The role of CD154-CD40 versus CD28-B7 costimulatory pathways in regulating allogeneic Th1 and Th2 responses in vivo

Monitoring regulatory T cells as a prognostic marker in lung transplantation

Lung transplantation is the major surgical procedure, which restores normal lung functioning and provides years of life for patients suffering from major lung diseases. Lung transplant recipients are at high risk of primary graft dysfunction, and chronic lung allograft dysfunction (CLAD) in the form of bronchiolitis obliterative syndrome (BOS). Regulatory T cell (Treg) suppresses effector cells and clinical studies have demonstrated that Treg levels are altered in transplanted lung during BOS progression as compared to normal lung. Here, we discuss levels of Tregs/FOXP3 gene expression as a crucial prognostic biomarker of lung functions during CLAD progression in clinical lung transplant recipients. The review will also discuss Treg mediated immune tolerance, tissue repair, and therapeutic strategies for achieving in-vivo Treg expansion, which will be a potential therapeutic option to reduce inflammation-mediated graft injuries, taper the toxic side effects of ongoing immunosuppressants, and improve lung transplant survival rates.

Imaging Tolerance Induction in Neonatal Mice: Hierarchical Interplay Between Allogeneic Adult and Neonatal Immune Cells

BACKGROUND

In Medawar's murine neonatal tolerance model, injection of adult semiallogeneic lymphohematopoietic cells (spleen cells [SC] and bone marrow cells [BMC]) tolerizes the neonatal immune system. An eventual clinical application would require fully allogeneic (allo) cells, yet little is known about the complex in vivo/in situ interplay between those cells and the nonconditioned neonatal immune system.

METHODS

To this end, labeled adult SC and BMC were injected into allogeneic neonates; interactions between donor and host cells were analyzed and modulated by systematic depletion/inactivation of specific donor and host immune effector cell types.

RESULTS

Consistent with effector cell compositions, allo-SC and allo-SC/BMC each induced lethal acute graft-versus-host disease, whereas allo-BMC alone did so infrequently. CD8 T cells from SC inoculum appeared naïve, while those of BMC were more memory-like. Age-dependent, cell-type dominance defined the interplay between adult donor cells and the neonatal host immune system such that if the dominant adult effector type was removed, then the equivalent neonatal one became dominant. Depletion of donor/host peripheral T cells protected against acute graft-versus-host disease and prolonged heart allograft survival; peripheral CD8 T-cell depletion together with CD4 T cell-costimulation blockade induced more robust tolerance.

CONCLUSIONS

This comprehensive study provides direct observation of the cellular interplay between allogeneic donor and host immune systems, adds to our previous work with semiallogeneic donor cells, and provides important insights for robust tolerance induction. Induction of transplant tolerance in neonates will likely require "crowd sourcing" of multiple tolerizing cell types and involve depletion of immune effector cells with costimulation blockade.

Gene-metabolite networks associated with impediment of bone fracture repair in spaceflight

Adverse effects of spaceflight on musculoskeletal health increase the risk of bone injury and impairment of fracture healing. Its yet elusive molecular comprehension warrants immediate attention, since space travel is becoming more frequent. Here we examined the effects of spaceflight on bone fracture healing using a 2 mm femoral segmental bone defect (SBD) model. Forty, 9-week-old, male C57BL/6J mice were randomized into 4 groups: 1) Sham surgery on Ground (G-Sham); 2) Sham surgery housed in Spaceflight (FLT-Sham); 3) SBD surgery on Ground (G-Surgery); and 4) SBD surgery housed in Spaceflight (FLT-Surgery). Surgery procedures occurred 4 days prior to launch; post-launch, the spaceflight mice were house in the rodent habitats on the International Space Station (ISS) for approximately 4 weeks before euthanasia. Mice remaining on the Earth were subjected to identical housing and experimental conditions. The right femur from half of the spaceflight and ground groups was investigated by micro-computed tomography (µCT). In the remaining mice, the callus regions from surgery groups and corresponding femoral segments in sham mice were probed by global transcriptomic and metabolomic assays. µCT confirmed escalated bone loss in FLT-Sham compared to G-Sham mice. Comparing to their respective on-ground counterparts, the morbidity gene-network signal was inhibited in sham spaceflight mice but activated in the spaceflight callus. µCT analyses of spaceflight callus revealed increased trabecular spacing and decreased trabecular connectivity. Activated apoptotic signals in spaceflight callus were synchronized with inhibited cell migration signals that potentially hindered the wound site to recruit growth factors. A major pro-apoptotic and anti-migration gene network, namely the RANK-NFκB axis, emerged as the central node in spaceflight callus. Concluding, spaceflight suppressed a unique biomolecular mechanism in callus tissue to facilitate a failed regeneration, which merits a customized intervention strategy.

Induction of immunological tolerance to myelinogenic glial-restricted progenitor allografts

The immunological barrier currently precludes the clinical utilization of allogeneic stem cells. Although glial-restricted progenitors have become attractive candidates to treat a wide variety of neurological diseases, their survival in immunocompetent recipients is limited. In this study, we adopted a short-term, systemically applicable co-stimulation blockade-based strategy using CTLA4-Ig and anti-CD154 antibodies to modulate T-cell activation in the context of allogeneic glial-restricted progenitor transplantation. We found that co-stimulation blockade successfully prevented rejection of allogeneic glial-restricted progenitors from immunocompetent mouse brains. The long-term engrafted glial-restricted progenitors myelinated dysmyelinated adult mouse brains within one month. Furthermore, we identified a set of plasma miRNAs whose levels specifically correlated to the dynamic changes of immunoreactivity and as such could serve as biomarkers for graft rejection or tolerance. We put forward a successful strategy to induce alloantigen-specific hyporesponsiveness towards stem cells in the CNS, which will foster effective therapeutic application of allogeneic stem cells.

Absence of recipient C3aR1 signaling limits expansion and differentiation of alloreactive CD8+ T cell immunity and prolongs murine cardiac allograft survival

Activation, differentiation, and expansion of alloreactive CD8⁺ T cells, the dominant effectors that mediate murine heart allograft rejection, requires allorecognition, costimulation, and cytokine-initiated signals. While previous work showed that alloreactive CD4⁺ T cell immunity entails immune cell-produced and locally activated complement, whether and how C3a receptor 1 (C3aR1) signaling impacts transplant outcomes and the mechanisms linking C3aR1 to alloreactive CD8⁺ T cell activation/expansion remain unclear. Herein we show that recipient C3aR1 deficiency or pharmacological C3aR1 blockade synergizes with tacrolimus to significantly prolong allograft survival versus tacrolimus-treated controls (median survival time 21 vs. 14 days, P < .05). Recipient C3aR1-deficiency reduced the frequencies of posttransplant, donor-reactive CD8⁺ T cells twofold. Reciprocal adoptive transfers of naive WT or C3ar1^-/- CD8⁺ T cells into syngeneic WT or C3ar1^-/- allograft recipients showed that T cell-expressed C3aR1 induces CD8⁺ T proliferation, mTOR activation and transcription factor T-bet expression. Host C3aR1 indirectly facilitates alloreactive CD8⁺ T cell proliferation/expansion by amplifying antigen presenting cell costimulatory molecule expression and innate cytokine production. In addition to expanding mechanistic insight, our findings identify C3aR1 as a testable therapeutic target for future studies aimed at improving human transplant outcomes.

Allograft rejection is associated with development of functional IgE specific for donor MHC antigens

BACKGROUND

Donor-specific antibodies of the IgG isotype are measured routinely for diagnostic purposes in renal transplant recipients and are associated with antibody-mediated rejection and long-term graft loss.

