Liver sinusoidal endothelial cells are insufficient to activate T cells

Autologous bone marrow-derived MSCs engineered to express oFVIII-FLAG engraft in adult sheep and produce an effective increase in plasma FVIII levels

Introduction

Hemophilia A (HA) is the most common X-linked bleeding disorder, occurring in 1 in 5,000 live male births and affecting >1 million individuals worldwide. Although advances in protein-based HA therapeutics have improved health outcomes, current standard-of-care requires infusion 2-3 times per week for life, and 30% of patients develop inhibitors, significantly increasing morbidity and mortality. There are thus unmet medical needs requiring novel approaches to treat HA.

Methods

We tested, in a highly translational large animal (sheep) model, whether the unique immunological and biological properties of autologous bone marrow (BM)-derived mesenchymal stromal cells (MSCs) could enable them to serve as cellular delivery vehicles to provide long-term expression of FVIII, avoiding the need for frequent infusions.

Results

We show that autologous BM-MSCs can be isolated, transduced with a lentivector to produce high levels of ovine (o)FVIII, extensively expanded, and transplanted into adult animals safely. The transplanted cells engraft in multiple organs, and they stably produce and secrete sufficient quantities of FVIII to yield elevated plasma FVIII levels for at least 15 weeks.

Discussion

These studies thus highlight the promise of cellular-based gene delivery approaches for treating HA.

Folic acid and RAAS blockers in ischemia/reperfusion-induced hepatic injury: A current mechanistic concept for understanding the incidence, significance & outcome

Hepatic ischemia-reperfusion injury (IRI) is not only one of the pathophysiological process involving the liver, but also a complex systemic process affecting multiple tissues and organs. IRI after liver transplant occurs due to in major resections and occlusion of vessels, or during the perioperative period, leads to acute liver failure which shows the dynamic process that involves two interrelated phases of local ischemic insult and inflammation-mediated reperfusion injury and has an impact on morbidity and mortality. The renin-angiotensin-aldosterone system (RAAS) is activated locally in the injured cells by the occurrence of I/R, which plays an essential role in the fate of the damaged tissue. However, a preclinical study explores the protective role of RAAS inhibitor in acute liver injury in a model of inflammation caused by ischemia and reperfusion. In-addition to RAAS blockers in monotherapy does not effectively block the complete pathway. Thus, the present study is designed to explore the effect of combined folic acid with RAAS blockers in combination, produce a synergistic effect. Moreover, in this review, we will describe the understanding of the possible incidence of downregulatory molecular mechanisms associated with renin-angiotensin-aldosterone system and the significance & outcome of the combination of folic acid and RAAS blockers in liver injury due to ischemia/reperfusion.

Design and Optimization of PLGA Particles to Deliver Immunomodulatory Drugs for the Prevention of Skin Allograft Rejection

Background: Recent advancements in therapeutic strategies have attracted considerable attention to control the acute organs and tissues rejection, which is the main cause of mortality in transplant recipients. The long-term usage of immunosuppressive drugs compromises the body immunity against simple infections and decrease the patients' quality of life. Tolerance of allograft in recipients without harming the rest of host immune system is the basic idea to develop the therapeutic approaches after induction of donor-specific transplant. Methods: Controlled and targeted delivery system by using biomimetic micro and nanoparticles as carriers is an effective strategy to deplete the immune cells in response to allograft in an antigen-specific manner. Polylactic-co-glycolic acid (PLGA) is a biocompatible and biodegradable polymer, which has frequently being used as drug delivery vehicle. Results: This review focuses on the biomedical applications of PLGA based biomimetic micro and nano-sized particles in drug delivery systems to prolong the survival of alloskin graft. Conclusion: We will discuss the mediating factors for rejection of alloskin graft, selective depletion of immune cells, controlled release mechanism, physiochemical properties, size-based body distribution of PLGA particles and their effect on overall host immune system.

Cellular and molecular targeting for nanotherapeutics in transplantation tolerance

The induction of donor-specific tolerance to transplanted cells and organs, while preserving immune function as a whole, remains a highly sought after and elusive strategy for overcoming transplant rejection. Tolerance necessitates modulating a diverse array of cell types that recognize and respond to alloantigens, including antigen presenting cells and T lymphocytes. Nanotherapeutic strategies that employ cellular and biomaterial engineering represent an emerging technology geared towards the goal of inducing transplant tolerance. Nanocarriers offer a platform for delivering antigens of interest to specific cell types in order to achieve tolerogenic antigen presentation. Furthermore, the technologies also provide an opportunity for local immunomodulation at the graft site. Nanocarriers delivering a combination of antigens and immunomodulating agents, such as rapamycin, provide a unique technology platform with the potential to enhance outcomes for the induction of transplant tolerance.

