experimental autoimmune neuritis (EAN) is a CD4-positive T cell-mediated monophasic axonal inflammatory neuropathy; interferon-γ is the key proinflammatory mediator. Experimental autoimmune neuritis is well suited for elucidating pathogenetic mechanisms underlying human acute axonal Guillain-Barré syndrome. Here, the functional role of the costimulatory molecule CD40 was defined by characterization of EAN in CD40-deficient mice. In contrast to immunized C57BL/6 mice, CD40-deficient mice were resistant to EAN owing to impaired priming of CD4-positive T-effector cells. To determine whether CD40 is a suitable candidate for the treatment of EAN, we administered monoclonal anti-CD40 antibody either before immunization or upon onset of neurologic signs. Prophylactic anti-CD40 treatment completely abolished CD4-positive T-cell priming. Therapeutic application of anti-CD40 prevented full activation of CD4-positive T cells that were in the process of priming and suppressed production of interferon-γ in peripheral lymph nodes, spleen, and serum, and of interleukin-6, interleukin-12p40, intercellular adhesion molecule-1, and vascular cell adhesion molecule-1, which are associated with activation of the nuclear factor-κB signaling pathway. This resulted in enhanced recovery by early generation of CD25-positive, Foxp3-positive, CD4-positive regulatory T cells. Thus, these experiments highlight the crucial role of CD40 as an important costimulatory molecule in EAN and suggest that it has potential as a therapeutic target in human neuritis.

Relative efficiency of porcine and human cytotoxic T-lymphocyte antigen 4 immunoglobulin in inhibiting human CD4+ T-cell responses co-stimulated by porcine and human B7 molecules

α1,3-Galactosyltransferase gene-knockout pigs transgenic for porcine cytotoxic T-lymphocyte antigen 4 immunoglobulin (pCTLA4-Ig) have been produced to reduce T-cell-mediated rejection following xenotransplantation. The level of soluble pCTLA4-Ig in their blood was greatly in excess of the therapeutic level in patients, rendering the pigs immune-incompetent. Soluble pCTLA4-Ig produced by these transgenic pigs was evaluated for binding to porcine and human (h) B7 molecules, and for its inhibitory effect on allogeneic and xenogeneic human T-cell responses. Porcine CTLA4-Ig-expressing peripheral blood mononuclear cells (PBMCs) and aortic endothelial cells (AECs) were evaluated for their direct inhibitory effect on hCD4+ T-cell responses. Soluble pCTLA4-Ig and purified hCTLA4-Ig showed similar binding to pB7 molecules, but pCTLA4-Ig showed significantly less binding to hB7 molecules. The pCTLA4-Ig and hCTLA4-Ig inhibited the response of hCD4+ T cells to pAECs equally, but pCTLA4-Ig was less successful in inhibiting the human allogeneic response. The hCD4+ T-cell response to PBMCs from pCTLA4-Ig pigs was significantly lower than that of non-pCTLA4-Ig pigs. Although pCTLA4-Ig was detected in the cytoplasm of pCTLA4-Ig-expressing pAECs, only a minimal level of soluble pCTLA4-Ig was detected in the supernatant during culture, and pCTLA4-Ig-expressing pAECs did not inhibit the xenogeneic direct human T-cell response. High-level tissue-specific production of pCTLA4-Ig may be required for sufficient immunosuppression for organ or cell (e.g., islets) transplantation.

Which anti-platelet therapies might be beneficial in xenotransplantation?

Xenotransplantation could provide an unlimited and elective supply of grafts, once mechanisms of graft loss and vascular injury are better understood. The development of α-1,3-galactosyltransferase gene-knockout (GalT-KO) swine with the removal of a dominant xeno-antigen has been an important advance; however, delayed xenograft and acute vascular reaction in GalT-KO animals persist. These occur, at least in part, because of humoral reactions that result in vascular injury. Intrinsic molecular incompatibilities in the regulation of blood clotting and extracellular nucleotide homeostasis between discordant species may also predispose to thrombophilia within the vasculature of xenografts. Although limited benefits have been achieved with currently available pharmacological anti-thrombotics and anti-coagulants, the highly complex mechanisms of platelet activation and thrombosis in xenograft rejection also require potent immunosuppressive interventions. We will focus on recent thromboregulatory approaches while elucidating appropriate anti-platelet mechanisms. We will discuss potential benefits of additional anti-thrombotic interventions that are possible in transgenic swine and review recent developments in pharmacological anti-platelet therapy.

Stimulatory and inhibitory receptor interactions in xenotransplantation

PURPOSE OF REVIEW

Cellular human antipig immune responses are increasingly recognized as an important barrier to successful clinical xenotransplantation. This review addresses the role of monocytes/macrophages, natural killer (NK) cells, and T cells in xenograft rejection. We focus on the receptor-ligand interactions that regulate the responses of these cells to porcine tissues and thus could be targets for immunomodulation.

RECENT FINDINGS

Activation of human monocytes by pig cells is partly due to the incapacity of porcine ligands to bind to inhibitory receptors such as signal regulatory protein alpha. Porcine UL16-binding protein 1 can functionally interact with human NK group 2D protein, thereby contributing to human NK cell activity. Transgenic pigs overexpressing human leukocyte antigen class E were generated. Cells from these pigs induced diminished NK-cell lysis, suggesting that human leukocyte antigen class E expression compensates for the inability of porcine ligands to bind to the inhibitory CD94/NK group 2A receptor on human NK cells. A new concept for the modulation of antipig T-cell reactivity may result from the finding that porcine antigen-presenting cells that overexpress human negative costimulatory PD ligands also induce diminished responses of human T cells.

SUMMARY

Disruption of stimulatory receptor-ligand interactions (e.g. by blocking antibodies or 'knockout/down' technologies) combined with transgenic overexpression of inhibitory ligands in porcine cells and tissues could be an effective approach to downregulate human antipig cellular immune responses.

Soluble CD40 ligand induces endothelial dysfunction in human and porcine coronary artery endothelial cells

The purpose of this study was to determine the effects and mechanisms of sCD40L on endothelial dysfunction in both human coronary artery endothelial cells (HCAECs) and porcine coronary artery rings. HCAECs treated with sCD40L showed significant reductions of endothelial nitric oxide synthase (eNOS) mRNA and protein levels, eNOS mRNA stability, eNOS enzyme activity, and cellular NO levels, whereas superoxide anion (O(2)(-)) production was significantly increased. sCD40L enhanced eNOS mRNA 3'UTR binding to cytoplasmic molecules and induced a unique expression pattern of 95 microRNAs. sCD40L significantly decreased mitochondrial membrane potential, and catalase and SOD activities, whereas it increased NADPH oxidase (NOX) activity. sCD40L increased phosphorylation of MAPKs p38 and ERK1/2 as well as IkappaBalpha and enhanced NF-kappaB nuclear translocation. In porcine coronary arteries, sCD40L significantly decreased endothelium-dependent vasorelaxation and eNOS mRNA levels, whereas it increased O(2)(-) levels. Antioxidant seleno-l-methionine; chemical inhibitors of p38, ERK1/2, and mitochondrial complex II; as well as dominant negative mutant forms of IkappaBalpha and NOX4 effectively blocked sCD40L-induced eNOS down-regulation in HCAECs. Thus, sCD40L reduces eNOS levels, whereas it increases oxidative stress through the unique molecular mechanisms involving eNOS mRNA stability, 3'UTR-binding molecules, microRNAs, mitochondrial function, ROS-related enzymes, p38, ERK1/2, and NF-kappaB signal pathways in endothelial cells.