OBJECTIVE

This study aimed to investigate whether MHC-specific antibodies of the IgE isotype are induced during allograft rejection.

METHODS

Anti-MHC/HLA IgE levels were measured in sera of mice grafted with skin or heart transplants from various donor strains and in sera of kidney transplant patients with high levels of HLA IgG. Mediator release was triggered in vitro by stimulating basophils that were coated with murine or human IgE-positive serum, respectively, with specific recombinant MHC/HLA antigens. Kidney tissue samples obtained from organ donors were analyzed by using flow cytometry for cells expressing the high-affinity receptor for IgE (FcεRI).

RESULTS

Donor MHC class I- and MHC class II-specific IgE was found on acute rejection of skin and heart grafts in several murine strain combinations, as well as during chronic antibody-mediated heart graft rejection. Anti-HLA IgE, including donor HLA class I and II specificities, was identified in a group of sensitized transplant recipients. Murine and human anti-MHC/HLA IgE triggered mediator release in coated basophils on stimulation with specific MHC/HLA antigens. HLA-specific IgE was not linked to atopy, and allergen-specific IgE present in allergic patients did not cross-react with HLA antigens. FcεRI+ cells were found in the human renal cortex and medulla and provide targets for HLA-specific IgE.

CONCLUSION

These results demonstrate that MHC/HLA-specific IgE develops during an alloresponse and is functional in mediating effector mechanisms.

IFN-γ production by memory helper T cells is required for CD40-independent alloantibody responses

Cognate T-B cell interactions and CD40-CD154 costimulation are essential for productive humoral immunity against T-dependent Ags. We reported that memory CD4 T cells can deliver help to B cells and induce pathogenic IgG alloantibodies in the absence of CD40-CD154 interactions. To determine cytokine requirements for CD40-independent help, we used CD40(-/-) mice containing differentiated subsets of donor-reactive memory Th cells as heart allograft recipients. Th1 and Th17, but not Th2, memory CD4 T cells elicited high titers of anti-donor Ab. Abs induced by Th17 memory CD4 T cells had decreased reactivity against donor MHC class I molecules and inferior ability to cause complement deposition in heart allografts compared with Abs induced by Th1 cells, suggesting a requirement for IFN-γ during CD40-independent help. IFN-γ neutralization inhibited helper functions of memory CD4 T cells in both CD40(-/-) recipients and wild type recipients treated with anti-CD154 mAb. Our results suggest that IFN-γ secreted by pre-existing memory helper cells determines both isotype and specificity of donor-reactive alloantibodies and can thus affect allograft pathology. This information may be valuable for identifying transplant patients at risk for de novo development of pathogenic alloantibodies and for preventing alloantibody production in T cell-sensitized recipients.

Primary vascularization of allografts governs their immunogenicity and susceptibility to tolerogenesis

We investigated the influence of allograft primary vascularization on alloimmunity, rejection, and tolerance in mice. First, we showed that fully allogeneic primarily vascularized and conventional skin transplants were rejected at the same pace. Remarkably, however, short-term treatment of mice with anti-CD40L Abs achieved long-term survival of vascularized skin and cardiac transplants but not conventional skin grafts. Nonvascularized skin transplants triggered vigorous direct and indirect proinflammatory type 1 T cell responses (IL-2 and IFN-γ), whereas primarily vascularized skin allografts failed to trigger a significant indirect alloresponse. A similar lack of indirect alloreactivity was also observed after placement of different vascularized organ transplants, including hearts and kidneys, whereas hearts placed under the skin (nonvascularized) triggered potent indirect alloresponses. Altogether, these results suggest that primary vascularization of allografts is associated with a lack of indirect T cell alloreactivity. Finally, we show that long-term survival of vascularized skin allografts induced by anti-CD40L Abs was associated with a combined lack of indirect alloresponse and a shift of the direct alloresponse toward a type 2 cytokine (IL-4, IL-10)-secretion pattern but no activation/expansion of Foxp3(+) regulatory T cells. Therefore, primary vascularization of allografts governs their immunogenicity and tolerogenicity.

Innate immunity and resistance to tolerogenesis in allotransplantation

The development of immunosuppressive drugs to control adaptive immune responses has led to the success of transplantation as a therapy for end-stage organ failure. However, these agents are largely ineffective in suppressing components of the innate immune system. This distinction has gained in clinical significance as mounting evidence now indicates that innate immune responses play important roles in the acute and chronic rejection of whole organ allografts. For instance, whereas clinical interest in natural killer (NK) cells was once largely confined to the field of bone marrow transplantation, recent findings suggest that these cells can also participate in the acute rejection of cardiac allografts and prevent tolerance induction. Stimulation of Toll-like receptors (TLRs), another important component of innate immunity, by endogenous ligands released in response to ischemia/reperfusion is now known to cause an inflammatory milieu favorable to graft rejection and abrogation of tolerance. Emerging data suggest that activation of complement is linked to acute rejection and interferes with tolerance. In summary, the conventional wisdom that the innate immune system is of little importance in whole organ transplantation is no longer tenable. The addition of strategies that target TLRs, NK cells, complement, and other components of the innate immune system will be necessary to eventually achieve long-term tolerance to human allograft recipients.

Morphological characteristics and co-stimulatory molecule (CD80, CD86, CD40) expression in tumor infiltrating dendritic cells in human endometrioid adenocarcinoma

OBJECTIVE

The purpose of this study was to investigate changes of the antigen-presenting function of tumor infiltrating dendritic cells (TIDCs) in human endometrioid adenocarcinoma.

STUDY DESIGN

The TIDCs from 45 cases of endometrioid adenocarcinoma were compared with 20 cases of normal human endometrial tissue, using transmission electron microscopic examination, and the expression of CD80, CD86, and CD40 was analyzed by flow cytometry.

RESULTS

In comparison with the control group, the ultrastructure of TIDCs in human endometrioid adenocarcinoma showed the following differences: numerous TIDCs were small in volume and round in shape but some were oval and multi-angular. The cytoplasmic processes were obviously decreased in number and stubbed. Round primary lysosomes with high electron-dense granules, and secondary lysosomes with high or low electron-dense granules were seen frequently in the cytoplasm. TIDCs contained much rough endoplasmic reticulum (RER). Vacuoles with flocculent electron-dense granules were rare. High electron-dense contents in the granules were near one side and the other side was bright. The nucleus became markedly small in volume, nephroid or hoofed in shape. The nucleus had little euchromatin and lots of heterochromatin under the nuclear membrane. The levels of expression of CD80, CD86 and CD40 on TIDCs were low or even nonexistent. The expression levels of CD80, CD86 and CD40 on DCs in human normal endometrium were significantly higher than those on TIDCs in endometrioid adenocarcinoma.

CONCLUSION

It is suggested that morphological differences and low expression of co-stimulatory molecules on TIDCs in endometrioid adenocarcinoma reflected the functional changes of the TIDCs in uptake, processing and presenting antigen, which may lead to the occurrence of tumor immune escape.