Overview on isolation, cultivation and identification of liver sinusoidal endothelial cells

Liver sinusoidal endothelial cells (LSECs) play an important role in the hepatic physiological and pathological processes, and they have become a hot research topic in recent years. This paper will focus on the isolation, cultivation and identification of LSECs by summarizing and reviewing the latest technologies and methods, with an aim to make a great contribution to the research of LSECs and their roles in the hepatic physiological and pathological processes.

Mechanisms of murine spontaneous liver transplant tolerance

Liver transplant is associated with the induction of peripheral immune tolerance. Liver allografts are accepted spontaneously in most combinations of mismatch in major histocompatibility complex, without any requirements for immunosuppression. Liver nonparenchymal cells (especially dendritic cells and Kupffer cells), costimulatory pathways, and activated T-cell apoptosis may contribute to the induction of liver tolerance. Therefore, liver tolerance is an active process that includes T-cell activation, proliferation, infiltration of the allograft, and T-cell apoptosis. Liver dendritic cells may modulate the amount of alloreactive T cells in liver graft recipients by expressing the coinhibitory molecule programmed death-ligand 1 and the immunosuppressive enzyme indoleamine 2,3-dioxygenase. Liver dendritic cells also may induce activated T-cell apoptosis and Foxp3+ regulatory T cells. Future studies may clarify the precise function of liver nonparenchymal cells, the interactions between programmed death-ligand 1 and other costimulatory signals, and the contribution of the liver microenvironment to the induction and expansion of Foxp 3 regulatory T cells.

Portal venous donor-specific transfusion in conjunction with sirolimus prolongs renal allograft survival in nonhuman primates

Pretransplant exposure to donor antigen is known to modulate recipient alloimmunity, and frequently results in sensitization. However, donor-specific transfusion (DST) can have a protolerant effect that is dependent on route, dose and coadministered immunosuppression. Rodent studies have shown in some strain combinations that portal venous (PV) DST alone can induce tolerance, and uncontrolled clinical use of PVDST has been reported. In order to determine if pretransplant PVDST has a clinically relevant salutary effect, we studied it and the influence of concomitant immunosuppression in rhesus monkeys undergoing renal allotransplantation. Animals received PVDST with unfractionated bone marrow and/or tacrolimus or sirolimus 1 week prior to transplantation. Graft survival was assessed without any posttransplant immunosuppression. PVDST alone or in combination with tacrolimus was ineffective. However, PVDST in combination with sirolimus significantly prolonged renal allograft survival to a mean of 24 days. Preoperative sirolimus alone had no effect, and peripheral DST with sirolimus prolonged graft survival in 2/4 animals, but resulted in accelerated rejection in 2/4 animals. These data demonstrate that PVDST in combination with sirolimus delays rejection in a modest but measurable way in a rigorous model. It may thus be a preferable method for donor antigen administration.

Suppressive efficacy and proliferative capacity of human regulatory T cells in allogeneic and xenogeneic responses

BACKGROUND

An understanding of the mechanisms that suppress the human anti-pig cellular response is key for xenotransplantation. We have compared the ability of human regulatory T cells (Tregs) to suppress xenogeneic and allogeneic responses in vitro.

METHODS

Human peripheral blood mononuclear cells (PBMC), CD4+ T cells, or CD4+ CD25- T cells were stimulated with irradiated human or wild type (WT) or alpha1,3-galactosyltransferase gene-knockout (GT-KO) pig PBMC in the presence or absence of human CD4+ CD25 high Tregs. In separate experiments, 5- (and 6)-carboxyfluorescein diacetate succinimidyl ester-labeled human CD4+ T cells were stimulated with human or pig PBMC. The expansion and precursor frequencies of allo- and xenoreactive Tregs were assessed by labeling with FoxP3 mAb and flow cytometric analysis.