Distinct strategies are required to suppress antigen-specific responses to genetically modified keratinocytes and fibroblasts

Keratinocytes and fibroblasts are potential targets of gene/cell therapy for genodermatoses. Immune elimination of genetically modified cells, however, presents a major impediment to effective therapy. Using ex vivo approaches to gene transfer, we have previously shown that expression of an antigen by either cell type in skin induces immune rejection of transplanted cells, although the nature of immune responses induced by these two cell types are distinct. In this study, we explore the efficacy of local immunosuppressive strategies to divert destructive immune responses from genetically modified fibroblast and keratinocytes. Expression of CTLA4Ig and, to a lesser extent, PDL1, by antigenic fibroblasts protected them from immune rejection resulting in long-term graft survival (>18 weeks). Similar treatment was not effective for antigenic keratinocytes. Long-term protection of transgenic keratinocytes was achieved through transient blockade of CD40/CD154 interactions during the first 2 weeks of cell transplantation. Although neither of these strategies induced antigen-specific tolerance, they were sufficient to prevent rejection of genetically modified cells. These results indicate that different strategies are required to protect antigenic cell types even within the same tissue. Moreover, induction of antigen-specific tolerance is not a necessary requirement for long-term survival of genetically modified skin cells.

Cross-presentation of antigen by diverse subsets of murine liver cells

Antigen cross-presentation is a principal function of specialized antigen-presenting cells of bone marrow origin such as dendritic cells. Although these cells are sometimes known as "professional" antigen-presenting cells, nonbone marrow-derived cells may also act as antigen-presenting cells. Here, using four-way liver cell isolation and parallel comparison of candidate antigen-presenting cells, we show that, depending on the abundance of antigen-donor cells, different subsets of liver cells could cross-present a hepatocyte-associated antigen. This function was observed in both liver sinusoidal endothelial cells and Kupffer cells even at very low antigen concentration, as well as when using soluble protein. Antigen cross-presentation by liver cells induced efficient CD8+ T-cell proliferation in a similar manner to classical dendritic cells from spleen. However, proliferated cells expressed a lower level of T-cell activation markers and intracellular interferon-gamma levels. In contrast to classical spleen dendritic cells, cross-presentation by liver antigen-presenting cells was predominantly dependent on intercellular adhesion molecule-1.

CONCLUSION

Hepatic sinusoids are an environment rich in antigen cross-presenting activity. However, the liver's resident antigen-presenting cells cause partial T-cell activation. These results clarify how the liver can act as a primary site of CD8+ T-cell activation, and why immunity against hepatocyte pathogens is sometimes ineffective.

Animal models of chronic allograft injury: contributions and limitations to understanding the mechanism of long-term graft dysfunction

Advances in immunosuppression have reduced the incidence of acute graft loss after transplantation, but long-term allograft survival is still hindered by the development of chronic allograft injury, a multifactorial process that involves both immunologic and nonimmunologic components. Because these components become defined in the clinical setting, development of animal models enables exploration into underlying mechanisms leading to long-term graft dysfunction. This review presents animal models that have enabled investigation into chronic allograft injury and discusses pivotal models currently being used. The mechanisms uncovered by these models will ultimately lead to development of new therapeutic options to prevent long-term graft dysfunction.

The role of T helper cell differentiation in promoting nerve allograft survival with costimulation blockade

OBJECT

Peripheral nerve allografts provide a temporary scaffold for host nerve regeneration and allow for the repair of significant segmental nerve injuries. Despite this potential, nerve allograft transplantation requires temporary systemic immunosuppression. Characterization of the immunological mechanisms involved in the induction of immune hyporesponsiveness to prevent nerve allograft rejection will help provide a basis for optimizing immunomodulation regimens or manipulating donor nerve allografts to minimize or eliminate the need for global immunosuppression.

METHODS

The authors used C57Bl/6 mice and STAT4 and STAT6 gene BALB/c knockout mice. A nonvascularized nerve allograft was used to reconstruct a 1-cm sciatic nerve gap in the murine model. A triple costimulatory blockade of the CD40, CD28/B7, and inducible costimulatory (ICOS) pathways was used. Quantitative assessment was performed at 3 weeks with nerve histomorphometry, walking track analysis, and the enzyme-linked immunospot assay.

RESULTS

The STAT6 -/- mice received 3 doses of costimulation-blocking antibodies and had axonal regeneration equivalent to nerve isografts, while treated STAT4 -/- mice demonstrated moderate axonal regeneration but inferior to the T helper cell Type 2-deficient animals. Enzyme-linked immunospot assay analysis demonstrated a minimal immune response in both STAT4 -/- and STAT6 -/- mice treated with a costimulatory blockade.

CONCLUSIONS

The authors' findings suggest that Type 1 T helper cells may play a more significant role in costimulatory blockade-induced immune hyporesponsiveness in the nerve allograft model, and that Type 2 T helper differentation may represent a potential target for directed immunosuppression.

Pig embryonic pancreatic tissue as a source for transplantation in diabetes: transient treatment with anti-LFA1, anti-CD48, and FTY720 enables long-term graft maintenance in mice with only mild ongoing immunosuppression

OBJECTIVE

Defining an optimal costimulatory blockade-based immune suppression protocol enabling engraftment and functional development of E42 pig embryonic pancreatic tissue in mice.

RESEARCH DESIGN AND METHODS

Considering that anti-CD40L was found to be thrombotic in humans, we sought to test alternative costimulatory blockade agents already in clinical use, including CTLA4-Ig, anti-LFA1, and anti-CD48. These agents were tested in conjunction with T-cell debulking by anti-CD4 and anti-CD8 antibodies or with conventional immunosuppressive drugs. Engraftment and functional development of E42 pig pancreatic tissue was monitored by immunohistology and by measuring pig insulin blood levels.

RESULTS

Fetal pig pancreatic tissue harvested at E42, or even as early as at E28, was fiercely rejected in C57BL/6 mice and in Lewis rats. A novel immune suppression comprising anti-LFA1, anti-CD48, and FTY720 afforded optimal growth and functional development. Cessation of treatment with anti-LFA1 and anti-CD48 at 3 months posttransplant did not lead to graft rejection, and graft maintenance could be achieved for >8 months with twice-weekly low-dose FTY720 treatment. These grafts exhibited normal morphology and were functional, as revealed by the high pig insulin blood levels in the transplanted mice and by the ability of the recipients to resist alloxan induced diabetes.

CONCLUSIONS

This novel protocol, comprising agents that simulate those approved for clinical use, offer an attractive approach for embryonic xenogeneic transplantation. Further studies in nonhuman primates are warranted.

TLR signals promote IL-6/IL-17-dependent transplant rejection

Acute allograft rejection has often been correlated with Th1 differentiation, whereas transplantation tolerance is frequently associated with induction of regulation. The discovery of the Th17 phenotype has prompted its scrutiny in transplant rejection. Although IL-17 has recently been observed in settings of acute allograft rejection and drives rejection in T-bet-deficient mice that have impaired type 1 T cell responses, there is little evidence of its requirement during acute rejection in wild-type animals. We and others have previously shown that TLR9 signaling by exogenous CpG at the time of transplantation is sufficient to abrogate anti-CD154-mediated acceptance of fully mismatched cardiac allografts. In this study, we investigated the mechanism by which acute rejection occurs in this inflammatory context. Our results indicate that CpG targets recipient hemopoietic cells and that its pro-rejection effects correlate both with prevention of anti-CD154-mediated conversion of conventional CD4(+) T cells into induced regulatory T cells and with the expression of IFN-gamma and IL-17 by intragraft CD4(+) T cells. Moreover, the combined elimination of IL-6 and IL-17 signaling abrogated the ability of CpG to promote acute cardiac allograft rejection. Thus, proinflammatory signals at the time of transplantation can change the quality of the effector immune response and reveal a pathogenic function for IL-6 and IL-17 in wild-type recipients.

Divergent role of donor dendritic cells in rejection versus tolerance of allografts

Little is known about heart tissue/donor dendritic cells, which play a key role in mounting alloimmune responses. In this report, we focus on three primary features of donor dendritic cells: their generation, their trafficking after transplantation, and their role in regulating tolerance versus rejection. Using transgenic mice as donors of heart allografts enabled us to monitor trafficking of donor dendritic cells after transplantation. Donor dendritic cells rapidly migrated into secondary lymphoid tissues within 3 h of transplantation. We found that the chemokine receptor CX3CR1 regulates the generation of heart tissue dendritic cells constitutively. Compared with wild-type hearts, CX3CR1(-/-) hearts contained fewer dendritic cells, and heart allografts from CX3CR1(-/-) donors survived significantly longer without immunosuppression. Unexpectedly, though, co-stimulatory blockade with anti-CD154 or CTLA4-Ig induced long-term survival for wild-type heart allografts but not for CX3CR1(-/-) heart allografts. Increasing the dendritic cell frequency in CX3CR1(-/-) hearts by treatment with Flt3L restored the anti-CD154-induced prolongation of CX3CR1(-/-) heart allograft survival. Compared with wild-type donors, depleting transgenic donors of dendritic cells before heart transplantation also markedly worsened chronic rejection under anti-CD154 treatment. These data indicate the importance of the CX3CR1 pathway in the generation of heart tissue dendritic cells and the divergent role of tissue/dendritic cells in rejection versus tolerance.

Murine mobilized peripheral blood stem cells have a lower capacity than bone marrow to induce mixed chimerism and tolerance

Allogeneic bone marrow transplantation (BMT) under costimulation blockade allows induction of mixed chimerism and tolerance without global T-cell depletion (TCD). The mildest such protocols without recipient cytoreduction, however, require clinically impracticable bone marrow (BM) doses. The successful use of mobilized peripheral blood stem cells (PBSC) instead of BM in such regimens would provide a substantial advance, allowing transplantation of higher doses of hematopoietic donor cells. We thus transplanted fully allogeneic murine granulocyte colony-stimulating factor (G-CSF) mobilized PBSC under costimulation blockade (anti-CD40L and CTLA4Ig). Unexpectedly, PBSC did not engraft, even when very high cell doses together with nonmyeloablative total body irradiation (TBI) were used. We show that, paradoxically, T cells contained in the donor PBSC triggered rejection of the transplanted donor cells. Rejection of donor BM was also triggered by the cotransplantation of unmanipulated donor T cells isolated from naïve (nonmobilized) donors. Donor-specific transfusion and transient immunosuppression prevented PBSC-triggered rejection and mixed chimerism and tolerance were achieved, but graft-versus-host disease (GVHD) occurred. The combination of in vivo TCD with costimulation blockade prevented rejection and GVHD. Thus, if allogeneic PBSC are transplanted instead of BM, costimulation blockade alone does not induce chimerism and tolerance without unacceptable GVHD-toxicity, and the addition of TCD is required for success.

Differential impact of CD154 costimulation blockade on alloreactive effector and regulatory T cells in murine renal transplant recipients

BACKGROUND

Although CD154 costimulation blockade prolongs allograft survival in multiple transplantation models, the underlying immunological mechanisms remain to be elucidated.

METHODS AND RESULTS

We used a murine orthotopic kidney allograft (KTx) model to analyze the impact of CD154 blockade on trafficking and function of alloreactive T effector versus T regulatory cells. A single dose of MR1 Ab treatment at the time of KTx significantly improved the survival of Balb/c KTx in naïve C57BL/6 recipients (mean survival time >100 days vs. 52 days in controls; P<0.005), and improved graft histology, as evidenced by decreased lymphocyte infiltration and preservation of tissue architecture (days 6-8). In the early posttransplant phase, fluorescence-activated cell sorting analysis revealed preferential depression of T effector (CD8+CD25+) and relative enrichment of T-regulatory (CD4+ CD25+ CD152+) cells selectively in KTx. This pattern was further supported by intragraft gene expression analysis, which showed increased FoxP3/Tbet ratio and simultaneously decreased granzyme B/IFN-gamma levels in Ab-treated recipients. Additionally, MR1 Ab selectively up-regulated intragraft CCL17, but suppressed CXCL9/CCL5, in parallel with increased CCR4/CCR8 but unaltered CXCR3 expression.

CONCLUSION

These results provide evidence, at both cellular and molecular levels, that CD154 blockade in murine KTx recipients differentially targeted T-effector and T-regulatory cell subsets by regulating intragraft induction of chemokines targeting distinct T-cell subsets.

A critical precursor frequency of donor-reactive CD4+ T cell help is required for CD8+ T cell-mediated CD28/CD154-independent rejection

Ag-specific precursor frequency is increasingly being appreciated as an important factor in determining the kinetics, magnitude, and degree of differentiation of T cell responses, and recently was found to play a critical role in determining the relative requirement of CD8(+) T cells for CD28- and CD154-mediated costimulatory signals during transplantation. We addressed the possibility that variations in CD4(+) T cell precursor frequency following transplantation might affect CD4(+) T cell proliferation, effector function, and provision of help for donor-reactive B cell and CD8(+) T cell responses. Using a transgenic model system wherein increasing frequencies of donor-reactive CD4(+) T cells were transferred into skin graft recipients, we observed that a critical CD4(+) T cell threshold precursor frequency was necessary to provide help following blockade of the CD28 and CD154 costimulatory pathways, as measured by increased B cell and CD8(+) T cell responses and precipitation of graft rejection. In contrast to high-frequency CD8(+) T cell responses, this effect was observed even though the proliferative and cytokine responses of Ag-specific CD4(+) T cells were inhibited. Thus, we conclude that an initial high frequency of donor-reactive CD4(+) T cells uncouples T cell proliferative and effector cytokine production from the provision of T cell help.

IL-10 and IL-4 in Skin Allograft Survival Induced by T-Cell Depletion plus Deoxyspergualin

The mechanisms mediating T-cell depletion plus 15-deoxyspergualin (DSG)-induced prolonged allograft survival or tolerance are uncertain. The purpose of this study is to evaluate the role of IL-4 and IL-10 in prolonged allograft survival induced by T-cell depletion plus DSG. MHC mismatched skin allograft transplantation was performed, using wild-type and three separate knockout (i.e., IL-4–/–, Stat6–/-, or IL-10–/–) mice as recipients. Induction therapy consisted of T-cell depletion and or brief course of DSG. The data demonstrate that monotherapy with T-cell-depleting mAbs or DSG prolonged skin allograft survival, compared to controls, in wild-type Balb/c recipients [median survival time (MST) = 25 and 21 vs. 10 days, p < 0.007]. T-cell depletion plus DSG further augmented skin allograft survival in wild-type animals relative to monotherapy (MST = 35 days vs. 25 and 21 days, p < 0.006 vs. mAbs or DSG only), and was equally effective in IL-4–/– and Stat6–/– recipients. In contrast, combined therapy was no better than monotherapy in IL-10–/– animals (p > 0.05). Furthermore, skin allograft survival after combined therapy was shorter in IL-10–/– versus wild-type recipients (MST 20 and 41 days, respectively, p < 0.001). IL-4-mediated signaling through Stat6 is dispensable for prolonged allograft survival induced by T-cell depletion plus DSG. In contrast, IL-10 appears to be important for prolonged allograft survival induced by combined therapy in this model.