RESULTS

The responses of human PBMC, CD4+ T cells, and CD4+ CD25- T cells to pig PBMC were stronger than to human PBMC (P<0.05). Human anti-GT-KO responses were weaker than anti-WT responses (P<0.05). Human CD4+ CD25 high Tregs suppressed proliferation of CD4+ CD25- T cells to both human and pig PBMC stimulator cells with the same efficiency. Alloreactive CD4+ CD25+ FoxP3 high responder T cells proliferated more than their xenoreactive counterparts (P<0.05), although xenoreactive CD4+ CD25+ T cells proliferated more than alloreactive cells (P<0.05). There was no difference in precursor frequency between allo- and xeno-reactive CD4+ CD25+ FoxP3 high cells.

CONCLUSIONS

Human T-cell responses to pig cells are stronger than to allogeneic cells. The human response to GT-KO PBMC is weaker than to WT PBMC. Although human Tregs can suppress both responses, expansion of CD4+ CD25+ FoxP3 high cells against pig PBMC is weaker than against human PBMC. More human Tregs may be required to suppress the stronger xenogeneic response.

Pretransplant infusion of mesenchymal stem cells prolongs the survival of a semiallogeneic heart transplant through the generation of regulatory T cells

In this study, we investigated whether mesenchymal stem cells (MSC) had immunomodulatory properties in solid organ allotransplantation, using a semiallogeneic heart transplant mouse model, and studied the mechanism(s) underlying MSC tolerogenic effects. Either single (portal vein, day -7) or double (portal vein, day -7 and tail vein, day -1) pretransplant infusions of donor-derived B6C3 MSC in B6 recipients induced a profound T cell hyporesponsiveness and prolonged B6C3 cardiac allograft survival. The protolerogenic effect was abrogated when donor-derived MSC were injected together with B6C3 hematopoietic stem cells (HSC), suggesting that HSC negatively impact MSC immunomodulatory properties. Both the induction (pretransplant) and the maintenance phase (>100 days posttransplant) of donor-derived MSC-induced tolerance were associated with CD4(+)CD25(+)Foxp3(+) Treg expansion and impaired anti-donor Th1 activity. MSC-induced regulatory T cells (Treg) were donor-specific since adoptive transfer of splenocytes from tolerant mice prevented the rejection of fully MHC-mismatched donor-specific secondary allografts but not of third-party grafts. In addition, infusion of recipient-derived B6 MSC tolerized a semiallogeneic B6C3 cardiac allograft, but not a fully MHC-mismatched BALB/c graft, and expanded Treg. A double i.v. pretransplant infusion of recipient-derived MSC had the same tolerogenic effect as the combined intraportal/i.v. MSC infusions, which makes the tolerogenic protocol applicable in a clinical setting. In contrast, single MSC infusions given either peritransplant or 1 day after transplant were less effective. Altogether these findings indicate that MSC immunomodulatory properties require HSC removal, partial sharing of MHC Ags between the donor and the recipient and pretransplant infusion, and are associated with expansion of donor-specific Treg.

N/A

N/A

Human hepatic sinusoidal endothelial cells can be distinguished by expression of phenotypic markers related to their specialised functions in vivo

The hepatic sinusoids are lined by a unique population of hepatic sinusoidal endothelial cells (HSEC), which is one of the first hepatic cell populations to come into contact with blood components. However, HSEC are not simply barrier cells that restrict the access of blood-borne compounds to the parenchyma. They are functionally specialised endothelial cells that have complex roles, including not only receptor-mediated clearance of endotoxin, bacteria and other compounds, but also the regulation of inflammation, leukocyte recruitment and host immune responses to pathogens. Thus understanding the differentiation and function of HSEC is critical for the elucidation of liver biology and pathophysiology. This article reviews methods for isolating and studying human hepatic endothelial cell populations using in vitro models. We also discuss the expression and functions of phenotypic markers, such as the presence of fenestrations and expression of VAP-1, Stabilin-1, L-SIGN, which can be used to identify sinusoidal endothelium and to permit discrimination from vascular and lymphatic endothelial cells.