CD4+ T lymphocytes are not necessary for the acute rejection of vascularized mouse lung transplants

Acute rejection continues to present a major obstacle to successful lung transplantation. Although CD4(+) T lymphocytes are critical for the rejection of some solid organ grafts, the role of CD4(+) T cells in the rejection of lung allografts is largely unknown. In this study, we demonstrate in a novel model of orthotopic vascularized mouse lung transplantation that acute rejection of lung allografts is independent of CD4(+) T cell-mediated allorecognition pathways. CD4(+) T cell-independent rejection occurs in the absence of donor-derived graft-resident hematopoietic APCs. Furthermore, blockade of the CD28/B7 costimulatory pathways attenuates acute lung allograft rejection in the absence of CD4(+) T cells, but does not delay acute rejection when CD4(+) T cells are present. Our results provide new mechanistic insight into the acute rejection of lung allografts and highlight the importance of identifying differences in pathways that regulate the rejection of various organs.

The emerging role of T cell Ig mucin 1 in alloimmune responses in an experimental mouse transplant model

T cell Ig mucin 1 (TIM-1) plays an important role in regulating immune responses in autoimmune and asthma models, and it is expressed on both Th1 and Th2 cells. Using an antagonistic TIM-1-specific antibody, we studied the role of TIM-1 in alloimmunity. A short course of TIM-1-specific antibody monotherapy prolonged survival of fully MHC-mismatched vascularized mouse cardiac allografts. This prolongation was associated with inhibition of alloreactive Th1 responses and preservation of Th2 responses. TIM-1-specific antibody treatment was more effective in Th1-type cytokine-deficient Stat4(-/-) recipients as compared with Th2-type cytokine-deficient Stat6(-/-) recipients. Subtherapeutic doses of rapamycin plus TIM-1-specific antibody resulted in allograft acceptance and prevented the development of chronic allograft vasculopathy. Allograft survival via this treatment was accompanied by a Th1- to Th2-type cytokine switch. Depletion of natural Tregs abrogated the graft-protecting effect of the TIM-1-specific antibody. Importantly, CD4(+)CD25(+) Tregs obtained from long-term survivors had enhanced regulatory activity as compared with naive CD4(+)CD25(+) Tregs. Consistent with this, TIM-1-specific antibody treatment both preserved Tregs and prevented the expansion of alloreactive effector Th1 cells in an alloreactive TCR transgenic adoptive transfer model. These studies define previously unknown functions of TIM-1 in regulating alloimmune responses in vivo and may provide a novel approach to promoting transplantation tolerance.

Blockade of the OX40 ligand prolongs corneal allograft survival

Although corneal transplantation is one of the most common tissue transplantations and is known to have a high graft acceptance rate, occasional corneal graft rejection remains a cause of blindness. OX40, a member of the TNF receptor superfamily, is expressed on activated T cells, and transmits a costimulatory signal by binding to OX40 ligand (OX40L) expressed on several cells with antigen-presenting functions. Using a blocking monoclonal antibody (mAb) against murine OX40L, we investigated the role of OX40 in a murine model of corneal transplantation. C3H/He mouse corneas were transplanted to BALB/c mice orthotopically. Administration of anti-OX40L mAb significantly reduced allograft rejection, and increased graft survival rate to 40% at 8 weeks after transplantation, while all corneas were rejected within 5 weeks in control IgG-treated mice. Similar reduced rejection was observed when wild-type donor corneas were transplanted to OX40L-deficient recipients. In vitro study revealed that the anti-OX40L mAb treatment reduced proliferative response and IFN-gamma production of draining lymph node cells in response to stimulation with donor alloantigen. These results demonstrate that OX40L blockade is effective for prolongation of corneal allograft survival by inhibiting recipient T cell activation.

Beta 3 integrins regulate lymphocyte migration and cytokine responses in heart transplant rejection

Integrin alpha v beta 3 is important for cell survival, signaling and migration, particularly during angiogenesis and tumorigenesis, where it has been proposed as a therapeutic target. alpha v beta 3 is up-regulated following transplantation and beta 3 polymorphisms are associated with increased acute kidney rejection, suggesting that alpha v beta 3 may also play a role in transplant rejection. Here, using a model of allogeneic heart transplantation, we show that allograft survival is prolonged in beta 3 integrin-deficient (beta 3(-/-)) mice. This is associated with Th2-type immune responses and reduced T-cell infiltration into grafts and T cells from beta 3(-/-) mice show impaired adhesion and migration, consistent with a role for alpha v beta 3 in transmigration. These studies provide evidence that targeting beta 3 integrins impairs recruitment of effector cells and alters cytokine production, so prolonging graft survival. We also show that low doses of blocking antibodies against leukocyte function associated antigen-1 (LFA-1)/alpha L beta 2 and very late antigen-4 (VLA-4)/alpha 4 beta 1, when combined with deletion of beta 3, lead to long-term survival of allografts with no evidence of chronic rejection. Hence we provide strong mechanistic evidence supporting previous genetic studies, demonstrate the involvement of beta 3 integrins in both acute and chronic rejection and identify beta 3 as a new target for immunosuppressive therapy.

Loss of transgene following ex vivo gene transfer is associated with a dominant Th2 response: implications for cutaneous gene therapy

Host responses to therapeutic gene products are potentially serious complications in cutaneous gene therapy. Controlling immune responses to the therapeutic antigen may therefore be critical for an effective therapy. Both ex vivo and in vivo gene transfer to epidermal stem cells has been shown to induce transgene-specific immune responses; however, whether the mechanism of immune activation is the same is not clear. In this study, we have characterized transgene-specific immune responses in an ex vivo model of epidermal gene transfer using green fluorescent protein as a model antigen and retrovirus-mediated gene delivery. Contrary to T helper (Th)1-type responses induced following in vivo gene transfer to epidermis, rejection of ex vivo-transduced keratinocytes was associated with Th2/eosinophilc responses. These responses were characterized by interleukin (IL)-4 and IL-5 production by T cells, a predominance of anti-green fluorescent protein IgG1 in serum, the presence of numerous eosinophils within rejected skin, and a lack of class I-restricted cytotoxic T lymphocyte response. Pretreatment of mice receiving ex vivo transduced keratinocytes with neutralizing anti-IL-5 antibody prevented eosinophil infiltration and prolonged survival of transduced epidermis. These data indicate a role for the Th2/eosinophilic pathway in rejection of ex vivo-transduced keratinocytes, suggesting different requirements for achieving tolerance for ex vivo and in vivo approaches to gene therapy.

Tolerance in Heart Transplantation: The Holy Grail, or an Attainable Goal?

The father of cardiac transplantation, Norman Shumway, famously predicted that tolerance was the future of the field, and always would be. Although his prediction remains true to date, significant progress has been made toward this goal, the "Holy Grail" for transplant clinicians. Current efforts are fueled by disappointing long-term outcomes associated with chronic immunosuppression, and the promise that partial or complete tolerance will impact long-term results favorably. This article provides a clinical definition of tolerance primarily based on lessons learned from animal heart allograft models. It reviews several promising strategies for inducing tolerance and detecting its presence through the use of biomarkers in peripheral blood or the graft, and outlines a possible path toward making this vision a clinical reality.

Immature Syngeneic Dendritic Cells Potentiate Tolerance to Pancreatic Islet Allografts Depleted of Donor Dendritic Cells in Microgravity Culture Condition

BACKGROUND

Previously we showed that pancreatic islets cultured for seven days in rotating bioreactors survived for >100 days in allogeneic recipients without immunosuppression. This survival coincided with almost complete elimination of "passenger" donor dendritic cells (DCs). Herein, we examined the necessity of DCs in the generation of CD4+ CD25+ T regulatory (Treg) cells.

METHODS

Allogeneic fresh islets or islets cultured for three days in bioreactors were transplanted to streptozotocin-induced diabetic Balb/c(stat4 -/-) as well as signal transducers and activators of transcription (Stat)4-deficient Balb/c(stat6 -/-) or Balb/c(stat4 -/-) mice. Some Balb/c recipients of fresh islet allografts were also treated with a tolerogenic protocol of anti-CD40 Ligand MR1 mAb and CTLA4Ig.

RESULTS

Islet allografts cultured for three days in bioreactors survived >100 days in all Balb/c(stat4 -/-) recipients and in 56% of Balb/c(stat6 -/-) recipients, but in none of the Balb/c recipients; the same recipients rejected fresh islet allografts. Purified T cells from long-term surviving Balb/c(stat4 -/-) recipients failed to transfer tolerance to SCID recipients of donor-type fresh islet allografts. In contrast, MR1/CTLA4Ig therapy induced tolerance to fresh islet allografts and their T cells adoptively transferred tolerance. When Balb/c or Balb/c(stat4 -/-) recipients of bioreactor-cultured islets were injected intravenously with immature syngeneic DCs, they became tolerant and developed potent alloantigen-specific CD4+ CD25+ Treg cells expressing Foxp3.

CONCLUSION

Allogeneic islets depleted of donor DCs by culture in bioreactors have almost twofold better acceptance in Balb/c(stat4 -/-) than in Balb/c(stat6 -/-) mice, but lack Treg cells. Additional injection of host immature DCs improves tolerance in Balb/c and Balb/c(stat4 -/-) recipients by inducing potent CD4+ CD25+ Treg cells.

Janus tyrosine kinases and signal transducers and activators of transcription regulate critical functions of T cells in allograft rejection and transplantation tolerance

Full activation of T cells requires three sequential signals. Engagement by antigen presenting cells (APC) delivers signals 1/2, whereas signal 3 is delivered by multiple cytokines to regulate the immune homeostasis by influencing proliferation, differentiation, and survival/death. Signaling by cytokines acting through their receptors is delivered by two major molecular families, namely Janus tyrosine kinases (Jaks) and signal transducers and activators of transcription (Stats). Findings obtained from mice genetically deficient in Jaks and Stats suggest that these molecules may serve as therapeutic targets to prevent allograft rejection, induce transplantation tolerance, and inhibit autoimmune disease and lymphoid-derived tumors. This review describes the role of Jak tyrosine kinases and Stat transcription factors and their putative function in regulating T and B cell activity.

Molecular signature of mice T lymphocytes following tolerance induction by allogeneic BMT and CD40-CD40L costimulation blockade

Tolerance induction by mixed chimerism and costimulation blockade is a promising approach to avoid immunosuppression, but the molecular basis of tolerant T lymphocytes remains elusive. We investigated the genome-wide gene expression profile of murine T lymphocytes after tolerance induction by allogeneic bone marrow transplantation (BMT) and costimulatory blockade using the anti-CD40L antibody MR1. Molecular functions, biological processes, cellular locations, and coregulation of identified genes were determined. A total of 113 unique genes exhibited a significant differential expression between the lymphocytes of MR1-treated Tolerance (TOL) and untreated recipients Control (CTRL). The majority of genes upregulated in the TOL group are involved in several signal transduction cascades such as members of the MAPKKK cascade (IL6, Tob2, Stk39, and Dusp24). Other genes involved in lymphocyte differentiation and highly expressed in the TOL group are lymphotactin, the estrogen receptors (ERs) and the suppressor of cytokine signaling 7. Common transcription factors such as ER 1 alpha, GATA-binding protein 1, insulin promoter factor 1, and paired-related homeobox 2 could be identified in the promoter regions of upregulated genes in the TOL group. These data suggest that T lymphoctes of tolerant mice exhibit a distinct molecular expression profile, which needs to be evaluated in other experimental tolerance models to determine whether it is a universal signature of tolerance.

STAT4: a critical regulator of inflammation in vivo

Signal transducer and activator of transcription 4 (STAT4) is a central mediator in generating inflammation during protective immune responses and immune-mediated diseases. In the 8 yr since their first description, STAT4-deficient mice have defined the role of STAT4 in a variety of in vivo model systems. Despite the extensive study and use of these mice, the exact role of STAT4 in vivo is still unclear. In this review, I focus on describing the phenotypes of STAT4-deficient immune responses to pathogens and in diseases. Comparing the effects of STAT4 deficiency among numerous model systems will further enhance the development of a systemic model of STAT4 function in vivo.

Allograft rejection requires STAT5a/b-regulated antiapoptotic activity in T cells but not B cells

STATs play key roles in immune function. We examined the role of STAT5a/b in allograft rejection. STAT5a/b-deficient mice showed a 4-fold increased survival time of heart allografts (p < 0.01). Unlike wild type, purified STAT5a/b-/- T cells transferred to Rag1-/- recipients failed to mediate heart allograft rejection until supplemented with STAT5a/b-/- B cells. In vitro, STAT5a/b-/- T cells did not proliferate in response to Con A or alloantigens but entered apoptosis within 48 h (95%). Activated STAT5a/b-/- T cells showed increased expression of proapoptotic (caspases, DNA repair genes, TNF/TNFR-associated factor family genes) and decreased antiapoptotic mRNAs in microarrays, while Western blots confirmed reduced antiapoptotic Bcl-2 and elevated proapoptotic Bax protein expression. Interestingly, at 24 h postactivation, STAT5a/b+/+ and STAT5a/b-/- T cells produced similar levels of IL-2, IL-4, IL-10, and IFN-gamma mRNA; ELISPOT assay showed an equivalent number of IL-4- and IFN-gamma-producing T cells in both STAT5a/b+/+ and STAT5a/b-/- splenic populations. Sera from STAT5a/b+/+ and STAT5a/b-/- rejectors had donor-specific IgM, IgG1, IgG2a, and IgG2b Ab, while STAT5a/b deficiency had no impact on B cell survival or proliferation in response to LPS. Compared with allografts from STAT5a/b+/+ recipients, heart allografts from STAT5a/b-/- recipients had markedly reduced infiltration by CD4 and CD8 T cells but increased infiltration by B cells and dense endothelial deposition of C4d, a marker of humoral rejection. Thus, activated STAT5a/b-/- T cells produce cytokines prior to entering apoptosis, thereby promoting differentiation of B cells yielding donor-specific IgM and IgG Ab that mediate allograft rejection.

Inhibition of Chronic Rejection by Antibody Induced Vascular Accommodation in Fully Allogeneic Heart Allografts

BACKGROUND

The potential role of altered antibody responses as an effector protective mechanism to induce graft accommodation has been widely investigated in xenogeneic responses. Here we investigate the protective effects of antibody binding to vascular endothelium in a fully mismatched allogeneic model of heart transplantation.

METHODS

ACI recipients of WF cardiac grafts were treated either with allochimeric [alpha1h ]-RT1.A class I major histocompatibility complex (MHC) extracts (1 mg/rat, p.v. day 0) or high dose of CsA (10 mg/kg/day, p.o., day 0-6). Cardiac allografts were evaluated at 100 days posttransplant by immunohistology for evidence of chronic rejection and/or vascular accommodation. Activation of apoptotic or antiapoptotic mechanisms was verified by DNA fragmentation (TUNEL) analysis.