Induction of regulatory T cells from mature T cells by allogeneic thymic epithelial cells in vitro

The ability of thymic epithelial cells (TEC) to re-educate mature T cells to be regulatory T cells has not been addressed. In the present study, this issue was directly investigated by co-culturing of mature T cells and allo-TECs. B6 macrophage cell line 1C21-cultured BALB/c splenocytes responded to B6 antigens in vitro. However, BALB/c splenocytes precultured with B6-derived TECs 1-4C18 or 1C6 did not proliferate to B6 antigens, but responded to rat antigens. Exogenous interleukin-2 (IL-2) failed to revise the unresponsiveness of these T cells. Allo-TEC-cultured T cells predominantly expressed Th2 cytokines (IL-4 and IL-10). B6 TEC-cultured BALB/c splenocytes markedly inhibited the immune responses of naïve BALB/c splenocytes to B6 antigens, but not to rat or the third-party mouse antigens. BALB/c nude mice that received naïve syngeneic splenocytes rejected B6 or rat skin grafts by 17 days postskin grafting; however, co-injection of B6 TEC-cultured BALB/c splenocytes significantly delayed B6 skin graft rejection (P < 0.01), with the unchanged rejection of rat skin grafts. These studies demonstrate that allo-TECs are able to 'educate' mature T cells to be regulatory cells, and suggest that regulatory cells derived from mature T cells by TECs may play an important role in T cell tolerance to allo- and auto-antigens.

Enhancement of NKT Cells and Increase in Regulatory T Cells Results in Improved Allograft Survival

BACKGROUND

Natural killer T (NKT) cells can serve as regulatory cells important in peripheral tolerance. In an experimental colitis model, it was shown that FK506 enhances the tolerizing effect of regulatory NKT cells induced by oral tolerance. We explored whether a subtherapeutic dose of FK506 could enhance the tolerizing effect of NKT cells induced by oral administration of donor spleen cells (SCs) in the pre-transplant period to prolong heart allograft survival.

METHODS

Heterotopic heart transplantation was performed from BALB/c to B6 mice. The B6 recipients were pre-treated with either BALB/c SCs (2 x 10(7)/mouse), or FK506 (1.0 mg/kg/d), or BALB/c SCs + FK506 by gavage every other day for a total of five feedings before transplantation.

RESULTS

Heart allograft survival was only significantly prolonged in the BALB/c SC + FK506 pre-fed mice. This was associated with a marked increase of NKT cells in both the liver and spleen of the recipients, and most importantly, 7 days after transplantation, an increase in CD25+CD4+ T cells expressing CTLA4 in the spleen.

CONCLUSIONS

In our model it appears that a subtherapeutic dose of FK506 enhanced the tolerizing effect of NKT cells induced by oral tolerance, prolonging allograft survival by generating CD25+CD4+ CTLA4 T cells. This appears to be an excellent in vivo model to generate regulatory T cells to allospecific transplant antigens.

Internalizing antibodies to the C-type lectins, L-SIGN and DC-SIGN, inhibit viral glycoprotein binding and deliver antigen to human dendritic cells for the induction of T cell responses

The C-type lectin L-SIGN is expressed on liver and lymph node endothelial cells, where it serves as a receptor for a variety of carbohydrate ligands, including ICAM-3, Ebola, and HIV. To consider targeting liver/lymph node-specific ICAM-3-grabbing nonintegrin (L-SIGN) for therapeutic purposes in autoimmunity and infectious disease, we isolated and characterized Fabs that bind strongly to L-SIGN, but to a lesser degree or not at all to dendritic cell-specific ICAM-grabbing nonintegrin (DC-SIGN). Six Fabs with distinct relative affinities and epitope specificities were characterized. The Fabs and those selected for conversion to IgG were tested for their ability to block ligand (HIV gp120, Ebola gp, and ICAM-3) binding. Receptor internalization upon Fab binding was evaluated on primary human liver sinusoidal endothelial cells by flow cytometry and confirmed by confocal microscopy. Although all six Fabs internalized, three Fabs that showed the most complete blocking of HIVgp120 and ICAM-3 binding to L-SIGN also internalized most efficiently. Differences among the Fab panel in the ability to efficiently block Ebola gp compared with HIVgp120 suggested distinct binding sites. As a first step to consider the potential of these Abs for Ab-mediated Ag delivery, we evaluated specific peptide delivery to human dendritic cells. A durable human T cell response was induced when a tetanus toxide epitope embedded into a L-SIGN/DC-SIGN-cross-reactive Ab was targeted to dendritic cells. We believe that the isolated Abs may be useful for selective delivery of Ags to DC-SIGN- or L-SIGN-bearing APCs for the modulation of immune responses and for blocking viral infections.