RESULTS

Allochimeric therapy resulted in inhibition of chronic rejection, absence of neointimal formation and induction of vascular accommodation of fully allogeneic WF hearts in ACI hosts. Such accommodation was evident by IgG and IgM vascular endothelial binding and marked reduction of DNA fragmentation. In contrast, CsA therapy resulted in marked neointimal proliferation, without evidence of vascular accommodation. Immunohistochemical analysis failed to demonstrate vascular endothelial antibody binding. Further, severe chronic rejection following CsA treatment was accompanied by marked DNA fragmentation.

CONCLUSION

Alteration of humoral immunity induces vascular accommodation in allogeneic transplantation. Vascular accommodation is the underlying mechanism for inhibition allograft vasculopathy following allochimeric MHC class I therapy.

A C/T polymorphism in the 5' untranslated region of the CD40 gene is associated with later onset of Graves' disease in Japanese

Graves' disease (GD) is an autoimmune disorder with genetic predisposition. CD40, which stimulates lymphocyte proliferation and differentiation, is an important immunomodulator and is expressed in the thyroid follicular cells as well as antigen-presenting cells. A single nucleotide polymorphism (SNP) at position -1 of the Kozak sequence of the CD40 gene has been reported to be associated with the development of GD. The aim of the present study was to investigate whether CD40 gene polymorphism confers susceptibility to GD in Japanese. CD40 gene polymorphisms were studied in Japanese GD patients (n = 324) and healthy control subjects without anti-thyroid autoantibodies or a family history of autoimmune disorders (n = 229). A C/T polymorphism at position -1 of the CD40 gene was measured using the polymerase chain reaction restriction fragment length polymorphism. There was no significant difference in allele or genotype frequency of the CD40 SNP between GD and control subjects. There was a significant decrease in the TT genotype frequency in the GD patients, who developed GD after 40 years old, than those under 40 year of age. These data suggest that the SNP of CD40 gene is associated with susceptibility to later onset of GD in Japanese.

Effects of combined T- and B-cell deficiency on murine ischemia reperfusion injury

B and T cells have been implicated in the pathogenesis of renal ischemia reperfusion injury (IRI); however, it is unknown if B and T cells interact in early injury responses, as seen in adaptive immune responses. Recent evidence has shown that B-cell deficient and T-cell deficient mice are partially protected from renal IRI. Renal IRI was induced in recombinase activating gene (RAG)-1 deficient mice, which lack both B and T cells. RAG-1 deficient mice from two different background strains were not protected from renal IRI. Adoptive transfer of either B or T cells into RAG-1 deficient mice led to a significant protection of renal injury, which was independent of effects on neutrophil trafficking. Neutrophil depletion in RAG-1 deficient mice did not protect from IRI. While deficiency of either B or T cells reduced IRI, combined lack of both is not protective. These results demonstrate that complex interactions between B and T cells are likely occurring in kidney IRI.

IDEC-131 (anti-CD154), sirolimus and donor-specific transfusion facilitate operational tolerance in non-human primates

CD154-specific antibody therapy prevents allograft rejection in many experimental transplant models. However, initial clinical transplant trials with anti-CD154 have been disappointing suggesting the need for as of yet undetermined adjuvant therapy. In rodents, donor antigen (e.g., a donor blood transfusion), or mTOR inhibition (e.g., sirolimus), enhances anti-CD154's efficacy. We performed renal transplants in major histocompatibility complex-(MHC) mismatched rhesus monkeys and treated recipients with combinations of the CD154-specific antibody IDEC-131, and/or sirolimus, and/or a pre-transplant donor-specific transfusion (DST). Therapy was withdrawn after 3 months. Triple therapy prevented rejection during therapy in all animals and led to operational tolerance in three of five animals including donor-specific skin graft acceptance in the two animals tested. IDEC-131, sirolimus and DST are highly effective in preventing renal allograft rejection in primates. This apparently clinically applicable regimen is promising for human renal transplant trials.

Effect of targeted disruption of signal transducer and activator of transcription (Stat)4 and Stat6 genes on the autoimmune diabetes development induced by multiple low doses of streptozotocin

The MLDS (multiple low doses of streptozotocin) model of diabetes was induced in Stat4(-/-), Stat6(-/-), and double-deficient Stat4(-/-)/6(-/-) mice to examine the role of STAT4/STAT6 deficiency in development of autoimmune diabetes. Cytokine production of T-cells from Stat4(-/-) mice confirmed a predominantly Th2-type immune response. Stat4(-/-) mice exhibited delayed onset and reduced severity of disease compared to wild-type (WT) mice. In contrast, STAT6 deficiency, with a predominant Th1 response, did not influence the kinetics or severity of MLDS-induced autoimmune diabetes. Interestingly, Stat4(-/-)/6(-/-) mice, with a prominent Th1-type response, experienced an accelerated and aggravated course of diabetes after MLDS, implicating a STAT4-independent Th1 response in the immunopathogenesis of MLDS-induced autoimmune diabetes. The sensitivity of islet cells from Stat4(-/-) or Stat4(-/-)/6(-/-) mice to cytokines and STZ was not different from that of islet cells of WT mice. Hence, the observed effects of STAT4 and STAT4/6 deficiency on MLDS-induced autoimmune diabetes are likely due to their effects on T-cell responses.

Different Competitive Capacities of Stat4- and Stat6-Deficient CD4+ T Cells during Lymphophenia-Driven Proliferation

The outcome of an immune response relies on the competitive capacities acquired through differentiation of CD4(+) T cells into Th1 or Th2 effector cells. Because Stat4 and Stat6 proteins are implicated in the Th1 vs Th2 generation and maintenance, respectively, we compare in this study the kinetics of Stat4(-/-) and Stat6(-/-) CD4(+) T cells during competitive bone marrow reconstitution and lymphopenia-driven proliferation. After bone marrow transplantation, both populations reconstitute the peripheral T cell pools equally well. After transfer into lymphopenic hosts, wild-type and Stat6(-/-) CD4(+) T cells show a proliferation advantage, which is early associated with the expression of an active phospho-Stat4 and the down-regulation of Stat6. Despite these differences, Stat4- and Stat6-deficient T cells reach similar steady state numbers. However, when both Stat4(-/-) and Stat6(-/-) CD4(+) T cells are coinjected into the same hosts, the Stat6(-/-) cells become dominant and out-compete Stat4(-/-) cells. These findings suggest that cell activation, through the Stat4 pathway and the down-regulation of Stat6, confers to pro-Th1 T cells a slight proliferation advantage that in a competitive situation has major late repercussions, because it modifies the final homeostatic equilibrium of the populations and favors the establishment of Th1 CD4(+) T cell dominance.

CD70 Signaling Is Critical for CD28-Independent CD8+T Cell-Mediated Alloimmune Responses In Vivo

The inability to reproducibly induce robust and durable transplant tolerance using CD28-B7 pathway blockade is in part related to the persistence of alloreactive effector/memory CD8(+) T cells that are less dependent on this pathway for their cellular activation. We studied the role of the novel T cell costimulatory pathway, CD27-CD70, in alloimmunity in the presence and absence of CD28-B7 signaling. CD70 blockade prolonged survival of fully mismatched vascularized cardiac allografts in wild-type murine recipients, and in CD28-deficient mice induced long-term survival while significantly preventing the development of chronic allograft vasculopathy. CD70 blockade had little effect on CD4(+) T cell function but prevented CD8(+) T cell-mediated rejection, inhibited the proliferation and activation of effector CD8(+) T cells, and diminished the expansion of effector and memory CD8(+) T cells in vivo. Thus, the CD27-CD70 pathway is critical for CD28-independent effector/memory CD8(+) alloreactive T cell activation in vivo. These novel findings have important implications for the development of transplantation tolerance-inducing strategies in primates and humans, in which CD8(+) T cell depletion is currently mandatory.

Mechanisms of tolerance induced by donor-specific transfusion and ICOS-B7h blockade in a model of CD4+ T-cell-mediated allograft rejection

The inducible co-stimulatory molecule (ICOS) has been shown to play a critical role in T-cell activation and differentiation, and the regulation of alloimmune responses in vivo. Using an MHC class II mismatched model of CD4(+) T-cell-mediated rejection, we found that treatment of mice with DST and ICOS-B7h blockade induced long-term skin allograft survival and donor-specific transplantation tolerance. ICOS blockade, either during antigen priming or during the effector phase, previously shown to alter the outcome of the immune response, had a similar effect on graft survival. DST and anti-B7h mAb reduced the frequency of IFN-gamma-producing allospecific cells but did not produce deviation to a T(H)2 phenotype. In an adoptive transfer model using ABM TCR transgenic mice directly reactive to I-A(bm12), DST and anti-B7h mAb reduced the number of allospecific CD4(+) T cells and increased CD4(+) T-cell apoptosis. These data demonstrate that DST and anti-B7h mAb induces transplantation tolerance to MHC class II mismatched skin grafts by a reduction of the alloreactive clone size that is, at least in part, dependent on apoptosis of host alloantigen-specific CD4(+) T cells.

Potential role for TL1A, the new TNF-family member and potent costimulator of IFN-gamma, in mucosal inflammation

TNF can potentiate IFN-gamma production by activated T cells and other members of the TNF-superfamily play key roles in this effect. A newly discovered TNF-superfamily cytokine (TL1A) could also be involved in initiating or promoting the Th1 response by enhancing IFN-gamma production. The purpose of this study was to assess the role of recombinant TL1A on IFN-gamma production by cultured PBMC and lamina propria LPMC and to determine whether TL1A expression is altered in inflammatory bowel disease. IFN-gamma, but not IL-4 or IL-10 production by PBMC and LPL, was dose-dependently augmented by TL1A (or by activation of its receptor, death domain receptor 3 [DR3], with specific mAb) independently of, but in synergy with, IL-12 and IL-18. T cell activating stimuli induced expression of TL1A on the cell membrane (mb-TL1A) in a fraction of peripheral blood (PB) T cells. In the intestinal mucosa, a fraction of lamina propria (LP) T cells, especially CD4+ cells, constitutively expressed mb-TL1A, and the fraction increased in mucosal inflammation. A higher fraction of cells also express the TL1A receptor DR3 in ulcerative colitis and Crohn's disease. TL1A transcript was several times more abundant in RNA from mucosal biopsies taken from inflamed Crohn's disease lesions than in those taken from uninvolved areas. Expression of TL1A and its receptor DR3 by lamina propria mononuclear cells (LPMC) could have significant influence on the severity of mucosal inflammation.

A single nucleotide polymorphism in the CD40 gene on chromosome 20q (GD-2) provides no evidence for susceptibility to Graves' disease in UK Caucasians

OBJECTIVE

A genome-wide screen in Graves' disease (GD) has shown linkage to chromosome 20q, designated GD-2. The gene encoding CD40, which stimulates lymphocyte proliferation and differentiation, maps to this region, and a single nucleotide polymorphism (SNP) at position -1 of the Kozak sequence within the gene has been reported to be associated with GD. The aim of this study was to determine whether this SNP of the CD40 gene confers susceptibility to GD in UK Caucasians.

DESIGN

A large case-control cohort consisting of 800 patients with GD, and 785 control subjects with no history of autoimmune disease, was used to genotype this SNP by polymerase chain reaction restriction fragment length polymorphism.

RESULTS

Despite adequate power (> 99%) to detect an effect, if present (odds ratio of 1.5), no significant difference in allele or genotype frequency of the CD40 SNP was observed between patients with GD and control subjects (P = 0.087 and P = 0.145, respectively).

CONCLUSIONS

These data suggest that this polymorphism of the CD40 gene is not associated with GD in the UK and is therefore not contributing to disease susceptibility in the chromosomal region designated GD-2.

Differential requirement for the CD40-CD154 costimulatory pathway during Th cell priming by CD8 alpha+ and CD8 alpha- murine dendritic cell subsets

Dendritic cells (DCs) regulate the development of distinct Th populations and thereby provoke appropriate immune responses to various kinds of Ags. In the present work, we investigated the role CD40-CD154 interactions play during the process of Th cell priming by CD8 alpha(+) and CD8 alpha(-) murine DC subsets, which have been reported to differently regulate the Th response. Adoptive transfer of Ag-pulsed CD8 alpha(+) DCs induced a Th1 response and the production of IgG2a Abs, whereas transfer of CD8 alpha(-) DCs induced Th2 cells and IgE Abs in vivo. Induction of distinct Th populations by each DC subset was also confirmed in vitro. Although interruption of CD80/CD86-CD28 interactions inhibited Th cell priming by both DC subsets, disruption of CD40-CD154 interactions only inhibited the induction of the Th1 response by CD8 alpha(+) DCs in vivo. CD40-CD154 interactions were not required for the proliferation of Ag-specific naive Th cells stimulated by either DC subset, but were indispensable in the production of IL-12 from CD8 alpha(+) DCs and their induction of Th1 cells in vitro. Taken together, in our immunization model of Ag-pulsed DC transfer, CD40-CD154 interactions play an important role in the development of CD8 alpha(+) DC-driven Th1 responses but not CD8 alpha(-) DC-driven Th2 responses to protein Ags.

Interleukin 13 Gene Transfer in Liver Ischemia and Reperfusion Injury: Role of Stat6 and TLR4 Pathways in Cytoprotection

Ischemia and reperfusion injury (IRI) represents the major problem in clinical liver transplantation. We have shown that transcription of signal transducer and activator of transcription 4 (Stat4) plays a key role in the mechanism of hepatic IRI, whereas local induction of interleukin 13 (IL-13) is cytoprotective. The disruption of innate Toll-like receptor 4 (TLR4) signaling prevents mouse livers from undergoing fulminant IRI. This study analyzes in vivo interplay between innate (TLR4) and adaptive (Stat6) immunity in Ad-IL-13 (recombinant adenovirus encoding IL-13) cytoprotection in hepatic IRI. Using a partial 90-min lobar warm ischemia model, groups of wild-type and Stat6-deficient knockout mice were assessed for the severity of hepatocellular damage at 6 hr postreperfusion. Unlike in wild-type mice, treatment of Stat6 knockout recipients with Ad-IL-13 failed to improve hepatic function/histology. The expression of mRNAs encoding tumor necrosis factor alpha/IL-1 beta and IL-2/interferon gamma remained depressed in the wild-type plus Ad-IL-13 group, but not in the Stat6 knockout plus Ad-IL-13 group. Ad-IL-13 increased antioxidant heme oxygenase 1 (HO-1) expression and prevented TLR4 activation in livers of Stat6-competent (wild-type) mice. In contrast, low HO-1 expression and enhanced TLR4 expression were recorded in Stat6 knockout recipients despite Ad-IL-13 therapy. Thus (1) Stat6 is required for Ad-IL-13 to prevent IRI, and (2) depression of TLR4 activation is Stat6 dependent. In conclusion, the Stat6 pathway operates as a key negative regulator in the hepatic inflammatory ischemia-reperfusion response. This study outlines requirements for Ad-IL-13 use to maximize the organ donor pool through the use of liver transplants despite prolonged ischemia.